The Fed and the Fasted State

In order to understand how the body gains and loses weight, you must understand how it uses energy. The body really only exists in one of two states – the fed and the fasted state. When we eat, the hormone insulin goes up and insulin is released. Now all foods stimulate different amounts of insulin release but few foods except for pure fat cause no insulin release at all. Insulin is really a type of nutrient sensor. It senses the ingestion of both carbohydrate and protein containing foods. Refined foods, particularly carbohydrates cause the highest release of insulin.

Our bodies need a continual source of energy for basic metabolic housekeeping – keeping the heart pumping blood, the liver and kidney detoxifying, the lungs sucking air, brain function etc. Obviously we need a source of energy for all that work and it must be continuously available. Since we do not eat food all the time, we have a system of storing food energy (in the liver and as body fat) for times where we are not eating.

The main mistake people make is believing that weight loss is a simple one compartment problem. That is, people think that all calories go into a single compartment and taken out of that same one.

Consider the energy balance equation: Fat = (Calories In) – (Calories Out). This is always true. Suppose that your weight is stable and you eat 2000 calories and burn 2000. What if you want to lose weight? You hope that you reduce dietary calories to 1500, and body fat will provide the other 500. Over time you lose body fat. That’s exactly what does not happen.

There are really two different places where our body can obtain energy

  1. food
  2. Stored food energy (glycogen in liver, or body fat)

But here’s the CRITICAL point. You can only get energy from one or the other, but not both at the same time.

Imagine a railroad track. Suppose you need 2000 calories to keep basic metabolic function normal. There are two different tracks where energy can come from – either food or stored food. You may only obtain energy from one source at a time. If you take energy from the first track, you cannot get any from the second and vice versa.

In the fed state, when you are eating, insulin levels are high. During that time, it makes sense to derive your energy from the food that you are eating. So what happens is that we shut down burning of stored food energy in the form of fat and glycogen. For all you technically inclined people, we say that insulin inhibits lipolysis and gluconeogenesis. This is a well known physiologic fact.

Throughout most of the day, assuming you eat 3 meals a day, this is the normal state of affairs. But what happens when you go to sleep? Because you are not eating, you are fasting. Insulin levels fall. You now need to pull some of the food energy you’ve stored away to keep your vital organs running. This is the reason you do not die in your sleep every single night.

As you fast, insulin levels fall. This is the signal to switch energy sources from food to stored food. You pull stored energy out from the liver (glycogen) and if that is not enough, body fat. Technically speaking, we say that we start glycogenolysis, gluconeogenesis and lipolysis when insulin levels fall.

If you fast for 24 hours, for example, what happens is that your body wants 2000 calories for that day’s energy bill. Since you are carrying around plenty of body fat, it’s no problem to supply that 2000 calories. Approximately 1/2 pound of fat will supply that easily and the body says “Whoa, I have tons of fat, take all you want’.  It is important to realize that this is a completely natural process. Humans have evolved this mechanism of food storage, and there is nothing inherently unhealthy about fasting. It’s all part of a natural balance of being in the fed state and the fasted state.

Another way to put it is that this. You either burn fat or store it. You can’t do both at the same time. The body is just not that stupid. If food is plentiful, you store food energy. If food is scarce, you burn food energy (body fat). The key hormonal regulator here is insulin. The change in insulin levels is what signals our body to go into fat storing mode or fat burning mode.

So what happens now if you are trying to lose weight by adopting conventional advice to reduce the dietary fat and calories, and eat 6 times a day. By doing so, you keep insulin levels high because you are eating lots of low fat bread, pasta and rice and eating all the time. This also happens in type 2 diabetes, where insulin resistance causes insulin levels to stay elevated.

Since insulin is high, you must get your energy from food, and cannot get any from your body fat stores. You reduce your calorie intake from 2000 calories to 1500 and hope against hope that you will lose weight. You do, at first, but then your body must adjust. Since you cannot get at your fat stores, if you are only getting 1500 calories in, you must reduce you calorie expenditure to 1500 as well.

So, you feel tired, hungry, cold because your body’s metabolism is starting to shut down. But the worst part? You don’t lose any more weight! Your weight loss starts to plateau, but you feel like crap. Over time, you start to regain some of that weight. So you decide that you’ve had enough and increase your caloric intake to 1700 – still lower than when you started. But, because you are taking in 1700 calories but only burning 1500 calories, your weight quickly goes back to what it was before you started the diet. Sound familiar to anybody?

The key to successful long term weight loss is not reducing calories. It’s reducing insulin. Because insulin is the switch that decides whether your body is burning food energy or stored food energy (body fat). If you are burning food, then you are not burning fat. It’s as simple as that. The key to accessing your body fat stores is to reduce insulin. You must let your body go into the ‘fasted’ state.

114 Responses

  1. Excellent post! It keeps getting clearer and clearer in my head : )

    Soo possibly stating the obvious: First eating lots of fat keeps insulin low. Then, can the body tell the difference between ingested fat and body fat? Meaning that eating a high fat diet isn’t really that much different from fasting.

    The only thing to deal with in this scenario is ingested protein. but maybe as long as glucogenosis is low you’re still OK to burn body fat. Then there’s that last bit to make sure you don’t eat too much fat to enable taping into the reserves. (And the other part, keep the protein in a “reasonable” level.)

    • Eating lots of fat will not keep your insulin low, it will at most turn a short high spike into a long medium spike, which arguably might be even worse. You have to cut carbs to get into ketosis, but to then burn your body fat you also have to cut fats. Dont fall into the high-fat low protein trap, nobody there has any abs to show.

      • Thank you. This is where I may have been going wrong should the protein be high then ?

        • look, hight fat diet doesn’t mean adding fat to everything. simply eat high fat foods , vegan or not, like avocado, meat (grassfed if you can) , coconut/almond milk instead of normal milk, non starchy veggies, and, like dr. jason explained in his book The obesity code, yes you can live without carbs but there are proof and he wrote it for us, that eating whole carbs and fasting provides an amazing healthy life. stick to a no carb diet and enjoy life if you can, unless you’re an expert in making keto desserts with coconut/almond flour, and their milks, etc. yes, high fat is possible without adding butter to everything, avoid processed oils too.

      • lass lassiter

        Don’t over complicate this…Eat meat!

    • Tommy None

      Brilliant breakdown!

  2. If you eat a fat-rich meal, and hence produce little insulin, then you will presumably still utilise the digested dietary fat as a direct energy source. That’s the fed state but in the absence of insulin. So the key to successful long term weight loss is not reducing calories … it’s a combination of remaining in the fasted state for longer while also reducing insulin levels while int he fed state. Correct?

    • Rese Plante

      This is what I also understand, very well said, thank you.

    • When you are in ketosis, cutting calories and lengthening the fasted state are the same.

      • Not exactly. Even after eating a ketogenic diet for some time, when I ate at a large calorie deficit for a prolonged time, my weight loss tapered off and I had symptoms of metabolism falling. It’s what brought me to Dr Fung. I did experience keto assisted fasting by keeping my blood sugar more stable into the fast and helping me feel less hungry – my body didn’t have to keep making that painful switch in and out of ketosis. But cutting calories in keto like a regular diet doesn’t work well – at least, it didn’t for me.

  3. Orvan Taurus

    The other thing from this is, “If not hungry, don’t eat.” thus extending the fast and maximizing use or stored reserves. Eat by the stomach, not the clock.

    • Well then, I would probably never eat cause I fasted without food ( only water ) for 9 days and didnt feel hunger at all during those days.

      Before that fast I used overeat because of strong food cravings (not hunger), but now I am still not hungry and have lost all food cravings. That fast changed my life to the better in so many ways.

      Now I basically dont eat for 16-18 hours and then eat during the 6-8 hours left. I must have reached balance and I am really losing fat now too, very quickly. I also try to fit in some weight training or floor ball before breaking the fast.

  4. New to fasting

    No where in the whole website does it mention how often should a person undertake fasting.

    Is it once a week?
    Is it 4 times a month?
    or Continue twice a week fasting till you hit the desired weight loss number??

    I guess it be very beneficial if Dr.Fung could answer this.


      Q: I try to combine 24 hours of fasting with longer periods. 3 days fasts every 2 weeks or 7 day fasts every third week or so. It is very flexible. I feel good during fasts as well. I manage to work, go every day by bicycle and even do my exercise 2-3 times/weak at the gym ( not very regularly). Have no medications or problems with my health either.
      Do you have any contra-indications on how often I should fast? Have read about fasts on your blog and even listened to your wonderful lectures on you tube and understands that it is individual and free up the experiment as long as you feel good. Yet, I am a little afraid (even though I am a registered nurse) because I combine short fasts periods (24 hours fasting) with the longer fasting periods quit often. Can it be too much of a good thing and dangerous for my health in a longer turm of time to do my fasts?

      Jason Fung: If you are feeling well, there is no contraindication, except in children, pregnant and breastfeeding. Also, if diabetic, medications may need to be adjusted.

    • Maya Aggani

      Dr Jason Fung has two books, i.e., the Obesity Code and the Complete Guide to Fasting. I strongly recommend these books if you are new to fasting. Regards

    • He wrote a book about fasting. He only reccommends long fasts (7-14 days) every 6 weeks I think. It could be longer, he recommends to be under medical supervision while attempting one of these longer fasts. You could simply do alternate day fasting. You eat every other day. There’s no set rules for fasting. Main thing is when you fast, fast. When you eat, eat! Don’t restrict calories on eating days, that could cause drop in metabolism.

      • “Don’t restrict calories on eating days, that could cause drop in metabolism.”

        Metabolism will drop only if your body can’t readily access its fat reserves. Consider the two track metaphor above. When the fat track is blocked by insulin due to frequent/constant eating, the body’s only other alternative during a diet where you are using more calories that you are taking in, is to reduce energy expenditure – lower your metabolism. Feeling tired and cold are common symptoms.

        However, if the fat track is not blocked by insulin – even during a diet, you’ll easily switch to fat as an energy source and never be hungry. As Dr. Fung says, feasts need to be balanced with an occasional fast.

        A most important point mentioned in both books is having a sufficiently large time interval between meals to allow insulin resistence to drop. Energy production within your body’s cells (within the mitochondria) then have the impetus to adapt to the lower glucose environment by ramping up fat utilization.

        How will you know when you are fully fat-adapted? As already mentioned, hunger doesn’t exist. The other point is that you can easily skip meals – even for days – and not care or notice.

        • RahulPolX

          Re: “Metabolism will drop only if your body can’t readily access its fat reserves.”

          There is this FastingTalk episode 20
          “20: Problem With One Meal A Day, Nursing, Marathon, True Hunger, Pain Relief, Black Coffee”
          at 15m30s
          where Megan Ramos says that eating one meal a day WILL result in drop in metabolism, similar to Calorie Reduction As Primary. Apparently OTHER Fasting Regimens (such as 16/8, or EVEN multiday fasts) CAN also have this problem.
          I dont understand her explanation.
          Her explanation left even the other host Jimmy Moore in confusion.

          In the “Fasting Regimens” blogpost, Dr Fung says that WHEN you experience a stall during FASTING, you “mix it up” i.e go for a longer fast and presumably come back to regular fasting schedule such as OMAD later.

          I would love to see blog posts from Dr Fung on this subject.
          Why would a fasting regimen lead to a stall well before one reaches goal weight, when the science says metabolism will NOT be impacted, and the fat-track is still open?

          • Her explanation is that constant variation – unpredictability – is critical to preventing the body from establishing an automatic response to a given stimulus. This makes sense for example when considering that muscles strengthen and increase endurance to meet a particular demand. Once there they don’t change further. They will however continue to adapt if the sequence or timing of a given set of exercises is changed.

            With OMAD as an example, the implication is that one’s metabolism learns to expect and reduce energy output during the unfed part of the day and to expect a single meal at a particular time. Merely changing the timing of that one meal (see circadian rhythms discussed in the book) could be enough to restart a loss.

          • Srinath

            I believe Meagan Ramos meant that with OMAD you shouldn’t eat just 800 calories. Go the whole hog. Max out your daily need. Or get close to it.

    • Every other day, eat a low carb, moderate protein, higher fat diet. On the intervening days either don’t eat at all, just drink water or eat a light supper. Additionally, buy the two books. I should point out a study done a year or so ago found that of all the diets, Atkins was best at initial weight loss and Weight Watchers was best at weight maintenance. Where I appear below to take issue with Dr Fung’s thesis, as it relates to insulin’s culpability, I am perfectly willing to accept that. Perhaps, in my case, I did not have an insulin issue which is why a calorie reduction as primary worked ‘so well’.

      • So Sasha says don’t eat high fat and you seem to be saying do eat high fat. I’m confused a bit. Is there an optimum or minimum/maximum fat that DrFung suggests. I’ve just started fasting and doing 22-24 hr fasts 4 days a week or so.

    • Further, Dr Fung has a whole series of YouTube vids. There is a six part series that, pretty much, mirrors Obesity Code, if saving $12 is a consideration. I think it’s called “The Etiology of Obesity”…something like that.

    • Dr. Fung states that he fasts 3 times a week to maintain his weight. He fasts for 23 hours and then has one single meal. I think he is very reasonable since he is already fit. However, for those who have loads of body fat to burn, I strongly belive he recommends fasting every day. At least that’s what I do. I fast every day for 23 hours, and eat normally during 1 hour windows until I’m fully satisfied. I belive that he prescribes longer fasting periods for some of his patients, but from what he says he normally recommends the 24 hours fasting or even less depending on the patient.

      All of my conclusions I drawn from his own words on this interview:


  5. I fast many different times. I do fasts daily until about 1-2pm, although sometimes I eat breakfast. Sometimes I fast until dinner. Sometimes I fast through dinner until “lunch” the next day. Sometimes I fast 3-5 days. I mix it up. Sometimes I fast a lot, two 40 hours fasts plus a 24 hour fast per week. Sometimes I fast a little. This week, I’m doing 18 hours fasts before I go on vacation, then I won’t fast much when on vacation. When I get back, I’d like to try a 1-week fast. We’ll see – the weekend is the hardest part.

    By the way, if I do longer fasts (48+ hours), I always get cold at least once at night, sometimes several nights.

    • I should say that I try to fast every week, with exceptions around vacations and maybe every once in a while to take a break and keep my body guessing. There are no rules for fasting. I personally have a hard time during “reentry”. I basically have water in me, and it takes a while for me to settle down, usually a day or more for fasts of several days. So, I make sure longer fasts are not near days I travel. Others don’t seem to have this problem to the extent I do.

      • BobM

        Not sure exactly what you mean but I find psyllium fiber taken a couple of hours before or the morning of the end of the fast and the next day help tremendously. I forgot during a recent fast and it was not pleasant

  6. Just a thought; is it possible to trick the body to burn stored fat by medically reducing insulin?

    • Dr. Lustig mentions this in some of his lectures, in obese children that oversecrete insulin, drugs that reduce insulin do result in weight loss.

  7. wang tao

    The theory is seem to make sense, but the truth is that bodybuilders are eat all over the day, there is no fasting, but at their game time is very low body fat levels. Dr. Feng, how to explain it?

    • Hi wang tao. Bodybuilders commonly consume more calories than they burn, as they are trying to increase muscle mass. In preparation for competition, during their “cutting phase,” they reduce their overall caloric intake – while still eating a high proportion of protein (the better to retain muscle tissue) – in order to lose body fat.

    • Ivan Kerr

      Wang Tao, bodybuilders also consume a lot of human growth hormone and steroids that help them gain muscle and burn calories. All of those drugs are bad for their health.

  8. Can’t you still burn body fat while not in ketosis? Will your body take from both glycogen and body fat? There are people who cut calories and they do lose weight, though in the long term they may gain it back. So are they insulin sensitive?

    • Patrick, I do not believe it is that simple. Ketosis is like 50 shades of gray. You can be slightly into ketosis which means you are burning fat. People who don’t eat at all for a week or two are deeper into ketosis, as would be shown on a keto stik. The whole, “though in the long term they gain it back”. That could be due to many reasons, principal among them is reverting to old diet. Yes, your body wants to restore its prior equilibrium, that doesn’t mean you have to let it. Eventually, it will accept the new equilibrium. I guess the meta message in my below post is, there is a danger making broad sweeping statements.

      I think you meant insulin resistant. That is a tricky thing as without specific tests one can only guess whether they are insulin resistant. Insulin resistance is allegedly caused by persistently high levels of insulin. If you are constantly snacking that is persistent, if you are constantly snacking on sugar, that is persistently high. breaking persistent and/or high and you are one your way to becoming more insulin sensitive.

  9. I like the fridge and freezer metaphor. And the coal-burning factory one. But I think of all the metaphors you’ve used to this point for explaining insulin’s role in switching between burning food in versus fat, this one is the clearest.

    • I concluded the coal burning factory is a false equivalency. For it to be an accurate analogy a CRaP diet would never work. Clearly that is 100% wrong. The body’s “prime directive” is “do not die”. It will in the absence of carbs, burn fat. In the absence of fat it will convert protein to carbs and burn those carbs.

  10. “You hope that you reduce dietary calories to 1500, and body fat will provide the other 500. Over time you lose body fat. That’s exactly what does NOT happen.”

    Here is where I have a HUGE problem. If Dr Fung is even somewhat wrong on this what else is incorrect.

    Over the span of a year I lost 125lbs by simply a CRaP diet and going to the gym 6 days/wk. Specifically, dropping 1000cal off the est TEE and, for the most part that 1000 cal/day plus 3600 cal est burned at the gym per wk, I lost roughly 2 1/2 lbs per week. When you factor in the periodic plateaus, I still lost over 2lbs/wk. 125 lbs /52 wks.

    “You reduce your calorie intake from 2000 calories to 1500 and hope against hope that you will lose weight. You do, at first, but then your body must adjust. Since you cannot get at your fat stores”

    Isn’t there an implicit contradiction there. You lose weight at first but you can’t get at your fat stores. By virtue of having lost weight where, if not from stored fat, did it come from?
    Again, 125lbs is more than ‘a little at first”.

    I simply don’t know how to square that circle. In fairness, Dr Fung, in Obesity Code points out several times “All diets work, all diets fail” (including fasting) which is why, per IDM, you have to “change it (fasting protocol) up often”.

    To hopefully lose the final 30 or so lbs, I have to just try and find something that works. And I do want to believe. I’d love to say, damn this works well.

    • What kind of Diet are you following though? That also plays a huge role…CRaP is usually paired with the wrong Foods as well (Carbs).

      The effect of eatin a High-Carb, Medium-Protein, Low-Fat diet is vastly different than Low-Carb, Medium-Protein, High-Fat.

      If you’re otherwise healthy, why don’t you just try it out and see if it works for you or not?

      • Not exactly Ryan. CRaP, which I never like for it’s obvious implication, stands for Calorie Reduction as Primary. Elsewhere I did state my initial diet. A bowl of Raisin Bran w/skim milk for breakfast, a ham (or turkey) sandwich on whole wheat or rye with swiss cheese melted. yum yum, a whatever dinner 1/3 cup of rice perhaps, broccoli or brussel sprouts, steak or hamburg. Calorie count was for the day, depending on whether my TEE was 2800 or 1200 or, at the end, 800.There was no garbage. Now, after I discovered Fung’s videos, I cut out wheat, cut out white (rice or potato or sugar) so no Raisin Bran, no breakfast, dinner no rice. meat and veggies but still a daily calorie count as mentioned above. I was pretty much at the 125lb point before I discovered Fung. Last month or two or three, I eat supper, no rice, no sugar etc. Effectively initially I lost a few lbs, but slowly (as expected) last week or so, nothing but water. I am not saying his diet doesn’t work (agn, all diets work, all diets fail). Ryan, how long have you been doing this? I’ve been doing it 2 yrs now…I pretty much have researched the shit out of it.

        • If I may ask, how old are you Walt? If you are young or athletic, then most diets will work.

          I am in my 50s. When I was in my 20s and early 30s all diets worked for me. None permanently but I do not blame the diet. Now, this IF plus LCHF seems to be working ok. Nothing else was working.

          Prior to this when I was not out of control, I usually do a moderate carb, whole carbs only, no grains (I am wheat intolerant anyway, will eat bean pasta and so on) high fiber, with protein and moderate fat. Averages out to 1500 calories a day which I used to track with varying accuracy. I go off and on this. I was on this from November to March and lost about 15 lbs very slowly. Then in March discovered fasting and around April 11, went LCMPHF. Have since lost about 22 lbs. I mostly only lose after a fast or so it seems. I weigh myself a day or two after the fast ends so I do not get overly excited by water weight.

          I agree that the statement that all diets work and that you cannot access stored fat on a CRAP diet is inherently contradictory. However, on some level I think there is truth there and it needs to be explained better

    • Dr Fung is actually 100% correct! If you are insulin resistant, THEN it is VERY difficult for your body to burn fat as the insulin keep the doors to your fat cells tightly closed. So, if you reduce your calorie intake from 2000 calories to 1500, and your body does NOT have access to your fat cells, (due to insulin resistance) your energy expenditure will get lower, your body will adjust and no fat burning will take place. Now add a fast!! Insulin will drop, the doors to your fat cells will open, and there you go:- YOU WILL BURN FAT!! You CAN lose 125 lbs by reducing your calorie intake and with exercise, (just as you say), BUT in six months time, you will start gaining all that fat back as you did not change your “SET” weight point. The ONLY way to bring down your “set” weight point is to REMOVE the CAUSE, – that is to remove insulin RESISTANCE!! Intermittent fasting is one way (the easy way) to do it, but following a HFLC diet or a ketogenic diet will also work just as fine!

      • Let me say this again. The body’s prime directive (Star Trek) is “DO NOT DIE”. If Fung was 100% correct the people in concentration camps would all die at normal weight. For primitive man, food supplies didn’t turn off like a light, after harvest they weened down. Sure, by dead of winter perhaps they were exhausted but that’s why man put food up for the winter. Thomas, I don’t know how long you’ve been doing this but, I am telling you what happened. You are telling me what Fung says ought to happen. What you’re doing is called willful denial. Good luck on your diet goals.

        • Christian

          Why do you keep saying this, like we’re supposed to take your comments to heart? Haha. You’re not the doctor, Walt. Stay in your lane.

        • First, primitive man, the ones we’re referencing, *didn’t* harvest. Fung is talking about before ‘civilization” when humans were still nomadic.

          That’s why you don’t eat grains, that’s why fasting isn’t bad for you (primitive man went without for days on end while hunting/gathering)

          Second, I’m not sure of your point on concentration camps.

          I think Fung’s point is, those people should have died long before they did, based on static metabolic assumptions and calories/day in.

          Third, again, on the c-camp prisoners – wtf are you talking about?
          Those poor people burned through all their carbs, all their fat and most of their muscle, which is why they were skin and bones.

          The body can’t go to zero metabolism, it takes energy to make your heart and brain work, and to power muscles when necessary.

    • Hi Walt. Good discussion. One thing that makes sense to me is that with calorie restriction, the body may think that “lean times” are here, that starvation is a risk, and so it damps down the metabolism. With fasting, the body thinks, “Hey, we better go out and hunt, so we need to keep the metabolism and energy levels up.” Dr. Fung may have said this or the like – I don’t remember.

      That may be a rather romantic way to view things, especially if one if predisposed to think that total fasting is good. However, if the described mechanics are true, then it would explain why cutting out 500 calories, for example, won’t necessarily result in the 1 lb. per week weight loss that one might expect.

      We’re all individuals, and I’m just one person, but personally I do feel much better with higher energy and less hunger when on a total fast – nothing but black coffee (nothing in it) and water – versus eating a little bit. I’m a believer that frequent ingestion of food, especially carbohydrates, maintains high insulin levels and perpetuates common problems, as with Type 2 Diabetes. Again, though, this is really just my anecdote, beyond what else I’ve read.

      I don’t think that what Dr. Fung has said rules out your experience. Even if we accept that at least for some people, lowering caloric intake does not give what should be the assumed weight loss (because of decreased metabolic rates), that doesn’t mean that the basic “in/out” equation is invalidated, and you going to the gym 6 days a week plus not eating all that many calories certainly had the effect of your weight loss. The overall effect, there, was much greater than any slowing of your metabolism.

      Congratulations on that large weight loss! I’m down 40 lbs. in two months and have over 100 left to go.

      • “then it would explain why cutting out 500 calories, for example, won’t necessarily result in the 1 lb. per week weight loss that one might expect”.

        I must have read OC 4 times. I’d get towards the end and say, ‘wait a minute, he just contradicted himself or I missed something”. So next full read. So what I did Doug is got MyFitnessPal on my iPhone and tablet. Entered my weight, goal, activity level, and 2lbs/week. That dropped my estimated TEE by 1,000 cals/day. In addition to that I worked up to burning, allegedly, 600cal/trip to gym 6 days per week. Some quick math and that’s, ideally, 3lbs/wk. I did this for about 12 months. I lost 125lbs. Dr Fung made a sweepingly generalized statement that what I did “doesn’t work that way”. Sorry doc, it DOES because it did. Yes, there were multiple plateaus but you work through them. This is why I only lost 125 not 156 (3×52). I did that before I knew who Dr Fung was. I discovered his webinars in may, at the 10 month in. So I tried to really control carbs, increase fat, always moderate on protein. Interesting thing, in OC and CGF he talks about low carb. Low carb is like under 100g. I was probably under 50g but it was bowl of Raisin Bran for breakfast, ham on whole wheat for lunch, ‘normal’ dinner, meat, veggie, spaghetti once/wk.
        Nobody should confuse what I say as trolling the good doctor. I am not. His analogies are good simplistic ways to make an analogy to his point but they don’t hold. As he states in OC,
        patient: “Will I lose weight if I stop eating”?
        doctor: “of course you will”.
        In both books he has graphic of breakfast-minifast-lunch-minifast-dinner-maxifast. There are always 2 small and one large fast/day. This as opposed to the current std diet breakfast-snack-lunch-snack-dinner-snack-maxifast. Insulin resistance requires persistently high insulin levels. Ho do you break insulin resistance? Break persistently high. By his own admission, what I did was having 2 small and one large fast every day. So, by that definition, I was indeed fasting. Also, Doug, in CGF under fasting liquids, cream, half and half, whole milk are acceptable. skim, not so much.
        Forty pounds in two months? Very impressive indeed! Don’t count on that. As I dropped my 125lbs and recorded in MFP it’s estimated TEE dropped as well. In fact, towards the end to maintain 2lbs/week I had to drop below 1,000 cals/day…not recommended. As Dr Fung himself said, for water only fast, figure 4lbs/week. SO think about it this way. Whether you are here now or will be later, your TEE will be 2,000 cal/day. If you are not eating you still need 2,000 cals/day to, you know, stay alive. A pound of fat is 3,500cals. Divide (2,000×7) by 3500. That’s 4lbs. Now, let’s say you are a construction worker, you are not at 2,000 cal/day you could be at 6,000cal/day so that would be 12lbs/week. My only point here is over the course of your weight loss, don’t be disappointed if your rate of loss drops, as you lose weight your TEE will also drop as there is less of you that needs to be kept alive. TEE, btw, is total energy expenditure. That is REE (resting energy expenditure)..if you were in a coma, + daily activity.

        NO, high carbs do not cause insulin resistance NO NO NO. Insulin resistance is caused by persistent and high insulin levels. As in grazing constantly. Fung points out there are people, like in Asia that have very high carb diets, they just do not graze all day long. and they didn’t start getting obesity and diabetes until they adopted a current western diet of constantly eating. If you haven’t read the two books (any of you) read the two books. I didn’t cure my diabetes by fasting. I cured it over the 12 months (actually much earlier) by having a calorie restricted diet. Google Roy Taylor Newcastle magnetic imaging centre “Reversing the Irreversible”. His clinical trial subjects had an 8 wk, essentially, Slim fast diet plus a small salad, around 700cals/day. In 8 weeks they went from diabetic to fat free liver and pancreas and normal FBG and A1C. Heres the link:

        • As a quick addendum. In both books he clearly states, “All diets work and all diets fail”. That includes fasting protocols as well as he does say on fasting, you will reach plateaus. Again, I encourage everyone who hasn’t read the books to read the books.

        • You raise some good points Walt. I think main criticism to CrAP diet by Fung or me is that they imply, that all the foods are the same by that view point. It’s just calories! While on low carb, you definitely consume less calories, but it’s because you have no insulin and there is no hunger – calorie restriction happens naturally. But if you eat 1500 calories of sugar and high carb – then it’s scenario designed to fail, because there is still high insulin.

          You probably did reduce those things? Also increased protein and vegetables/salads?

          Insulin resistance also happens mostly from intrahepatic fat accumulation – mostly it’s because of sugar (fructose) in our diet. And yes, prolonged hyperinsulinaemia.

        • Martin Williams

          Hello Walt. You quote some research into VLCD:
          Google Roy Taylor Newcastle magnetic imaging centre “Reversing the Irreversible”. His clinical trial subjects had an 8 wk, essentially, Slim fast diet plus a small salad, around 700cals/day. In 8 weeks they went from diabetic to fat free liver and pancreas and normal FBG and A1C.
          The science seems to be showing that if you reduce your calories to, say 1000-1800 per day you will cause your body to reduce its metabolism to compensate. But that going further, taking the daily calories to around 600-800 or less, produces a turnaround wherein meatabolism is actually increased. This always seemed crucial to me.

          • Hi Martin, I believe I’ve been mentioning Dr Taylor over the last several blog entries of Dr Fung. I, actually, discovered him and his research almost a year before I even knew who Dr Fung was. My dietitian told me at our first meeting I had a chronic incurable, progressive disease. I proved her wrong as I wanted to do my own research. Ironically, she wasn’t interested.

            I haven’t seen that evidence you mention on 600-800. I am not saying I question it, merely I haven’t seen it. This is why I think my hypothesis is so important. Get into a water fasting state, steady stable state. Go for as long as possible to compensate for statistical noise and figure out what you body is actually burning per day. That is your new TEE, one can adjust up or down depending on activity but maintaining that caloric budget should provide for a steady state weight. Do people honestly want to be on a strict/extreme diet for life? Sure, eating every other day is novel but, I suspect to most, not something they want to do for life. Not where the rubber meets the road. In the euphoria of a newly discovered ‘try this’, sure that is, what did Greenspan call it, “irrational exuberance”. If it turns out my TEE on a water fast is 2000 or even 1750 I am pretty comfortable I do not have a damaged metabolism. If it’s 500, yeah, I have an issue.

        • Walt, I do agree that sometimes we see some overly-general comments, even from Dr. Fung. On the daily 500 calorie deficit and the presumption that this will result in a 1 lb. per week weight loss, perhaps it would be better said that “This does not happen for many people” (because of a slowing metabolism). The unqualified statement that it “does not happen” will indeed not be true for every given individual. Whether or not your metabolism slowed by a lesser calorie intake, I think your going to the gym 6 days a week took care of that and more.

          I’m not saying that a high-carb diet, per se, causes insulin resistance. I agree with what you said here: “Insulin resistance is caused by persistent and high insulin levels. As in grazing constantly. Fung points out there are people, like in Asia that have very high carb diets, they just do not graze all day long. and they didn’t start getting obesity and diabetes until they adopted a current western diet of constantly eating.”

          Yeah, no doubt – if somebody hasn’t gained weight, to take a pretty simple view of things, then the odds of getting Type 2 diabetes are vastly lowered, regardless of the components of their diet. Also agree that “constantly grazing” is likely a bad thing when insulin levels are a problem. What I said was: ” I’m a believer that frequent ingestion of food, especially carbohydrates, maintains high insulin levels and perpetuates common problems, as with Type 2 Diabetes.” If we have a constant-grazer, they’re certainly frequently ingesting food, and carbs provoke more of an insulin response than the other stuff, making it all the worse.

          Roy Taylor’s video – I’ve watched the whole hour+ thing, and it’s great; I think it should be required viewing for many people.

        • Walt congratulations on your weight loss first of all. The biggest loser story that it tells perhaps brings up the biggest area of concern for you. All of these people gained the weight back. All of them. Once they stopped exercising excessively and went to the gym a normal amount their bodies just stopped. The gains they had were often even worse than their starting weights. Gaining weight is pretty demoralizing but I’ve have to say gaining, losing and gaining it back would the worst feeling of all.

          What you are doing may have some results over time but is it sustainable? would you start gaining it back as your body has not changed it’s set point? probably. If IF can be the difference between long term success without regain what do you have to lose by trying (no pun intended)?

        • You said it yourself – you should have lost 154 pounds, not 125.

          Obviously 125 is still terrific (Congratulations) but the point is you didn’t lose what you should have lost based on calories in and calories out.


          I think Fung would say because your metabolism slowed down.

    • Hi Walt – I have also lost weight doing a terrible diet with calorie restriction + exercise. What happened is that I burned out on doing exhausted exercise all the time and having to count every single thing I ate. As soon as I slacked off, the weight rebounded hard. I didn’t even try for nearly 10 years because it seemed like such a battle for every ounce, and would so quickly come back.

      After keto + fasting, even when I recently stopped trying to lose weight for several months because of life events, my weight remained completely stable. That was when I maintained a more or less low-carb diet, eating to satiety. During a 10-day vacation I started eating desserts & sweets and rapidly gained 8 pounds. I came home and gained 3 more pounds because my cravings were out of control by then. Now my blood sugar is acting as messed up as it ever did – and I’m currently on day 2 of a 7-day fast to help right this floundering ship real fast.

      I do believe the old-fashioned weight loss is possible – but it is like swimming up stream. Most people do not have the fortitude to struggle and feel deprived over such long periods of time. I don’t. Keto and fasting help me lose weight effortlessly, and a lazy low-carb diet will maintain it. Now I know that my body will always react badly to sugar. I could have a treat maybe 2-3 times a month, but that’s it. It’s especially helpful to plan treats and plan to fast the next day to resume low-carb. I can’t wait to be back in keto for a while and have these sugar cravings go away again.

      • Woot, I believe people are reading into what Dr Fung says. I believe many people on here have never read his books so they just are true believers not based on facts but rather faith. I am not saying fasting doesn’t work, in fact Fung himself states and shows a 3 meal / day std diet, from up until late 70’s included 2 small and 1 large fasting period. People assume this is a zero sum thing that, for fasting to work, calorie reduction cannot. All I am saying, with examples, is that is untrue. Fung does not help matters where, in his second or third sentence he says it doesn’t work…it does. Now, as for rebound weight. That is controllable and not written in the stars. All of Dr Taylor’s research efforts, after the 8 weeks essentially most everybody, if not everybody, regained some of the weight back, as I recall, they lost about 30lbs and gained back 6lbs and stabilized there.The net is they lost 24lbs on avg over 8 weeks on a restricted calorie diet…full stop. This wasn’t a one off finding, it was consistent across all of his trials, with increased participants, increased duration of T2D and increased ages. Dr Fung himself said one should expect about a 1/2 lb per day weight loss from fasting. People who say (and I fully believe) that they lost 30lbs in 2 weeks of fasting, will find, from what Fung says, is that most of that will come back as it was bowel contents and water. Once you come out of fasting they will return. So really, we’re just parsing words. After I stopped my reduced calorie diet of 1 yr, yes, I gained back a little. I had returned to a more normal diet, no donuts, no candy, no ice cream but more normal. I stopped going to gym (gave it a rest) and while I wasn’t anal about calories I probably stayed at or below 1800/day. I gained back maybe 10 lbs. Then over T-day/C-day I gained back a few more but I am still simply ‘over weight’ as far as BMI. I started as like the second level of obese. I ended at ‘overweight’ I am still at overweight. My goal is to reach ‘normal’. Stretch goal, the low end of normal. Except for two meals, surrounding my birthday, I haven’t eaten in a week. Ketogenic is a tool, fasting is a tool, it is not the entire arsenal of tools. “If one thing doesn’t work, try something else” -> Costanza rule as referenced by Dr Fung.

    • Christopher Hamilton

      Hi Walt,

      I have been in your position several times before. The first time I lost 100lbs through a crap diet I championed it too. But the benefit of hindsight is that I can speak from the “post loss” phase that you have yet to experience.
      What I experienced was a stubborn refusal of my body to burn that last few pounds, which I eventually resigned to live with. I threw out those old clothes and bought a new wardrobe two sizes smaller vowing to never go back. Problem was that my body had other ideas. It took some time but eventually no matter what I did I gained the weight back, even while religiously counting calories. I now realize the reason was that I was losing mass but I wasn’t changing my setpoint.
      Just because you lose fat does not mean you burn it, fatty stool and urine is common during crap diets, the body does want to get rid of the excess tissue if you exercise. The real test is what happens when you stop.
      I lost 70lbs fasting and took a break for three months. During that time I ate whatever and however much I wanted (spoiler: my wants changed and I no longer have uncontrollable desire for the terrible food I used to) and did not gain the weight back.
      It is basic biology that a cell cannot burn fat and sugar at the same time, important to note that different tissues switch to fat at different rates (between 12-36 hours depending on the tissue), but changing the setpoint should be the real goal. Not just weight loss but fat loss, and not just for a year, but for a lifetime.
      That has been my experience anyway.

  11. “You must let your body go into the ‘fasted’ state.”

    Per graphic depictions in Obesity Code, Complete Guide to Fasting, and Dr Fung’s YouTube vids, you go into fasted state even when you sleep and between meals. He makes the point that the obesity and diabetes epidemic we’re in started late 70’s when we went from mom’s saying to snack it will ruin your dinner (3 meals/day) to breakfast-snack-lunch-snack-dinner-snack such that you essentially spent the day in a high insulin state storing more and more body fat, that the sleep cycle could not burn off so the net calories was +. You want the net calories per day to be less than or equal to zero.

    • Walt, you’re right that it’s a relative deal – that when sleeping or between meals we are “fasting.” I totally agree that for weight loss or weight stability we want the net calories to be less than zero or at zero.

      If a person feels good doing it that way – just eating less, then I’d say no problem. An otherwise healthy person at a desirable weight operates that way anyway – over time their caloric balance is right about zero, regardless of what they are eating, exactly. What I think makes the difference for some of us is that with calorie reduction, we feel “bad,” with low energy, lots of hunger and cravings, etc.

      Many times I’ve tried certain diets, all of them featuring less calories overall than how I normally operated. It was very common for me to go 3 or 4 days and then say the heck with it, bust the diet, go on an eating binge, etc. – it seemed too hard to adhere to the diets for a long enough time.

      With total fasting, I just plain feel better, and it’s easier to continue. Having the days of “zero calories” makes it easy to have a net caloric deficit for a week, for example. Beyond the basic “in/out” equation, I do think there is something to the notion of getting the body used to burning fat, to becoming “fat-adapted,” at least for some of us, especially after years of gaining weight.

      • I don’t disagree with that Doug. However. With fasting, and he points this out in his books. They took 2 groups one on IDF of 2,000 one day and 500 the next, as I recall, and the other group 1500/day. The total cals/week worked out pretty much the same. and the results after a year were pretty much the same. I think the difference was in blood chemistry. I’ll leave researching that to the reader. ;-). Up until the end of last week I was in a perpetual 21/3 fast..that is 21 hrs of fasting 3 hours of feasting every day. So, insulin was low most of the day and high once a day. I didn’t lose but maybe a couple of pounds. In the books it says that under that protocol weight loss will be slow and steady. According to my Ketonix 2017, I was constantly in ketosis. Since about last Thursday I’ve been in a 7 day fast except for my birthday dinner fri and the kids took us out sunday. I am still in ketosis. I may end it fri or may go until next fri.

        • I replied to you above but can’t edit it to add… I don’t lose weight eating this way, either. I have to do 24+ hour fasts to see weight loss.

          I think it depends on how insulin sensitive you are. My insulin is a bit messed up. What really worked great for me was switching it up a lot, being irregular about length of fasts. This suits my personality & lifestyle anyway. Anything I do very regularly, my body will adjust to.

          • I hear ya, they should allow, if not edit, delete such that one can copy into clipboard, delete, add another comment, paste, and edit, like on tweeter. For the longest time that’s effectively what I was doing a 21 (or 22 or 23) hour fast every day. I lost a few pounds then stopped losing. On fasting talk Megan poo poo’d that as there is no fasting that is reduced calorie and reduced calorie doesn’t work. WAIT… that is fasting for 20+ hours and feasting for 1-4 hrs. Even in CGF, if not OC, Fung writes that will provide slow, albeit steady, weight loss. He also adds people, regardless of their fasting protocol, will hit a wall. When that happens change to a different fasting protocol. Sounds a lot like do Atkins, when that fails to produce desired results, switch to South Beach or Weight Watchers. In other words if fasting works for someone and seamlessly fits into their life style, great!!! No one should read me as do not fast. I am just repeating Fung’s own admonition, all diets work and ALL diets fail.

        • Walt, you said: “They took 2 groups one on IDF of 2,000 one day and 500 the next, as I recall, and the other group 1500/day. The total cals/week worked out pretty much the same. and the results after a year were pretty much the same.”

          Makes sense to me. I think the important differences will be in what works best for a given individual. A steady 1500 calories per day would not work well for me, whereas repeating 3000/0 would be better. In reality, I’m very disorganized about it, but persistent. Some days start as total fasts, but end up with one meal, small or large, much like your 21 hours fasting/3 hours feasting.

          • Yep, I agree. They did not mention blood chemistry at all so they were just focusing on weight.

  12. I am new to IF and have struggled with understanding the concept, until now. Thank you for explaining it in simple terms that are easy to understand!

  13. One guestion. How would one increase his metabolism back to prior levels, assuming he has CR for a while and f.x. lowered his metabolism from 2000cal to 1500cal?
    Would fasting here help or hurt in the effort to increase metabolism back to prior levels?

    • An essential question Svavar. I looked long and hard for the answer and just recently got it.
      Longer fasts, eat lots of fat.

    • If you have lost weight, your resting metabolism will be lower. Even if you change your muscle/fat ratio, it will not make much difference. Smaller body = less calories. You have to get used to exercising more if you want raise your overall TEE.

  14. Is intermittent fasting (18 hours no eating just coffee and water) enough to lower insulin? I enjoy my meal time with my family at night, so the 24+ hour fasts are difficult. I have 10-15 pounds to lose to get where I want to be. I’m a size 4 but super flabby and very small boned. I lost my baby weight after my first two kids by cutting carbs and running. After my third child I’ve struggled with the last 10-15 pounds. Also how bad is it to drink wine as fas as causing or leading to insulin resistance. I’ve read mixed beliefs. I drink only dry White wine. Also, would exercise help at all in losing weight or my body would just compensate for the additional activity?

    • Stephen T

      Tina, 18 hour fasts are easily long enough to take you into fat burning mode, assuming you’re not adding milk to the coffee or consuming large amounts of carbs before you fast. Our body uses the carbs first before going to the stored fat. When we eat we generate insulin, then it comes down. Once our insulin level drops, we can access our fat stores for fuel.

      I exercise regularly, and it’s beneficial in many ways, but nearly irrelevant for weight loss, unless you do ridiculous amounts. Exercise is good for our health and keeping the body firm, but essentially it’s what and when we eat that determines our weight.

      I’m not an expert, but I think any white wine contains more sugar than red. If you’re eating sensibly and doing some fasting, some white wine isn’t going to lead to insulin resistance, which is a result of a chronically high and long insulin response too many times for the body to cope. However, the sugar in the wine might well slow down weight loss by adding carbs that you’ll need to use before you can access your fat stores. It depends on your goals and how quickly you want to get there.

      You don’t have to be perfect to be good.

  15. Hello people, I want to share this study with you:

    “Insulin Resistance as a Predictor of Gains in Body Fat, Weight, and Abdominal Fat in Nondiabetic Women: A Prospective Study”

    Do you think that there are factors that have been overlooked? I want to hear your thoughts, this really confuses me…

    • There is something interesting that happened in this study. The women who didn’t complete their food logs and dropped out? When they followed up with these women later, there was NO difference in the high-low insulin groups. Only the women who kept their food logs the whole time had a different outcome!

      It makes me wonder if the fact of keeping a food log and being followed made some of those with high IR (bad eating habits) a bit more aware of what they were doing – so they saw the best outcome.

      • Thanks for your comments, your supposition about the high IR group is exactly what the researchers thought too:

        “Although there was no intentional treatment or intervention associated with the present study, women with the highest body at levels initially, and therefore the highest levels of IR, may have been more motivated to lose weight following the baseline assessments than the leanest women, who were more insulin sensitive. Differences in motivation may account for differential behavior change, which could explain why those with the highest levels of IR (and therefore the highest initial weights) tended to gain less weight over time than their counterparts.”

        We can’t know exactly what happened, it was just an observational study.

    • I didn’t find that that there were any (biological) differences in weight changes between the three groups; in 18 months, gaining 1 kg or losing 0.5 kg is about the same to me, even weight fluctuations from day to day would explain them.
      As far as insulin resistance being helpful in weight loss/ maintenance, that might be the reason fro the HFLC advantage, if there is one: when the body ignores insulin signaling, fat is being released from fat stores…

  16. What happens if I eat say 50-100 calories worth of carb in form of a biscuit or a bread while being on fast? Do I immediately go to burning carb but it won’t be enough for more than an hour so what happens after an hour because insulin will not immediately go down if I understand correctly ? would I suddenly start feeling tired after a while?

    • It depends on the individual. 50-100 calories worth of carbs in a biscuit or a bread would make me feel exhausted and wanting a nap within an hour, make me hungry & obsessed with food and stop my bodyfat-burning for 2-3 days. But others would have no problem eating 12-25 g of junk carbs.

    • A spoon of nuts or other fat would be a better option

    • Stephen T

      Parth, the biscuit or bread ends your fast because it will generate an insulin response and turn off fat burning. It may well make you feel hungry when the insulin brings your blood-glucose back down.

  17. A good diet, even with moderate carb (adapted to the activity), with whole foods (and thus low on insulin response), is also effective at losing fat.
    Although ketosis/fasting is the “optimal” approach (I still find it a bit to extreme if you’re not obese or with a medical condition requiring it), it doesn’t mean it is the ONLY solution to lose fat.

    • Technically it’s true. But emotionally this is not what we want to achieve. Right now, we don’t recognise and even ignore or despise the most powerful tool which is fasting followed by lowcarb/keto. We must talk about it and bend public attention. Of course you can loose weight on plant only diet – it’s low on insulin. But you see, the thing is the insulin response and we want to maximise it. It happens by doing fasting. Nobody denied other ways of loosing what, they are just not interesting for us.

      • Why plant only diet ? Why Dr. Fung compares his approach to 6 meals a day of white bread ? As if there is nothing in between, healthy and with low insulin response, without having to go keto or extended fasts.

  18. William Brady

    When you fast you enter ketosis, which is the result of your body making ketones to fuel the brain from fat. How is it that I remain in ketosis, as measured by keto sticks, after having eaten low carbohydrate meal of salad, nuts, seeds and dressing? I think this suggests a special case of a dual track, doesn’t it?

    • All foods, carbs, proteins, fats, add calories. Your body has a set caloric requirement. If you are in a keto adopted state and you add 200 cals or more it is stored in the liver as glycogen. At that level it is converted to glucose and used very quickly if it wasn’t used upon digestion. That is way under your body’s requirement so it would resume converting fat for kidneys, heart, the 25% of brain that cannot use ketones. If you ingest enough to derail ketosis then you body would have to reestablish that state. I was told having a mere cube of sugar would stop ketosis. This is something easily verifiable. For instance, last Friday was my 66th birthday. My wife took me out Fri night, our kids took us out Sunday. per Ketonix breath analyzer, I was still in ketosis 10-20PPM but as of yesterday, I am over 40ppm. So those two meals (mainly deserts) did have an impact, but I didn’t have to start from scratch to be full bore ketosis.

  19. I used to be fit and fat. I have weight trained regularly for the last forty years. At one point, as I went through a power lifting stage, my weight went up to 290 lb. Although I was extremely strong, I also developed metabolic syndrome, so I needed to change my ways. As Dr. Fung points out, losing the first 10% of body weight is relatively easy. It only takes a few months and can be done with a variety of dietary internventions. Usually, however, a weight loss plateau ensues, and in my case it was extremely difficult to get off.

    Turning to eating clean and hiking and biking more than 5000 km a year, I found that I could maintain the initial weight loss, but I could not drop any additional weight in spite of the fact that I still was carrying quite a bit of body fat. By chance, when reading up on how to combat leptin resistance, I came across the notion of using a fasting regime to bring my hormones back into a healthy state. It worked. I lossed another 30 lb. Then, I came across Dr. Fung’s approach and I found confirmation about what I had stumbled upon. Presesntly, I am following a variation of his approach. I fast 13-14 hours five days a week and do a 23 hour fast twice a week. I have done so for three months and I don’t find the full day fasts all that difficult. So far so good.

    One thing though is that my health gains have changed. Because I continue to weight train, I am not loosing any additional weight. However, my body composition is changing: a higher percentage of lean body mass and a lower percentage of body fat. I am nearly sixty years old and have been obese for more than twenty years. Putting the discussion about the relevance of BMI aside for a moment, I take pleasure in wathching the shadow of a six pack slowly emerging through my belly fat. As well, my lipid profile and blood pressure have returned to normal. I no longer have metabolic syndrome, which for me is the most important result of all my efforts. Next month, I am going to try my first three-day fast. Looking forward to see how I do.

    If you would like to learn more about my path, check out my blog;


  20. Slightly different topic. I have long wondered about ‘damaged’ metabolism. I know of the medical way to test, involved and expensive. I believe I have devised a pretty good substitute. It involves fasting for, ideally, at least a week.
    Once in a fasted state, ketone at 40mg/dl or better or maybe 80mg/dl. higher is better
    1) weigh yourself
    2) do not ingest food for 1 week
    3) weigh yourself again
    4) multiple (end weight – start weight) by 3,500 and divide that by 7.
    5) that number should be your TEE
    6) if you did not workout or go to gym or engage is physical activity that number should be Resting Energy Expenditure * 1.2. The 1.2 is the adjustment to REE (coma) to factor in walking around, showering, going to the mall … whatever that isn’t laying on your back.
    If the number is > 1200(f) or > 1800(m) you are likely fine. If it’s 500, not so fine. The reason for a week is even if your bowels are empty you bladder may not be. Water has weight so the longer the time period the less impact minor weight fluctuations will be.

    When doing a long term fast, your body is still constantly feeding. You are not adding food so you are measuring what your body needs vs what you are feeding it. That came to me yesterday and I am excited to start.

    • Walt, on “damaged metabolism” – I’m assuming this means lowered…? I think your 1.2 multiple for resting energy expenditure (normal living, not working out) versus the basal metabolism is right on, i.e. our heart, lungs, brain, liver, and kidneys use up around 75% or 80% of the calories, with muscle tissue burning the rest.

      With that as a given, there doesn’t seem to be much room for much decline, unless the body really thinks it’s starving and drastically slowing things. I know some people don’t take well to fasting, but – anecdotally, to be sure – I think more people feel tired, cold, etc., with calorie restriction versus outright fasting. Either way, I would think that a really low figure like 500 calories per day for true resting energy expenditure would have people feeling incredibly bad, if such a low number is even possible.

    • Doug, 500 may be something of an exaggeration. However, in the Ken Hall research on season 14 of Biggest Loser some of the dropped metabolism of the contestants was upwards of 600cals below what Mifflin St Jeor would have predicted. If the body did that in the attempt to for it gain weight on the food you were consuming. What Dr Fung has said and Megan Ramos has said is, as I answered up top, fast for longer periods of time and eat more fat. What neither has said is whether that is a permanent condition or temporary. For those that watched BL, season 14 was, as I recall, with the father/son team and the son got seriously thin. He regained 80% of his original weight then had Bariatric Surgery. Of merely fasting and eating lots of fat would have cured him it would have saved tens of thousands of dollars. Of course, I think he won that season so he had the money to spend. Page 239 of Obesity Code lists how the body responds to a fast, phase 5 is protein conservation and it’s when HGH and excess adrenaline is released to raise metabolism. The question is, does it raise it permanently or just while your fasting? I have never seen any conclusive stmt. Megan said on FastingTalk that she had been working with this woman, and I think she did say 500cal/day equilibrium and after a year got her up to 1500cals. Presumably that is from fasting. So for the people on here that have done the circuit and hit their target weight, are they still on a restricted protocol? Fasting 3 days/wk for life is, sounds to me, a very restricted diet. Really, it had just come to me the night before I posted that experiment. If that works that should give me a baseline to what, presumably my body wants for cals.

      • Walt, wow, man – such a drastically lowered metabolism must make the person feel like absolute heck. While I don’t know, my gut feeling is that the body will continue to adapt to whatever the current conditions are, after getting the boost in HGH and adrenaline, so likely going back to a relative more “normal” state when the fast ends.

        Fasting 3 days per week = very restricted indeed, and I would certainly hope that such is not required to maintain one’s desired weight. However, being mindful of calories and the whole ‘permanent lifestyle changes’ deal no doubt applies, for most of us. (Sigh…)

        Fascinating stuff – how the body works and what happens when we do different dietary things.

        • Fascinating stuff indeed! Fung and Ramos are conspicuously absent on what return to normal life is. That may be because they assume so long as you reduce sugar, reduce refined carbs, fix your problem and return to the new normal, reduced carbs. That would work for me. However, following my thread, and this is insufficient sample size my TEE has been approx 1200cal/day. That is with, perhaps, 325cal burned 5 days / week. The interesting thing is, Fung, as best I can tell, doesn’t actually push ketogenic, rather fasting, neither does Mosley, he favors Mediterranean diets and 5-2 fasting.
          Even more interesting is that Jimmy Moore, coauthor of CGF had a weekly podcast with either Megan Ramos or, first of every month, Dr Fung. Even as late as the first friday of June, those two decided to discuss insulin resistance first friday in July. Now, it’s just Jimmy, no Dr Fung, no Megan Ramos. One possibility is Dr Fung was adamant about not discussing one’s medical situation, rightfully so. It seemed to me the questions they were getting from listeners were of the “I’ve got this problem”. aka seeking medical advice. I suspect that’s why we don’t see him responding here to people, yes, he could lose his license by handing out free medical advice to non-patients. Certainly there are people on here, one comes to mind Sten, that have done the fasting, restored their ‘ideal’ weight and, I would suspect, be back to maintenance mode.
          For the last couple of weeks I’ve been fasting. Prior to that I was doing a 21/3 fast per 21 hrs, feast 3. I never understood why, per Megan, that constituted a starvation diet, there was a large fasting period and a defined ‘feasting’ period. Then, noticing I wasn’t losing weight, but clearly in ketosis, I ventured into a 6/1 day fast. Fri is date night so I figured if I was ketogenic then I wouldn’t do any harm. Well, my birthday was earlier this month and we went out for date night then, on Sun, our kids took us out. So, I kinda went off script then. By Wed I was back to an 80mg/dl ketone level. The next Fri our daughter came took us out and I was again off script. I’ve never left ketosis but the other night my feet were cold. As I’ve said elsewhere, I’m an engineer, I tend to solve puzzles and this…is a puzzle. Anyway….

          • NicoleS

            They left the podcast because Jimmy Moore and Megan and Jason had different views on how the show was conducted. My understanding was they wanted it more professional (less goofy) than Jimmy Moore. This caused a rift and they went their separate ways. The hope is they start their own podcast.

            Walt – I am an engineer as well but I think you are focusing too much on a “one-fits all model”. Although questioning everything is never a bad thing. The thing is – your puzzle is for you to solve, as my puzzle is for me to solve. Each of us has a different puzzle. Dr. Fung’s and the rest of IDM’s goal is to provide us with as many pieces as you can get to solve your own puzzle.

            Restrictive diet is all about perspective. People love to work out 6 days a week to keep in shape. But their diet is flexible. As soon as they stop – they gain but they are willing to stick with the gym method. To me that is way too restrictive! Some people love their carbs and function well on them! I did not. Giving them up 80% of the time is fine with me to maintain my weight is worth the trade off. Why? Because it works for my lifestyle and body! I love not having to eat all day a few days a week because it frees up so much time. It works for me! Do I fall off the wagon occasionally and gain a small amount? Yes, but I also now know the tools on how to get back on track and as time goes on, its becoming easier and easier to rebound back. Its my puzzle. I don’t demonize people who insist on following the SAD diet and get results. If they feel good – great!

            Here’s the thing; just like in engineering – I do have a problem when people insist there is only one way something can be done and there is no room for creativity. Based on the podcasts, books and all of IDM’s blogs – I believe that is what they are trying to preach. On the flip side, there are tons of people who just want people to solve their puzzles with no thought input into it. There is nothing wrong with that either.

          • Nicole, thanks for that! Yes indeed, I also complained about the giggles and yucks…very unprofessional. It does seem like it broke all of a sudden, As of June 2nd Dr Fung and Jimmy were planning their July joint podcast. What you said makes perfect sense as I was getting to the point where I was seriously questioning the utility. It did strike me the three of them routinely contradicted what they had previously said. I don’t see the value of turning over Megan’s old role at IDM to her husband. Who’s going to pay money to talk to someone who doesn’t know what they are talking about.?

            I think you misunderstand my point/questions. For instance, if the point of IDM is long period of fasting and shorter period of eating, a 21hr fast and 3 hr feast fits that bill. If you’re familiar with IPO, I am not arguing about the process or output, rather the input. You can’t say something categorically does not work when there is plenty of proof it does work. That lessens one’s argument. To that extent, your analogy suffers, the process part is cooked in. One’s metabolism isn’t programmable, it is what it is. One changes the input to affect output. However, it could be ‘damaged’. So according to OC pg 239 bottom of page the metabolism isn’t raised until day 5 of a fast. So, presumably that means someone doing IDF is SOL as they never hit day five. So if IDM’s advice is to fast longer yet they don’t recommend people fast longer than 42 hours, hitting that 5 day mark is…impossible? So let’s say someone fasts for 7 days, or 14, they enter protein conservation phase, what happens on day 15? Nowhere do they answer that.

            There’s not a lot of ambiguity in human anatomy and physiology. Sure, some people may want to sweat to the oldies, others fast 2 days/week, others fast every other day. I am not arguing or debating the best approach because, as you said, there is no best approach for everyone.

  21. Roger Bird

    There is no mystery about when your metabolism takes a dive. Put your hands on your kidney area (best) or just your tummy, and if they are really cold, then your metabolism is down, unless your hands are cold for some other reason. For me putting my cold hands on my kidney area can be shocking. If you are lethargic and have cold feet and/or hands, then your body is trying to track your reduced calories in. This is not the end of the world. Just keep on track with the no calories and Mr. or Mrs. Body will grasp the picture and start raising your metabolism.

    • That’s interesting Roger, thanks! However, another question I have is this. Given the ‘magic’ of fasting comes at day 5+ with phase 5, Protein Protection, which is where there is a surge of HGH and adrenaline. Presumably once you break the fast the adrenaline and HGH stops thereby lowering metabolism . The prologue to my above post was this. I’ve been dieting, either formally, Atkins, weight watchers, etc for some time and had pretty good luck short term. By that I mean 36lbs or so. 2 years ago this summer I was diagnosed w/T2D and went full bore on the MFP calorie reduction. I promised myself 1 yr. I lost 125lbs. So yay! What’s interesting is I gave MFP my then current weight and said I wanted to lose 2lbs/wk. As I lost weight I adjusted it in the app and it adjusted my daily caloric intake appropriately. With the exception of a few plateaus MFP was pretty much spot on. Moral of the story is, prior to and during that year, my metabolism was accurately modeled by Mifflin-St Jeor.

      The issue I have now is does Mifflin St. Jeor still accurate predict my caloric threshold per day. Meta question is, will I need to maintain a fasted state in order to have a stabilized weight? Ideally the answer is no, once I hit my desired weight so long as I maintain that weight adjusting up for activity level, will that suffice for life?

      I haven’t eaten, essentially, for a week. I did have a fairly keto dinner with our son and his family. Right now for the last couple of days I have a urine and BrAce keto level of just shy of 80mg/dl, dark purple. Last night when I went to bed my feet weren’t cold but they weren’t toasty warm either. However, sometimes they are, like the night before that and right now. Same with my arms and hands. Sometimes they are toasty warm sometimes a tad cool. From my hypothesis above, if my metabolism is 500cal/day it will tell me, if it’s 2000 cals/day it’ll tell me and I’ll have another data point.

  22. Could somebody in Walt’s real life intervene and help him with the manic episode he is clearly having?

    • Absolutely Jimmy, if you don’t have anything constructive to add, troll. So dignified, so adult.

  23. When fasting what can be done about getting a bad taste in your mouth? After a week. Thank you;)

    • Kayleen, by “bad taste” is it maybe fruity or a little bit like nail polish remover? When in ketosis acetate is exhaled and that, depending on what you mean by bad taste, could be what you are sensing. Try mouth wash or brush your teeth more regularly to act like mouth wash. A week would be about the right amt of time.

  24. Charlene

    Perfect analogy & the visual–made it crystal clear.
    Thank you

  25. hypothetical:

    -eat 2000 throughout the day, staying in “fed” mode” – body uses those calories and doesn’t burn fat, stores excess
    -eat 2000 at one time, body uses some, stores the rest, then uses those stores during the rest of the day as needed

    What’s the difference, doesn’t it still come down to calories in vs calories out? A slight calorie burn increase from not slowing metabolism is the only one I see.

    • Hi bcarney. I agree – many times there won’t be much if any difference, there. If insulin resistance is a problem/concern, then eating many times versus once would usually result in higher insulin levels, on average, but one’s weight would not be much affected, I think. If one doesn’t have a problem with insulin levels and one maintains a constant weight at 2000 calories per day, then things are balanced and it’s as you say. Where I can see a possible difference is in cases where the person is burning less or more than 2000 calories a day – persistent weight gain or loss usually has quite an effect on the interrelated cycles that our digestion, liver and pancreas undergo, although I think same as above – if one is not having a problem with insulin resistance then for the weight gain case that could well not be a big deal – and whether eating once or frequently the end weight result would be almost exactly the same.

  26. On “returning to normal life” after we reach a desired weight, things are not adding up for me.

    During 30 years of often horrendous excess, I “only” gained an average of 5 lbs. per year. At 3500 calories per pound of body weight, that would total 17,500 calories. *Or* – an average of 335 calories per week. Wow – that seems so little to me. As in would I have actually stayed the same weight had I merely consumed 335 less calories per week?

    “Excess” – a big day for me would be something like having 4 bacon, egg and cheese breakfast sandwiches, no lunch, and then 2 large pizzas for supper. Wouldn’t eat all the pizza at one sitting, but by 9 or 10 p.m. it would all be gone. That’s like an 8000 to 8500 calorie day. Didn’t average that, but a “small” day would still usually feature 3000-4000 calories, often with an abominable amount of carbohydrates.

    Normal digestion, normal metabolism, normal activity level for a non-working-out adult with a usually not-very-physical job. I know that as we gain weight, our resting metabolism usually burns more calories per day, but not nearly enough to account for what I’m thinking – that cutting out an average of 335 calories per week would have made no appreciable difference at all, rather than a constant weight being maintained. Seems to me that many, many calories must have been “wasted” somehow, and that they did not actually go into the bottom-line of my weight.

    The same for maintaining my desired and hoped-for weight, should I get there. If it would only be a matter of taking in 335 calories less per week, that seems too easy. And the same for 500 calories or 1000 or 1500 per week. Fasting works almost perfectly for me and to just miss one day per week of eating is not a problem. That should take care of less calories per week, certainly up to 1500 or so. It feels like there must be more to it than that – as with the seemingly “slow” weight gain while eating very large numbers of calories per day – the equations are not making sense to me.

    • Doug, I think the key is knowing what your body is doing. By that I mean, Mifflin-St Jeor is a recognized and standard measure for one’s estimated REE. There’s another equation added to that REE, it’s a hyphenated last name, that adds the factor for activity level. It’s an average which means for all those outside of, say, mean +/- 1 std deviation, it simply doesn’t work. I think it comes down to this, what is one’s actual REE and from that factor activity to determine TEE. The next thing is how sensitive are one’s cells to insulin? That can be normalized over time by breaking the persistent and high contributors. So long as one is resistant to insulin then the body is not functional normally and, effectively, all bets are off. My understanding is fasting is likely the quickest way to break that. Then, as I was theorizing above, don’t eat at all for 5 or more days after you’ve hit a ketone level of 80mg/dl. You’ll work your way up to that. Before you formally start that however, weight yourself, At the conclusion weigh yourself again then take the weight loss * 3500 / # days under test to get a close approximation to your actual TEE for that period. Seems to me, only from there can one fashion an alternate day fasting scheme. As Megan, eventually acknowledged, if you eat too much fat, yes, you’ll gain weight.

  27. Walt, that sounds very sensible. Seems to me that the “all bets are off” also applies when eating a vary large amount of calories, often – that we won’t gain as much weight as we should, just going by caloric calculations. Not that that’s a bad thing. At another end of the spectrum, the Mifflin-St. Jeor equation paints a fairly strict picture for those who are at a desired weight, i.e. there won’t be many calories to play with, before one gains weight. So, and no surprise – looks like we also need some persistent and high effort to stay within the caloric budget we’re then faced with, making the “lifestyle changes” that are often pretty darn profound.

    • Mifflin-St Jeor is based upon a normal metabolism. Perhaps a statistically avg metabolism. You throw in Biggest Loser contestants or someone feverishly working out at the gym to drop and they don’t have normal metabolisms. The reason I mentioned that is from an earlier post of your about where the starting line is.

      What I was attempting to get at with Nicole, I honestly don’t care if one does caloric reduction or intermittent fasting or CICO. What I care about is how is it that fasting 21 hrs/day and eating 3 hrs …well that is just wrong and will lead to damaged metabolism but eating 2500 cal one day and 0 cal the next is perfectly fine. In fact, both, ultimately, are calorie reduction as primary.. as in the later case the avg per day calorie count is 1250 cal (calorie reduction as primary) and in the first case, assuming that 3 hr interval you ate royally 1250, that is an avg daily calorie intake of … wait for it….1250 cals, precisely what the other case was. Nobody explains that difference and, in the end, it’s still Calorie Reduction as Primary, or as Dr Fung likes to call it, a CRaP diet. They both have a fasting period and a feasting period. Maybe there is a difference but it has yet to be explained. As even Megan admitted, eat enough bacon and you’ll gain weight. There is a keto-calculator web site to help manage a ketogenic diet and if you input too high of a fat value, it will tell you you will gain weight. So google keto-calculator.ankerl and see if that helps you…actually, just add a dot com to the end and voilà.

      • r41nier

        Well maybe when your fasting Calorie Reduction becomes Secondary or just a side effect of the Intermittent Fasting. I think it’s just a matter of semantics. So maybe Dr Fung is right in that CRaP will not work if you use it as the primary basis of your diet.

  28. These illustrations are a little too simple. I get that the BMR drops to support the reduced calories in, but caloric restriction obviously doesn’t STOP people from burning fat for energy. The whole issue with The Biggest Loser diet is they lose the fat, but their BMR is so jacked it all comes back when they can’t keep up the diet. These posts don’t illustrate that mechanic and instead describe an on/off switch for fat burning. How are people on conventional diets losing fat in the beginning and at what rate does the BMR slow to match input energy? I would imagine something to the effect of a somewhat gradual adjustment due to the stress of competing with insulin to pull out fat reserves. — Or is all the fat loss just occurring at night time, using gluconeogenesis to replenish depleted glycogen stores? — Also, for people who have tanked their BMR, how do they raise it back up aside from overfeeding? How long does it take to recalibrate BMR?

  29. Sean Raymond

    It is very important that people appreciate that lipolysis does NOT = lipid oxidation. Even if insulin is low, and lipolysis is activated as in the fasted state the fuel mix is NOT 100% fatty acids liberated from the fat stores whilst the body will only burn what it needs to. Numerous metabolic ward studies have now shown that reducing insulin does not = enhanced fat loss despite the anticipated increase in lipolysis. I repeat – the body will only burn what it needs to. Sad to say but the weight loss in any study, be it low CHO or intermittent fasting has consistently come down to a matter of calories in v calories out.

    Dr Fueng, in this very post seems to become muddled in the point he is making. He builds an argument which says that the body can only burn either stored energy in the fasted state or dietary energy in the fed state. He then completely contradicts this by saying when a person reduces their calorie intake from 2000 to 1500kcals they lose weight and furthermore, the only reason this stops is due to set point theory where the body acts against the weight loss to prevent more by ramping down our BMR.

    Dr Feung – I ask you – how was that weight loss achieved if that person ate 6 meals as you say – presumably insulin levels would have been high and a fed state kept constant throughout the day? That does not appear to tally with the central point of this post.

  30. Hi there!
    I have been almost professionally involved in sports (working out even 8-9 times a week) and tried really tons of different eating plans/patterns. I always had a great problem with hunger (especially hunger for sweets) and the more often I eat the worse it got. Despite a really huge amount of workouts (I am a long-distance runner and a crossfitter) I have never fully met my fitness and weight goals. No matter how much I exercised (and how intense workouts I did) I just couldn’t get below 22/23 BMI. In the case of running, it’s extremely important to weigh as little as possible (of course within reason) but I just couldn’t get rid of the fat I still had and… the hunger. Fortunately, I discovered IF and it dawned on me that I was doing it all wrong! I have now been on IF for more than two weeks and I already see wonderful results (and I don’t see any loss in terms of strength/endurance during my workouts). What’s best about it is that my life stopped circulating around diet/eating and preparing meals (and often overeating) and my mind became sharp clear. I am now planning to do IF (17:7 with one 24 h fast in a week) by end of August and then measure all the results/draw conclusions but I am expecting something amazing but see it as a life-time project.

  31. So I have just started intermittent fasting. During my fast I drink coffee and “Diet” cranberry juice. It has 5 calories per serving and 2 carbs. I also water it down at a 50/50 ratio so you can cut those numbers in half. I probably drink 64oz of this %50 mix per fasting day which means 32oz is the juice. That means I get 20 calories and 8 carboydrates. Is that enough to take me out of ketosis? Should I switch to straight water and coffee which have zero calories? Also I take medicine that requires food so I usually have a hard boiled egg at that time or a spoon full of cottage cheese or a small bit of cheese (2oz). Will that take me out of ketosis and if so for how long?

  32. Sebastian perez

    Dr. Fung, please answer me this one question… If fat has virtually no effect on insulin and without an insulin spike there is no fat storage then in theory, I could ingest unlimited fat and lose body fat? Please explain this relations between low insulin calories and body fat reduction/increase.

    Thank you kindly for all you provide us.

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