Keto-adaptation: what it is and how to adjust

What is keto-adaptation?

Keto-adaptation is the process of shifting your metabolism from relying mostly on glucose for fuel, to relying mostly on fat-based sources of fuel. Not only does fat oxidation itself increase, but your body starts producing enough ketones that they can be used as a significant source of fuel as well. Ketones are derived from partially metabolized fat, and they can be used in many of the same tissues of the body as glucose can, including much of the brain. The benefits of using fat and ketones rather than glucose for fuel are many, and are the main subject of this site. However, it takes time for the metabolism to adjust to producing and using ketones at a significant rate. Even though changes are evident within days of carbohydrate restriction, improvements continue for weeks.

In brief:

  • Carbohydrate-based fueling is a self-perpetuating cycle: it runs out quickly, and every time you eat more carbs you delay adaptation to fat-burning.
  • Fat-based fueling is sustainable, because it allows access to a very large store of energy without you frequently stopping to refuel. Blood sugar is maintained though precise internal processes without wild swings. These two together create a desirable flow of even, stable energy, mood, and alertness.
  • There is a delay between first reducing the amount of carbohydrates that you eat, and having a smoothly running fat metabolism. In the intervening days, you may feel slow, or even unwell. These symptoms can be minimized by making sure to eat lots of fat, staying hydrated, and using salt liberally. Other electrolytes may also be helpful to add -- homemade broth makes a good supplement. Keep carbs consistently low, or you will never adapt and the process will go on indefinitely.

Carbohydrate-based fueling is a self-perpetuating cycle.

The body can store only relatively small amounts of glucose, in the form of glycogen. About 100 grams can be stored in the liver, and about 400 grams can be stored in the muscles. Muscle glycogen can only be used by the muscle it is stored in — it can't go back to the bloodstream — so the liver glycogen is the only source that can be used to keep blood sugar stable, and provide fuel for the brain. If you are not making use of ketones for fuel, then this is not enough glucose to get through a typical day, let alone a day when you are doing something strenuous. If you depend on glucose metabolism, then you have to frequently replenish your glycogen stores or you will begin to feel tired, physically and mentally.

There are basically two ways to get the necessary glucose, and only one of them involves eating it. The first is to eat carbohydrate. Unfortunately, every time you ingest more than a small amount of carbohydrate, it stops all progression toward keto-adaptation. So this strategy is a Catch-22. It makes you continually dependent on dietary carbohydrate. It locks you in, because supply is limited, but restocking prevents other fuels from becoming available.

The other way to get glucose is to let the body make its own on demand out of protein. This process is called gluconeogenesis. Gluconeogenesis is the reason that eating carbohydrate is not necessary, even though some amount of glucose is manufactured and used internally. This is analogous to any other internally produced nutrient, such as vitamin D, which we don't need to ingest, because the body makes it in response to sun exposure, or to a hormone, like adrenaline, that we make and use every day, but don't need to get from food.

One of the benefits that comes directly from this physiological mechanism is that on a keto diet you will no longer need to eat so often. Skipping a meal does not become an emergency, or even a problem. A lot of people have problems with mood, cognition, and wakefulness if they don't eat frequently. On a keto diet your blood sugar will naturally become steady, and the advice to eat every 3 hours to prevent hypoglycemia will become irrelevant.

What exactly happens during keto-adaptation?

In their recent book The Art and Science of Low Carbohydrate Living, Volek and Phinney describe two stages of keto-adaptation. In the first few days of a keto diet, your body is still running on glycogen stores. This is the toughest part of the process, because in order to break the vicious cycle of glucose-based metabolism, you have to avoid eating carbohydrates, even though your glycogen stores are dwindling. Fat metabolism is still not optimized, and ketone production hasn't become significant.

Another noticeable effect in the first days is water loss. One of the inefficiencies of glycogen storage is that it needs to be stored with water. It takes about 3 or 4 grams of water to store a gram of glycogen [1] . This means that as you deplete your glycogen stores you could lose up to 2 kg of water! Not only that, but high circulating insulin levels cause water retention by inhibiting sodium excretion (see e.g. [2]). The keto diet lowers insulin levels and increases insulin sensitivity, allowing excess fluid to be released. These combined effects are the origin of the claim that the weight lost on keto diets is due to water loss. In the very beginning, this is true, but subsequently, of course, it is not.

When glycogen runs out, you start producing ketones, and some are excreted in the urine. This is easy to measure, and some keto dieters use it to know if they are hitting a low enough level of carbohydrate restriction. This also marks the beginning of the second stage of keto-adaptation. Ketones are now becoming available for fuel, but they haven't yet risen to their stable adapted level. There is an interesting interplay between ketone use in the muscles and the brain. When ketone levels are low, the muscles tend to use them directly for fuel, but as levels increase, the muscles use them less, turning to fat for fuel instead. The brain, on the other hand, uses ketones proportionally to their concentration in the blood. This means that at low levels of ketones, the brain's supply is not much affected, because the muscles intercede, but above some threshold, the brain's supply rapidly becomes much higher. At this point, the brain can rely on ketones, and since it is no longer susceptible to running out of fuel, the need to eat frequently throughout the day to maintain mental function disappears. The muscles in turn now rely on fat: they finally have access to a virtually unlimited supply of energy, which is particularly valuable for athletes.

Much confusion has been generated by scientists not recognizing one or both stages of keto-adaptation. A few studies have been publicized claiming that low carbohydrate diets worsen mental or physical performance (e.g. [3], [4]). On reading the details, it turns out that the testing was done in the first few days of carbohydrate restriction. Obviously, these studies are not valid criticisms of the keto diet, except as measurements of the initial adaptation cost. They do not reflect the longer-term outcome.

How to make keto-adaptation as quick and painless as possible

As noted above, the difficult part of keto-adaptation is the first stage. There are two reasons. The first is that glucose is less available, but fat and ketone metabolism haven't effectively taken over. The best strategy for coping with this is to eat a lot of fat. Even if you eventually wish to get most of your fat from your fat stores, you do not normally need to restrict it in the diet, and especially not now. Fat is an important source of essential fatty acids and nutrients. Moreover, ingesting fat with protein helps to moderate the insulin response. A keto diet is not a high protein diet, it is a high fat diet. Do not fear it. Eat plenty of fat during keto-adaptation to ensure you have energy available.

The second difficulty is a result of the sodium excretion and transient rapid water loss we mentioned. If care is not taken to replenish sodium and water, both sodium and potassium are sometimes lost too rapidly. This can cause tiredness, weakness, and headaches. Be sure to get enough sodium: about 5 grams per day, or 2 teaspoons of table salt, will help prevent these symptoms.

Adequate potassium may be necessary to preserve lean mass [5], and magnesium deficiency can lead to muscle cramps, as well as fatigue and dizziness. Both of these minerals are abundant in meat, but are easily lost though cooking: into the water, if the meat was boiled, or the drippings otherwise. In addition to taking care to preserve the liquid from meat, acute effects can be cut short through supplementing potassium and magnesium by capsule. We recommend regularly drinking broth.

Finally, keep your dietary carbohydrates low. The worst scenario is to eat some every few days -- you will set yourself back, and be in perpetual limbo. Now is not the time to experiment with your carbohydrate tolerance, or eat foods you aren't sure about the content of. Commit to a very low level of carbohydrate intake, and stay with it consistently for at least long enough to get ketone production in full force. Most people we have talked to, if they experienced any discomfort at all, felt fully functional within 4 or 5 days. However, metabolic changes continue for at least two weeks and often more [6]. We recommend a 30 day trial at near zero levels of carbohydrate, to give yourself a chance to experience a completely keto-adapted state.


  • The USDA National Nutrient Database for Standard Reference is a large database of nutrients including carbohydrate levels of whole foods and fast foods both.
  • Testing strips for urine ketones are useful for figuring out if you are getting into ketosis. We haven't tried this brand, but it's currently a good price. We've used Ketostix, and they work fine.
  • A fancier tool is a blood ketone meter. It works just like a glucose meter. In fact it doubles as one. This is better than urine testing, because it is more accurate, and it measures actual blood concentration. However, the test strips are pretty expensive.

Further Reading:


[1] Evidence type: experimental.
Olsson, K.-E. and Saltin, B. (1970), Variation in Total Body Water with Muscle Glycogen Changes in Man. Acta Physiologica Scandinavica, 80: 11–18. doi: 10.1111/j.1748-1716.1970.tb04764.x
"19 subjects performed prolonged heavy arm and leg exercise after which they had a protein and fat diet for three days. Thereafter they switched to a carbohydrate enriched diet during a 4-day period. The measurements were performed on the 3rd day and then repeated on the 7th day. The glycogen concentration in the thigh and the arm muscles was 4.5 and 2.6 g/kg wet muscle on the 3rd day and increased with the carbohydrate enriched diet to 19.9 and 16.9 g/kg wet muscle, respectively. Body weight increased 2.4 kg during this period of 4 days. The total body water increased 2.2 1 which is assumed to be caused by the glycogen storage in the muscles and the liver. The amount of glycogen stored was calculated to be at least 500 g, which means that 3-4 g of water is bound with each gram of glycogen."

[2] Evidence type: review of a variety of experimental conditions.
R. A. DeFronzo (1981) The effect of insulin on renal sodium metabolism: A review with clinical implications. Diabetologia Volume 21, Number 3, 165-171, DOI: 10.1007/BF00252649
Data are discussed which demonstrate that insulin plays an important role in sodium metabolism. The primary action of insulin on sodium balance is exerted on the kidney. Increases in plasma insulin concentration within the physiological range stimulate sodium reabsorption by the distal nephron segments and this effect is independent of changes in circulating metabolites or other hormones. Several clinical situations are reviewed: sodium wasting in poorly controlled diabetics, natriuresis of starvation, anti-natriuresis of refeeding and hypertension of obesity, in which insulin-mediated changes in sodium balance have been shown to play an important pathophysiological role."

[3] Langfort J, Zarzeczny R, Pilis W, Nazar K, Kaciuba-Uścitko H. The effect of a low-carbohydrate diet on performance, hormonal and metabolic responses to a 30-s bout of supramaximal exercise. Eur J Appl Physiol Occup Physiol. 1997;76(2):128-33.
The aim of this study was to find out whether a low-carbohydrate diet (L-CHO) affects: (1) the capacity for all-out anaerobic exercise, and (2) hormonal and metabolic responses to this type of exercise. To this purpose, eight healthy subjects underwent a 30-s bicycle Wingate test preceded by either 3 days of a controlled mixed diet (130 kJ/kg of body mass daily, 50% carbohydrate, 30% fat, 20% protein) or 3 days of an isoenergetic L-CHO diet (up to 5% carbohydrate, 50% fat, 45% protein) in a randomized order.
The main conclusions of this study are: (1) a L-CHO diet is detrimental to anaerobic work capacity, possibly because of a reduced muscle glycogen store and decreased rate of glycolysis; (2) reduced carbohydrate intake for 3 days enhances activity of the sympathoadrenal system at rest and after exercise.

[4] D'Anci KE, Watts KL, Kanarek RB, Taylor HA. Low-carbohydrate weight-loss diets. Effects on cognition and mood. Appetite. 2009 Feb;52(1):96-103. Epub 2008 Aug 29.
In the present experiment, cognitive effects of a low-carbohydrate diet were compared to those of another popular weight reduction diet over a 3-week period.
These data suggest that after a week of severe carbohydrate restriction, memory performance, particularly on difficult tasks (e.g., backward compared to forward digit span; spatial memory), is impaired.

Comment: This paper is interesting. The low carb dieters experienced memory deficits one week into the diet, and long term memory problems later, but the long term memory experiments were from memories that were formed at that same one week point, and so the problems were likely to be from poor memory formation, not poor recall ability. The authors suggest that cognition was better after more carbohydrate was added, but in the latter two weeks of the experiment the amount of carbohydrate added was very low, and the subjects were still well within ketogenic levels. So this isn't a very compelling explanation. It seems much more plausible to us that this improvement was from keto-adaptation. While we don't completely agree with the analysis of the authors, they did not state such a ridiculous interpretation of their findings in their paper as they did in the press: Science Daily reports:
A new study from the psychology department at Tufts University shows that when dieters eliminate carbohydrates from their meals, they performed more poorly on memory-based tasks than when they reduce calories, but maintain carbohydrates. When carbohydrates were reintroduced, cognition skills returned to normal.

"This study demonstrates that the food you eat can have an immediate impact on cognitive behavior," explains Holly A. Taylor, professor of psychology at Tufts and corresponding author of the study. "The popular low-carb, no-carb diets have the strongest potential for negative impact on thinking and cognition."

Whereas the abstract itself was more factual:
"Results showed that during complete withdrawal of dietary carbohydrate, low-carbohydrate dieters performed worse on memory-based tasks than ADA dieters. These impairments were ameliorated after reintroduction of carbohydrates. Low-carbohydrate dieters reported less confusion (POMS) and responded faster during an attention vigilance task (CPT) than ADA dieters. Hunger ratings did not differ between the two diet conditions. The present data show memory impairments during low-carbohydrate diets at a point when available glycogen stores would be at their lowest. A commonly held explanation based on preoccupation with food would not account for these findings. The results also suggest better vigilance attention and reduced self-reported confusion while on the low-carbohydrate diet, although not tied to a specific time point during the diet. Taken together the results suggest that weight-loss diet regimens differentially impact cognitive behavior."

In other words, except for the memory problems that can be accounted for by keto-adaptation, the low carb dieters had equal or better cognitive performance than the ADA dieters, and yet this is cited as proof of the opposite!

[5] Evidence type: explanation and comparison of experiments.
Stephen D Phinney (2004) Ketogenic diets and physical performance. 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."

[6] Evidence type: experiment.
Oliver E. Owen, Philip Felig, Alfred P. Morgan, John Wahren, and George F. Cahill, Jr. Liver and kidney metabolism during prolonged starvation. J Clin Invest. 1969 March; 48(3): 574–583.
"Blood glucose and insulin concentrations fell acutely during the 1st 3 days of fasting, and alpha amino nitrogen after 17 days. The concentration of free fatty acids, β-hydroxybutyrate, and acetoacetate did not reach a plateau until after 17 days."


  1. Into my RSS feeder you go! ;) Very nice beginning post with lots of info, written in a clear, easily accessible style. I look forward to more to come and have only one suggestion/question.

    How did you come to your ketogenic way of eating and what is it that it has done/is doing for you that impresses you sufficiently to have ostensibly made it a permanent way of eating and to have given you the motivation to take this information and put it into an accessible, clear form for a varied and broad audience?

  2. mem:

    Thank you for the kind words!

    I'm of two minds about posting our personal stories. On the one hand, I think it helps writers if they are honest and open about where they are coming from, and I think it helps readers if they have an idea of the background, motivations, and biases of writers.

    On the other hand, a major theme of this blog is that people can and should discriminate among *types of evidence*, and avoid basing their health choices on unreliable kinds of evidence. Personal stories are, of course, *anecdotal evidence*, which is both one of the least reliable and most seductive kinds of evidence.

    Some people — in fact probably *most* people — have difficulty understanding and remembering arguments about dry facts, but can't forget a compelling personal story with drama and a happy ending. I'm uncomfortable with the thought that people will be unduly influenced by the memorable stories of our personal lives.

    Also some *different* people are very suspicious of anecdotes about health practices. Those folks detect the smell of snake oil when they read unverified stories of health improvements, especially when it sounds "Too good to be true.". I respect the skepticism of those people, and it would be a bit of a shame to turn them off by posting about exactly how the keto diet appears to have helped us. :-)

    On the gripping hand [*], I like to err on the side of openness when in doubt, so I would be more comfortable posting the story of how we got here. Accompanied by a prominent label saying that such stories are *anecdotal evidence*, and are not a reliable guide to your own beliefs about health. Let's see what Amber thinks.

    [*] That's an old science fiction/hacker culture reference.

  3. HI, maybe relevant: same general idea, other expression: http://www.grc.com/health/lowcarb.htm

  4. Wow.
    Incredible first blog post. I can't find anything to disagree with.
    I was on a ketogenic diet myself for four months straight. No real problem except for some nocturnal muscle cramps that resolved with potassium and magnesium supplements. Tincture of time may have also helped. I eat 50 to 100 g of digestible carb daily now, so probably not in ketosis.

    One thing I would mention is that we can also make some glucose, although not much, from the glycerol spine of the triglyceride molecule.


  5. Steve:

    Thank you for the kind words! I'm glad to have an informed reader like yourself.

    Why did you switch from a ketogenic diet to a diet of 50 to 100 grams of digestible carbohydrate?

    Thanks for the note about glucose production from triglyceride. I've just downloaded this paper for future study: Gerich-2001-“Renal Gluconeogenesis—Tts Importance In Human Glucose Homeostasis”. Ooh, and there is this: Kaleta-2012-“Against The Stream: Relevance Of Gluconeogenesis From Fatty Acids For Natives Of The Arctic Regions”, which Mike Eades tweeted the other day. It says that glucose can be produced from fatty acids.

    I have so much more to learn...

  6. Tom:

    Thanks for the link. Hey—I recognize that guy! Steve Gibson has worked in software engineering and computer security for a long time, and I've seen his name and occasional posts by him. (I too work in software engineering and computer security. And now that I think about it, I too have done so for a long time!)

    It's fun to see that he's taking up a ketogenic diet kick.

    I like his bibliography page:


    I'm going to read more about this book "Deadly Harvest"...

  7. Thank you for your informative and concise article. I've been on a ketogenic diet for about 3 weeks and have ran into a few problems due to not educating myself properly before jumping into the diet. I ended up in the ER for a panic attack, but I wasn't aware of what it was when it happened (that was first the time).

    I started having bouts of reactive hypoglycemia which I think triggers the panic attacks. I am not diabetic, I checked my A1C two weeks ago and it was at 5.6 which isn't that great though. But it has come down from 5.9 from about a year ago when I had no idea about the ketogenic diet.

    After reading your article I suppose I am not cutting out enough carbs from my diet and I am in the limbo you mentioned. I fry a lot of eggplants and baby squash in coconut oil and/or butter and eats lots of avacados and meats mostly. But I fear I'm eating too many vegatables which might be keeping me in the state of limbo.

    Any thoughts?

    Thanks again for your precise and informative article, it has given me the confidence that I can overcome these symptoms by sticking with it.

  8. Hi ARM,

    Thank you for writing.

    We publish this blog as a way to communicate with the public about generic factual information that we've learned. If you need specific advice about your health, then you need someone who is trained in medicine (neither of us are) and who is familiar with your condition and your history. Please talk to your personal doctor.



    P.S. Please continue reading our blog, and suggest to your doctor that he or she do so as well! ☺

  9. The adaption phase is interesting. First time I tried to get into Ketosis it nearly killed me. I woke up in bed on the fourth night after cutting carbs, with my head spinning and only just managed to summons the strength to get to the bathroom. It was the first of about 200 trips over the next few days. I had extreme fatigue, nausea and kidney pain too. It's possible I got sick at a coincidental time, because my symptoms were so severe.

    I have a short memory, so tried again recently, supplementing with sodium much earlier in the process. It was much, much easier that time. I felt fine generally and could even lift weights without problem. When I tried to play sport though it became very apparent I had not yet adapted. I tired very early and other people noticed that I was off.

    I'd like to get into a usable Keto state, but I hope it doesn't take weeks to be able to do physical things properly.

    1. Hi, Mike. I can't say what was happening in your case. Nausea, fatigue, and kidney pain are all signs of dehydration. It is easy to get dehydrated during keto-adaptation, and it would make sense that sodium would help with that, by encouraging water retention, as would drinking more.

  10. Hi and thanks for the excellent article. Question for you: does beta-oxidation necessarily mean ketosis? Just reading J Stanton's article on "low carb flu" at Gnoll and it seemed like you could be burning fat without being in a ketogenic state.

    1. Hi, Tom. This is a great question. Ketone bodies are always being produced, but when carbohydrate intake is constantly high, ketone levels stay low. It's not called ketosis until they get above a threshold around 0.5 mM. You can definitely still burn fat without being in ketosis. One difference, though, is that since you don't have a large supply of ketones to go around, you will need to use more glucose than you otherwise would.

      Respiratory Quotient (RQ) gives an indication of how much fat a person is burning. Pure carbohydrate would be 1.0, and pure fat, about 0.7. In a normal person on a non-ketogenic diet, it's about .85. Petro Dobromylskyj estimates that a keto-adapted person would have an RQ of about .81. You might enjoy his post about that: http://high-fat-nutrition.blogspot.ca/2011/10/adipostat-ballon.html

  11. Hi! Great site! I'm trying to find an email address to contact you on to ask if you would please consider adding a link to my website. I'd really appreciate if you could email me back.

    Thanks and have a great day!

    1. Thank you, Emily. If you posted a link to your site, either here or on your blogger profile, we could take a look. Currently, we do not have any links to other sites posted, except those in references, but we will probably add links at some point.

  12. I have been pretty much ketogenic for six months with fantastic energy etc. But every so often I am hit with mild bouts of carb flu — enervation and low mood. Sometimes my cab intake might slide up a little bit — too much fruit for example — but largely I'm pretty good and very consistent. Any idea why this is happening? Does the carb flu work in reverse? Or could it be somehow I'm not properly adapted? (I'm able to do a 24 hour intermittant fast with little effort so would have thought I am). Curious for your thoughts on this.

    1. Hi, Paul. I don't know. It seems like that could be any number of things or combinations of things. You could test whether it correlates with your blood levels of beta-hydroxybutyrate, though, or even with blood sugar.

  13. Great post.

    I'm the kind of idiot that lost weight low-carb and somehow went back to what I was doing prior to low-carb and gained all of my weight back and more.

    I'm now low carb again and have lost 67 pounds in 6 months. I knew about ketosis, but until the last couple of days I didn't know anything about keto adaptation. Maybe I heard about it, but I wrongly assumed it was the same as ketosis.

    One thing I would like to say is that I can get into ketosis really quickly with one hard full body weightlifting session and a long cardio session. However, I do mean hard...squats, bench press and lat pulls to empty the muscles out and then 3 hours of cardio (cycling seems the best way for me since I love it). I could get into ketosis the same day I started with an overload of exercise and would avoid some of the severe cravings that I would get if I just allowed myself to get into ketosis over several days of low carb. I recently had been having cheat meals and getting back into keto right away, but now that I've been reading about keto adaptation, I don't know if I'm doing myself more harm by doing that.

    Long story short, can 1 "cheat" meal take you completely out of keto adaptation or do you have to have to string together several cheat meals over a series of days to be back at step 1?

    Also, a lot of the reading said limiting carbs to 50 per day. I haven't found anything that says what's the most you can have at a meal. I don't think you can have 50 carbs at one meal and then none for the rest of the day and have that be okay. Any comments?

    1. Hi, Eric. Congratulations on the 67 pounds!

      I don't have hard answers to your questions.

      As far as I know, it's an open question whether or to what degree a "cheat" sets back keto-adaptation. One thing you could do, though, is measure your blood ketones (rather than urinary, which I assume is how you currently know when you are back in ketosis?). Volek and Phinney allude to performance improvements that continue for weeks, but I'm not sure exactly what they are, or whether they are reflected in blood ketones. Still, it would be helpful to know if you are in the 0.5 to 3.0 range they recommend and how long it takes to get there given different starting points.

      Your second question is also interesting to me. Obviously eating 200g of carbs once every 4 days would have a different effect than 50g once a day, and surely 10g 5 times a day would be different still. It's likely to be quite individual, considering the range of carb intakes that people need to stay in ketosis. Here again, I would advocate measuring. Find out what level of blood ketones you usually have while fasting, how it changes given different per-meal carb levels, and how long it takes to get back to fasting levels.

      Tell us what you find out!

  14. I was wondering about potassium after adaptation. Are there any special things I should do or is eating adequate protein enough? Also, I once ate nothing but animal products for eight weeks on a bet. I found I quite enjoyed it but felt I would have enjoyed it more if I could have had a small side of vegetable or use them as a condiment. Would that sort of diet be sustainable do you think? Toward the end of my eight weeks I must admit I didn't always feel my best. My husband thinks I was not eating enough. I liove what I've read so far and will be visiting regularly.

  15. Hi, and thank you for the wonderful article! I have a question regarding fat intakes. After becoming keto adapted, if a person still has substantial weight to lose (30 to 50 lb), would it be wise to cut dietary fat so that the body uses stored fat rather than dietary fat?

    If so, should this be done gradually, and how low should the fat be reduced? I realize that this would effectively create a high protein diet...


    1. It would be high protein by percent, but not in absolute terms.

      There are mixed opinions on this. Personally, I lost 50 lbs without any fat restriction, and the times I have tried restricting fat, while I did lose a little faster, I felt bad during it, and the extra loss rebounded when I stopped.

  16. Guys, this blog is fabulous. So well written and researched.

    I'm excited to read your forthcoming article on cortisol levels and health, my interest stemming from an understanding of the sympathetic nervous system ("fight or flight") as the release mechanism for cortisol, and it's compliment, the parasympathetic nervous system ("rest and digest") as a pathway to health and happiness.

    "About 100 grams can be stored in the liver, and about 400 grams can be stored in the muscles." There is also glycogen in the brain [1]! Are you familiar with glycogen supercompensation [2]? The idea is that you can exhaust glycogen stores (muscle, liver, and brain), e.g., via exercise, and that replenishing them immediately immediately afterwards over time (a month in the referenced studies) leads to an increased basal capacity, and thus an increased ability to expend energy in low-blood sugar situations. My question for you is this: how might a keto diet affect glycogen consumption *and*, if keto does not somewhat ameliorate the need for large glycogen stores, how might it affect glycogen replenishment? You might roll your eyes, I think, at the closing line of the NYTimes article wherein I found the cited papers: "a bottle of chocolate milk or a banana might be just the thing your brain is needing."

    Really excited about trying this out for a month. Do you have a link to a guide for n00bs? Pretty sure I don't have my head around what I can and can't eat to properly restrict carb intake.

    Cameron (Nathan's old roomie =])

    [1] Brain glycogen decreases during prolonged exercise. http://www.ncbi.nlm.nih.gov/pubmed/21521757
    [2]Brain glycogen supercompensation following exhaustive exercise. http://www.ncbi.nlm.nih.gov/pubmed/22063629.)

    1. Hi, Cameron. I made a comment about super-compensation here: http://www.ketotic.org/2012/07/ketogenic-diets-and-stress-part-i.html?showComment=1342927275613#c924081495691657061 Super-compensation is great, but you still can't get anything like fat-store capacity.

      Volek and Phinney say that keto-adapted athletes also use glycogen more efficiently. I can't find the reference at the moment, though.

      Yes, I would certainly roll my eyes at that article. It's a sad state of affairs we're in.

      For a beginner, I would highly recommend getting the latest Atkins book: The New Atkins for a New You by Westman, Phinney, and Volek. It will have everything you need to know from a practical point of view. http://www.amazon.com/New-Atkins-You-Ultimate-Shedding/dp/1439190275/

    2. Oops! Already went and bought Volek and Phiney's classic, art/science of low carb living. Will keep the other title in mind.

      Thank you again for the blog. I'm almost three weeks into the diet, and am loving it.

    3. Oh, that's a great choice, too, it's just more theoretical than practical. I'm glad you are having success!

  17. Great site! Lots of questions on my mind. Here is one for you along with some commentary. Fat for fuel as an adaptation for survival is unquestionable. But is it the best for explosive type requirements ala "cross fit?" It seems to me that as a way to survive and the probable way we hunted and gathered required us to burn and use fat as our primary source of fuel. However today a lot of us are interested in health and to increase our "weekend warrior'' performance times. Is fat and a keto diet the best choice?
    I also believe that honest fact based discussions by us "lay people" with a keen curiosity and a desire to improve our health and lives can lead to some pretty amazing "discoveries." Look forward to your reply.


    1. This is a big contentious issue, and I'm going to mostly skirt it. I don't think most people will have a problem with it, but if there is a problem, what will happen is that you will become hypoglycemic. (See the section about Mat Lalonde in http://www.ketotic.org/2012/07/ketogenic-diets-and-stress-part-i.html).

      If you are experiencing this, you might want to try a Targeted Ketogenic Diet (TKD). Essentially, you take 25-50 g of fast carbohydrates (preferably dextrose) 30 minutes before your workout. You should be back in ketosis almost immediately after. Test it.

  18. Hi there,

    I went through exactly what the article described (the diffrent phases of adaptation). I am now fully keto-adapted after almost 7 weeks of low carb / high fat / moderate protein diet. The result is wow! I can fast for a full day and be very active without suffering from hunger or weakness. I don't think about eating all the time and I get a lot of time for some cool activities. I just eat when I am hungry and stick to the low carb / high fat / moderate protein diet. i have little clue as to how much carbs I have in my current diet but I presume it is really small because I only eat veggies and barely any fruits at all (a few berries once in a while). The major source of energy is fat (oils, butter, eggs, ghee - I just made my own today, meat fat, etc) while I eat meats and nuts for proteins. I consider this a REAL TANSFORMATION, it's like being reborn.

  19. In the post, you write "When ketone levels are low, the muscles tend to use them directly for fuel, but as levels increase, the muscles use them less, turning to fat for fuel instead.". Doesn't fat oxidation always mean ketone production and then use by brain/muscles? Or is there a fat oxidation pathway that doesn't involve the production of ketones? thanks. Great website.

    1. Hi Neeraj, sorry for the long delay. I think what Volek and Phinney are saying is that when the amount of circulating ketones gets to a high enough level, the ketone bodies themselves will be used for fuel even by the muscles. Below that point they will be reserved for the brain.

    2. I think you reversed it, probably accidentally. This is what I read in the book, The Art and Science of Low Carbohydrate Living:

      "Meanwhile, the body is undergoing a complex set of adaptations in ketone metabolism[99]. Beta-hydroxybutyrate and acetoacetate are made in the liver in about equal proportions, and both are initially promptly oxidized by muscle. But over a matter of weeks, the muscles stop using these ketones for fuel. Instead, muscle cells take up acetoacetate, reduce it to beta-hydroxybutyrate, and return it back into the circulation. Thus after a few weeks, the predominant form in the circulation is beta-hydroxybutyrate, which also happens to be the ketone preferred by brain cells (as an aside, the strips that test for ketones in the urine detect the presence of acetoacetate, not beta-hydroxybutyrate). The result of this process of keto-adaptation is an elegantly choreographed shuttle of fuel from fat cells to liver to muscle to brain."

      I had thought that it was time-dependent and that the levels of BHB go up because the muscles both stop using ketones and start making BHB out of acetoacetate. But, of course, the level of ketones, would also go up over time.

    3. Oliver, I do sometimes make mistakes, but I'm not sure what you think is mistaken here. I don't see anything inconsistent. Could you be more specific about what I may have "reversed"?

    4. Sorry. I was replying to the comment right above mine where you said:

      " I think what Volek and Phinney are saying is that when the amount of circulating ketones gets to a high enough level, the ketone bodies themselves will be used for fuel even by the muscles. Below that point they will be reserved for the brain."

      It's the opposite of what's in the original post, which seems to be correct and says:

      "When ketone levels are low, the muscles tend to use them directly for fuel, but as levels increase, the muscles use them less, turning to fat for fuel instead"

      I love your work, by the way. I don't mean to criticise. Just want to avoid confusion. :)

    5. Friendly criticism is good! I'm not sure about why I wrote what I wrote just above. I appear to have said that there is an even higher threshold after which both brain and muscles use ketones, but I don't know if that was a mistake, or if I got it from V&P somewhere. I'll check. Thank you for pointing it out!

    6. Oliver, I think I may have just phrased things badly above. I think the best answer to the original question is that muscle fueling isn't an either/or situation. When keto-adapted, muscles are using more fat, but they are still also using ketones. It's just that when blood ketones are higher, muscles use relatively less of what's available. Presumably this is because high levels of ketones indicate low levels of glucose, which means the brain now needs to get priority for the ketones. But if there is so much in the blood that the brain's needs are met, there will be more available to the muscles as well.

      Thank you for pointing out the potential confusion.

  20. Amber: Nothing but meat for four years!?!? I think massive acidosis is coming your way. Aren't you worried about that?

    1. I'm not sure what you mean. Are you confusing ketosis with ketoacidosis? Or are you talking about the common misconception that certain foods have a significant effect on blood pH? I'm not worried about either of those things. I'd like to address them in the myths section, but I'm quite busy with my thesis right now.

      There is a good description of ketosis vs. ketoacidosis here: http://www.ketogenic-diet-resource.com/ketoacidosis.htm, and a series about the pH myth starting here: http://chriskresser.com/the-ph-myth-part-1

  21. Hi Amber - Thanks for this blog, it's a great resource. A question: I'm about a week into keto-adaptation, consuming 10g carb, 85g protein, and 300g fat daily (and supplementing with salt, magnesium, and potassium, among other micronutrients). I find that my mental alertness and physical energy level are generally solid until my first substantial meal, after which I fatigue significantly and become rather listless. I assume that this has something to do with a gluconeogenetic insulin spike (since I don't seem to be taking in enough carbs to cause much of an insulin response) followed by something going on with serotonin/orexin (a la http://www.ncbi.nlm.nih.gov/pubmed/15488646) - I'm currently experimenting with meal size to see if taking in a bit less protein at one time might reduce this effect. Have you ever experienced this or heard about it? Could this be something that levels out as I become more keto-adapted?

    1. You said you experience this dip in mental alertness and physical energy after a "substantial meal." It could be that it's not the quantity of protein necessarily, but rather the total overall quantity of food, from *any* source. Remember, digestion is an energy-intensive process. When we consume a large quantity of food, the body shuttles energy/resources toward the GI tract to deal with the influx. (This is why I think people tend to be semi-comatose after Thanksgiving dinner. It certainly has nil to do with the tryptophan in the turkey. It could be the huge bolus of carbs, but more likely it's just the sheer volume of food, regardless of macronutrients.)

      You might try just making the meal a little smaller and see what happens.

  22. I haven't heard of that kind of experience. Have you looked at your blood sugar before and after the slump?

    1. No I haven't, thanks for the suggestion. I'll check it out!