The crux of intermittent fasting

It is less than futile, in fact, it is outright nonsensical, to argue in favour of or promote an explanation that is in contradiction with observational evidence. What is required is to find, or at least try to find, a sound and well-founded explanation. And not just for some of the observations, but for each individual observation, as well as for the entire ensemble of observations. This is what we should do.

Fasting means not eating; everyone knows that. The meaning of the word has been loosened to include not consuming appreciable amounts of calories, as in doing a green juice fast, for example, but which should instead rightly be called a cleanse. The expression intermittent fasting implies a cycle of some kind, and is used to mean not eating for periods of 16, 18, 24 or 48 hours, but on a regular basis, like every week or even every day.

Fasting has been known and recognised for its often quasi-miraculous curative effects for thousands of years. Indeed, it is possible to find accounts of individuals recovering from just about any ailment and disease imaginable simply from fasting long enough. It seems, however, that fasting as a healing modality, has, over the past couple of centuries, steadily grown less popular in the medical profession and, as a consequence, also in the general population.

A resurgence of scientific interest over the last decades in the benefits of fasting for treating various degenerative conditions like arthritis and cancer, but also for extending healthy lifespan about which I will write at one point in the future, has brought it back into the spotlight, especially in circles of optimal health enthusiasts, which includes some gym go-ers and body builders interested not so much in optimal health, but mostly in losing fat and gaining muscle.

Therefore, there has been quite a few people trying out or adopting intermittent fasting for periods of a few weeks to a few months, or even longer, but reading things here and there shows that they have had varying success given their initial motivations, whatever those might have been.

Ori Hofmekler was one of the first to popularise the idea of intermittent fasting with his book The Warrior Diet. He has continued to write and to encourage intermittent fasting for a wide range of benefits, especially in regards to the goal of improving body composition, as one of his last titles expresses perfectly: Maximum Muscle, Minimum Fat.

Dr Hertoghe, the world famous endocrinologist and anti-ageing specialist, as well as Mark Sisson (Primal Blueprint) have also been vocal and influential proponents of intermittent fasting for a while. More recently, Dr Mercola did several interviews with Hofmekler, and wrote a few articles on the topic, sharing his experience and enthusiasm for the health and fitness benefits intermittent fasting can bring. These are just some of the well known players that I know of and respect in the natural health community, that have endorsed and promoted this kind of cyclical fasting.

Naturally, as is the case for almost any topic we can think of, there are opposing opinions and, in fact, bashing of intermittent fasting as a means to improve health and body composition, especially in the popular fitness and gym culture. And, as is also the case for almost any topic we can think of, contradictory views and opinions are usually caused by misunderstanding, or at least, incomplete understanding of the elements involved, and in particular the more subtle ones.

On the one hand, we have the proponents claiming that we can very effectively get much healthier, with much improved energy levels, mood, digestion, and natural detoxification and excretion of metabolic acids; normalise and recover the optimal balance of specific hormones, and eventually, of the entire hormonal system; over time lose all excess body fat reserve, increase flexibility and hasten recovery, better preserve our precious muscle tissue and build more very efficiently. And these are just some of the claimed (but also documented) benefits of intermittent fasting.

On the other hand, the nay-sayers and bashers report that these claims are more than just false, they are, in fact, often the exact opposite of what they have found or seen for themselves or in others coming to them for help and expert advice. Reports of feeling really terrible, with massive headaches, bad digestion, awfully low energy levels, and thus, obviously, very bad and destructive moods; loss of some fat but also, over time, of lots or maybe even most of their muscle tissue; extreme hunger, with frightening ravenousness when evening mealtime comes around, leading to monstrous, uncontrolled and uncontrollable overeating without discrimination of food kinds or quality, and over time, showing obvious signs that can be identified as those associated with eating disorders.

How is it possible to have research, studies and documented cases—plenty of documented cases—that provide observational evidence—proof, if you prefer—that support the claims of both of these camps? How can we observe and actually measure such profoundly different consequences in different people that are supposed to follow comparable diets, consequences that are diametrically opposed to one another. In other words, observational evidence that appears to be completely and totally contradictory?

A simple approach, the one espoused by many, maybe most, of the intermittent fasting bashers, is to just say that proponents are wrong and imagining things, letting themselves be fooled by the hype, but actually blind to the reality of the detrimental consequences of practicing cyclical fasting.

For me, the only satisfactory approach is the one that seeks to explain all the observations, to reconcile all the observational evidence, and make sense of the entire ensemble of information available through a physiology and biochemistry based explanation that is complete. I also think it is fair to say that there are more better informed proponents than there are opponents, but this is not obviously the case, and I would thus not bet much on this claim.

Here it is, the crux of the matter, the one single crucial element needed to understand and explain the wide spectrum of apparently contradictory observations that is overlooked because it is misunderstood:

The body’s response to intermittent fasting is entirely dependent upon the state of one’s metabolism, and everything about it hinges on the physiology of nutritional ketosis. 

In fact, the vast majority of the benefits of intermittent fasting are those derived from nutritional ketosis but heightened by the fasted state, and therefore, can only become manifest if the fasting individual is keto-adapted and remains in nutritional ketosis most of the time.

You might be thinking: what in the world is nutritional ketosis, and where’s the explanation for the contradictory observations? Nutritional ketosis is the metabolic state in which the liver manufactures ketone bodies from fat to provide fuel for the brain cells that can only use glucose or ketones for their energy needs. This only happens if and when circulating insulin levels are low, and when blood glucose stays below 80-90 mg/dL for a period of 24-48 hours (generally speaking, on average, and in normal circumstance). The reason is fat will not be burned for fuel is there is plenty of glucose in the blood, and in order to burn fat, insulin must be low.

This metabolic state is induced either by fasting—this is the quickest but also most extreme way to do it, or by eliminating insulin-stimulating carbohydrates (sugars and starches) from the diet—this is by far the easier and obviously much more sustainable way to do it. The longer it is maintained, the better adapted the metabolism becomes. But before ketones are produced to fuel the brain, the body goes through metabolic changes to which it tries to adapt as best it can. The most important but also most severe of them all, is the fundamental shift from using glucose as the primary fuel, not just for the brain, but for all cellular energy needs in the body, to using fats, both from body fat reserves and from food.

The bane of our time is global, chronically elevated insulin levels. Hyper-insulinemia, as it is technically called, sits squarely as one of the root cause of all the diseases of civilisation that kill most (90%) of us today, more or less uniformly across the planet. What does this have to do with our considerations of intermittent fasting? It has everything to do with it:

Insulin is the master hormone that orchestrates the metabolism in what relates to storage and usage of macronutrient (carbs, fats, and proteins) at the cellular level.

Chronically elevated insulin always and inevitably leads to insulin resistance. Insulin resistance means that cells do not respond to insulin as they should, and require ever increasing concentrations of insulin in order to move glucose into the cell. And ever increasing concentrations of insulin means ever increasing inability to use fat cellular fuel, with particular difficulty in unlocking and tapping into the usually greatly overabundant reserves of body fat.

What is truly remarkable is that insulin resistance, even if it has been developing and growing steadily with each passing day and with each high carb meal or snack over our entire lifetime, it can be reversed in weeks when insulin-stimulating carbs are eliminated from the diet: 48 hours to enter nutritional ketosis; one week for water retention release, initial intestinal detox and basic adaptation to fat-burning; four weeks for functional keto-adaptation; and 8 weeks for complete keto-adaptation.

Eliminating insulin-stimulating carbs eliminated the need for large insulin secretions by the pancreas. Therefore, both glucose and insulin concentrations steadily decrease with time, and eventually fat-burning and ketone production kicks in, marking the first step in the transition of the metabolism from sugar-burning to fat-burning, which is what we referred to as fat- or keto-adaptation.

There is a catch though: before fat-burning and ketone production begins, the metabolism of the insulin resistant individual will go through withdrawal from its sugar addiction. First, sugar levels start to drop. After a number of hours, 3 to 4 hours say, blood sugar is too low to supply enough fast-burning glucose to cells for their metabolic activities. Because insulin remains high, and because the body is highly insulin resistant, as we said, it is not possible to use fat from the body’s fat stores. Therefore, it is the liver that comes to the rescue and begins to convert its stores of glycogen into glucose and pumping that into the bloodstream to provide cellular fuel.

Within a few hours, however, the glycogen in the liver is depleted, and blood sugar drops once again, and lower still. Because the body remains unable to tap into its fat reserves due to the state of insulin resistance, it has, at this point, no choice but to turn to muscle tissue, from which it is far easier to breakdown protein and manufacture glucose than it is to start burning fat. And thus, the muscles are eaten away in order to provide the glucose to all of the multitude of insulin resistant (sugar-addicted) cells throughout the organism.

We now come to the final analysis of our observational evidence in regards to intermittent fasting, and consider two scenarios that can explain, as it rightly should, the ensemble of observations in its entirety, and thus clarify and reconcile the apparent contradictions that are seen, and which lead to serious confusion about the issue, even, and maybe especially, among our health, fitness and bodybuilding experts.

Scenario 1: We take a perfectly keto-adapted person who has been eating a diet devoid of insulin-stimulating carbs for a long time, and who therefore always has very low glucose and insulin levels, and as a consequence, exquisite insulin-sensitivity. What happens if they stop eating? Nothing special, really. Their body is always using fat and ketones to supply all healthy body and brain cells with their metabolic energy needs. So, if there is no fat that is provided through the digestive system, then it is taken, without any trouble or noticeable changes in energy levels or concentration, from the body’s fat reserves that are always plentiful, even in the leanest among us with single digit body fat, because 1 gram provides 9 calories, which means that we need only about 200 g for a whole day of normal activities, and have at least 5 kg at any given time (8.5% fat on 60 kg body weight).

Moreover, if we exercise during the fast, there is no noticeable difference because at low intensity, cellular energy needs are taken care of by fat which is continuously released from the fat stores into the bloodstream, while at higher intensity the glycogen stored in the muscle cells themselves, can be used in the form of quick burning glucose together with additional supply from the liver than converts its stores of glycogen if need be (if stress hormones are secreted).

So, biking and working out with weights, for example, is perfectly fine and actually feels great. Even more interesting is the fact that stimulating the muscular system by exercising while fasting triggers the release of various hormones in addition to growth hormone for which there is nothing more effective than fasting, whose purpose is primarily to preserve those physiologically important muscle tissues as essential for functional survival, while breaking down to recycle the proteins of other tissues which are not required like lumps, tumours, and scar tissue. And this means that the hormonal environment created by exercise under fasting conditions is conducive to both preserving and building more muscle, all the while also expediting and maximising fat-burning. And this is what is observed.

Hunger is present at times, but is certainly far from being problematic. There are no headaches, no stomach pains, no sleepiness, no scattered mental discursiveness, no problems concentrating or working. Sitting down to eat the evening’s nutrient-dense, enzyme-rich and high fat meal with adequate amounts of protein for tissue repair and muscle building, is nourishing, perfectly satisfying, and well digested throughout the evening and night, as long as we eat several hours before going to bed. No over-eating, no cravings, no psychological disturbances, no problems at all. A picture of perfect metabolic efficiency.

Scenario 2: We take an average but pretty active person from the general population who eats a standard diet with plenty of insulin-stimulating carbs, both simple sugars, and complex carbs in the form of pasta, rice, whole grain bread, etc (70% of calories), and who therefore always has high blood glucose and insulin levels, and as a consequence, pretty strong insulin resistance. What happens if they stop eating? We saw this earlier: blood glucose drops, but not insulin; the liver starts to pump out glucose to pick up the slack, and runs out after about 3-5 hours; sugar drops once more, but not really the insulin; since fat stores cannot be tapped into, muscle tissue is broken down to manufacture glucose; longer period of fasting means more muscle breakdown.

If we exercise gently, things are fine at first because we can tap into the glycogen stored in the muscles, but will soon get much worse because we increase the energy demands, but continue to be unable to use body fat stores, and therefore increase the rate at which muscle tissue is broken down, especially if we do weights and high intensity training.

Low intensity aerobic exercise depletes glycogen from the muscles and when it runs out, we feel exhausted, completely flat out. (This is the same as hitting “the wall” in long distance events, and only occurs because the body cannot readily tap into its fat reserves: a well keto-adapted athlete never really hits any such walls!) Far worse is high intensity exercise, which causes more intense and faster muscle breakdown, the higher the intensity, the more muscle breakdown.

Waking up in the morning after a night’s sleep (and unconscious fast), we are starving, dearly longing for the bread, the jams, the cereals, the orange juice, the waffles, the maple syrup, and everything else we can imagine, but we hold out and go to work. Every hour is excruciating, terrible headache, hunger pains throughout the abdominal cavity, but when these subside, we are falling asleep, with a complete inability to concentrate on anything at all. We feel like shit.

By the time evening rolls around, we are so ravenous we would eat a horse. So we sit down and eat, and eat, and eat everything we can get our hands on: pizza, pasta with sauce and cheese, garlic bread with butter, steak and potatoes or french fries, and then desert, sweets, oh man, we waited all day to eat, and now we can eat anything and everything we want, because tomorrow we’ll be starving again for the whole day. We get up in the morning, and the whole cycle starts over again.

Over time we kind of get used to it, but because we don’t understand the most essential element of the whole thing—nurturing nutritional ketosis—we remain just as insulin-resistant, every day we feel shitty, every night we eat like a pig, and throughout the whole time, more or less, we break down muscle, and our insulin resistance prevents appreciable fat loss. After doing this for a while and seeing the detrimental effects of this regime, we go seek help from a fitness expert. They tell us that this intermittent fasting thing is a load of shit, and as them, grow instantly convinced that all the stuff people say about the benefits it can bring for optimal health and improved body composition is also a load of shit: if it didn’t work for me, then it simply cannot work for anyone.

Unfortunately, neither we nor the fitness expert understands enough physiology, biochemistry, and endocrinology to be able to make sense of these conflicting and contradicting accounts, personal experiences, and observations reported in the scientific literature, and just settle into this view that it really is a load of BS, and that it might work a little, sometimes, on some people, but not on others, and no matter what, it always leads to pathological states of mind, if not full fledged eating disorders.

It is my hope, however, that you are now able to see how these very observations, as conflicting, contradictory, and certainly quite puzzling as they may seem at first, can be explained and reconciled marvellously well in light of a better understanding of the basic principles of energy metabolism, and of the remarkable but unfortunately almost universally misunderstood state of nutritional ketosis, that most medical professionals usually mistake for the pathological condition of diabetic ketoacidosis.

Finally, in closing, I have a confession to make: I have been experimenting with intermittent fasting in one form or another for many years now. I never eat anything before midday, and on most days until about 14:00, which makes it an approximately 18-hour fast from 20:00 the night before. On weekends, I fast until noon, and then go do weight training. On those days, I usually eat for the first time around 17:30, and make that my single meal of the day. On some days I eat a large lunch and dinner to increase my overall calorie and protein intake. I usually workout 3-4 times a week, and usually in the late afternoon-early evening.

I have not experienced loss of muscle since I dropped the insulin-stimulating carbs from my diet in 2007. Both muscle tone and strength is maintained very well even after long periods without resistance training. I have, however, never made a particular effort to gain muscle mass. This year, I would like to see how much muscle I can put on, and will thus put the science to the test for myself. If you are interested, don’t worry, I’ll keep you posted. If you’re not, then that’s fine too.

But if there is a single thing you must remember from what I wrote, it is this: you can only really benefit from intermittent fasting when you are keto-adapted, and remain in a state of nutritional ketosis the majority of the time. Otherwise potential benefits are lost, and the practice can become rather detrimental.


How long do you think these hunters hunt each day? Do you think they have a big breakfast before going, or a large lunch while they are out? How long do you think they are out before they settle back around the fire in their village to have their main meal of the day? And what do you think they will eat when they do return with their catch of the day?

(This article was written after reading this article by Dani Shugart on T-Nation sent to me by a friend who knew I would have some remarks to make, and probably some clarifications to bring to it.)

20 thoughts on “The crux of intermittent fasting

  1. It´s not neccessary in my opinion to intermittent fast every single day. What works wonders in my experience is to exercise on a empty stomach if convinient for you. It can take some weeks to adapt if the person is burning primarily sugars but it´s worth the effort. Then have a recovery meal and continue with the normal scheduele for the day. It really rejuvenates and improves body composition. If someone fells the need to fast until dinner it can be done with good quality whey protein and low mineralized water one day per week or so.
    And the green juices doesnt work well for everyone, if you are too alkaline already you don´t need that, and 1/3 of the population run too alkaline.
    I agree with the wild herbs to make tinctures with or juice but the cruciferous veggies impaired adrenal function.
    Thanks for the article


    • Thanks for sharing your experience Ernesto. It is probably true that quite a lot of people (yes, maybe a third) do not produce enough hydrochloric acid in the stomach for the complete breakdown of protein, and maybe this is what you are referring to as “too alkaline”. But I’m willing to bet everything I have that nearly 100% of the population is in a state of chronic acidosis ranging from mild to severe, which leads to tissue acidosis, and in all cases increasing with time; the population is definitely not too alkaline. There is a maybe subtle but very important difference between having a stomach that is too alkaline from the lack of proper secretion of HCl, and having blood and tissues that are too alkaline, something that is extremely rare, and in fact, very difficult to achieve.


  2. First I want to say how much I love your writing! I find myself intellectually passionate about reaching my optimal health and defying aging, but my psychological dependence on using food as comfort always gets in the way. It is as if I have double personalities when it comes to food; marked by a few weeks of conscious eating followed by gorging on sugar. I know that overcoming binge eating is dependent upon my overcoming the use of food as a crutch.
    This summary about me leads me to my questions. I’ve been discouraged from intermittent fasting as a woman, because I’ve read it does not confer the same benefits as it does for men. This article particularly in particular states this.

    Can you please offer any insight/experience as to if it may be detrimental for women? I’m also interested to hear your thoughts on whether carb “refeeds” are necessary for someone who wants to maintain ketosis long term.

    Moreover, I’d love your personal advice on using ketosis and intermittent fasting as a way to overcome an unhealthy connection with food. Does long term ketosis put one into a state wherein they don’t even WANT the donut when they’re sad or stressed? That’s really what it comes down to for me. As a med student with a little background in the biochemistry that you speak about so eloquently, I can appreciate the detrimental nature of hyperinsulinemia, but the cookies still have such immense power! I apologize for such a long rant, but health advice is so clouded by personal beliefs instead of being rooted in real science these days, and I have yet to come across someone who is as amazingly knowledgeable as you are on this topic while maintaining objectivity and an open mind. Even if you cannot get to my questions, I will continue to follow your blog passionately, as you are giving me the information I so desperately need in my life. Thank you for everything!


    • Thank you very much Caitlin. I deeply appreciate your comments. It is indisputable that men and women are different, especially in regards to their hormonal system. This became very clear to me when two colleagues of mine whom I had encouraged and eventually convinced to give up the carbs, both independently reported that even though they were losing body fat on a more or less continuous slope day after day, they found that during their periods, they not only plateaued for about a week without losing any more fat, but they were particularly hungry. You may know this for yourself, but I know for sure that my wife is always more hungry during her periods. This makes perfect sense, of course, because everything about us is regulated by hormones and oestrogen makes us all more hungry and fatter, while testosterone makes us all leaner and more muscular, men and women alike.
      The only first hand experience I can talk about is with my wife who has been doing most of what I do and write about for as long as I have (about 6 years now), albeit with a sometimes significant delay and with less enthusiasm and vigour about the whole thing (but she’s coming around very well, and feeling the difference tiny little details can make). And yes, I have seen how intermittent fasting works differently in us, especially in regards to fat burning, but how it is nonetheless quite beneficial.
      In truth, I have always done intermittent fasting not really for losing fat, because I am already very lean, but for the more profound health benefits of increased metabolic efficiency, starving and killing off sugar-dependent pathogens of various kinds (yeast, fungi, moulds, viruses, anaerobic cancer cells), intestinal cleansing and healing, intensive alkalisation and hydration of the tissues, cellular regeneration and repair, and everything else that is not yet known. What I didn’t appreciate until a few years ago, is exactly the central point I made in the article above, and that I was happy to see Mark appreciates very well, which is that one should not do intermittent fasting unless they are perfectly well keto-adapted. He includes this in his IF pre-reqs: “like being fat-adapted, getting good and sufficient sleep, minimizing or mitigating stress, and exercising well”. This is very important for all the reasons I presented.
      The other important observation I made is that IF always works better when combined with exercise and in particular, weight training. Particularly so for my wife (any maybe all women) has had excellent results in terms of feeling great and strong, and improving body composition in a short time. Naturally, all optimal health strategies are all for the long term and need to be nurtured and maintained. It is more on the timescale of months and years that we see the most significant positive changes.
      Finally, about food cravings, the only thing I can say for sure because I have seen it and felt it very clearly, and this is independently of how much of a psychological eater we are (and we all are to a certain extent), you need to be extremely strong willed and determined in the first days and week, to overcome the cravings for sugar or starches. This is hard (much harder for some than for others) because it is like overcoming a drug addiction, very similar, in fact, to a heroin addiction (researchers have found). But within a week or two, the hormonal system comes back into balance, and the cravings subside. Eventually, they disappear almost completely.
      There is no doubt that it is far easier and much better to avoid exposure to nefarious temptation like sweets: if you don’t see them or smell them, then it’s far easier to avoid eating them :) This is the way it is for everyone, me included. Some people I know didn’t have any problem, but they were people that didn’t really eat sweets at all anyway. For everyone though, with time, you become really powerfully willed (also greatly empowered by this), and can do whatever you decide to do, not disturbed or distracted in the least by things that would have caused nothing short of an emotional, food-related upheaval for you in the past. Four weeks of complete abstinence is what most people need to get over the addiction. Then, it’s maintenance, and gets easier and easier with each passing day, week and month. It’s really worth it. Truly.


    • Just realised, Caitlin, that this response will be three years old but, to answer your question about “Does long term ketosis put one into a state wherein they don’t even WANT the donut when they’re sad or stressed?” The answer is yes it does imo. I began LCHF over a year ago now and worried about how I would cope without my go-to carbs that I used to “feel better”. In actual fact, I soon realised that I no longer needed them. I get along just fine without that stuff, probably because now I’m outside the crazy carb-binge-cycle, I see it for what it was. Carbs are not necessary, I don’t want them in my life any more, they caused misery, stress, ill-health and depression/anxiety.


  3. Thanks so much for your response Guillaume! It helps to hear your wife’s experiences. I plan to implement your advice and will follow up with results.


  4. Thank you for your excellent posts again. I’m really impressed your sub 3 hours marathon which is close to elite level. This is my personal experience of my daily intermittent fasting of 16 hours during which time I run 90- 120 minutes with no water taking with 60 or less % of my heart rate. I assume that I’m in ketonic mode. After run, I feel not hungry at all. I assume I burn fat, not much glucose, but not sure. I ran few marathons almost not taking sugar with very little water between 4-5 hours. Last two years I completed 6 marathons in barefoot. I plan to run barefoot Boston marathon barefoot on April 21 next week. My goal is just to cross the finish line. Speed is not my priority but my health being 72 years 9 month old guy! My question is, if I run anaerobically, that how I can increase mitochondria capacity or numbers to enhance my endurance capacity. I’m not so sure whether my practice is right or wrong approach. Without hesitation, your posts are so valuable to me.

    With best regards.


    • Hi Tyson: I would recommend you try to drink as much as you can, without overdoing it, of course, starting with a little water, and gradually increasing how much you drink when you run. This is especially critical for longer periods of time, like during a marathon. Also, I would recommend drinking water (for 1 litre) with salt (1/2 tsp) and sodium bicarbonate (1/2 tsp) with a little stevia to sweeten and 3 drops of essential oil (orange or lemon) to flavour. This is my personal sports drink, and it makes a huge difference in performance for me. Dehydration, electrolyte depletion as acidosis can all be life threatening, but combined is far worse. You don’t need to eat sugar at all, but you could consider having coconut oil in capsules or something of the sort, or coconut milk in a smoothie form. For the mitochondria, the most important to keep them healthy is minimising free radical damage by taking lots of antioxidants: liposomal vitamin C, vitamin B3 (niacinamide), astaxanthin, turmeric, hydrogen boost, A/D/K2 (these are the ones I take), and whatever else you fancy. All antioxidants are antioxidants, but they all work differently.


  5. You convinced me to go ahead and completely eliminate carbs. I was still getting about 100g a day.

    But I have always been a bodybuilder or powerlifter in my life. I have slowly been mixing crossfit style stuff into my powerlifting routine.

    I’m 170 right now and in my second week of low carbs (shifting to no carb). I’m already low fat (around 9-10%).

    My goal is to get to 187 over the next 3 years. I’ll let you know how it goes.

    Thanks for all your hard work.



    • Right on man! You’ll see and feel the difference, I guarantee it. I also lift, but I’m a featherweight at 60 kg (132 lbs). A couple of years ago I was 56 kg and 7-8% fat and decided to try to put on muscle. Since, I’ve put on 4 kg of muscle remaining the whole time at 7-8% fat, and can now deadlift 145 kg (320 lbs) and bench 95 kg (210 lbs). A few tips: make sure you have a lot of unrefined salt with your meals, eat plenty of healthy animal protein but focus on eating lots of fat from the meat and from coconut oil. One day per week, eat lots of carbs. The purpose of this is to boost IGF-1, which is needed to keep burning fat and putting on muscle. Keeping on a VLC diet the rest of the time will keep insulin at rock bottom to maximise fat burning and insulin-sensitivity. If you keep reading through the archive, you will be convinced not only that it is beneficial for your performance to go VLC, but that it is the only way to live in optimal health for as long as possible looking young and feeling great. Keep me posted on your progress. Also you should consider getting a complete blood test done to check how things are:


  6. “Right on man! You’ll see and feel the difference, I guarantee it.”

    I already am. I mean I haven’t really lost any strength or had any performance issues. I do feel like my brain is on fire though (in a good way). I’m thinking so much more clearly. I’m also running very “hot”. I don’t know if it’s simply because burning fat gives off more heat than burning glucose?

    I had some serious posture and mobility issues so I have been working on those as well. Had to give myself a crash course in anatomy (which is turning into a sorta of homemade B.A. at this point) amongst other things I needed to work on.

    All in all the last year has been a lot of really questioning what my definition of health really is and deciding that what I was doing was nowhere near enough. Sick and tired of being sick and tired you know? And although I “looked” good that wasn’t enough for me.

    “I also lift, but I’m a featherweight at 60 kg (132 lbs). A couple of years ago I was 56 kg and 7-8% fat and decided to try to put on muscle. Since, I’ve put on 4 kg of muscle remaining the whole time at 7-8% fat, and can now deadlift 145 kg (320 lbs) and bench 95 kg (210 lbs).”

    Those are great numbers. I was only pulling 400lbs (single rep at 175lbs) on a good day! My bench is 205lbs (5 sets of 5) for reps. Squats I have had to completely take off all the weight. Turns out – not only was my diet terrible – I had seriously dysfunctional movement patterns in addition to the mobility issues mentioned above.

    “A few tips: make sure you have a lot of unrefined salt with your meals, eat plenty of healthy animal protein but focus on eating lots of fat from the meat and from coconut oil.”

    I had never suspected that I wasn’t getting enough salt. I enjoy it but I never added it to food (and if I did it was refined table salt to french fries) and it was actually not very prevalent in my diet once I half cleaned it up. I’ve started adding a teaspoon to every liter I drink unless I feel like I’ve had enough. My BMR is high. I eat about 4,000 kcal plus a day. Do I need to drink more water on account of my eating more?

    Ugh. I hate meat fat but I’ll try. Is there a way that I can eat lean meat and make up for the animal fat some way? Is high fat ground meat ok?

    “One day per week, eat lots of carbs. The purpose of this is to boost IGF-1, which is needed to keep burning fat and putting on muscle. Keeping on a VLC diet the rest of the time will keep insulin at rock bottom to maximise fat burning and insulin-sensitivity.”

    Awesome. So a refeed is ok! That’s good news. Does it matter exactly what kind of carbs? Starchy?

    “If you keep reading through the archive, you will be convinced not only that it is beneficial for your performance to go VLC, but that it is the only way to live in optimal health for as long as possible looking young and feeling great.”

    I have been. I laugh because my Dad has sorta always been interested in “health” and has always danced around with juicing, supplementation, and whatnot and I always laughed at him and told him it was unscientific hippie shit.

    I needed to see the biochemistry and the physiology behind it all and you were able to really drive that home. I’ve been around Mark’s Daily Apple and a lot of other similar stuff but they don’t get at the subject they way you do. I appreciate your approach. You’ve really opened up the subjects (endocrinology, the kidneys, the liver, etc.) in a way that has really inspired me to do my own research. But you laid the groundwork for me.

    So I really appreciate it.

    “Keep me posted on your progress. Also you should consider getting a complete blood test done to check how things are”

    Will do man.

    I am due some blood work for my physical this year. I’ll be getting in soon.


    Liked by 1 person

    • Burning fat gives off less heat than burning glucose and in time you should have a decrease in body temperature; that’s good because you decrease systemic inflammation and rate of ageing. You are probably just feeling differences due to the changing metabolic regime of your body. Better mental clarity, however, is expected and indeed quite welcome when we feel it. More water and more salt: aim for 4 litres and 10-15 g (2-3 teaspoons). To increase fat, you can put coconut oil or coconut cream on your meat (that’s what I do). For the carbs once a week (or every two or three weeks depending on your aims for fat loss versus healing by staying in nutritional ketosis), stay away from grains and grain products. Stick to honey, unrefined sugar, potatoes and rice. Finally, make sure you get all the extra tests I list that are not parts of the standard blood tests. All are important and needed to paint a complete picture of what’s happening inside.


  7. Gidday from New Zealand Guillaume. Love your work! Came to your site a couple of weeks ago via your comment on Peter Attia’s “IFIK” post; seems we have been treading the same paths.

    I’m particularly interested in the application of nutritional ketosis in the sphere of resistance weight training (BTW, impressive lifts relative to your bodyweight man; I’ve been meaning to check out Doug McGuff’s “Body by Science” stuff). I’ve been a competitive bodybuilder for the last 30+ years, practicing various cyclical ketogenic diets (CKD) for the last 20 years (Dan Duchaine’s Body Opus, Lyle McDonald’s Ultimate Diet, Vince Gironda’s Ultimate Definition course, etc), as well as several IF protocols (Brad Pilon’s ESE, Ori Hofmekler’s Warrior Diet). Recently, in light of the work of the usual suspects on the field of VLCD (Taubes, Attia, Bowden, Volek & Phinney), I’ve switched to full-time nutritional ketosis (NK). Your masterful writing here is a revelation – it ties together all my previous strands in healthful living, and some!

    My question relates to your comment above re: a carb re-feed day once per week. At a competition weight of 86kg, 183cm tall, 4% bf, I realise that I’m probably maxing out my natural potential in terms of muscle mass, and I’m not terribly interested in gaining masses of further size anyhow, just sculpting specific muscle groups whilst living as healthfully as I possibly can now as my number one priority (bodybuilders are notoriously excessive protein consumers and I’m finding now that hydration and alkalisation are key in my efforts to reduce acidity-related aches and pains). However, my fat loss/ability to stay super-lean on VLCD is not as great as I would have hoped and I’m wondering whether 18 months of IF and regular calorie deficit, combined lately with a VLCD has impacted my IGF-1 to cause such a slowdown (BTW, I don’t consume more than 60-80g protein/day these days). You obviously think there is value in a weekly carb-up day. Could this kick fat loss into a higher gear? I love living in NK and I’m a bit reluctant to go back to such a CKD system given that, as you’ll be aware, Volek & Phinney believe that each time carbs are consumed the process of keto-adaptation starts again, requiring 2-3 weeks to get back to full NK. Do you practise this re-feed yourself on a regular basis, or only when you wish to ‘muscle up’? If you do, what are your preferred carb choices? Any further insights would be greatly appreciated.

    Many thanks in advance Guillaume – I’ll continue to devour your work and refer others.



    • Hi Tim, and thanks for writing. I am honoured to have such a well-read and informed person as you both reading and appreciating this blog. Thank you for all your comments and questions. Here are some of my thoughts on them:

      I have been on a VLCHFMP diet for 7 years and in NK most of this time. It is only in the last couple of years that I have increased animal protein significantly but still getting about 70% of my calories from fat. The greatest value of NT is the wide spectrum of health benefits that come from keeping the body in this mode of function. It is particularly important for anyone recovering or healing from something as serious as MS and as silly as a cold, but it is just as powerful in preventing illness (colds, flus, cancer, diabetes, heart disease, etc) from developing. Having said, high performance and extraordinary use of the body require special considerations, as you very well know already.

      In particular, we know that insulin is necessary for life and that macronutrients are shuttled into cells through its action, but we also know it is quite toxic, and that causes disease to develop and accelerates ageing at the most fundamental cellular level. The issues for high performance and sustained muscle gains and fat loss are related to the fact that keeping insulin super low will bring down leptin and IGF-1, and also potentially slow down thyroid function. Sustained for a long time, NK will induce a steady state that will make it hard to gain muscle and burn more fat. Calorie deficit will definitely do this. It makes perfect sense that the body adapts to this or any other sustained conditions in the way that ensures best survival probability. An analogous illustrative case is chronic dehydration in which cells buildup thicker cholesterol walls to better retain the water available, and the kidneys keep recycling more uric acid in order to better extract water out of the urine by having a greater gradient in the medium through which the nephrons pass. Although this is necessary for survival and the person will not feel it, it is not optimal for health and the body definitely feels it and suffers from it.

      I have experienced a lot with IF and calorie deficit, and while I think IF is really good, sustained calorie deficit is not good at all: it causes everything to slow down (feeling low and slow, feeling cold and tired) and makes it virtually impossible to lose any fat, even when in NK, because the body is getting the signal that there is not enough food and is trying to retain its reserves. I know this from years of experimenting with my wife for whom we have seen that the only way to loose fat is to eat more and have high carb days once in a while to stimulate IGF-1 while keeping insulin low the rest of the time. That’s because insulin will spike, IGF-1 will follow, but then insulin will drop quickly and remain low as long as there is no glucose in the blood. IGF-1 will stay up much longer.

      With all this in mind, the body does not want to stay at 4% bf because that’s extreme. From personal experience, I think it is easy to stay at 7-8% without any effort: it’s my steady state since I took up VLCHF. But this could not be done without weight training. Most people that don’t train or exercise will go down to 10-15% and stay there. So, for you and anyone trying to get to super low bf, it is crucial to stimulate IGF-1 once in a while. You don’t need to do it once a week; every two weeks would be fine, I think. But you don’t even need to do that if you don’t have the need for it. I would think you shouldn’t bother getting down to 4% unless you have a competition. You can easily stay as I have around 7-8 the rest of the time, without even trying. And since you don’t want to put on muscle mass, but obviously want to keep all the muscle you have, then staying in NK with enough calories almost all the time will make sure you don’t loose any muscle because keeping insulin super low ensure no muscle wasting (as long as there are enough calories from fat). So this is what I recommend you try: VLCHFMP all the time; high carb day (or weekend) every week, two or three depending on your competitions, always with enough calories, but IF is perfectly fine.

      For the carbs you can have dates, unrefined sugar, honey, rice and potatoes; that way you never have grains and gluten and stick to whole foods. Tons of fruit and fructose is really bad for the liver and pancreas and everything else. Don’t have lots of carbs with lots of protein because this will cause indigestion and bloating, burps and acid reflux. Another thing is that you can minimise both fat storage from and time in circulation of the glucose on high carb days by draining the glycogen reserves from the muscles and liver as much as possible beforehand. In this way, the glucose will mainly get stored as glycogen and not as fat. Keep me posted.


      • Pure gold my friend – thank you so much for your response Guillaume – swift, comprehensive and illuminating as always. Having spent this weekend carb loading I swear I’ve leaned out noticeably already :-) I’m probably in the same boat as your wife – your symptomatic description of the metabolic slow down concomitant with prolonged calorie deficit mirrors my experience exactly. In fact, in charting my bodyweight weekly over the past 12 months, I’m surprised how remarkably stable it has been, even with 2x 24hr fasts/week and after a 72hr water fast as well. I see now that none of these tools are effective anymore in reducing body fat much below 10% because calories have been too low for too long whilst I’ve clung to the ‘calorie in vs calorie out’ model.

        In short, my aim now is to establish a new steady state of 6-8% bf by continuing my 20hr/day fasting Mon-Fri; two coconut/fat-based meat meals (~4pm and 8pm) with only water, green juices and salt throughout the day. On Friday evening after my ‘grand depletion’ whole body workout, I’ll start carbing and continue through to Sunday evening (using your valuable tips, thank you). Its a bit like a homecoming for me – back to Duchaine’s system I loved and excelled with 20 years ago, only this time with more emphasis on the cleansing, hydrating, and alkalising during my daily fasts. Will also increase fat and protein on these days to stay around BMR, but, with the addition of lots of whole food carbs, go well over this calorie level on the weekend to stoke my metabolic fires to the max. My body and I are really excited about this; I’ll certainly keep you posted on progress.

        Cheerio for now and thanks again,

        Liked by 1 person

  8. Hi Guillaume. Thank you kindly for your bountiful and well explained information you have shared. I find it extremely eye opening as someone who strives for optimal body nutrition through, clean eating, both cardio and resistance training, as well as IF.
    My aim is to establish an effective IF routine based on my diet. I am vegetarian, I also do not eat any dairy whatsoever. Instead my diet comprises mainly of fruit, veg, green juice, protein shakes, and large intakes of healthy fats. Healthy fats being avocados, virgin olive oil, coconut oil, hemp oil, nuts and seeds, which I consume daily. As for grains, I only eat small amounts of oats, quinoa and brown rice, supplementing based on exercise intensity.
    To add I take protein shakes daily, with spirulina, hemp protein, pea protein, chia, flax, and other seeds, due to the fact that I may otherwise not be consuming enough protein. Besides which I eat boiled eggs and legumes to aid in protein consumption.

    The eye opening information that you have shared has made me question whether or not my vegetarian diet of eating lots of fruit and vegetables somehow does not support effective demonstrations of IF in order for me to maintain muscle whilst burning body fat.
    I shall however continue to try different approaches and listen to my body.

    Thanks again for your valued wisdom shed on these aspects of optimum nutrition.


    • Hi Daniel, if you keep reading you’ll understand why you should drop the carbs and start eating meat. But I’ll let you come to this conclusion yourself. I can tell you immediately, though, that being vegetarian from 18 to 38 is surely the worst mistake I’ve ever made, and will unfortunately never fully recover from it. If you want measurable, download my essential blood test reference sheet and go get these tests done. You’re welcome to contact me again when you have them.

      Liked by 1 person

  9. Hi Guillaume, thanks so much for this very interesting article. It was shared to my intermittent fasting group in Facebook.

    I’m a 49-year-old woman and I’m currently doing a program of strength training using progressively-increasing weight on barbells (squat, deadlift, bench press, overhead press and barbell rows.) I’m using the Starting Strength method.

    I usually fast from 8pm to around 11am or 12 the next day, and train fasted in the morning three times per week. I wonder if you might have insight to offer about how much protein per day I should be eating to maximise strength gain and recovery. I have been aiming for about a gram of protein for every pound of body weight. I usually get half of that from a grass-fed whey protein powder and the rest from meat, dairy and eggs.

    I try to keep carbs low and vegetables high but the focus on protein has made it difficult for me to get as much veggies as I used to before I started lifting. I used to just eat a single big meal of mostly veggies with extra virgin olive oil and a little meat on the side most days. Now the protein sort of crowds everything else out and I’ve had to cut back on fat and vegetables both, even with my increase to eating twice a day.

    To make it a little more complicated I have a not-great waist to hip ratio, so I’d really like to lose more fat, but the prevailing wisdom is that any attempt to lose fat while doing this program will severely compromise recovery and could lead to stalling progress or even overtraining.

    Do you have any advice to offer me fire how I should be programming my nutrition to support my training goals while also keeping an eye on overall health?

    Thanks and best wishes, Jessica in Santa Cruz, CA

    Liked by 1 person

    • Hi Jessica, I think your training is perfect, for the good reason that it’s basically what I do as well. Make sure you always use as much weight as you can without compromising the form and technique of the lifts. Your fasting schedule is also excellent, especially with training after a long fasting period. That’s the best. I don’t advocate a measurement-based approach to eating, even though I use CRON-o-meter because I like data.

      From many years of experience, I find that when we keep carbs low (and by that I mean 10% or less of total calories), satiety is the best guide to how much we should eat. For example, having a huge 500 g steak with all its fat or with lots of added butter and plenty of salt after a workout in the middle of the afternoon, I simply won’t be hungry until the next day midday. Digestion during many hours before bedtime, and I sleep like a baby. This way, we can extend the fast to 20-22 hours without any hunger. Making sure you drink plenty of alkaline water the whole day before eating is very important. I do this regularly, and find it a great way to nourish well, fast long, and not feel hungry. I never eat if I’m not hungry, just because it’s time, and I always sleep better at night if I’m not too full. Alternatively, you can do as you do, and eat two smaller meals per day. I also do this regularly, especially during the week.

      For losing excess body fat, I would recommend trying a zero carb diet for a while, eating one big meal per day, but limiting the fat (no added fat). This will do several things to help in using body body fat reserves: it will keep you satiated and feeling nourished; it will provide plenty of protein to sustain muscle tissue and weight training efforts, you will not lose mass nor strength; by sticking to zero carbs and one meal per day, insulin will be as low as we can hope, which will force the body to function by burning fat, and by limiting added fats, you will force the body to use its own reserves. The amazing thing is that you should be able to keep your workout routine, keep feeling strong, burn a lot more body fat, and function on about 1000-1200 calories per day without feeling hungry. Try this for a month and see what happens.



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