Babies thrive under a ketogenic metabolism

Some people, even some scientists who study ketogenic metabolism, have the idea that ketogenesis is somehow abnormal, or exceptional; an adaptation for emergencies only. We disagree.

One reason we think a ketogenic metabolism is normal and desirable, is that human newborns are in ketosis. Despite the moderate sugar content of human breast milk, breastfeeding is particularly ketogenic. This period of development is crucial, and there is extensive brain growth during it. Although the composition of breast milk can be affected by diet [1], it is reasonable to assume that breast milk has always been ketogenic, and this is not an effect of modernisation.

When the brain is in its period of highest growth, and when the source of food is likely to be close to what it evolved to be for that period, ketones are used to fuel that growth.

If nothing else, this suggests that learning is well supported by a ketogenic metabolism. It is also consistent with the ability of ketogenic diets to treat a variety of seemingly unrelated brain disorders and brain trauma.

In brief

  • Newborn infants are in ketosis. This is their normal state.
  • Breastfeeding is particularly ketogenic (compared to formula feeding).
  • Breastfeeding longer (up to a point) is associated with better health outcomes.
  • This suggests the hypothesis that weaning onto a ketogenic diet would be healthier than weaning onto a high-carb diet.
(Mark-up ours) https://lh4.googleusercontent.com/-Qkco6a-yHU4/UuLtMjR7QjI/AAAAAAAABzk/pGq63wexS2A/w1042-h468-no/ketonemiaTable.png

Human babies are in ketosis

Soon after birth, human babies are in ketosis, and remain so while breastfeeding [2]. They use ketones and fats for energy and for brain growth.

When this has been studied, in the first couple of hours after birth, babies aren't immediately in ketosis. There is a short delay [3]. During that brief period before ketogenesis starts, lactate (confusingly not to do with lactation) becomes an important fuel to suppport the brain [4]. Some researchers speculate that this delay in ketogenesis could be because of a limited supply of carnitine, which is supplied by milk, but they also note that glycogenolysis and gluconeogenesis (the process by which glucose is made out of protein) are not active immediately [5]. Therefore, it could simply be the case that ketogenesis takes time to get started. In other words, it may just be keto-adaptation.

Note, though, that the mothers of these babies were unlikely to have been ketogenic. As it happens, if the mother is in ketosis (as has been studied through fasting), ketone bodies will pass through the placenta and be used by the fetus [5], [6]. At the same time, gluconeogenesis is induced in the liver of the fetus, likely as a result of the insulin-to-glucagon ratio [7], [8]. Therefore, it is possible that the fetus of a ketogenic mother would already be independently ketogenic at birth.

Breastfeeding is probably healthy

Many positive associations between exclusive breastfeeding for at least 3-6 months and the later health of the child have been reported. For example, intelligence has been positively correlated with length of time breastfeeding. The data is conflicting and prone to confounds [9], although we found a few studies that appear to have addressed those confounds and still showed an effect [10], [11], [12]. There have also been correlations found between breastfeeding and protection from developing diseases, such as asthma and allergies [13], type 1 and type 2 diabetes [14], and epilepsy [15].

Observational correlations are good sources of hypotheses, but can't establish causality. Unfortunately, these hypotheses are hard to test. We suppose that breastfeeding is healthy mainly because we clearly evolved to breastfeed.

Breastfeeding is ketogenic

The medical focus in the 20th century was heavily influenced by the discovery of micronutrients, and because of this, we have been looking for the secret of the healthfulness of breast milk by examining what nutrients it contains. However, one significant difference between breastfeeding infants and those drinking formula is that they are in deeper ketosis [16]. It is not known why. It could be a property of the milk, or something else about the feeding. In any case, regardless of mechanism, the fact is that breastfeeding is more ketogenic. It is possible that the reason that longer breastfeeding is generally associated with better health, is because it represents a longer time in ketosis.


  • The period in which human brains grow the most, and in which food is least likely to be different from evolutionary conditions, is a ketogenic period. This suggests that a ketogenic metabolism is excellent for learning and development.
  • Breastfeeding in humans is particularly ketogenic. We hypothesise that the positive associations between health and longer breastfeeding may be due to extending the period of ketosis in infancy.
  • A related hypothesis we offer is that extending the period of ketosis after breastfeeding, by weaning onto ketogenic foods such as homemade broth [*] and fatty meat, rather than cereal, fruit, and starchy vegetables, would further promote brain development and reduce risk of disease.
[*]Homemade, because it is rich in fat, unlike the boxed varieties which have almost none.


References and notes


Evidence type: review

Sheila M. Innis
Adv Nutr May 2011 Adv Nutr vol. 2: 275-283, 2011

"The fatty acids needed by the mammary gland for synthesis of TG for secretion in milk are obtained by uptake of fatty acids from plasma and de novo synthesis in the mammary gland (7). Fatty acid synthesis in the mammary gland, however, is unusual. Commencing with acetyl CoA, malonyl CoA 2 carbon units are added to the growing fatty acid with elongation terminated at a carbon chain length of 14 or less by the mammary gland-specific enzyme thioesterase II rather than at 16 carbons, as occurs in the liver and other tissues (7, 8). Synthesis and secretion of 10:0, 12:0, and 14:0 into milk is increased in lactating women consuming high-carbohydrate diets, whereas the secretion of the 18 carbon chain unsaturated fatty acids, which are derived by uptake from plasma, is decreased (4, 9, 10). Overall, reciprocal changes in mammary gland-derived medium-chain fatty acids (MCFA) and plasma-derived unsaturated fatty acids allows the milk fat content to be maintained under conditions of varying maternal dietary fat and carbohydrate intake. The levels of unsaturated fatty acids, including 18:1(n-9), 18:2(n-6), 18:3(n-3), 20:5(n-3), 22:6(n-3), and trans fatty acids in human milk, however, vary widely, with the maternal dietary fat composition being one of the most important factors contributing to the differences in the levels of unsaturated fatty acids in the milk of different women (4, 8, 11–14). In contrast, the levels of 16:0 in milk from women in different countries and with different diets is relatively constant at 20–25% of the milk fatty acids regardless of differences in the maternal diet fat content or composition (4). Possible exceptions include lower levels of 14–18% 16:0 described for milk from women in Gambia (15), some vegans and vegetarians (16, 17), and the Arctic Inuit (18)."


Evidence type: review of experiments in humans and rats

Medina JM, Tabernero A.
J Neurosci Res. 2005 Jan 1-15;79(1-2):2-10.

"Striking changes in the fuel supply to the tissues occur during the perinatal period because the transplacental supply of nutrients ends with a period of postnatal starvation (presuckling period) followed by adaptation to a fat-rich diet."


"Ketone bodies are a major fuel for the brain during the suckling period and hence the stimulation of ketogenesis at birth is an important metabolic event in adaptation of the newborn to extrauterine life. Ketogenesis is active during late gestation in human fetal liver and the activity of ketogenic enzymes sharply increases immediately after birth in the rat (Hahn and Novak, 1985; Bougneres et al., 1986). In addition to modulation of enzyme activities, the control of ketogenesis also depends on the availability of fatty acids. The increase in fatty acid concentrations that occurs after delivery is due to breakdown of triacylglycerol in white adipose tissue present in human newborns at birth. In the rat, however, plasma fatty acids mostly come from hydrolysis of triacylglycerols from the mother’s milk because of the lack of white adipose tissue at birth. Nevertheless, in both species, once lactation is active fatty acids come from the intestinal hydrolysis of milk triacylglycerols, which may be absorbed directly without passage through the lymph (Aw and Grigor, 1980)."


"The increase in the activities of ketogenic enzymes together with the increase in the availability of fatty acids occurring immediately after delivery result in enhancement of ketogenic capacity of the liver (Girard,1990). This is responsible for the increase in ketone body concentrations observed postnatally. In fact, plasma ketone body concentrations are the main factor controlling the rate of ketone body utilization by neonatal tissues (Robinson and Williamson, 1980). In addition, activities of enzymes involved in ketone body utilization either increase during the first days of extrauterine life, as in the rat (Page et al., 1971), or are already induced during early gestation, as in the human brain (Patel et al., 1975). Moreover, newborn rat brain contains acetoacetyl-CoA synthetase, a unique enzyme that allows an important portion of carbon atoms from ketone bodies to be incorporated into lipid via a highly efficient cytosolic pathway (Williamson and Buckley, 1973). Indeed, there is a strong correlation between lipid synthesis and the activity of this enzyme during brain development (Yeh and Sheehan, 1985). Moreover, ketone body transport across the blood–brain barrier using the monocarboxylate carrier is maximal during the suckling period, in keeping with the idea that ketone bodies play an important role in brain development (Cremer, 1982; Conn et al., 1983). "Ketone bodies are utilized by the newborn brain as a source of energy and carbon skeletons and are incorporated into fatty acids, sterols, acetylcholine, and amino acids (Robinson and Williamson, 1980; Bougneres et al., 1986). Ketone bodies, however, seem to be the major source of carbon skeletons for sterol synthesis during brain development and play a decisive role in the synthesis of brain structures during myelinogenesis (Robinson and Williamson, 1980; Miziorko et al., 1990). Ketone bodies are utilized evenly by neurons, astrocytes, and oligodendrocytes (Edmond et al., 1987; Lopes-Cardozo et al., 1989; Poduslo and Miller, 1991), indicating that they are ubiquitous substrates for brain cells. Acetoacetyl-CoA synthetase activity, however, is higher in oligodendrocytes than in neurons or astrocytes, confirming the special role of oligodendrocytes in myelinogenesis (Pleasure et al., 1979; Lopes-Cardozo et al., 1989; Poduslo and Miller, 1991)."


Evidence type: review of experiments

Ward Platt M, Deshpande S.
Semin Fetal Neonatal Med. 2005 Aug;10(4):341-50.

"During the first 8 h after birth, newborn infants have been shown to have rather low plasma ketone body concentrations despite adequate levels of precursor free fatty acids (FFAs), reflecting limited capacity for hepatic ketogenesis.30 Thereafter, from 12 h of age, healthy term infants show high ketone body turnover rates (12e 22 mmol kg/min) approaching those found in adults after several days of fasting,14 and during days 2 and 3 after birth they exhibit high ketone body concentrations quantitatively similar to those observed after an overnight fast in older children (Fig. 2).15 Such ketone body concentrations may account for as much as 25% of the neonate’s basal energy requirements during this time. Thus vigorous ketogenesis appears to be an integral part of extrauterine metabolic adaptation in the term human neonate."


Evidence type: review of experiments in humans and rats

Medina JM, Tabernero A.
J Neurosci Res. 2005 Jan 1-15;79(1-2):2-10.

"Although the supply of metabolic substrates is maintained mostly during the perinatal period, there is an apparent lack of mobilization of energy reserves immediately after delivery; i.e., during the presuckling period. During this period, the maternal supply of glucose has ceased and alternative substrates have not yet been released. In the rat, fatty acids come exclusively from the mother’s milk because of the lack of white adipose tissue at birth. Consequently, free fatty acids are not available in the rat before the onset of suckling (Mayor and Cuezva, 1985; Girard, 1990). In the case of human newborns, however, fatty acid mobilization occurs immediately after birth, although the onset of ketogenesis is delayed, probably as a consequence of a limited supply of carnitine, which is provided mainly by the milk (Hahn and Novak, 1985; Schmidt-Sommerfeld and Penn, 1990). In addition, glycogenolysis and gluconeogenesis are not active immediately after birth, resulting in very low concentrations of plasma glucose (Mayor and Cuezva, 1985; Girard, 1990). In these circumstances, lactate may play an important role as an alternative substrate. In fact, lactate accumulates in fetal blood during the perinatal period and is removed rapidly immediately after delivery (Persson and Tunell, 1971; Juanes et al., 1986)."


Evidence type: presumably this is a review. We could not get the full text, so for us this is evidence by authority

Shambaugh GE 3rd.
Fed Proc. 1985 Apr;44(7):2347-51.

"Pregnancy is characterized by a rapid accumulation of lipid stores during the first half of gestation and a utilization of these stores during the latter half of gestation. Lipogenesis results from dietary intake, an exaggerated insulin response, and an intensified inhibition of glucagon release. Increasing levels of placental lactogen and a heightened response of adipose tissue to additional lipolytic hormones balance lipogenesis in the fed state. Maternal starvation in late gestation lowers insulin, and lipolysis supervenes. The continued glucose drain by the conceptus aids in converting the maternal liver to a ketogenic organ, and ketone bodies produced from incoming fatty acids are not only utilized by the mother but cross the placenta where they are utilized in several ways by the fetus: as a fuel in lieu of glucose; as an inhibitor of glucose and lactate oxidation with sparing of glucose for biosynthetic disposition; and for inhibition of branched-chain ketoacid oxidation, thereby maximizing formation of their parent amino acids. Ketone bodies are widely incorporated into several classes of lipids including structural lipids as well as lipids for energy stores in fetal tissues, and may inhibit protein catabolism. Finally, it has recently been shown that ketone bodies inhibit the de novo biosynthesis of pyrimidines in fetal rat brain slices. Thus during maternal starvation ketone bodies may maximize chances for survival both in utero and during neonatal life by restraining cell replication and sustaining protein and lipid stores in fetal tissues."


Evidence type:

Herrera, Emilio
Endocrine, Volume 19, Number 1, October 2002 , pp. 43-56(14)

"During early pregnancy there is an increase in body fat accumulation, associated with both hyperphagia and increased lipogenesis. During late pregnancy there is an accelerated breakdown of fat depots, which plays a key role in fetal development. Besides using placental transferred fatty acids, the fetus benefits from two other products: glycerol and ketone bodies. Although glycerol crosses the placenta in small proportions, it is a preferential substrate for maternal gluconeogenesis, and maternal glucose is quantitatively the main substrate crossing the placenta. Enhanced ketogenesis under fasting conditions and the easy transfer of ketones to the fetus allow maternal ketone bodies to reach the fetus, where they can be used as fuels for oxidative metabolism as well as lipogenic substrates."


"Increased gluconeogenesis from glycerol and ketogenesis from NEFA may benefit the fetus, which at late gestation is at its maximum accretion rate and its requirements for substrates and metabolic fuels are greatly augmented. The preferential use of glycerol for gluconeogenesis and the efficient placental transfer of the newly formed glucose may be of major importance to the fetus under these fasting conditions (Fig. 2), in which the availability of other essential substrates such as amino acids is reduced (30,34). Placental transfer of ketone bodies is highly efficient (35), reaching fetal plasma at the same level as in maternal circulation (29). Ketone bodies may be used by the fetus as fuels (36) and as substrates for brain lipid synthesis (37)."


Evidence type: review We could not get the full text, so for us this is evidence by authority

Girard J.
Biol Neonate. 1986;50(5):237-58.


Birth in most mammalian species represents an abrupt change from a high-carbohydrate and low-fat diet to a high-fat and low-carbohydrate diet. Gluconeogenesis is absent from the liver of the fetus of well fed mothers, but can be induced prematurely by prolonged fasting of the mother. Gluconeogenesis increases rapidly in the liver of newborn mammals in parallel with the appearance of phosphoenolpyruvate carboxykinase (PEPCK), the rate-limiting enzyme of this pathway. The rise in plasma glucagon and the fall in plasma insulin which occur immediately after birth are the main determinants of liver PEPCK induction. When liver PEPCK has reached its adult value, i.e. 24 h after birth, other factors are involved in the regulation of hepatic gluconeogensis. In order to maintain a high gluconeogenic rate, the newborn liver must be supplied with sufficient amount of gluconeogenic substrates and free fatty acids. An active hepatic fatty acid oxidation is necessary to support hepatic gluconeogenesis by providing essential cofactors such as acetyl CoA and NADH. The relevance of animal studies for the understanding of neonatal glucose homeostasis in man is discussed."


Evidence type: review of experiments:

Kalhan S, Parimi P.
Semin Perinatol. 2000 Apr;24(2):94-106.

(emphasis ours)

"Studies in human and animal models have consistently confirmed the dependence of the fetus on the mother for supply of glucose so that the fetus in utero under normal physiological circumstances does not produce glucose. However, most gluconeogenic and glycogenolytic enzymes have been shown to be present early in fetal development. The exception is the cytosolic phosphoenol pyruvate carboxykinase, which is expressed (at least in the rat) immediately after birth. 12-14 The appearance of gluconeogenic enzyme activity in the liver in relation to birth in the rat fetus and newborn is displayed in Figure 2. As shown, PC and glucose-6-phosphatase activity are expressed in the fetus, are relatively low at birth, and increase rapidly thereafter. Fructose 1,6-diphosphatase activity increases before birth. In contrast, phosphoenol pyruvate carboxykinase activity is absent in the fetus and rapidly increases immediately after birth, so that hepatic gluconeogenesis is completely absent in utero and appears in the immediate newborn period 2,14,5 GNG, however, can,be induced in utero by prolonged maternal starvation, prolonged hypoglycemia in the mother, or by direct injection of cyclic adenosine monophosphate (cAMP) into the fetus. 16-18 In addition, some studies have showed incorporation of tracer carbon from lactate into glucose in rat fetus and glutamine carbon into hepatic glycogen in sheep fetus. 4,5,19 The significance of these latter observations remains unclear."


Evidence type: meta-analysis

Walfisch A, Sermer C, Cressman A, Koren G.
BMJ Open. 2013 Aug 23;3(8):e003259. doi: 10.1136/bmjopen-2013-003259.

"The association between breastfeeding and child cognitive development is conflicted by studies reporting positive and null effects. This relationship may be confounded by factors associated with breastfeeding, specifically maternal socioeconomic class and IQ.

Design Systematic review of the literature.

Setting and participants Any prospective or retrospective study, in any language, evaluating the association between breastfeeding and cognitive development using a validated method in healthy term infants, children or adults, was included.

Primary and secondary outcome measures Extracted data included the study design, target population and sample size, breastfeeding exposure, cognitive development assessment tool used and participants’ age, summary of the results prior to, and following, adjustment for confounders, and all confounders adjusted for. Study quality was assessed as well.

Results 84 studies met our inclusion criteria (34 rated as high quality, 26 moderate and 24 low quality). Critical assessment of accepted studies revealed the following associations: 21 null, 28 positive, 18 null after adjusting for confounders and 17 positive—diminished after adjusting for confounders. Directionality of effect did not correlate with study quality; however, studies showing a decreased effect after multivariate analysis were of superior quality compared with other study groupings (14/17 high quality, 82%). Further, studies that showed null or diminished effect after multivariate analysis corrected for significantly more confounders (7.7±3.4) as compared with those that found no change following adjustment (5.6±4.5, p=0.04). The majority of included studies were carried out during childhood (75%) and set in high-income countries (85.5%).

Conclusions Much of the reported effect of breastfeeding on child neurodevelopment is due to confounding. It is unlikely that additional work will change the current synthesis. Future studies should attempt to rigorously control for all important confounders. Alternatively, study designs using sibling cohorts discordant for breastfeeding may yield more robust conclusions."


Evidence type: observational

Florey CD, Leech AM, Blackhall A.
Int J Epidemiol. 1995;24 Suppl 1:S21-6.

"OBJECTIVE: To determine the relationship between type of infant feeding and mental and psychomotor development at age 18 months.

METHOD: A follow-up study of children born to primigravidae living in Dundee and booked into antenatal clinics in the City of Dundee (Local Authority District) from 1 May 1985 to 30 April 1986. The study population was 846 first born singletons, of whom 592 attended for developmental assessment at age 18 months. The main outcome measures were the Bayley Scales of Infant Mental and Motor Development.

RESULTS: Higher mental development was significantly related to breast feeding on discharge from hospital and according to the health visitors' notes at about 2 weeks after discharge after allowing for partner's social class, mother's education, height, alcohol and cigarette consumption; placental weight and the child's sex, birth weight and gestational age at birth. After adjustment for statistically significant variables, the difference in Bayley mental development index between breast and bottle fed infants was between 3.7 and 5.7 units depending on the source of feeding data. No differences were found for psychomotor development or behaviour.

CONCLUSION: The study provides further evidence of a robust statistical association between type of feeding and child intelligence. However, the literature is replete with suggestions for potential confounding variables which offer alternative causal explanations. To unravel what is an important clinical and public health question, further research should concentrate on randomized trials of supplemented formula feeds for children of mothers opting for bottle feeding and on epidemiological studies designed to disentangle the relation between method of feeding, parental intelligence and social environment."


Evidence type: observational

Belfort MB, Rifas-Shiman SL, Kleinman KP, Guthrie LB, Bellinger DC, Taveras EM, Gillman MW, Oken E.
JAMA Pediatr. 2013 Sep;167(9):836-44.

"Breastfeeding may benefit child cognitive development, but few studies have quantified breastfeeding duration or exclusivity, nor has any study to date examined the role of maternal diet during lactation on child cognition.

OBJECTIVES: To examine relationships of breastfeeding duration and exclusivity with child cognition at ages 3 and 7 years and to evaluate the extent to which maternal fish intake during lactation modifies associations of infant feeding with later cognition.

DESIGN, SETTING, AND PARTICIPANTS: Prospective cohort study (Project Viva), a US prebirth cohort that enrolled mothers from April 22, 1999, to July 31, 2002, and followed up children to age 7 years, including 1312 Project Viva mothers and children.

MAIN EXPOSURE: Duration of any breastfeeding to age 12 months. MAIN OUTCOMES AND MEASURES:

Child receptive language assessed with the Peabody Picture Vocabulary Test at age 3 years, Wide Range Assessment of Visual Motor Abilities at ages 3 and 7 years, and Kaufman Brief Intelligence Test and Wide Range Assessment of Memory and Learning at age 7 years.

RESULTS: Adjusting for sociodemographics, maternal intelligence, and home environment in linear regression, longer breastfeeding duration was associated with higher Peabody Picture Vocabulary Test score at age 3 years (0.21; 95% CI, 0.03-0.38 points per month breastfed) and with higher intelligence on the Kaufman Brief Intelligence Test at age 7 years (0.35; 0.16-0.53 verbal points per month breastfed; and 0.29; 0.05-0.54 nonverbal points per month breastfed). Breastfeeding duration was not associated with Wide Range Assessment of Memory and Learning scores. Beneficial effects of breastfeeding on the Wide Range Assessment of Visual Motor Abilities at age 3 years seemed greater for women who consumed 2 or more servings of fish per week (0.24; 0.00-0.47 points per month breastfed) compared with less than 2 servings of fish per week (−0.01; −0.22 to 0.20 points per month breastfed) (P = .16 for interaction).

CONCLUSIONS AND RELEVANCE: Our results support a causal relationship of breastfeeding duration with receptive language and verbal and nonverbal intelligence later in life."


Evidence type: observational

Julvez J, Guxens M, Carsin AE, Forns J, Mendez M, Turner MC, Sunyer J.
Dev Med Child Neurol. 2014 Feb;56(2):148-56. doi: 10.1111/dmcn.12282. Epub 2013 Oct 1.

"AIM: This study investigated whether duration of full breastfeeding is associated with child neuropsychological development and whether this association is explained by social, psychological, and nutritional factors within families.

METHOD: Participants in this study were a population-based birth cohort in the city of Sabadell (Catalonia, Spain). Females were recruited during the first trimester of pregnancy between July 2004 and July 2006. Information about parental characteristics and breastfeeding was obtained through questionnaires. Full breastfeeding was categorized as never, short term (≤4mo), long term (4-6mo), or very long term (>6mo). A trained psychologist assessed the neuropsychological development of children at 4 years of age (n=434) using the McCarthy Scales of Children's Abilities (MSCA).

RESULTS: Full breastfeeding showed an independent association with child general MSCA scores after adjusting for a range of social, psychological, and nutritional factors (>6mo, coefficient=7.4 [95% confidence interval=2.8-12.0], p=0.011). Maternal social class, education level, and IQ were also associated with child neuropsychological scores, but did not explain breastfeeding associations. Omega-3 (n3) fatty acid levels were not associated with child neuropsychological scores.

INTERPRETATION: Very long-term full breastfeeding was independently associated with neuropsychological functions of children at 4 years of age. Maternal indicators of intelligence, psychopathology, and colostrum n3 fatty acids did not explain this association."


Evidence type: observational

I Kull, M Wickman, G Lilja, S Nordvall, and G Pershagen
Arch Dis Child. 2002 December; 87(6): 478–481. doi: 10.1136/adc.87.6.478 PMCID: PMC1755833

"Aims: To investigate the effect of breast feeding on allergic disease in infants up to 2 years of age.

Methods: A birth cohort of 4089 infants was followed prospectively in Stockholm, Sweden. Information about various exposures was obtained by parental questionnaires when the infants were 2 months old, and about allergic symptoms and feeding at 1 and 2 years of age. Duration of exclusive and partial breast feeding was assessed separately. Symptom related definitions of various allergic diseases were used. Odds ratios (OR) and 95% confidence intervals (CI) were estimated in a multiple logistic regression model. Adjustments were made for potential confounders.

Results: Children exclusively breast fed during four months or more exhibited less asthma (7.7% v 12%, ORadj = 0.7, 95% CI 0.5 to 0.8), less atopic dermatitis (24% v 27%, ORadj = 0.8, 95% CI 0.7 to 1.0), and less suspected allergic rhinitis (6.5% v 9%, ORadj = 0.7, 95% CI 0.5 to 1.0) by 2 years of age. There was a significant risk reduction for asthma related to partial breast feeding during six months or more (ORadj = 0.7, 95% CI 0.5 to 0.9). Three or more of five possible allergic disorders—asthma, suspected allergic rhinitis, atopic dermatitis, food allergy related symptoms, and suspected allergic respiratory symptoms after exposure to pets or pollen—were found in 6.5% of the children. Exclusive breast feeding prevented children from having multiple allergic disease (ORadj = 0.7, 95% CI 0.5 to 0.9) during the first two years of life.

Conclusion: Exclusive breast feeding seems to have a preventive effect on the early development of allergic disease—that is, asthma, atopic dermatitis, and suspected allergic rhinitis, up to 2 years of age. This protective effect was also evident for multiple allergic disease."


Evidence type: review of observational studies

Pereira PF, Alfenas Rde C, Araújo RM.
J Pediatr (Rio J). 2014 Jan-Feb;90(1):7-15. doi: 10.1016/j.jped.2013.02.024. Epub 2013 Oct 16.

"Objective the aim of this study was to perform a review to investigate the influence of breastfeeding as a protective agent against the onset of diabetes in children.

Sources non-systematic review of SciELO, LILACS, MEDLINE, Scopus, and VHL databases, and selection of the 52 most relevant studies. A total of 21 articles, specifically on the topic, were analyzed (nine related to type 1 diabetes and 12 to type 2 diabetes).

Data synthesis the duration and exclusivity of breastfeeding, as well as the early use of cow's milk, have been shown to be important risk factors for developing diabetes. It is believed that human milk contains substances that promote the maturation of the immune system, which protect against the onset of type 1 diabetes. Moreover, human milk has bioactive substances that promote satiety and energy balance, preventing excess weight gain during childhood, thus protecting against the development of type 2 diabetes. Although the above mentioned benefits have not been observed by some researchers, inaccuracies on dietary habit reports during childhood and the presence of interfering factors have been considered responsible for the lack of identification of beneficial effects.

Conclusion given the scientific evidence indicated in most published studies, it is believed that the lack of breastfeeding can be a modifiable risk factor for both type 1 and type 2 diabetes. Strategies aiming at the promotion and support of breastfeeding should be used by trained healthcare professionals in order to prevent the onset of diabetes."


Evidence type: observational

Sun Y, Vestergaard M, Christensen J, Olsen J.
J Pediatr. 2011 Jun;158(6):924-9. doi: 10.1016/j.jpeds.2010.11.035. Epub 2011 Jan 13.

"OBJECTIVE: We asked whether breastfeeding reduces the risk of epilepsy in childhood.

STUDY DESIGN: We included 69 750 singletons born between September 1997 and June 2003 in the Danish National Birth Cohort and observed them to August 2008. Information on breastfeeding was reported by mothers in two computer-assisted telephone interviews at 6 and 18 months after birth. Information on epilepsy (inpatients and outpatients) was retrieved from the Danish National Hospital Register. Cox proportional hazards regression models were used to estimate incidence rate ratios and 95% CIs.

RESULTS: Breastfeeding was associated with a decreased risk of epilepsy, with a dose-response like pattern. For example, children breastfed for 3 to 5, 6 to 8, 9 to 12, and ≥ 13 months had a 26%, 39%, 50%, and 59% lower risk of epilepsy after the first year of life, respectively, compared with children who were breastfed for <1 month. The association remained when we excluded children who had adverse neonatal conditions or children who were exposed to adverse maternal conditions during pregnancy.

CONCLUSIONS: The observed protective effect of breastfeeding may be causal. Breastfeeding may decrease epilepsy in childhood, thereby adding another reason for breastfeeding."


Evidence type: controlled human experiments

"Our summary statistic, median peak kb [(ketone body)] concentration (Table 6), is significantly higher in the BF [(breastfed)] group compared with other feed groups for the SGA [(small for gestational age)] infants analyzed separately. We further explored the relationship between the blood glucose concentration and kb response by finding the kb concentration at the lowest blood glucose level for each infant at >24 hours of age (Fig 3, Table 6). Especially at low blood glucose values, infants who receive breast milk show some of the highest values for blood kb concentration. Our data show that exclusive formula feeding does not necessarily protect against low blood glucose values. Hence, the SGA FF [(formula fed)] infant could be doubly at risk of both low blood glucose values with a reduced kb response. No BF infant had both low blood glucose and low kb levels. For LGA [(large for gestational age)] infants, low blood glucose values were offset by kb concentrations of the same order of magnitude previously demonstrated for AGA [(appropriate for getstaional age)] infants6 (Fig 3)."


"Mammalian animal studies have shown that the postnatal induction of the enzymes involved in β-oxidation within the mitochondria requires the presence of long-chain fatty acids.15 The carnitine palmitoyltransferase system, which controls movement of long-chain fatty acids into the mitochondria, represents a major rate-limiting step in ketogenesis in the suckling rat. Long-chain fatty acids play a pivotal role in the posttranscriptional regulation of carnitine palmitoyltransferase 1 during the immediate postnatal period. We speculate that a factor present in breast milk but absent in formula milk augments ketogenesis in human neonates in the same way. Carnitine is known to have a central role in β-oxidation of fats: it is responsible for the transport of fatty acyl-coenzyme A across the inner mitochondrial membrane.16 During the suckling period, the demand for carnitine exceeds the rate of endogenous synthesis by up to 50%.17 Indeed, healthy, full-term infants fed formulas devoid of carnitine showed reduction in ketogenesis and an accumulation of fatty acid precursors in the plasma. Although breast milk– and cow’s milk– derived formulas contain equivalent amounts of carnitine,18 it may well be that there are significant differences in bioavailability. When compared with breastfed control subjects, infants who were fed a standard formula that was not supplemented with carnitine demonstrated markers of carnitine deficiency.19 Furthermore, we hypothesized that high intakes of energy and protein associated with early formula feeding may “switch off” or dampen the crucial glucagon surge, central to regulation of fuel availability in the immediate postnatal period."



Language Barriers: Preferred Fuel

by Amber Wilcox-O'Hearn

As a linguist, I am often struck by the way phrasing and word choices not only reflect biases, but can actually create them [1]. Again and again in my researches into dietary science, I come upon expressions and turns of phrase that make Low Carb, High Fat diets seem intuitively unhealthy or illogical.

One such phrase is “Preferred Fuel”.

What is a preferred fuel?

Technically, a preferred fuel is simply one that is used first when there is more than one type available.

For many (but not all) of the tissues and organs in the body, glucose is a “preferred fuel”, meaning that if glucose is available, those tissues and organs will use it before using most other fuels, even if they are also present.

People sometimes take this to mean that glucose is the best fuel; the fuel that would make you most healthy. Choosing and preferring are things people do when they have decided that something is “better” than something else. So, whether or not the physiologist who coined the term intended it, this terminology leads the reader to think that the preferred fuel is the one that is inherently a better choice. However, this is not correct. Sometimes the opposite is true. Sometimes it depends on what else is going on.

One analogy I like is that of spending. Many people take a large portion of their hard-earned pay cheques and make a payment on their debts. No matter what else they do, they do that first. Does this mean it is what they “prefer” to spend their money on? In some sense, yes! By the Doctrine of Revealed Preference [2], it is by definition what they prefer. And yet most people would not count this kind of obligation as one of their choices. There is another phrase, “disposable income” for spending associated with choice. The reason paying debts is preferred in this way, is that one seeks to avoid the consequences of not paying. In fact, in most cases, for most people, paying debts is a better choice than not paying them. What it does not mean, however, is that people prefer to have debts to pay in the first place!

To bring this back to the realm of human metabolism, there are several substances that can be used for fuel, including fat, protein, ketones, glucose (which is the kind of fuel carbohydrates provide), and alcohol. Alcohol is a strongly preferred fuel [3]. It is metabolized right away, even if there are other fuel sources around. This is not evidence that alcohol is the best fuel, but rather that it is what the body wants to get rid of immediately. Getting rid of the alcohol is a better choice than leaving it around to do damage. The same is often true of glucose. High blood sugar is toxic, and so whenever there is excess available it will get used or stored as quickly as possible.

We don't mean to imply that being used for fuel first always means a substance is toxic. What is a good "choice" in a system as complex as the human body is not always obvious. For example, the heart uses acetoacetate (a ketone body) before glucose, but uses primarily fat, even in glycolytic dieters [4].

What about the brain?

It is true that the brain has need for some amount of glucose, even under a ketogenic metabolism. That is one reason why gluconeogenesis (the ongoing production of glucose in the liver) is important, whether you are ketogenic or not. This ensures a steady supply of glucose into the bloodstream, and keeps blood sugar in healthy bounds: enough for the brain, but not too much. Under ketogenic conditions, though, the brain's need for glucose is drastically reduced, because other fuels, such as ketone bodies and lactate take the place of most of it [5].

Lactate may be preferred over glucose in the brain [6], [7]. Using lactate instead of glucose has neuroprotective properties not unlike those seen with ketosis [8]. It might even be the case that a primary use of glucose in the brain is to be turned into lactate by astrocytes [8], [9]. We still have much to learn.


Next time you see the phrase “Preferred Fuel”, remember that it really just means the order in which different fuels are consumed. There are various context-specific reasons a particular fuel might be used before other ones, and it has nothing to do with its inherent healthiness.



See for example:

Fausey, Caitlin M., and Lera Boroditsky.
Psychonomic bulletin & review 17.5 (2010): 644-650.

Evidence type: controlled randomised experiment

"When bad things happen, how do we decide who is to blame and how much they should be punished? In the present studies, we examined whether subtly different linguistic descriptions of accidents influence how much people blame and punish those involved. In three studies, participants judged how much people involved in particular accidents should be blamed and how much they should have to pay for the resulting damage. The language used to describe the accidents differed subtly across conditions: Either agentive (transitive) or non-agentive (intransitive) verb forms were used. Agentive descriptions led participants to attribute more blame and request higher financial penalties than did nonagentive descriptions. Further, linguistic framing influenced judgments, even when participants reasoned about a well-known event, such as the “wardrobe malfunction” of Super Bowl 2004. Importantly, this effect of language held, even when people were able to see a video of the event. These results demonstrate that even when people have rich established knowledge and visual informa - tion about events, linguistic framing can shape event construal, with important real-world consequences. Subtle differences in linguistic descriptions can change how people construe what happened, attribute blame, and dole out punishment.


From Investopedia

"Definition of 'Revealed Preference'

"An economic theory of consumption behavior which asserts that the best way to measure consumer preferences is to observe their purchasing behavior. Revealed preference theory works on the assumption that consumers have considered a set of alternatives before making a purchasing decision. Thus, given that a consumer chooses one option out of the set, this option must be the preferred option.

"Revealed preference theory was introduced by Paul Samuelson in 1938. Since then it has expanded upon by a number of economists and remains a major theory of consumption behavior. The theory is especially useful in providing a method for analyzing consumer choice empirically."


See for example:

Ethanol and lipids. Lieber CS, Savolainen M. Alcohol Clin Exp Res. 1984 Jul-Aug;8(4):409-23.

"The interaction of ethanol with lipid metabolism is complex. When ethanol is present, it becomes a preferred fuel for the liver and displaces fat as a source of energy."


Ethanol Causes Acute Inhibition of Carbohydrate, Fat, and Protein Oxidation and Insulin Resistance. John J. Shelmet, George A. Reichard, Charles L. Skutches, Robert D. Hoeldtke, Oliver E. Owen, and Guenther Boden J Clin Invest. 1988 April; 81(4): 1137–1145.

"We conclude that ethanol was a preferred fuel preventing fat, and to lesser degrees, CHO and protein, from being oxidized. It also caused acute insulin resistance which was compensated for by hypersecretion of insulin."


Evidence type: authority

Biochemistry. 5th edition.
Berg JM, Tymoczko JL, Stryer L.
New York: W H Freeman; 2002.

"Unlike skeletal muscle, heart muscle functions almost exclusively aerobically, as evidenced by the density of mitochondria in heart muscle. Moreover, the heart has virtually no glycogen reserves. Fatty acids are the heart's main source of fuel, although ketone bodies as well as lactate can serve as fuel for heart muscle. In fact, heart muscle consumes acetoacetate in preference to glucose."

Public Note to Self: "functions almost exclusively aerobically, as evidenced by the density of mitochondria" is relevant to the idea that ketogenic diets increase mitochondrial number. There is preliminary evidence of this, as discussed previously. This statement leads me to believe that it should be unsurprising if decreased reliance on glucose had this effect.


Evidence type: controlled experiment

O. E. Owen, A. P. Morgan, H. G. Kemp, J. M. Sullivan, M. G. Herrera, and G. F. Cahill, Jr.
J Clin Invest. 1967 October; 46(10): 1589–1595. doi: 10.1172/JCI105650 PMCID: PMC292907

(Measurements on three people after 38-41 days of fasting)

"Turning to Table V, the average glucose uptake, after subtracting the amount glycolyzed to lactate and pyruvate, is 0.145 mmole/liter (2.6 mg/100 ml). This is markedly less than the usual 9-10 mg/100 ml observed in our laboratory while the techniques which little or no production of lactate or pyruvate was observed (25-28). Similar data were observed in our laboratory while the techniques and methods used to study these fasted subjects were validated. With measured cerebral blood flow of 45 ml/100 g of tissue per min, and assuming a brain size of 1400 g the 24 hr glucose oxidation would approximate 24 g, which agrees well with the theoretical maximum of 33 g calculated from nitrogen execretion and glycerol from adipose tissue as described above. The third confirmatory evidence for this marked reduction in glucose metabolism has been data, which obtained from hepatic and renal vein catheterization studies, demonstrated that the liver almost totally ceases to synthesize glucose from amino acids and that the kidney assumes the role of the major source of this diminished amount of glucose daily produced and consumed during starvation."


Evidence type: non-human animal experiments

Matthias T. Wyss, Renaud Jolivet, Alfred Buck, Pierre J. Magistretti, and Bruno Weber
The Journal of Neuroscience, 18 May 2011, 31(20): 7477-7485; doi: 10.1523/JNEUROSCI.0415-11.2011

"Cerebral energy metabolism is a highly compartmentalized and complex process in which transcellular trafficking of metabolites plays a pivotal role. Over the past decade, a role for lactate in fueling the energetic requirements of neurons has emerged. Furthermore, a neuroprotective effect of lactate during hypoglycemia or cerebral ischemia has been reported. The majority of the current evidence concerning lactate metabolism at the cellular level is based on in vitro data; only a few recent in vivo results have demonstrated that the brain preferentially utilizes lactate over glucose. Using voltage-sensitive dye (VSD) imaging, beta-probe measurements of radiotracer kinetics, and brain activation by sensory stimulation in the anesthetized rat, we investigated several aspects of cerebral lactate metabolism. The present study is the first in vivo demonstration of the maintenance of neuronal activity in the presence of lactate as the primary energy source. The loss of the voltage-sensitive dye signal found during severe insulin-induced hypoglycemia is completely prevented by lactate infusion. Thus, lactate has a direct neuroprotective effect. Furthermore, we demonstrate that the brain readily oxidizes lactate in an activity-dependent manner. The washout of 1-[ 11C]L-lactate, reflecting cerebral lactate oxidation, was observed to increase during brain activation from 0.077 Ϯ 0.009 to 0.105 Ϯ 0.007 min Ϫ1. Finally, our data confirm that the brain prefers lactate over glucose as an energy substrate when both substrates are available. Using [18F]fluorodeoxyglucose (FDG) to measure the local cerebral metabolic rate of glucose, we demonstrated a lactate concentration-dependent reduction of cerebral glucose utilization during experimentally increased plasma lactate levels."


Evidence type: review of experiments

Medina JM, Tabernero A.
J Neurosci Res. 2005 Jan 1-15;79(1-2):2-10.

"Lactate metabolism is particularly relevant in the brain, in which lactate is preferred over glucose, glutamine, or ketone bodies (Arizmendi and Medina, 1983; Fernandez and Medina, 1986; Vicario et al., 1991)."

Note that the references in this passage are either in rat brains or in glucose-6-phosphatase deficient children, so the unqualified generalisation as stated here is not warranted.


Evidence type: non-human animal experiments

Johanne E. Rinholm, Nicola B. Hamilton, Nicoletta Kessaris, William D. Richardson, Linda H. Bergersen, and David Attwell
J Neurosci. 2011 January 12; 31(2): 538–548. doi: 10.1523/JNEUROSCI.3516-10.2011

"In the brain's grey matter, astrocytes have been suggested to export lactate (derived from glucose or glycogen) to neurons to power their mitochondria. In the white matter, lactate can support axon function in conditions of energy deprivation, but it is not known whether lactate acts by preserving energy levels in axons or in oligodendrocytes, the myelinating processes of which are damaged rapidly in low energy conditions. Studies of cultured cells suggest that oligodendrocytes are the cell type in the brain which consumes lactate at the highest rate, in part to produce membrane lipids presumably for myelin. Here we use pH imaging to show that oligodendrocytes in the white matter of the rat cerebellum and corpus callosum take up lactate via monocarboxylate transporters (MCTs), which we identify as MCT1 by confocal immunofluorescence and electron microscopy. Using cultured slices of developing cerebral cortex from mice in which oligodendrocyte lineage cells express GFP under the control of the Sox10 promoter, we show that a low glucose concentration reduces the number of oligodendrocyte lineage cells and myelination. Myelination is rescued when exogenous L-lactate is supplied. Thus, lactate can support oligodendrocyte development and myelination. In CNS diseases involving energy deprivation at times of myelination or remyelination, such as periventricular leukomalacia leading to cerebral palsy, stroke, and secondary ischaemia following spinal cord injury, lactate transporters in oligodendrocytes may play an important role in minimising the inhibition of myelination that occurs."


Evidence type: conceptual integration of experiments

Yudkoff M, Daikhin Y, Melø TM, Nissim I, Sonnewald U, Nissim I.
Annu Rev Nutr. 2007;27:415-30.

"The oxidation of glucose provides essentially all energy needed to maintain cerebral function. Glycolysis may be relatively more prominent in some cells or in specific sub-cellular compartments. Thus, the filopodia of astrocytes are too narrow to accommodate mitochondria, and these cells will activate glycolysis (and glycogenolysis) in order to provide the energy that maintains their vital function of removing from the synaptic cleft much of the glutamate and K+ that presynaptic neuronal terminals release upon depolarization (24, 46). The fate of the pyruvate generated via glycolysis remains a topic of active inquiry and debate. It may be that astrocytes do not immediately oxidize all pyruvate produced via glycolysis. Instead, they may convert some pyruvate to lactate and release the latter to the extracellular fluid, from which neurons extract it and oxidize it as a fuel. Neurons can respire on lactate (102), but they may require glucose as a substrate if they are to maintain large internal pools of glutamate and aspartate (125). Astrocytic release of lactate and sub-sequent neuronal oxidation may constitute a mechanism by which neuronal and metabolic activity are effectively coupled (33, 66). "


How much protein is enough?

It seems, from clinical claims and numerous anecdotes, that protein intake has to be below some threshold for ketogenesis to continue, all else being equal. (Conditions are rarely equal: the effects of fat intake, calorie intake, the profile of amino acids in your diet, the type of fat in your diet, exercise, and frequency of eating also matter!)

It is commonly assumed that excess protein gets immediately turned into glucose by gluconeogenesis. However, we've shown in a series of articles (part 1, part 2, part 3, part 4) that such a mechanism is highly unlikely — excess protein does not just get immediately turned into glucose.

The evidence points to gluconeogenesis being driven by demand for glucose, not supply of protein.

However, it does appear that above a certain level of protein intake ketogenesis declines. So regardless of mechanism, as ketogenic dieters, we probably still need to limit protein.

It's not clear how much is too much.

But how much is enough? It is important not to turn a healthy, ketogenic diet into an unhealthy starvation diet! In this article we review some answers to this question, and some unanswered questions.

In Brief

  • It's important to get enough protein.
  • The RDA for protein is too low: if you are like most people, your health will suffer if you eat as little protein as the RDA requires.
  • Getting the minimum may not be optimal, but getting less than the minimum would be a mistake.
  • There are several different conditions that are commonly believed to affect protein requirements. In particular, exercise and weight loss have both been said to increase protein needs. We couldn't find definitive support for either of those beliefs.
  • We are most interested in studies that apply to keto dieters. Evidence from experiments on the Protein-Sparing Modified Fast is quite likely to apply to keto dieters. However, experiments on Protein-Sparing Modified Fasts leave out an important factor: fat intake, which may reduce protein requirements by reducing the need to use protein for energy.
  • We estimate that females should get at least 1.2 g/kg of ideal weight per day, and males at least 1.4 g/kg of ideal weight. [Edit 2014-01-11: (this may possibly be lowered by fat intake; see below)]

Let's head off confusion by distinguishing different ways to measure protein intake. You'll sometimes see protein intake expressed in terms of percent of total calorie intake. For example, the USDA recommends 10-35% of calories from protein. But this measures how much you are eating, not how much you are using! If you are losing weight, then (hopefully!) some of the calories you are burning are coming from your body fat instead of from your diet. Measuring protein requirements as a percent of intake ignores those calories. In this case, the percent of protein you are eating would be higher than the percent you are using.

A better way to express protein requirements is in terms of body weight. You are made in large part out of protein and so the more of you there is, the more protein you need to maintain your structures. We have seen protein requirements in the form of percent of your ideal body weight, percent of your lean mass, or simply percent of your body weight. These make more sense than percent of calories in this context.

Protein is essential to the body

Protein is necessary for virtually every biological process. Enzymes, antibodies, cellular receptors, and collagen are just a few examples of protein structures, but there are maybe 2 million different proteins functioning in the body [1]. Getting too little protein to provide for these structures could adversely affect many aspects of health, especially growth and maintenance of bone and muscle, and immune function [2], [3], [4]. Although the body recycles the amino acids that proteins are built from (this is called protein “turnover”), there are also constant losses that need to be replaced (“obligatory nitrogen losses”) [5].

The RDA is not enough

The lowest estimates of minimum requirements we have seen is the USDA RDA (it's now called RDI) of 0.8g per kg of body weight per day (for adults) [6]. Even they admit, in their 1000+ page explanation of macronutrient RDAs (RDAs for protein, fat and carbohydrate) from the Institute of Medicine, that the method they used to determine adequate protein levels (called “nitrogen balance”) is likely to result in underestimates [7].

Because of this, and because there was a flaw in the mathematical model that was used to derive the recommendations, a 2010 study reanalysed the same data that was used to generate the USDA RDA recommendations. They concluded that the recommendations should be 50% higher than they are [8]. That is, they conclude that for most people, 1.2g/kg/day of protein intake is necessary.

There is also experimental evidence that suggests the RDA is inadequate [9].

Different conditions may require different amounts of protein

An issue with using the results of these studies, is that, as with any physiological experiments, when you change the base conditions, the results may suddenly no longer apply. Changes that might make these conclusions inapplicable include what happens during high levels of physical activity, weight loss, or when consuming different levels of macronutrients. Specifically we want to know if protein requirements change when keto-adapted.

Exercise conditions

Whether higher levels of exercise increase protein needs is controversial.

Some studies suggest that endurance exercise increases the need for protein because protein is oxidised (used for energy) during the exercise [10]. However, there is also evidence that after a period of training this oxidation is limited by downregulation of the necessary enzymes [11]. That is, after doing it regularly, the body learns to spare the protein and stops letting it be used in that way. In particular, it is the BCAAs (branched chain amino acids) that appear to be oxidised [11].

Since BCAAs are known to be elevated in keto dieters, it's possible that any such effect would be minimal for us in the first place or that the downregulation has already taken place.

In fact, infusing people with beta-hydroxybutyrate (the ketone body we check for in the blood to see if someone is in deep ketosis) reduces leucine oxidation and promotes protein synthesis [12].

(Leucine is a BCAA — it is probably the most important BCAA for ketogenic metabolism. More on that another day.)

As for weight lifting, it seems intuitive that if you are building muscle, you will need more protein. Some studies seem to show this, but others actually show the reverse [13], [14], [15]. The subjects in those studies, of course, were not on keto diets.

These facts taken together seem to suggest that when you adapt to a hormonal state that favours muscle preservation or gain, whether it is a ketogenic state, or the state of regular exercise stimulus, it reduces the need for protein. Indeed, ketosis is known to be protein-sparing, and that may mean that you actually need less protein.

Protein requirements and weight loss

We have seen it asserted that weight loss itself increases the need for protein. However, the only studies we have seen that claim to prove it are flawed [16], [17]. It is still possible that weight loss requires more protein, but we haven't yet been convinced either way.

Note that this is different from the claim that higher protein diets improve weight loss (even when carbohydrates are not ketogenically low), which has shown repeatedly [18], [19], [20], [21], [22]. Since protein is generally taking the place of carbohydrate, we would certainly expect that to be true.

Relatedly, it is often claimed that weight loss is necessarily accompanied by some loss of lean mass. This has a plausible mechanism. For one thing, in people with lots of excess fat, more muscle, bone, and other infrastrucure has been built to carry the excess weight, and as the stimulus of the weight of the fat recedes, the extra muscle built to hold it might atrophy. Nonetheless, there are some studies of keto diets used for weight loss in which lean mass was preserved or even increased, for example in [24] and [25].

Protein requirements for keto dieters

Since retaining lean mass requires sufficient protein (among other things), studies in which keto dieters retained lean mass must have been protein adequate. Note that the reverse is not true: if a study had keto dieters losing lean mass, that doesn't imply that protein intake was inadequate. Other factors, such as mineral intake [23], and activity level and type [24] can effect muscle retention.

The Protein-Sparing Modified Fast

One particular kind of ketogenic weight loss diet that specifically aims to provide just enough protein to prevent muscle loss is called a Protein-Sparing Modified Fast. The developers of the Protein-Sparing Modified Fast were hypothesising that fasting would be the perfect therapy for the treatment of obesity, if it weren't for the resulting detrimental and dangerous loss of lean mass. They discovered that by adding enough protein, subjects lost fat effectively, but without losing lean mass. In particular, it was found that males preserved lean mass at 1.4 g/kg ideal body weight, and females at 1.2 g/kg ideal body weight [25]. This is particularly relevant for us, since the Protein-Sparing Modified Fast is a ketogenic condition.

Adding fat into the mix

In addition to the effects of being keto-adapted, we would like to know what the effect of the amount of fat in the diet has, if any, on protein requirements. It is plausible that if for some reason the rate of oxidation of fat stores were limited, that some dietary protein might be oxidised for fuel. If this were the case, then the addition of fat should lessen protein requirements. In other words, if there is a rate limit to getting fat out of fat stores, then adding sufficient dietary fat to make up for the energy requirements not met by adipose tissue would spare protein. On a keto diet, since carbohydrates are limited, and protein levels that are too high are undesirable (though how high is "too high" is not well understood), energy balance is made up by dietary fat. (And besides, fat is an important source of essential fatty acids and nutrients.) Unfortunately, we don't know of studies that test this in either weight loss or weight maintenance conditions.


It is important to get enough protein. We looked at the RDA, and that is certainly too low, so we looked for other sources of evidence. We also tried to determine if some common conditions would alter the amount needed, without coming to any strong conclusions.

We wanted to find evidence that would be relevant to ketogenic dieters in particular. Studies based on the Protein-Sparing Modified Fast don't match our needs exactly, since we eat lots of fat, but at least the participants were in ketosis. Based on those studies, we think females need at least 1.2 g/kg of ideal body weight, and men at least 1.4.

However, we still don't know how high protein can be before it interferes with ketosis, and this is likely to vary by individual. Moreover, we don't know if it would be better for your health to have just the minimum, or to have substantially more. It is certainly plausible that having more would allow for better functioning.



Evidence type: authority


"The word “proteome” is derived from PROTEins expressed by a genOME, and it refers to all the proteins produced by an organism, much like the genome is the entire set of genes. The human body may contain more than 2 million different proteins, each having different functions. As the main components of the physiological pathways of the cells, proteins serve vital functions in the body such as:

  • catalyzing various biochemical reactions, e.g. enzymes;
  • acting as messengers, e.g. neurotransmitters;
  • acting as control elements that regulate cell reproduction;
  • influencing growth and development of various tissues, e.g. trophic factors;
  • transporting oxygen in the blood, e.g. hemoglobin; and
  • defending the body against disease, e.g. antibodies.

Evidence type: experimental

Castaneda C, Charnley JM, Evans WJ, Crim MC.
Am J Clin Nutr. 1995 Jul;62(1):30-9.

"A 9-wk study of adaptation to marginal protein intakes was conducted in 12 elderly women. Subjects were randomly assigned to two groups fed a weight-maintenance diet containing either 1.47 (low) or 2.94 (adequate) g protein.kg body cell mass-1.d-1 (0.45 and 0.92 g.kg body wt-1.d-1, respectively). Mean nitrogen balance in the low-protein group remained negative throughout the study. These subjects experienced significant losses in lean tissue, immune response, and muscle function. The adequate-protein group was in nitrogen balance throughout the study, without changes in lean tissue, and with improvements in immune response, serum immunoglobulins, albumin, total protein values, and muscle function. Thus, elderly women fed the low-protein diet accommodated to the diet by compromising functional capacity, whereas those fed the adequate diet maintained functional capacity."


Evidence type: summary of experiments

Peng Li, Yu-Long Yin, Defa Li, Sung Woo Kim and Guoyao Wu.
British Journal of Nutrition (2007), 98, 237–252 doi: 10.1017/S000711450769936X

"A deficiency of dietary protein or amino acids has long been known to impair immune function and increase the susceptibility of animals and humans to infectious disease. However, only in the past 15 years have the underlying cellular and molecular mechanisms begun to unfold. Protein malnutrition reduces concentrations of most amino acids in plasma. Findings from recent studies indicate an important role for amino acids in immune responses by regulating: (1) the activation of T lymphocytes, B lymphocytes, natural killer cells and macrophages; (2) cellular redox state, gene expression and lymphocyte proliferation; and (3) the production of antibodies, cytokines and other cytotoxic substances. Increasing evidence shows that dietary supplementation of specific amino acids to animals and humans with malnutrition and infectious disease enhances the immune status, thereby reducing morbidity and mortality."


Evidence type: observational

Bonjour JP, Ammann P, Chevalley T, Rizzoli R.
Can J Appl Physiol. 2001;26 Suppl:S153-66.

"Among osteotrophic nutrients, proteins play an important role in bone development, thereby influencing peak bone mass. Consequently, protein malnutrition during development can increase the risk of osteoporosis and of fragility fracture later in life. Both animal and human studies indicate that low protein intake can be detrimental for both the acquisition of bone mass during growth and its conservation during adulthood. Low protein intake impairs both the production and action of IGF-I (Insulin-like growth factor-I). IGF-I is an essential factor for bone longitudinal growth, as it stimulates proliferation and differentiation of chondrocytes in the epiphyseal plate, and also for bone formation. It can be considered as a key factor in the adjustments of calcium-phosphate metabolism required for normal skeletal development and bone mineralization during growth. In healthy children and adolescents, a positive association between the amount of ingested proteins and bone mass gain was observed in both sexes at the level of the lumbar spine, the proximal femur and the midfemoral shaft. This association appears to be particularly significant in prepubertal children. This suggests that, like for the bone response to either the intake of calcium or weight-bearing exercise, the skeleton would be particularly responsive to the protein intake during the years preceding the onset of pubertal maturation."


Evidence type: summary of experiments

"As protein deficiency declines, the efficiency with which amino acids are reutilized increases, but small amounts of amino acids are continuously degraded, and their nitrogen is lost from the body even when no protein is being consumed. These losses are termed obligatory nitrogen losses. If protein intake declines below the amount of these obligatory losses, the amount of nitrogen excreted by the body will exceed the amount consumed, and the body will be in a state of negative nitrogen balance. As protein intake is increased, nitrogen balance will become less negative until, at some point, a steady state will be reached such that nitrogen intake will equal nitrogen loss; i.,e., nitrogen balance will be zero. An estimate of adult requirements for protein or amino acids can therefore be obtained from measurement of the minimum amount of protein or amino acid nitrogen that must be consumed to just balance body nitrogen losses."

[6]Dietary Reference Intakes: Macronutrients

Evidence type: summary of experiments

"The nitrogen balance method does have substantial practical limitations and problems. First, the rate of urea turnover in adults is slow, so several days of adaptation are required for each level of dietary protein tested to attain a new steady state of nitrogen excretion (Meakins and Jackson, 1996; Rand et al., 1976). Second, the execution of accurate nitrogen balance measurements requires very careful attention to all the details of the procedures involved. Since it is easy to overestimate intake and underestimate excretion, falsely positive nitrogen balances may be obtained (Hegsted, 1976). Indeed, an overestimate of nitrogen balance seems consistent throughout the literature because there are many observations of quite considerable apparent retention of nitrogen in adults (Oddoye and Margen, 1979). This observation is biologically implausible because (a) adults do not normally accrete body protein, and (b) the magnitude of the positive nitrogen balances is inconsistent with stability of body weight."

Comment: That last statement is odd. It could be seen as denying the evidence. We actually find it plausible that adults could accrete protein to a greater extent than currently assumed (more on this in a subsequent post). And of course, as every dieter knows, body weight can be stable even while lean mass is increasing, if fat is simultaneously decreasing.


Evidence type: meta-analysis of experiments

Elango R, Humayun MA, Ball RO, Pencharz PB.
Curr Opin Clin Nutr Metab Care. 2010 Jan;13(1):52-7.

"This review discusses recent evidence that suggests a significant underestimation of protein requirements in adult humans.


Traditionally, total protein requirements for humans have been determined using nitrogen balance. The recent Dietary Reference Intake recommendations for mean and population-safe intakes of 0.66 and 0.8 g/kg/day, respectively, of high-quality protein in adult humans are based on a meta-analysis of nitrogen balance studies using single linear regression analysis. We reanalyzed existing nitrogen balance studies using two-phase linear regression analysis and obtained mean and safe protein requirements of 0.91 and 0.99 g/kg/day, respectively. The two-phase linear regression analysis is considered more appropriate for biological analysis of dose-response curves. Considering the inherent problems associated with the nitrogen balance method, we developed an alternative method, the indicator amino acid oxidation technique, to determine protein requirements The mean and population-safe requirements in adult men were determined to be 0.93 and 1.2 g/kg/day and are 41 and 50%, respectively, higher than the current Dietary Reference Intakes recommendations.


The indicator amino acid oxidation-based requirement values of 0.93 and 1.2 g protein/kg/day and the reanalysis of existing nitrogen balance studies are significantly higher than current recommendations. Therefore, there is an urgent need to reassess recommendations for protein intake in adult humans."


Evidence type: experimental

Anna E. Thalacker-Mercer,1 James C. Fleet,1 Bruce A. Craig,2 and Wayne W. Campbell
J Nutr Biochem. 2010 November; 21(11): 1076–1082.

"Previous studies have suggested that the current RDA for protein (0.8 g•kg−1•d−1) is inadequate to maintain protein homeostasis [5, 32-34], fat-free mass, and skeletal muscle cross-sectional area in older adults [7, 35] while protein intake above the RDA may be needed to maintain lean body mass and type I muscle fiber cross sectional area in older women [5, 6]. The results of our study reveal a molecular signature of a biological response to inadequate dietary protein intake that is consistent with this hypothesis. We believe that the observation that transcripts for “muscle and organ development” and “cell differentiation” increase when the protein intake is greater than the RDA (i.e. cluster C5 in Figure 1) and previous phenotypic data [5-7, 32-35] suggest that there are positive responses to consuming protein in quantities greater than the RDA in skeletal muscle. Thus, our array data are consistent with previous reports that suggest a higher protein intake contributes to a healthier physiological profile [5, 6, 36] and better muscle responses to resistance training [37]. The study duration was not, however, sufficient to directly link changes in the skeletal muscle transcript profile with previously reported phenotypes of adaptation and accommodation [5-7, 32-35]."


Evidence type: experiment

Lemon PW, Dolny DG, Yarasheski KE.
Can J Appl Physiol. 1997 Oct;22(5):494-503.

"Six healthy men completed three 1-hr bouts of treadmill walk-jogging at low (L; 42 +/- 3.9% VO2max), moderate (M; 55 +/- 5.6%), and high (H; 67 +/- 4.5%) exercise intensity in order to determine whether moderate physical activity affects dietary protein needs. Both sweat rate and sweat urea N loss were greater (p < .10) with increasing exercise intensity. Seventy-two hour postexercise urine urea N excretion was elevated (p < .05) over nonexercise control (26.6 +/- 2.96 g) with both M (31.0 +/- 3.65) and H (33.6 +/- 4.39), but not L (26.3 +/- 1.86), intensities. Total 72-hr postexercise urea N excretion (urine + sweat) for the M and H exercise was greater than control by 4.6 and 7.2 g, respectively. This suggests that 1 hr of moderate exercise increases protein oxidation by about 29-45 g, representing approximately 16-25% of the current North American recommendations for daily protein intake. These data indicate that the type of exercise typically recommended for health/wellness can increase daily protein needs relative either to sedentary individuals or to those who exercise at lower intensities."


Evidence type: review of experiments

Tarnopolsky M.
Nutrition. 2004 Jul-Aug;20(7-8):662-8.

"Human skeletal muscle can oxidize at least eight amino acids (alanine, asparagine, aspartate, glutamate, isoleucine, leucine, lysine, and valine; 70); however, during exercise, the branched-chain amino acids (BCAA: isoleucine, leucine, and valine) are preferentially oxidized (43, 49, 58, 70). The BCAA are transaminated to their keto-acids via branched-chain aminotransferase (BCAAT), with subsequent oxidation occurring via branched-chain oxo-acid dehydrogenase enzyme (BCOAD; 8, 9). The amino-N group is usually transaminated with α-ketoglutarate to form glutamate, which is then transaminated with pyruvate to form alanine or aminated via glutamine synthase to form glutamine (15, 57). The BCOAD enzyme is rate limiting in BCAA oxidation, with about 5 to 8% being active (dephosphorylated) at rest, and 20 to 25% being active during exercise (8, 49)."


(Thank you to Bill Lagakos for pointing us to this study.)

Evidence type:

Nair KS, Welle SL, Halliday D, Campbell RG.
J Clin Invest. 1988 Jul;82(1):198-205.

"Because intravenous infusion of beta-hydroxybutyrate (beta-OHB) has been reported to decrease urinary nitrogen excretion, we investigated in vivo metabolism of leucine, an essential amino acid, using L-[1-13C]leucine as a tracer during beta-OHB infusion. Leucine flux during beta-OHB infusion did not differ from leucine flux during normal saline infusion in nine normal subjects, whereas leucine oxidation decreased 18-41% (mean = 30%) from 18.1 +/- 1.1 mumol.kg-1.h-1 (P less than 0.01), and incorporation of leucine into skeletal muscle protein increased 5-17% (mean = 10%) from 0.048 + 0.003%/h (P less than 0.02). Since blood pH during beta-OHB infusion was higher than the pH during saline infusion, we performed separate experiments to study the effect of increased blood pH on leucine kinetics by infusing sodium bicarbonate intravenously. Blood pH during sodium bicarbonate infusion was similar to that observed during the beta-OHB infusion, but bicarbonate infusion had no effect on leucine flux or leucine oxidation. We conclude that beta-OHB decreases leucine oxidation and promotes protein synthesis in human beings."


Evidence type: uncontrolled experiment

Pikosky M, Faigenbaum A, Westcott W, Rodriguez N.
Med Sci Sports Exerc. 2002 May;34(5):820-7.

"Healthy children (N = 11, 8.6 +/- 1.1 yr, 33.7 +/- 9.4 kg, 131 +/- 9.6 cm, BMI = 19.1 +/- 3.4) participated in a supervised resistance-training program 2 times.wk-1 for 6 wk. 15N glycine methodology was used to assess nitrogen flux (Q), protein synthesis (PS), protein breakdown (PB), and net turnover ([NET] = PS - PB) before (PRE) and after (POST) resistance training. Percent body fat (%BF), fat-free mass (FFM), fat mass (FM), and energy and protein intakes were also determined. PRE/POST measurements of 1RM for the chest press and leg extension were used to examine strength gains.


Gains associated with the chest press and leg extension were 10% and 75% (P < 0.001), respectively. Significant increases (P < 0.05) were noted for weight, height, FFM, and FM. Energy and protein intake remained constant. Significant decreases (PRE vs POST) were observed for Q (1.22 +/- 0.1 vs 0.75 +/- 0.05 gN.kg-1.d-1, P < 0.001), PS (6.48 +/- 0.47 vs 3.55 +/- 0.30 g.kg-1.d-1, P < 0.001), and PB (5.24 +/- 0.41 vs 2.96 +/- 0.30 g.kg-1.d-1, P < 0.01) after 6 wk of resistance training. NET was also reduced (P = 0.07, 1.24 +/- 0.31 vs 0.59 +/- 0.20 g.kg-1.d-1).


Resistance training resulted in a downregulation in protein metabolism, which may be energy based. Future studies are needed to clarify energy, as well as protein, needs in young children participating in this form of exercise."


Evidence type: uncontrolled experiment

Hartman JW, Moore DR, Phillips SM.
Appl Physiol Nutr Metab. 2006 Oct;31(5):557-64.

"It is thought that resistance exercise results in an increased need for dietary protein; however, data also exists to support the opposite conclusion. The purpose of this study was to determine the impact of resistance exercise training on protein metabolism in novices with the hypothesis that resistance training would reduce protein turnover and improve whole-body protein retention. Healthy males (n = 8, 22 +/- 1 y, BMI = 25.3 +/- 1.8 kg.m(-2)) participated in a progressive whole-body split routine resistance-training program 5d/week for 12 weeks. Before (PRE) and after (POST) the training, oral [15N]-glycine ingestion was used to assess nitrogen flux (Q), protein synthesis (PS), protein breakdown (PB), and net protein balance (NPB = PS-PB). Macronutrient intake was controlled over a 5d period PRE and POST, while estimates of protein turnover and urinary nitrogen balance (N(bal) = N(in) - urine N(out)) were conducted. Bench press and leg press increased 40% and 50%, respectively (p < 0.01). Fat- and bone-free mass (i.e., lean muscle mass) increased from PRE to POST (2.5 +/- 0.8 kg, p < 0.05). Significant PRE to POST decreases (p <0.05) occurred in Q (0.9 +/- 0.1 vs. 0.6 +/- 0.1 g N.kg(-1).d(-1)), PS (4.6 +/- 0.7 vs. 2.9 +/- 0.3 g.kg(-1).d(-1)), and PB (4.3 +/- 0.7 vs. 2.4 +/- 0.2 g.kg(-1).d(-1)). Significant training-induced increases in both NPB (PRE = 0.22 +/- 0.13 g.kg(-1).d(-1); POST = 0.54 +/- 0.08 g.kg(-1).d(-1)) and urinary nitrogen balance (PRE = 2.8 +/- 1.7 g N.d(-1); POST = 6.5 +/- 0.9 g N.d(-1)) were observed. A program of resistance training that induced significant muscle hypertrophy resulted in reductions of both whole-body PS and PB, but an improved NPB, which favoured the accretion of skeletal muscle protein. Urinary nitrogen balance increased after training. The reduction in PS and PB and a higher NPB in combination with an increased nitrogen balance after training suggest that dietary requirements for protein in novice resistance-trained athletes are not higher, but lower, after resistance training."


Evidence type: uncontrolled experiment

Moore DR, Del Bel NC, Nizi KI, Hartman JW, Tang JE, Armstrong D, Phillips SM.
J Nutr. 2007 Apr;137(4):985-91.

"We aimed to determine the impact of intense resistance training, designed to increase lean body mass (LBM), on both fasted and fed whole body protein kinetics in untrained young men. Twelve healthy males (22 +/- 2 y of age; BMI, 24.3 +/- 2.4 kg/m(2)) participated in a 12-wk (5-d/wk) resistance training program. Before and after training, a primed constant infusion of [1-(13)C]leucine was used to measure whole body leucine turnover, protein breakdown, and nonoxidative leucine disposal in the fasted and fed states. Participants were studied during 5-d controlled diet periods that provided a moderate protein intake [1.4 g/(kg body wt . d)]. We estimated protein turnover and nitrogen balance. Training increased LBM (61.6 +/- 6.9 vs. 64.8 +/- 6.7 kg, P < 0.05). After training, whole body leucine turnover was reduced (P < 0.01) in both fasted (167 +/- 18 vs. 152 +/- 17) and fed (197 +/- 23 vs. 178 +/- 21) states [all values micromol/(kg LBM . h)]. Training-induced decreases (P < 0.01) in protein breakdown occurred in the fasted (165 +/- 18 vs. 144 +/- 17) and fed (111 +/- 23 vs. 93 +/- 20) states. Following training, nonoxidative leucine disposal was similarly reduced (P < 0.01) in the fasted (144 +/- 18 vs. 126 +/- 18) and fed (151 +/- 20 vs. 133 +/- 19) states. Nitrogen balance was more positive after training (13.7 +/- 8.1 vs. 33.4 +/- 12.5 g/(kg LBM . d), P < 0.01) indicating an increased retention of dietary nitrogen. Intense resistance training alters whole body protein kinetics in novice weightlifters regardless of feeding status. The increase in nitrogen balance after training demonstrates a more efficient utilization of dietary nitrogen, suggesting that protein requirements for novice weightlifters are not elevated."


Evidence type: experimental

L J Hoffer, B R Bistrian, V R Young, G L Blackburn, and D E Matthews.
J Clin Invest. 1984 March; 73(3): 750–758.

"A randomized comparison trial of two very low calorie weight reduction diets was carried out for 5 or 8 wk in 17 healthy obese women. One diet provided 1.5 g protein/kg ideal body weight; the other provided 0.8 g protein/kg ideal body weight plus 0.7 g carbohydrate/kg ideal body weight. The diets were isocaloric (500 kcal). Amino acid metabolism was studied by means of tracer infusions of L-[1-13C]leucine and L-[15N]alanine. After 3 wk of adaptation to the diets, nitrogen balance was zero for the 1.5 g protein diet but -2 g N/d for the 0.8 g protein diet. Postabsorptive plasma leucine and alanine flux decreased from base line by an equal extent with both diets by approximately 20 and 40%, respectively. It was concluded that protein intakes at the level of the recommended dietary allowance (0.8 g/kg) are not compatible with nitrogen equilibrium when the energy intake is severely restricted, and that nitrogen balance is improved by increasing the protein intake above that level. Basal rates of whole body nitrogen turnover are relatively well maintained, compared with total fasting, at both protein intakes. However, turnover in the peripheral compartment, as evidenced by alanine flux, may be markedly diminished with either diet."

Comment: The authors have assumed that the RDA is adequate, which would imply that the condition of weight loss had increased protein needs. However, since we have seen that the RDA is not, in fact adequate, the conclusion is unwarranted. I.e., the study was not controlled for people not losing weight.


Evidence type: experimental

W J Smith, L E Underwood and D R Clemmons.
The Journal of Clinical Endocrinology & Metabolism February 1, 1995 vol. 80 no. 2 443-449

"Sixteen adult subjects (7 males and 9 females), aged 22-40 yr, were recruited and assessed in the same manner as the children [i.e. by advertisement, and determined to be healthy by a battery of tests.] They consumed a diet that provided 35 Cal/kg IBW and 1 g protein/kg IBW for the first 3 study days. Nonprotein calories were provided as 70% carbohydrate and 30% lipid. On study days 4-9, half of the 16 subjects received only 17 Cal/kg IBW, but continued to receive 1 g protein/kg IBW.


"During the 6 days of calorie restriction, the adults lost 1.7 2 0.1 kg (mean 2 SD) [...]. Baseline nitrogen balance in the adults (mean of days 2 and 3) was -82 2 47 mmol/day (mean + SE) and declined to -196 2 40 mmol/day (the mean of study days 8 and 9; P < 0.05)."

Comment: The authors showed that when healthy adults were given a constant amount of protein, but two different levels of calories, nitrogen balance was more negative in the lower calorie condition. However, both diets were still high enough in carbohydrate to be non-ketogenic, and the difference between the diets was primarily a carbohydrate difference. In a non-keto-adapted state, carbohydrates can spare protein, because your metabolism is much more dependent on glucose for fuel. That means that reducing carbohydrates will require more protein for gluconeogenesis. After keto-adaptation, many tissues use ketones instead, and this spares protein. So we would expect that lowering carbohydrates without keto-adapting would negatively affect nitrogen balance. Therefore, we can't conclude that the negative nitrogen balance in this study reflects increased protein needs from caloric restriction alone, because it could be that the same caloric deficit in a keto-adapted state would have different results. It would be interesting to see an analogue of this study in keto-adapted people. We are not aware of any such study.


Evidence type: randomised controlled trial

Baba NH, Sawaya S, Torbay N, Habbal Z, Azar S, Hashim SA.
Int J Obes Relat Metab Disord. 1999 Nov;23(11):1202-6.

"Thirteen male obese hyperinsulinemic normoglycemic subjects were divided into two groups and fed hypoenergetic diets providing 80% of their resting energy expenditure (REE). One group received a high-protein diet (HP; 45% protein, 25% carbohydrates, and 30% fat as percent of dietary energy) and the other a high-carbohydrate diet (HC; 12% protein, 58% carbohydrates and 30% fat).


"Weight loss was higher in the HP than HC group (8.3+/-0.7 vs 6.0+/-0.6 kg, P<0. 05). There was a decrease in body fat in both groups, whereas body water decreased significantly more in the HP group. REE decreased more in the HC than the HP group (-384.3+/-84.6 vs -132.3+/-51.0 kcal, P<0.05). Serum total cholesterol, triglycerides and LDL cholesterol decreased significantly to a similar extent in both diet groups, while HDL cholesterol was decreased significantly only in the HP group. Mean fasting insulin decreased significantly in both diet groups and reached the normal range only in the HP group."


Evidence type: randomized controlled trial

Labayen I, Díez N, González A, Parra D, Martínez JA.
Forum Nutr. 2003;56:168-70.

"DESIGN: Eleven obese (BMI>30) women were randomly assigned to a 10w dietary intervention study comparing HP (30% protein) or HC (55% carbohydrate) energy restricted diets providing 30% energy fat content. Substrate utilisation was evaluated by indirect calorimetry. Body weight and composition (Bod Pod) and blood measurements were performed before and after weight loss.

RESULTS: On average, the individuals on the HP dietary group lost 4.4 kg more than those in the HC program (p<0.50), which was mainly due to a fat mass loss (3.7 kg, p<0.05) with no statistical differences in lean body mass reduction. These losses were accompanied by a significant decrease in fasting leptin in the HP group (-52%; P<0.05). On the other hand post-absorptive lipid oxidation decreased in the HC group (-48%) and remained unchanged in the HP groups.

CONCLUSIONS: The replacement of some dietary carbohydrate by protein in energy restricted diets, improves weight and fat losses and specifically promotes lipid oxidation in the fasting state, without major different in lean body mass depletion."


Evidence type: randomized controlled trial

Evangelista LS, Heber D, Li Z, Bowerman S, Hamilton MA, Fonarow GC.
J Cardiovasc Nurs. 2009 May-Jun;24(3):207-15. doi: 10.1097/JCN.0b013e31819846b9.

"[T]his feasibility study was conducted to compare the effects of an HP, hypoenergetic diet (40% total energy from carbohydrates, 30% from protein, and 30% from fat), a standard protein (SP), hypoenergetic diet (55% total energy from carbohydrates, 15% from protein, and 30% from fat), and a conventional diet (high carbohydrates, low fat, high fiber, with no energy restrictions) on body weight and adiposity in patients with HF and increased BMI greater than or equal to 27 kg/m2 and DM.


"The current report reflects data from the first 14 patients who consented to participate in the study; recruitment and enrollment are still ongoing. The patients were randomized to the HP (n = 5), SP (n = 5), and conventional diets (n = 4), respectively.



Comment: Gee, look at that cholesterol. Not quite statistically significant (because the group size was small) but highly suggestive.


Evidence type: experimental

Pasiakos SM, Cao JJ, Margolis LM, Sauter ER, Whigham LD, McClung JP, Rood JC, Carbone JW, Combs GF Jr, Young AJ.
FASEB J. 2013 Sep;27(9):3837-47. doi: 10.1096/fj.13-230227.

"The purpose of this work was to determine the effects of varying levels of dietary protein on body composition and muscle protein synthesis during energy deficit (ED). A randomized controlled trial of 39 adults assigned the subjects diets providing protein at 0.8 (recommended dietary allowance; RDA), 1.6 (2×-RDA), and 2.4 (3×-RDA) g kg(-1) d(-1) for 31 d. A 10-d weight-maintenance (WM) period was followed by a 21 d, 40% ED. Body composition and postabsorptive and postprandial muscle protein synthesis were assessed during WM (d 9-10) and ED (d 30-31). Volunteers lost (P<0.05) 3.2 ± 0.2 kg body weight during ED regardless of dietary protein. The proportion of weight loss due to reductions in fat-free mass was lower (P<0.05) and the loss of fat mass was higher (P<0.05) in those receiving 2×-RDA and 3×-RDA compared to RDA. The anabolic muscle response to a protein-rich meal during ED was not different (P>0.05) from WM for 2×-RDA and 3×-RDA, but was lower during ED than WM for those consuming RDA levels of protein (energy × protein interaction, P<0.05). To assess muscle protein metabolic responses to varied protein intakes during ED, RDA served as the study control. In summary, we determined that consuming dietary protein at levels exceeding the RDA may protect fat-free mass during short-term weight loss."


Evidence type: randomised prospective study

Flechtner-Mors M, Boehm BO, Wittmann R, Thoma U, Ditschuneit HH.
Diabetes Metab Res Rev. 2010 Jul;26(5):393-405. doi: 10.1002/dmrr.1097.

"Obese subjects received instructions for an energy-restricted diet with a calorie deficit of 500 kcal/day and were randomly assigned to either high-protein (1.34 g/kg body weight) or conventional protein (0.8 g/kg body weight) diets for 12 months. Protein-enriched meal replacements were used to enrich one arm of the diet with protein throughout the study. In all, 67% of the participants completed the 1-year study.

"RESULTS Subjects following the high-protein diet lost more body weight and more fat mass compared with those on the conventional protein diet, whereas the loss of fat-free mass was similar in both diet groups. Biochemical parameters associated with the metabolic syndrome improved in both diet groups. Improvements were modestly greater in subjects with the high-protein diet. After 12 months of treatment, 64.5% of the subjects in the high-protein diet group and 34.8% of the subjects in the conventional diet group no longer met three or more of the criteria for having the metabolic syndrome."


Evidence type: explanation and comparison of experiments.

Stephen D Phinney.
Nutrition & Metabolism 2004, 1:2 doi:10.1186/1743-7075-1-2

"An example of what happens when these mineral considerations are not heeded can be found in a study prominently published in 1980 [18]. This was a study designed to evaluate the relative value of "protein only" versus "protein plus carbohydrate" in the preservation of lean tissue during a weight loss diet. The protein only diet consisted solely of boiled turkey (taken without the broth), whereas the protein plus carbohydrate consisted of an equal number of calories provided as turkey plus grape juice. Monitored for 4 weeks in a metabolic ward, the subjects taking the protein plus carbohydrate did fairly well at maintaining lean body mass (measured by nitrogen balance), whereas those taking the protein only experienced a progressive loss of body nitrogen.

"A clue to what was happening in this "Turkey Study" could be found in the potassium balance data provided in this report. Normally, nitrogen and potassium gains or losses are closely correlated, as they both are contained in lean tissue. Interestingly, the authors noted that the protein only diet subjects were losing nitrogen but gaining potassium. As noted in a rebuttal letter published soon after this report [19], this anomaly occurred because the authors assumed the potassium intake of their subjects based upon handbook values for raw turkey, not recognizing that half of this potassium was being discarded in the unconsumed broth. Deprived of this potassium (and also limited in their salt intake), these subjects were unable to benefit from the dietary protein provided and lost lean tissue. Also worthy of note, although this study was effectively refuted by a well-designed metabolic ward study published 3 years later [20], this "Turkey Study" continues to be quoted as an example of the limitations of low carbohydrate weight loss diets."


Evidence Type: experiment

Volek, Jeff S., Erin E. Quann, and Cassandra E. Forsythe.
Strength & Conditioning Journal 32.1 (2010): 42-47.

"We performed a similar experiment in overweight/obese men who were placed in a low-fat diet group that restricted fat to less than 25% of energy or a very low–carbohydrate ketogenic diet group that reduced carbohydrate to less than 15% energy. Both groups also participated in a resistance training program (see Practical Applications) (16). Body composition was assessed using dual energy x-ray absorptiometry before and after the 12-week program. The results were compared with non-training diet only groups. As expected, the low-carbohydrate diet group lost more fat, which was associated with greater decreases in insulin. Resistance training, independent of diet, resulted in increased lean body mass without compromising fat loss in both diet groups. The most dramatic reduction in percent body fat was in the low-carbohydrate diet resistance training group (25.3%), followed by low-fat resistance training(23.5%), low-carbohydrate diet only (23.4%), and low-fat diet only (22.0%) groups. These data show for the first time that resistance training is a potent stimulus to protect lean body mass in men consuming a low-carbohydrate diet, while still allowing for significantly greater fat loss."


Evidence type: summary of experiments

PG Lindner, GL Blackburn.
Obesity/Bariatric Med, 1976, pp. 198--216

"The question that remained to be answered was what amount of protein was necessary to maintain positive energy nitrogen balance ⁹³ for a time sufficient to allow the obese individual to reach his normal size.

"Blackburn, et al investigated this question while also measuring the biochemical and clinical aspects of what he termed the protein-sparing modified fast (PSMF). One hundred forty-six patients (111 outpatients) were followed at the Massachusetts Institute of Technology Clinical Research Center while undergoing a comprehensive weight reduction program that included nutritional education, behavior modification, exercise, and the PSMF. ⁹⁴'⁹⁵ He found that in males, nitrogen (N) balance was obtained at 1.4 gm protein daily/kg ideal body weight (IBW) and in females, N balance was obtained at 1.2 gm/kg IBW. Outpatients tolerated the PSMF well in a wide variety of lifestyles and occupations and invariably found it easier than a balanced deficit diet. Ingestion of 40 to 80 gm of carbohydrate in addition to protein, however, markedly reduced ketosis and reistated hunger.⁹⁶"