Obesity – Solving the Two-Compartment Problem – Fasting 21

One of the major mistakes made by the Calories In/ Calories Out (CICO) hypothesis is the presumption that energy is stored in the body as a single compartment. They consider that all foods can be reduced to their caloric equivalent and then stored in a single compartment in the body (Calories In). The body then uses this energy for basal metabolism and exercise (Calories Out).

This model looks something like this:


All energy is stored in that one compartment. However, this model is a complete fabrication. It does not exist. This known mis-understanding has led to general acceptance of the CICO theorem. According to this model, by reducing the amount of calories going in, or increasing the amount going out, you may reduce the amount of body energy stored as fat.

Of course, this Eat Less, Move More (or Caloric Reduction as Primary) strategy has a known success rate of about 1% or a failure rate of roughly 99%. This does not deter any of the medical or nutritional authorities to question the sagacity of their advice, though.

To better understand how energy is stored in the body, it is more accurate to use a two compartment model. Dr. Kieron Rooney’s diagram demonstrates that the body is able to derive energy from 3 sources – glucose (carbs), fat or protein. However, protein is not stored as an energy source and is only used when there is excessive dietary protein after which it is turned to glucose.

So, this leaves two potential fuel sources – glucose and fat – and these are stored in different compartments. Glucose is stored in the liver as glycogen – a molecule that is composed of long chains of sugars. This is easily accessible to the body, but there is a limited amount that is able to be stored. After that threshold is reached, the body stores fat. Think of glycogen like a refrigerator. It is very easy to move food in and out of the fridge, but the storage space is limited.473497631

Body fat is much more difficult to access, but you may store unlimited amounts. Dietary fat is directly added to the body’s fat stores. Excessive carbohydrates are turned into fat by the process known as De Novo Lipogenesis (DNL). Think of body fat as a freezer that you store in your basement – you can store lots of food in the freezer but it is more difficult to get at it compared to the fridge. You can also store more than 1 freezer in the basement if you need more space.Macro oxidation

As you eat, the body stores energy. As you don’t eat (fast), the body must take stored energy from the body to burn for fuel. But it does not take equal amount from both compartments (fat and glycogen). Glycogen is burned almost exclusively until it is finished – this can last 24-48 hours of pure fasting.

This is logical since it is much easier for the body to get at the glycogen. Think about it this way. If you buy groceries, you first store it in the fridge. Once it is full, then you start to store it in the freezer. When it comes to taking food out to eat, you start by eating the food in the fridge.

zh10080957560005Only after almost the glycogen is already burned for energy does the body turns to its stores of fat. Similarly, only when the food in the fridge is gone do you want to go downstairs to that cold dank basement to get the food in the freezer. It takes more effort. You do not burn equal amounts of glucose and fat. For example, if your glycogen ‘fridge’ is full, you will not use any of your fat in the ‘freezer’. If you need 200 calories of energy to go for a walk, you take that exclusively out of the glycogen with none of the fat being burned.

The two compartments for energy are not burned simultaneously, but sequentially. You need to empty out the fridge before you can start using the food in the freezer. In essence, the body can either burn sugar or fat, but not both. This is controlled partially by insulin, and also directly by the Randle cycle – described in 1963. This is also sometimes called the glucose-fatty acid cycle.

In isolated heart and skeletal muscle cell preparations, Randle and his colleagues were able to show that cells that were using glucose for energy were inhibited from using fat and vice versa without any interference from insulin or other hormones. This biochemical mechanism directly forbids the body from using both fuels at once. You either burn sugar or fat, but not both. You can see from the diagram that using glucose eventually leads to the production of Malonyl-CoA which inhibits the use of fat (LCFA – Long Chain Fatty Acid).2CompartModel

So, why can’t you lose weight using the CICO method? Because it is based on the incorrect idea that all calories are equal. When you store food energy (calories), it is stored as sugar (glycogen) in the ‘fridge’ and fat in the ‘freezer’. But you must burn through the sugar first before you can start burning fat.

So, now you want to lose body fat. The first thing you need to do is clear out the sugar in your refrigerator. However, if you are continually filling up your fridge 3-6 times a day with sugar, then you will never start burning the fat in the freezer. The CICO method ignores the two compartment problem and pretends that all calories are stored equally and burned equally (single compartment), even though this has been known to be false for at least 50 years. This is the equivalent of the standard calorie restricted diet of eating 3-6 meals a day with a relatively high carbohydrate (50-60%) content.

You imagine that since you are filing up the fridge with less glucose, it will eventually empty. However, this does not happen. Why? Because, as you start putting less food in the fridge, your body senses that and starts to get antsy. So, it starts to make you hungry and want to eat more. If you don’t fill it up, it will decrease your metabolism so that it is burning less energy.

What’s the solution? First, you could follow a Low Carb, High Fat (LCHF) diet. By severely restricting the amount of carbohydrates, we keep our glucose fridge empty. Now any energy that must be burned must come out of fat freezer. This essentially turns the two compartment problem into a single compartment problem.2CompartFasting

Second, you could try intermittent fasting (IF). Fasting essentially burns through all the stored sugars in the fridge quickly. Will you get hungry? Yes, probably. But if you push through that, your body is forced to burn fat for energy. The metabolism does not slow down because of the compensatory hormonal changes of fasting. After several days, hunger is also suppressed – the mechanism is unknown, but likely related to the ketone production.

The bottom line is this. You can store energy in the form of sugar or fat. In the fasted state – you can either burn sugar or fat for energy, but not both. If you are continually supplying your body with sugar, it will not burn fat.

Fasting provides a very quick way to start burning fat. It provides a solution to the two compartment problem. The reason why the Calorie pundits never understand why their model doesn’t work is because they have fundamentally mis-understood the problem as a single compartment.

Update Jan 28, 2016

I belatedly realized that I forgot to add this section. Actually, it didn’t update, so I thought it was in here but it actually wasn’t. Sorry.

There is one more critical input into the system. How easy is it to get food energy from the freezer? If the freezer is locked away in the basement behind steel gates and barred, then it will be very difficult to get the fat out. What’s the main hormone that controls it? The answer is… insulin. (Actually, insulin is the answer to most of the questions on this blog)

It’s well known that insulin inhibits lipolysis. That’s a fancy way of saying that insulin stops fat burning. Well, that’s normal. Insulin goes up when you eat, so it tells the body to start using the incoming food energy and stop using the fat in the freezer.

So, if your insulin is high from insulin resistance, you may find that your body is not able to get at the fat in the freezer. So, as you lower the incoming calories (Caloric Reduction as Primary strategy – Eat Less) your body is unable to get any fat to burn. So it compensates by reducing caloric expenditure. Hence basal metabolism falls.

If you are 8 years old, your insulin resistance is minimal and fasting insulin is low. That means it’s really easy to get at the fat in the freezer. It’s like the freezer is right beside the fridge. Easy Peasy. So, if you simply reduce calories, your body can easily compensate by getting some fat out of the freezer.

This explains the time dependence of obesity. That is, those that have been obese for a long time have a much, much harder time losing weight. Because their insulin resistance is high causing elevated insulin levels all the time.

85 Responses

  1. THAT made sense! I can’t wait for the book.

  2. I have a question on fasting. If I sip bone broth occasionally during the duration of my fast. Is that still considered as a fast? Thanks so much

    • Dr. Fung allows bone broth during a fast.

      • I had tried sipping bone broth during a fast. But it only made me hungrier and more difficult to fast. Black coffee however, helps to reduce my hunger pangs v easily.

      • The statement below was taken from a blog post from this site. I am just wondering if sipping bone both may activate secretion of GLP-1 and insulin? Also, is there a place on this site or other websites that provides more detailed instructions on doing a fast? Thanks so much

        “Even non nutritive sweeteners, which have no calories at all, can stimulate the insulin response. Sucralose, when studied in obese human volunteers, raises the insulin level 22% higher than water. The GI tract and the pancreas can detect sugars through taste receptors similar to those in the mouth. This may activate secretion of GLP-1 and insulin.”

    • Carl Davis

      No because the broth has protein particles and fat that will elicit an insulin response. You could still lose weight but it is far better to go with the water fast as after a brief period of 48-72 hours when you burn off your glucose you will have many ketones circulating throughout your body for energy and your hunger will become depressed. Continue the fast until you feel genuine hunger than break the fast. I have found this the most difficult part of the fast so be careful as you could ruin many of the benefits of the fast by eating too much too soon. Try and start with the bone broth for a day or two (depending on how long you’ve fasted – the longer over 10 days means more gradual resumption to solid food.)

      • fat doesN’T stimulate insulin

        • Jesse, it actually does but to a far lessor extent than do simple carbs, complex carbs, and protein. Somewhere Dr Fung did a jpeg on that.

    • The general rule of thumb for breaking your fast is that 50 kcal breaks it.

  3. Dear Dr Jason Fung.

    A few days ago I found your site , listened to lectures on yt and I love it!
    You will save the lives of many people who have lost hope that recovery is possible.
    I am very grateful, thank you very much. Blessings.

  4. I’m a little confused. I thought the body used glycogen during anaerobic activity (e.g., sprinting) and a combination of fatty acids and glucose during other activity (e.g., slow jog). When it comes time to make up for a caloric deficit (either under feeding or during fasting) your body can use glycogen (from liver and muscle cells) and can release fat from adipose tissue (provided insulin levels are low) to make up the caloric deficit. Doesn’t the body metabolize fatty acids during exercise while you’re at a fractional level of maximum heart rate? (say, 75% of max heart rate). If you do not swallow down large doses of sugar following exercise and eat a small meal of high fat, moderate protein but total calorie count below that needed to support all body functions, won’t your body start lipolysis due to low levels of insulin?

    To say that the body ONLY burns glucose (glycogen) until exhausted and THEN turns to fatty acids and starts lipolysis (releasing fat from adipose tissue) seems to be …. wrong. What am I missing? :-/

    • You are not missing anything, you said it yourself: “due to low levels of insulin”. The way it works in normal people is the way you described. However, many people that need to lose fat, have very high levels of insulin. Me included, after many months of LC my insulin is still over the upper “normal” level (which is not normal, as we now know). This high insulin will not let you access the freezer much. This high insulin will make you need to exhaust the glycogen store before slowly turning to the fat store.

      • Bernard P.

        Isabela, the answer to your problem is *fasting*. Low-carb is not enough, because proteins also stimulate insulin production, along with the lower carbs. You have to starve the body completely to make the insulin lower.
        Also, fasting means fasting. Too many people are talking about 14-hour and 16-hour “fasts”, or are finding reasons to eat during fasts.
        The best compromise is 24-hour alternate-day day fasting.
        As time passes, your body weight will decrease, as fat is burned off. At the same time, insulin sensitivity will improve, as the body benenfits from sustained periods with low insulin levels.

        • Bernard, as fasting lowers your insulin levels does that improvement remain long after fasting, do you know

          • Elena

            Insulin goes up as soon as we eat. For non-diabetics glucose will go down and insulin will follow. For diabetics (insulin resistant) glucose will linger in the bloodstream and insulin will stay high until glucose goes away (long time). Next meal has to be when glucose level is low, otherwise insulin will be high all the time. This is my understanding of diabetics problem.

    • I must say I am confused here as well. I have been a keen follower of Dr. Fung’s writing since I first came across his blog and have high respect for his work.
      I like how the posts are made simply understandable with analogies used etc.

      However I am not sure if things were not too oversimplified in this particular post reading statements like:
      “Dietary fat is directly added to the body’s fat stores.”
      “Only after almost the glycogen is already burned for energy does the body turns to its stores of fat.”

      My understanding has been that (especially during aerobic activities), the body will use a mixture of both glycogen and fat as source of energy.

      • “Dietary fat is directly added to the body’s fat stores.”

        I don’t understand that one either, thought that fat is just a different high density/calorie energy source that will not spike your insulin levels and be absorbed and stored more slowly.

        “Only after almost the glycogen is already burned for energy does the body turns to its stores of fat.”
        “My understanding has been that (especially during aerobic activities), the body will use a mixture of both glycogen and fat as source of energy.”

        My understanding has always been is that glycogen is used first then once depleted the body switches over to fat as energy source. So to get to fat burning as energy source you must deplete glycogen first, which means longer harder workouts to get to that fat.

        From my little experience and experimenting with fasting I have much greater fat loss when working out in a completely fasted state and much of the time with same or greater energy levels, but for me it must be in a completely fasted state. Also what amazes me is that once I have completed a workout in a fasted state is how I have little to no hunger. Completed a 2 hour intense mountain bike ride after fasting 22 hours the other day and was amazed how I had zero hunger.

        • I think one of the answers to these questions is that the body’s store of glycogen in the liver is limited. I read somewhere that on average about 500 calories is stored and once depleted, over a few hours, one gets hungry again and refills the stores. Exercising in a fasted state will mean that the fridge is empty and you begin to get at the stuff in the freezer right away. This fasted state can be as little as 3 or 4 hours especially if you are on a low carb regime. The protein goes to the muscles and the fat goes to add to fat stores and there is no sugars to promote insulin production so the body burns fat. The glycogen stores are not all that high from what I read but most people find it hard to work through 500 calories in a session. Most are lucky to do about 200 calories so “You can’t outrun a bad diet”.

    • I wonder if the fuel mix occurs in separate organs for example muscles running on glycogen with the heart running on fatty acids or similar. At rest I oxidise 70% fat, 15% protein and 15% carbohydrate according to respiration analysis.

    • Carl Davis

      It is true that the body will access glucose before it will access free-fatty acids. We evolved for hundreds of thousands of years and perhaps millions (2.6) on a virtually no-carbohydrate diet) and our bodies are virtually the same as our paleolithic ancestors. Our bodies evolved using free-fatty acids and ketones as the main source of energy. In essence we have perverted our bodies by consuming grains and starches that provoke and insulin response form our pancreas to sweep out the “poison” that is carbohydrates. As long as insulin is sweeping though the body lipolysis or the burning of fats cannot occur. I recommend reading the book, “Eat Bacon, Don’t Jog” by Grant Petersen to get your body right. Once you get through the “Atkins fog” which may take from 2-3 weeks as you transition from a “sugar burner” to a “fat burner” you will lose weight, retain lean muscle mass, have more energy and go for 12-16 hours or so without feeling that gnawing hunger sugar burners feel.

      As a metaphor burning glucose for energy is akin to burning watered down gasoline in a high performance engine that doesn’t completely com bust and therefore leaves carbon residue in the pipes while burning fat is akin to burning premium, high octane fuel that burns cleanly and leaves nary a trace of reside as it combusts completely.

  5. When I started reading this, I thought the two compartments were going to be visceral and subcutaneous fats. I’m glad, however, to learn about this logic mistake CICO rests on.

    But I still am curious: is it harder to lose subcutaneous fat than visceral, or is it just me? [By harder, maybe I mean: it takes longer, or the body guards it more jealously (especially in someone like me, who has calorie restricted off and on the last 30 of my 44 years), or something else.]

    • Visceral is usually the first to go which is a good thing as it is metabolically more active than subcutaneous.
      In general visceral is more vascular and contains a higher % of large adipocytes plus having more glucocorticoid and androgen receptors than subcutaneous.
      Meaning it is very much easier for visceral fat to release fatty acids once your insulin is under control.

      As subcutaneous is less vascular than visceral and compared to visceral it is much more susceptible to vessel constriction to conserve body temp which can further limit lipolysis.

      • Excellent news about the visceral fat going first! Apparently, that is the most dangerous type in metabolic syndrome.

  6. I like this analogy. I’m curious though about the very small percentage of people that DO lose weight on a high carb/low calorie diet where they don’t fast and aren’t in ketosis. How you you describe their weight loss with the fridge/freezer analogy. Are they constantly going back/forth between glucose/fat burning? Or are their glycogen stores not filling up and during the long overnight fast is where they are losing fat, a little at a time?

    • They are mostly part of the 99% or athletes. You can lose weight on many kinds of diets, but 99% gain it back in the long run.

  7. Brilliant article Dr Fung, that explains a lot. But does this mean that short fasts (up to 2-3 days) are vastly inferior to longer fasts because the sugar stores (fridge goods) are never totally used up and the body is never really into ketosis and digging into the “basement freezer”? Some people succeed on the 5:2 diet but I am not sure how that can work. Would appreciate your opinion on this, thanks

    • Dianne, I don’t think so, if you’re eating a low carb, high fat diet. You’ll already be burning fat when you begin to fast. I’ve done a few 5-day fasts, a bunch of 3-day fasts, one 2-day fast (just finished this one), and many other types of fasts (typically, I no longer eat breakfast and sometimes don’t eat breakfast or lunch).

      • BobM, my problem is that although I eat generally LCHF, my grams of carbs are generally more 60 -100g per day. I have big trouble staying ketogenic. When using pee sticks I find I am not in ketosis till day 3 – and although I have achieved a 7 day fast followed by 2 x 2.5 day fasts during this month – I seem to have trouble with massive hunger at the point where ketosis kicks in properly 🙁

        • Deb Griffith

          I just “left” a group of keto followers, and have practiced some myself here and there. I started last April with 5:2, then 4:3, and added low carb along the way, to achieve a 40 lb loss, and have maintained it.
          Ketosis , most agree, uses the 20 grams or less carbs per day , depending on the individual. You might be able to eat 50 a day, but it would be rare. And it sounds like not. And when you do find you sweet spot spot, it can take 2-3 days AVERAGE, again, each person is different.

          The shorter fasts, even the 16 :4, 19:5, 2 day, etc, give you results because any amount of time that is very low in carbs and light on protein , or is completely without food, won’t raise insulin levels, and so will allow you to use stored fat. Naturally, the longer you can go, and the least you eat, the better you will do. It is nice to juggle the methods, like Bob mentioned.

          Hope that clarifies it!

  8. I’ve tried IF and it turns me into a raging lunatic. I do not do well. I have read that fasting is different for women because of hormonal differences between men and women.
    I have also tried keto (never can get my electrolytes right I think) and plain low carb.
    I am on a break from low carb because after three weeks my energy was still very low and my moods. Oh my moods. Very unstable.

    So, my question is, what mechanism might be at play that I am unable to do even low carb without disastrous effects?


    • This has been my experience with fasting and lchf….I am also a woman….for the first few months of using a ketogenic diet, I did not fast, but I was pretty darn faithful to my program (<20g carbs). I lost 40 lbs that way, but eventually hit a stall. That's when I added IF and some high intensity interval training. The fasting was not difficult, other than thinking I should be hungry. I fast regularly now, looking forward to brain health, body health, regenerated cellular health. Anyway, the point I'm taking forever to get to is this: If intermittent fasting is turning you into a raging lunatic, then just do lchf for a couple months. See if that is enough for you to achieve your goals. If it is, you're good. If not, then at least you have a few months of fat adaptation before adding IF, and taking that time to get fat adapted might make IF easier. It truly did for me.

  9. This is the clearest explanation of this I’ve ever seen. Thanks for this!

    Would fasting lead to adrenaline rushes at night and difficulty sleeping as a result? Also, what do you when you’re fasting and need to take medications, vitamins or supplements that require being taken with food?

  10. Great article. Well put and I can see it demonstrated in my own body over and over after a year of IF/zero-carb.

    I am surprised by this phrase:
    “If you don’t fill it up, it will decrease your metabolism so that it is burning less energy.”

    A few months ago I thought you had a blog that adamantly went against the theory of slower metabolism?

    But I believe it to be true. My ultimate question is “Why decreased metabolism when cutting glucose?” I’ve noticed this in myself. If I try to eat limited carbs in my diet or if I have a carb meal after a week of no carbs, my metabolism DOES seem to slow down (and energy drops accordingly) as the carbs are being burned off. Right after consuming carbs, I will become extremely hyper but then will eventually move to a state of complete exhaustion. If I stop all carbs (zero carb), I seem to properly switch to fat-burning mode and have a higher level of energy (and better weight loss). This switch from glucose-burning to fat-burning trips me up almost any time I eat carbs. I go through approx. a 24-hour period of extreme fatigue I call “zombie fatigue”.

    • Thanks Kelly for posting your comment. My husband is diabetes 2 and we do high protein/fat with occasional carb cheats…? but he’s been having a lot of “zombie fatigues” in the past 8 mo and maybe the carbs are doing it. Also wondering how Splenda affects him. He has SO much in his coffee or probiotic lemonade. Trying to get him on Stevia…slowly. Thx
      But wondering… You just don’t do any carbs? How does one do that? Also do you not feel faint when you fast?

      • Karen, in my experience as a T2D, my body treats artificial sweeteners the same way it does pure sugar. My BS goes balistic. Even Stevia has the same effect. I found out by metering before and after taking the sweetener. Has your husband ever done that? Your body can’t tell the difference: sweet is sweet, from whichever source it comes. It’s the taste buds on the tongue that feels that something sweet (carbs) is enterig the body and that causes an insulin rush to occur (fine if you’re healthy, not if you’re a T2D). If he is trying to control his diabetes, he should definitely do some metering around his sweeteners. He will be amazed at the effects. I know I was, that is why I stopped the pronto.

      • I think artificial sweeteners also raise my insulin levels. That would explain why drinking diet soda makes fasting insufferable. I can fast without issues for days, but as soon as I drink a diet coke, an hour later I start feeling sluggish and very hungry (even though hunger was near nonexistent just an hour before). I guess it has something to do with the pancreas reacting to flavor? It makes sense too, cause increased insulin lowers my blood sugar way down, not knowing there is no actual glucose being added to my blood circulation, and that increases hunger.

      • Hi, Karen. Sorry I never saw this comment from you. Yes, after fighting with my weight and always being 25-50 lbs over weight and walking around with 110-140 blood sugar levels, I realized I was ready to doing something different (even things very against the norm). This is how I got to zero-carb. There are a few Facebook groups and a subreddit with people that practice this lifestyle. It was a bit tough in the beginning. I pretty much have cut out all vegetables and all dairy, mostly as an experiment. But after 4 weeks I was completely convinced this has been my problem all along. My body is just extremely sensitive to carbs. Today, with no medication, I walk around 137 pounds and I have no weighed so little in my entire adult life. My energy is (finally) way up, I don’t get sleepy after meals, and best of all, my blood sugar is typically always in the EIGHTIES. 8-0. I have been eating this way for 9 months and just found out I am pregnant (which is something I have been trying to do for 3 years). 🙂 For anyone at the end of their rope, I encourage you to research it more and try it. Even just for 2-4 weeks. It certainly won’t kill you and you might find it to be amazing. Feel free to email me at kelly systers [at] gmail with questions.

      • Karen, I have found that switching from coffee with Splenda to tea with lemon and no sweetner is a lovely way to boost energy and lower BG ( i also have T2D). Plus, saves a bunch of money with the cost of coffee and splenda being so high! 🙂

        • OMG… Kelly and I aren’t differentiated in this thread!! How to do that?

  11. I get really confused about muscle loss in all of this.

    I went low carb while marathon training and ended up losing 4 lbs of muscle. It seems I have to eat carbs but if I want to lose weight I can’t. There must be a way to do this without wasting muscle.

    I have been just eating carbs before and after my workouts and I lost some weight but I’ve been stuck now for 3 weeks and just can. Drop any more. I’m scared to drop more carbs for fear that I will just lose muscle.

    • Just my personal unprofessional thoughts about this (i ran a couple of marathons myself if that’s worth anything):

      1.) Doesn’t it seem odd to you that as a marathon-runner – which is only a very small subset of the population – you even have to struggle with weight-loss? Most people can’t do a 5k at the speed you do 42k and some don’t have that struggle at all.

      2.) What you consider low-carb might not be low enough to make the switch. If you lower the carbs but don’t go low enough you starve yourself instead of “going to the freezer” and your metabolism will go down and catabolize muscle because it has not established the access to the fat-stores (making the enzymes etc.. to utilize body-fat)

      3.) Attempting to make that switch during a marathon training is IMHO a VERY VERY VERY (!!!) BAD idea! You have to plan ahead and adjust your decisions. Think long-term (i know that’s difficult sometimes). You are trying to do something difficult under the worst possibly conditions. Don’t!

      4.) Are you sure about the muscle-loss? Could it be part water you lost? Marathon runners are not especially known for being muscular and even if you lose some, muscle that is lost can be regained relativly easy compared to building new muscle.

      I personally have not lost any muscle at all, not even during water-fasts. I have however reduced my cardio-workouts (running, cycling) and increased weight-training.

      Good luck! 🙂

    • How sure you losing muscles? It’s more certainly water and glycogen stored in the muscles.

  12. @Jack

    I have the same problem of muscle loss during fasting & end of fasting week. I am also confused on how to regain lost muscle mass as it may jeopardise the efforts to combat insulin resistance if I increase caloric intake with protein. We request Dr.Fung to guide us meantime if any other member has any insight please post your experiences & suggestions.

  13. Madeline Winter

    Thanks for the incisive article. I have been struggling with a ketogenic diet for six months. I have not lost a single pound. Sometimes, I would loose a few, but then regain them inexplicably. I was taking a lot of fat in the form of coconut oil and butter, moderate protein and very low carb, often under 10 grams. I hear of other women in the same situation. This article makes clear what I have often suspected, that I am just never tapping into my fat stores. I have been working towards longer and longer fasting periods, which seems to have helped me to loose a few inches around my waist, but no scale weight. I have also been working out more often. I love this diet and I have experienced many benefits from it, so I’m in this for the long haul. At 66, I often say that I have nowhere else to go. I am looking into more strategies to help me fast for over 24 hours. I am hopeful, and every post I read here is increasing my hope.

  14. With all this YOu say it is impossible to lose fat on a moderate fat and carb diet eating 6 meals a day like all the bodybuilder (even natural) do who almost never use fasting because the fear of losing muscle, or vegetarians who eat 500+ gramm ch per day… Or I misunderstood something…

  15. Is there a place on this site or other websites that provides more detailed instructions on doing a fast? Thanks so much

  16. Filippo B.

    then what about respiratory quotient?Is it a lie all?What about that maraton man at 42 km go against the wall because he finished all glicolit energy and the fatty acid don’t to be used whitout these.To me the fisiologys have taught that fat fire at the flame of the carbohydrates.This combination is less efficient in principiant and than this improves whit advance of training

  17. OK I have been “fasting” for about 8 mons. I do an eighteen fast for 5 days a week with a few 22-24 hr thrown in when I can. Is this good enough or do I have to fast for a longer time. When I do eat it is always low carb so I have maintained a 42 lb weight loss but have stopped loosing. After more research now I have found out that the stevia in my black coffee has not been a true fast? So in order to loose more weight and to help my BS would my schedule be ok or would giving up my coffee while fasting kick start my weight loss again? Do I have to do a 2-3 day fast? I can’t imagine doing that for two reasons. First I would probably kill my kids (JK lol ) but worried my FBS will start to rise due to liver dump.
    Thank you.

    • Martin Williams

      Alison, here is the opinion of a nobody. I have found it necessary to count calories on a alternate-day protocol. If I follow Krista Varady’s pattern, i.e., 500-600 calories (from any source, including junk food) on a ‘fasting’ day, and ad libitum eating on an eating day, then I don’t lose. My efforts are seriously compromised by the amount of alcohol I drink. But even if I remove that for a period, I still have to count calories.

      The way I think of it is this: Even if everything the advocates of LCHF say is bullshit, then fasting is still bound to work, even if you think of it as the practise of deferred gratification. Fung himself has said that whatever science discovers about nutrition and weight loss in the future, fasting is an assured way of losing weight because it’s about long ish periods of eating nothing (or very little).

      Krista Varady found that her subjects typically consumed no more than 115% of their maintenance calories on eating days. But even if you were to find, like I have, that counting is necessary, then it is, at least, far less burdensome to do so every other day. (Counting on fasting days – if you have an alllowance – is hardly counting at all.) And counting becomes streamlined if you eat similar meals often.

      Sorry if this rambled. I’m fasting tomorrow, and on the hard cider tonight.


  18. @ Allison

    I am in very similar situation like you.I eat one meal a day i.e. every day at 7.30 PM. I drink coffee with cream an cinnamon without any sweetener. I have lost 40 pounds and just cant go further.I came across an interesting explanation i.e. Set Point Weight Theory which explains as under :

    According to the set-point theory, there is a control system built into every person dictating how
    much fat he or she should carry – a kind of thermostat for body fat. Some individuals have a
    high setting, others have a low one. According to this theory, body fat percentage and body
    weight are matters of internal controls that are set differently in different people.
    • The set-point theory was originally developed in 1982 by Bennett and Gurin to explain why
    repeated dieting is unsuccessful in producing long-term change in body weight or shape. Going
    on a weight-loss diet is an attempt to overpower the set point, and the set point is a seemingly
    tireless opponent to the dieter.
    • The ideal approach to weight control would be a safe method that lowers or raises the set point
    rather than simply resisting it. So far no one knows for sure how to change the set point, but
    some theories exist. Of these, regular exercise is the most promising: a sustained increase in
    physical activity seems to lower the setting (Wilmore et al. 1999).
    • According to the set-point theory, the set point itself keeps weight fairly constant, presumably
    because it has more accurate information about the body’s fat stores than the conscious mind can
    obtain. At the same time, this system pressures the conscious mind to change behavior,
    producing feelings of hunger or satiety. Studies show that a person’s weight at the set point is
    optimal for efficient activity and a stable, optimistic mood. When the set point is driven too low,
    depression and lethargy may set in as a way of slowing the person down and reducing the
    number of calories expended.
    • The set point, it would appear, is very good at supervising fat storage, but it cannot tell the
    difference between dieting and starvation. The dieter who begins a diet with a high set point
    experiences constant hunger, presumably as part of her body’s attempt to restore the status quo.
    Even dedicated dieters often find that they cannot lose as much weight as they would like. After
    an initial, relatively quick loss, dieters often become stuck at a plateau and then lose weight at a
    much slower rate, although they remain as hungry as ever.
    • Dieting research demonstrates that the body has more than one way to defend its fat stores.
    Long-term caloric deprivation, in a way that is not clear, acts as a signal for the body to turn
    down its metabolic rate. Calories are burned more slowly, so that even a meager diet almost
    suffices to maintain weight. The body reacts to stringent dieting as thought famine has set in.
    Within a day or two after semi-starvation begins, the metabolic machinery shifts to a cautious
    regimen designed to conserve the calories it already has on board. Because of this innate
    biological response, dieting becomes progressively less effective, and (as generations of dieters
    have observed) a plateau is reached at which further weight loss seems all but impossible

    Adapted from Integrative Group Treatment for Bulimia Nervosa by Helen Riess, M.D. and Mary Dockray-Miller
    Questions about this topic? Contact the Center for Health Promotion and Wellness

  19. Thank you, Dr Fung, for this and the many other interesting and helpful posts. I made a request to my public library to purchase your book, and I am the first on the reading list when it is available in March!

    I am currently eating according to the 5:2 approach. In addition to LCHF, I have had good luck in the past with doing a 3 to 5 day “fat fast”, i.e., 1,000 to 1,200 calories of 90% calories from fat. (I did this for about a year, once every three or four months.) For me, a fat fast acts like a re-set; if things are stalling on LCHF only, then the fat fast seems to get things going again. It is difficult for the first day or two, but by day three it is much easier and my energy and ability to focus are excellent. Also, my ketone levels are significantly higher by day three. However, the challenge with the fat fast is that it is hard to maintain meals over several days of 90% fat, especially if cooking for a family.

    So now I’m thinking about combining the two things: two days of IF where dinner is a meal of 90% fat. I’m wondering if this would extend the fat burning from the “freezer” (using your analogy), even if I have a meal of the 500 calorie limit for me on IF. I welcome your thoughts on this approach.

    • Karen, What do you eat when you are on your “fat fast” days. I would love to know.

      • Jo, I eat healthy fats, especially avocado, walnuts, flax meal, olives and olive oil, and hemp seeds. Dana Carpender has a small book called “Fat Fast” with 50 recipes that are helpful. But that said, I find that it is much harder to eat this way, even for just a couple of days, than it is to simply fast for two days a week and then eat LCHF most days.

  20. james proffitt

    This is not meant as a challenge but stems from confusion. How can the very obese lose massive body fat on juice fasts or otherwise consuming copious fruits?

    • The Calorie Reduction method technically works so only getting a couple hundred calories a day in juice will let you lose weight, the problem is the sugars in the fruit keep your body producing insulin meaning you get all the downsides of the traditional diet like constant hunger, mood swings, and your body set weight doesn’t actually change so you put the pounds back on easily.

  21. Two connected questions. Some authorities claim that on the fasting day a limit of 500 calories or one-fifth daily intake will work. In support of this, you have in a video on Larry his wife having success on a short-term fast of about 18 hours instead of the full alternate day fasting. (both are obese and Larry has type-2 diabetes).

    Second question, in your examples (video on diabetes cured with diet) of bariatric surgery, there is a cure rate for type-2 diabetes of between 80 and 90%; and most are cured or nearly cured within two weeks. I assume that during that period while recovering they are fed with intravenously. What is in their IV? Is it glucose and other nutrients and how many calories of glucose? (I tried finding out about the IV using google and failed)

  22. Rather a luxury problem soved….
    In March 2013 my husband invited me to a cruise. Wow wonderful but….my dressy clothes didn’t fit anymore and I didn’t want t o buy a bigger size for this occasion, so…I HAD to lose weight!
    Google gave the solution and I found Zoe Harcombe and dietdoctor.
    Three months later I fitted in my long skirt and “old” cocktail dresses.
    I lost 7 kilos in total and now, three years later my weight is still 52 kilos, slimmer than ever!. And lowcarb is our lifestyle…
    Not bad for an 80 year old!
    If I can do it, you can do it!

  23. Another very clear and informative article. Many thanks, Dr. Fung.

  24. Hi to all,
    I’m trying to understand, while on LCHF routine, what factor determents –
    when to burn body fat and when to burn fat that comes from food?
    As it seems to me, if the fat consumption is regular, there’s no reason to get to the “basement” for energy.
    What am I missing?

    • I think this is the point of fasting: to make sure no fat is coming in, so the “basement” (stored) fat has to be used as energy provider

  25. Bernard P.

    From the 6th paragraph of this post:

    “Dietary fat is directly added to the body’s fat stores.”

    Dr. Fung, I’m confused about this. Is it as simple as that? After watching and reading everything on this web site, I was under the impression that eating fat is not fattening per se. This sentence is raising questions in my mind about the manner in which fat is metabolized.

    Maybe you could write a post about the metabolism of dietary fat?

    • Actually even I have the same doubt.. All this while, I thought dietary fat doesn’t make me fat. Only insulin does that.

    • Let’s not forget, if the total energy expenditure (TEE) your body needs for the day is 2400 k/calories, then you can’t expect to eat 3,600 calories of fat per day and lose weight…. Right?

  26. hi, I lately read a paper “Kevin Hall -Calorie for calorie, dietary fat restriction risult in more body fat loss…” CelMet 22-3 sept 2015 that seems to disagree with insulin hypothesis. What do you think about ?

  27. Dr. Fung,
    this entire website is very illuminating. Congratulations for the great work. Have been hearing about the role of carbohydrates and insulin in obesity for a long time, but never in such a rigorous and systematic way.

    I am however still confused about two aspects of the theory presented and would appreciate if you could clarify them:

    1) Let’s say an obese, insulin-resistant subject with an estimated RMR of 2000kcal starts an LCHF diet. For the sake of simplicity, let’s say he eats at his RMR – 2000 calories – hypothetically at 100% Fat. At this level of calories and fat, the insulin response should be low. However why the body should lose stored fat if exactly enough energy is supplied via dietary fat?
    It seems that to lose weight he should create a calorie deficit. This deficit would mobilise fat, as the subject is minimising insulin response via the 100% Fat nutrition (again, hypothetically…). Wouldn’t this behaviour however also elicit a response from the body to lower the RMR via the thermostat effect you talk about? So our subject seems doomed even by going 100% Fat… Clearly there is a tie-in that I am missing here.
    2) Let’s assume the same subject goes instead on a ‘macro-balanced’ 16:8 IF schedule, with a caloric deficit of 500kcal. I understand the benefits created during the fasting period. However cramming the 1500 calories should generate a maxi-surge in insulin levels. So if we believe that an IF protocol brings superior results when compared to a standard 1500kcal 5meals-a-day diet we are implicitely saying that yes, the insulin response is very high but less than proportional. In other words, the fed-state insulin response negates only a fraction of the weight loss benefit obtained during the fasting period. This appears to me a logical explanation, but have not found any analysis of the insulin profile over a fast-fed cycle which shows the superiority of this approach.

    Many thanks

    • The first point was probably not clearly expressed.
      The tie-in would be the concept of ‘weight set-point’. However how this re-set could happen (assuming it is possible?) it is not clear to me.
      Regular exercise? Long-term IF/LCHF? Both?

      • I am wondering if eating only when BG is lower than personal A1C (average BG), and eating Low Carb so the glucose does not go high again and insulin too (basically eating from the low insulin index foods) would lower in time the Weight Set Point. Theoretically this method will continuously lower A1C through fast (eating only one has low BG) and low carb.

  28. […] Original Article by Jason Fung @  IntensiveDietaryManagement.com  […]

  29. […] As mentioned before, short term storage of food energy (glycogen) is like a refrigerator. The food energy goes in and out easily, but there is limited storage. Long term storage (fat) is like a freezer. Food is harder to get to, but you can store much more of it. If you eat 3 times a day, it’s like you go shopping for food 3 times a day and any leftovers get stored in the fridge. If there is too much for the fridge, it goes into the freezer. […]

  30. […] As mentioned before, short term storage of food energy (glycogen) is like a refrigerator. The food energy goes in and out easily, but there is limited storage. Long term storage (fat) is like a freezer. Food is harder to get to, but you can store much more of it. If you eat 3 times a day, it’s like you go shopping for food 3 times a day and any leftovers get stored in the fridge. If there is too much for the fridge, it goes into the freezer. […]

  31. A few years ago I gave up bread, flour, pasta, rice, potatoes and so on. No weight loss. Then I gave up sugar, pies, cakes, sweets, candy. No weight loss. Then I discovered the Keto diet and I lost 15lbs before hitting a plateau. Mind you I never left Obesity. Now I have discovered Keto and fasting and I am dumb founded no weight loss. I did however getting my FBS from 105 down to 95 each morning. I am a menopausal 5’1 female and weigh 165 and feel I will always weigh 165.
    I have not been able to fast past 46 hours at one time. I am now eating one meal per day 800 calories with a meat and lots of vegies with real butter. I eat sunflower seeds as my late night snack and of course I drink coffee and tea with half/half most of the day.
    I will continue to do this for the blood sugars but I have pretty much given up on the idea my waist will ever be under 35 inches.

  32. I recently did a 5-day liquid-only fast. I started on a Sunday evening at about 7-pm (my last meal) and had nothing but water, coffee (usually black, but sometimes with heavy cream or a little half-n-half), and tea till the following Friday evening. That Friday, to break my fast, I had a cup of hot chicken broth about 30-mins or an hour before having a couple of fried eggs. I had no problems getting back on track with my low carb, high fat, moderate protein (LCHFmP) way of eating after that.

    Before starting my fast I, too, wondered if I would have difficulty with hunger or energy. In fact, just the opposite was true for me. Sure, occasionally I felt some hunger pangs, but some water or coffee and a simple distraction at work kept me going. The hunger pangs quickly subsided on their own. I lost 7-lbs in the process and felt GREAT the entire time. I could have easily gone longer, but I just chose not to.

    To those who have tried to fast and found themselves ravenous, I would suggest they take a serious look at the number of carbs they are ingesting every day. Use an app like MyFitnessPal to actually track your food. You may be surprised to find you’re well above 20-grams of carbohydrate a day. Do NOT subtract fiber from your carb count. Use TOTAL carbohydrate to track. If you are truly 20-grams of total carbohydrate per day, or lower, and still find hunger an issue when trying to fast, they you’re likely getting too much protein in your diet which also triggers insulin. Once you get your carbs AND protein in their proper balance and you eat that way for a few months, then fasting should be a breeze for MOST people. I’m sure there are some exceptions as our bodies are extremely complicated, but it takes diligent effort to become truly fat-adapted over a carb dependent metabolism.

    Oh, I don’t believe checking for ketones in the urine is the best indicator of ketosis. You MUST check the blood to be sure and those strips are way too expensive. So, it’s best to just be sensitive to one of the symptoms of ketosis – metallic taste in your mouth from acetone (one of the three primary ketones).

    Good luck!

  33. […] let’s think about this problem in the context of the 2 compartment model of obesity that we have used before. There are two compartments for body energy. We take calories in as food. This gets stored in the […]

  34. What do you think of the Lemonade Cleanse?

  35. […] can either burn fat, or burn sugar. These two fuel systems are separate and do not interact (see Randle Cycle for more details). When insulin levels are high, then the body runs on glucose. During that period, […]

  36. […] can either burn fat, or burn sugar. These two fuel systems are separate and do not interact (see Randle Cycle for more details). When insulin levels are high, then the body runs on glucose. During that period, […]

  37. […] can either burn fat, or burn sugar. These two fuel systems are separate and do not interact (see Randle Cycle for more details). When insulin levels are high, then the body runs on glucose. During that period, […]

  38. […] Intensive Dietary Management. (2016, jan). Obesity – Solving the Two-Compartment Problem – Fasting 21. Hämtad 2016-07-20 från https://intensivedietarymanagement.com/obesity-solving-the-two-compartment-problem/ […]

  39. It makes a lot of sense. However, why did I lose more than 30 pounds with calories in/out method? Not saying fasting doesn’t make sense, I just don’t understand why discrediting the method if it worked for me. I am sure I am missing something.

  40. […] has a 1% success rate and a 99% failure rate according to Jason Fung’s article entitled “Obesity – Solving the Two-Compartment Problem – Fasting 21”. Furthermore Fung states another mistake made is the “Calories In / Calories Out (CICO) […]

  41. “But you must burn through the sugar first before you can start burning fat.” As a simplistic explanation this makes a lot of sense, but if taken literally, it’s obviously false. Blood sugar drops to 0 before any fat oxidation kicks in? You’d die first. Clearly it’s not a step function as this quoted sentence implies. It must be a sigmoidal function, but the shape parameter (Hill coefficient) governing it would be really interesting to know, and even more, what factors affect the shape parameter?

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