Caloric Reduction vs Fasting – Part 9

posted in: Fasting, Health and Nutrition | 71

Some would argue that the beneficial effect of fasting is due to the caloric reduction. But why is there such a striking difference between reducing calories and fasting? Caloric Reduction as Primary (CRaP) has been tried innumerable times, and failed virtually every single time. Yet fasting is often effective where simple caloric reduction is not. The short answer is that the beneficial hormonal changes that happen during fasting are entirely prevented by the constant intake of food. It is the intermittency of the fasting that makes it so much more effective. This prevents the development of resistance as detailed in the previous post.

Let’s compare the failed CRaP technique to the intermittent fasting (IF) one. Let’s quickly review the conventional advice to portion control, or reduce daily caloric intake. We often hear the advice to simply reduce 500 calories a day and expect to lose 1 pound of fat per week. Success is as rare as humility in a grizzly bear, but that doesn’t stop well meaning, but idiotic health professionals from recommending it. After all, who hasn’t tried to portion control strategy of weight loss. Who has been able to maintain long term weight loss? Does it work? No.

It is always a little surprising to me how fervent the calorie believers are. From a purely practical standpoint, consider this. We, as medical professionals, have advised people for at least 40 years to control their calories. We tell them that is all about Calories In, Calories Out. Technically true, it turns out that the Calories Out, the part we do NOT control is vastly more important than Calories In. Nevertheless, doctors such as Dr. Katz, continue to advise cutting their calories and pretend that they will lose weight.

Dr. David Katz - Calorie Believer
Dr. David Katz – Calorie Believer

But it has never worked. The failure rate is 98%. Practical personal experience shows that this is likely to be true. So, whatever else you may believe, caloric reduction DOES NOT WORK. This is a proven fact. Proven in the bitter tears of a million believers. But, no matter how many times I tell a calorie enthusiast, I get the uncomprehending gaze of an anxious monkey.

So, what happens with this CRaP strategy? A detailed review can be found in the Calories series earlier. Essentially, the body tends to maintain a body set weight (BSW).  The body is initially able to lose some weight. However, as weight goes down, the body compensates for this weight loss by trying to regain the lost weight. Hormonal mediators of hunger (ghrelin) increase. This means that measures of hunger and desire to eat increase. This happens almost immediately and persists almost indefinitely.

Next, the body’s metabolism starts to shut down. In response to a 30% decrease in calories, there is a roughly 30% decrease in total energy expenditure. We start to feel tired, cold, and we have little energy for things like exercise.

As the body’s TEE decreases, the weight loss starts to slow down and then plateau. Eventually the weight starts to go back on, even as we continue to follow the diet. So the metabolic adaptations to CRaP is an increase in hunger and a decrease in basal metabolism. So, as you diet, you feel hungry, tired, cold and generally miserable. Does this sound familiar to any dieters? Probably sounds familiar to every dieter. This is what Dr. Ancel Keys had shown decades ago in his Minnesota Starvation Experiment.

The worst part is that this strategy is guaranteed to fail. It has been proven by science long ago. The huge 50,000 woman randomized trial (Women’s Health Initiative) of the low fat low calorie diet proved to be an utter failure for weight loss. The problem with this strategy is that it does not address the long term problem of insulin resistance and high insulin levels. Since the insulin sets the ‘BSW thermostat’ – the body keeps trying to regain the lost weight.

Here’s the bottom line. As you reduce calories, appetite goes up, and TEE goes down. You reduce Calories In, but Calories Out goes down, too. This is failure guaranteed 100%. It’s as stupid as cracking the safe of your own bank.

Intermittent Fasting

As we recently detailed in the fasting series, the hormonal changes that happen in IF are completely different. In contrast to CRaP, during fasting, appetite goes down and TEE goes up. The body is trying to lose weight and helping you along. The main point is that it addresses the long term problem of insulin resistance. During caloric reduction alone, you do not get any of the beneficial hormonal adaptations of fasting.CRaP vs IER

The hormonal adaptations are completely different, as we have discussed so far in this series. Glucose and insulin go down and stay down.

During IF, the intermittent nature of the intervention helps to prevent the insulin resistance problem. A recent trial – The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomized trial in young overweight women – compares CRaP to IF. In this study, 107 women were randomized to two strategies.  The first was a 25% continuous energy restriction (CER) – similar to the CRaP strategy of portion control. The second strategy was intermittent energy restriction (IER). Patients were allowed normal intake on 5 days a week, but only 25% of their usual calories on 2 days of the week – very similar to the 5:2 diet of Dr. Michael Mosley.

Let’s assume the usual caloric intake was 2000 calories per day. With CER, calories are reduced to 1500, or 10,500 calories over 1 week. With IER, weekly calories are 11,000 calories per week. So this study effectively keeps caloric intake steady – or even favouring the CER group slightly. The basic diet was a Mediterranean style diet with 30% fat.Harvie1

Over 6 months, what were the results? In terms of weight loss and fat loss, there were no significant difference although the IER tended to do better (5.7 vs 5.0 kg weight loss, 4.5kg vs 3.2kg fat loss).

But the real important part of the study was the effect on insulin and insulin resistance. After all, I’ve spent the last 60+ blog posts arguing that insulin and insulin resistance are the key factors in obesity and weight gain.Harvie3

What happens to insulin levels? Well, there is a clear, substantial improvement in insulin levels favouring the IER group. Even more impressive is the change in insulin resistance. This is measured by HOMA, which is a comparison of fasting glucose to fasting insulin.

In the CER group, there is virtually no change in their insulin resistance (IR). Because there is no change in IR, this will continue to lead to higher insulin levels in a vicious cycle. These higher insulin levels perpetuate the higher IR.

This is the long term problem of weight loss. This is exactly the part of the equation that is typically ignored and leads to the typical weight regain. It is the intermittency of the diet that makes it effective.

We can look back at human history. Fasting has been used for the last 2000 years as a tremendously effective method of controlling obesity. Portion control (CRaP) has only been used extensively for the last 50 years with stunning failure. Yet, pundits such as Dr. Katz and others continually scream at us through books, TV, and online to reduce calories. Don’t they think we’ve tried that?

But the one strategy that does help, fasting, is continually belittled as a dangerous practice akin to blood letting and voodoo. The problem with most diets is that they ignore the biological principle of homeostasis – that is the ability of the body to adapt to changing environments. The body has a preferred state. If you move away from it, the body will adapt to it. For example, if you are in a dark room and suddenly go into the bright sunlight, you will momentarily be blinded. However, within moments, your body will adapt.

The same applies to weight loss. If you try to keep a constant diet, the body will adapt to it. This means that successfully dieting requires an intermittent strategy, not a constant one. This is a crucial difference.

The difference is between restricting some foods all the time (CER) and restricting all foods some of the time (IER). This is the difference between failure and success.

Start here with Fasting part 1

Continue with Fasting part 10

71 Responses

  1. It’s good you used a study with women. My wife and I are both intermittent fasting, but we’ve read conflicting information with regard to the benefit of IF for women. She is experiencing a benefit, but it’s much slower than mine. I’m losing weight at a rate I find difficult to believe it’s so high, whereas my wife’s scale is only nudging down slowly.

    • Deb Griffith

      I also started with 5:2 and at first, the weight dropped off pretty good, then slowed. So after reading all the info here and on other sites and books, started 4:3 and dropped more carbs. This was better. Then, after reading “Good calories, Bad calories”, I went all in! I have been doing 16:8 (fast from dinner to lunch the next day), and adopted a ketogenic diet (eat lots of meat and good fats…cut out all carbs except what is in the meat and fats), no fruit, no veggies. I exercise half an hour, twice a week, weights after.

      The weight is literally melting off. I started at 179 at the middle of April, and weighed at 155.4 thks morning. 3.2 lbs in the past 5 days gone. It can be done. And I am postmenopausal. And take pain meds for chronic back pain.

      One thing that Gary Gaines wrote in that book is that every body is different. Some can lose eating a lot of carbs, others mini.Also carbs, but some people just can’t tolerate them at all and will not lose weight. That is me. My body sees a piece of bread or veggie and it just grabs it and stores it right on my hips! Not everything works for everyone. You have to experiment and find what works for you. Tell her not to get discouraged!

      • Deb Griffith

        I should also say that my main, original goal was to get rid of my cravings for carbs and sweets. This seems to do the trick. I also take several supplements (fish oil, potassium, magnesium, vitamin c, etc), and a daily “shot” of milk of magnesia. Both the fasting, pain meds, and little fiber tend to constipate!

      • I’m with you — if I have any carbs that aren’t vegetables, I seem to gain weight that takes days or weeks to come off again. Also, I get famished for one-two DAYS afterwards. I think that’s insulin resistance. With IF, this has become better, but I still eat LCHF and try to eat any wheat or other high carbohydrate meals very, very infrequently. It’s difficult at times, though. For instance, we had a “parents night out” last night and went shoe shopping for me. I don’t remember the last time I went shoe shopping, so all of my shoes were literally falling apart. We only had a limited time (3 hours total), so we ate at a Mexican-themed restaurant. They had “low carb” quesadilla and burritos, both with steak. But I’m sure the tortillas were not that low carb, and wheat affects me badly at times.

        When you say 4:3, does that mean you’re not eating at all for three days, or you only eat dinner three days, or what? Currently, we are not eating at all one day a week and skipping breakfast and lunch one day per week. I’ll also not eat breakfast a few times per week. I eat LCHF as much as possible, my wife does too but can have a few episodes of resorting to popcorn (she needs something salty and we haven’t found an appropriate substitute). We’ve also tried to only eat three meals per day on the days we eat all day. No more “snacks” (which for me were broccoli and fish, for instance), no more eating before bed, etc. It doesn’t always work: I had a “snack” (ground meat with hot sauce) last night before bed. I try to avoid that, though.

        • Deb Griffith

          That’s a cute story about your shoe shopping! Anyway, I was doing 3 fasting days a week, which are actually 36 hours in length, and calories were 500 for that time period. It worked for a while (it is technically called the Fast Beach Diet”), but it is hard for me to count calories and grams and portions. That’s how I got into the mostly meat plan. I can’t remember exactly what I told you earlier, but in his book “Good calories, Bad calories”, Gary Raines tells of early explorers who lived with the Inuit tribe in Alaska, and ate nothing but meat (protein and fat), and were very healthy. No one believed them when they got back so they did a 12 month study, and again, were perfectly healthy. And they are to satiety, never counted calories or anything. I said, that’s for me!
          I really wanted rid of my cravings. I was terrible, and I felt like a drug addict! Then read that carbs and sugar can be addicting in the same way. Same part of the brain. Weird, huh?!
          So that is where I am now. It may change in the future..I am always reading and learning. Found another interesting site called the Eating Academy. Lots of good articles there too.
          Have a good evening!

          • Deb, It is Gary Taubes and he has teamed up with Peter Attia at Nu Science so you are in good company.

          • Deb Griffith

            Yep, Taubes; auto correct changed it!

        • Pork rinds would be far better for your wife than popcorn.

          • Pork rinds are extremely hard to find in my area. Old Dutch tastes best. When you find them pick them up plus extras !!!!!

          • I agree with that, but I think she’ll have a hard time with pork rinds, although I can eat them. We tried salted seaweed: I found it too fishy, and my wife hated it.

            Baked prosciutto is good, but that requires us to make it.

            Personally, I don’t crave salty foods, but she does.

          • “Pork rinds would be far better for your wife than popcorn.”

            I very much doubt it.

        • Hi Bob, we had been in the habit of having popcorn that we popped ourselves with a little salt and butter, but not having it anymore. I have found some very lightly salted pumpkin seeds at Trader Joe’s that have done the trick in replacing the popcorn. Others we have tried seem to be all salt and not palatable to me. These have a nice crisp to them with just enough salt and I don’t find them dry and difficult to swallow as some others. Don’t know if TJs is near you

    • Margaret p

      To reply to the salty cravings, I found out that I needed the salt and potassium. I put a pinch of sea salt and nu salt in my filtered water with lemon juice. That way I do not need to use a sweetener.
      I am 62 year old women. I believe that my being on the CRaP diet for at least 40 years has something to do with the problems I had with achieving keto sis . I found out that I could only eat like 9 oz of protein a day, to lose weight on the ketogenic diet. I had the low level of energy, coldness etc that Dr. Fung talks about. I did lose weight quickly. I was very happy to find Dr. Fung diet. I had been fasting for 36 hours and then eating for a day. I have reached an AIC of 5.1 , lost 68 pounds. I have gone off 5 of my 6 meds. I am slowing down my weight loss. I have started to just fast for 24 hours and then eat for supper and eat the next day. I still keep the carbs to vegetables. I have treated myself to fresh fruit about once a week.
      i feel that I can live with this diet. The old CRaP diet never worked for me. I was at 236 pounds, and at the point they wanted to give me insulin shots. My daughter found the LCHF. My life has changed. The LCHF diet helped me lose weight, but when I changed to Dr.Fung fasting I saw a change in the insulin and insulin resistance. I also had a great improvement of my stomach irritations. The fasting gave my stomach a time to heal.
      Thank you Dr. Fung, please keep fighting the established medical practices. My family doctor and my heart specialist are watching me , they think this is dangerous. They can not refute the fact that for the first time in 15 year I have lost weight, my blood sugar is controlled and that my blood pressure is normal and no swelling or fluid build up and this without taking drugs, and just following a diet.

      Dr. Jason Fung” Thanks. It is great to hear that you’re doing so much better.

    • lasslassiter

      Maybe she should try increasing her protein intake being it has the highest TEF ( Thermal Effect of Food) of all nutrients

  2. Bernard P.

    It’s ironic that the authors of the 107-women study you quote seems not to want to believe their own results, and thus end up minimizing the better results with IER:

    “CONCLUSION: IER is as effective as CER with regard to weight loss, insulin sensitivity and other health biomarkers, and may be offered as an alternative equivalent to CER”

    Their own results show that they should have written “more effective.”

    In addition, their version of IER is not a true fast, but a severe (75%) caloric restriction on two consecutive days a week. Participants are still eating, but less. There is no 24 hour period without eating, like in a true alternate day fast. Thus the study is not designed to maximize the hormonal benefits of fasting.

    • That’s a shame given the significance of the difference in IR: “group by month 6 interaction, P=0.001”
      =99.9 % that it is not coincidence.

    • You’re right, “fasting” is two days of very low calorie diet. So, it might not be intermittent fasting, depending on how the subjects ate their meals. It’s only about 650 calories, so it’d be hard to have three meals with that.

  3. Pertinent both to this post and to Valerie’s sharply worded, but referenced and on-point critique under the The Ancient Secret of Weight Loss – Fasting Part 8 post, I enjoy this quote by Art De Vany:

    ‘Vary Intake’

    “Our ancestors lived with feast and famine. Research indicates that chronic or intermittent fasting improves health. I do it the easy way. Never chronically; your mind and body will not accept it [De Vany’s opinion: others have a different experience, and De Vany himself concedes that chronic fasting improves health]. And you will lose vital lean body mass; muscle and organ mass. Easy intermittent fasting is skipping meals randomly and eating to fill later. I like to skip dinner now and then. Another variant is to have breakfast on a day when you plan a hike or travel on a plane and don’t eat the rest of the day.

    “It is best to be active when you fast so as to signal your genes to conserve protein (muscle mass). Being active also deepens the temporary negative energy balance of the intermittent fast. I think the research is pointing to transitory alternations between positive and negative energy balance as the underlying mechanism for the positive effects of fasting [emphasis added]. For some individuals, this is the final tool needed to bring their fasting insulin down.”

  4. In reply to BobM listen to Zoe Harcombes lecture at the lchf conference in SA. She says women have to be patient but they will get there in the end. The weight is dropping off my husband and it is very slowly creeping off me.

  5. Jennifer

    Dr Fung, in regards to your comment “If you try to keep a constant diet, the body will adapt to it”, does this not apply to consistent IF? If I do 24h fasting every day (eating only dinner) or 16:8 every day wouldnt the body adapt to that type of dieting too after a while? Also, I am doing 2-3 24hr fasts per week and the weight is very slowly going down (I only have 3-4kg to loose, i’m helathy and not overweight and not on any meds) , is it dangerous to do 24h fasts every day until I reach my weight goal (and then go down to 1-2 times a week)? Or will it stress my body trying to get results too quickly (and being on constant calorie deficit as I dont eat more than 1000kcal when breaking my 24hr fasts)? Thanks!

    Dr.Jason Fung: We often find, in our clinic, that daily 24 hour fasting is less effective than occasional longer fasts.

    • Jennifer

      Thank you Dr Fung!
      How long and how often would you say is better? 36h? 72h? Longer? Once a week? Once a month? And during these longer fasts is pure fat ok to consume (cocount oil or butter in coffee for example)?

      I very much appreciate you take the time to respond to your comments/queries, thank you!!!

      • Deb Griffith

        I’m obviously not the Dr, but wants to let you know that I did 5:2 for a while an It was two 36 hours “fasts” , with 500 calories in each 36 hour time period. A lot of successes are attributed to this program. I have since moved on to 16:8 five or six days a week, eating very low carbs/moderate protein/ high fat.

        • Hi Deb,

          I’m late to this party in terms of it’s October 2016…lol. When you say 16 8, you fast for 16 hours and eat for 8 so if I fast from let’s say 7pm until 11am the next day? Then you eat low carb, healthy fat, lean protein and you’re losing weight?

          I just saw that the 24 hour over and over isn’t effective. I’m a little afraid of 5:2, since it seems you could eat WAY too much on the 5. LOL

  6. Can we have wheat grass juice (wheat grass powder + water) during the longer fasts such as 36hr fast or the 48 hr fasts? Will it interfere with our weight loss?

  7. I have been doing 16:8 LCHF for many many weeks and the weight loss has stalled. Then I added two days of 21 hrs fasts and still the weight doesn’t budge. I am getting very discouraged and wonder how little one must eat to lose “the last 10 lbs” which is allll belly fat.

    • By any chance, are you losing inches? I am also going through a period where there is not much weight loss inspite of the 22 hr fasts but my clothes have become lose. I wonder if I should try the 36 or 48 hr fasts in order to see some difference in weight.

      • Thank you for your comment Sarah… to answer your question, maybe. 😉 I see from other people’s posts (see Jesse below) that what I have been doing is pretty lightweight in the ‘fasting practice’ but after a few months of really keeping clean on carbs and doing what I have been, I’d like to see the scale move. I am post meno so maybe that plays into it. But I go 21 hrs fasting and I am done. As a mother I am constantly preparing food for the kids and being in the kitchen just gets me obsessed with finally ending the fast. With a salad! I am just frustrated I guess, b/c I would like to go back to only a 16:8 eating pattern and cut the longer fast days out. Anyway… back to my original question, How little do you have to eat to lose some weight?

        • Deb Griffith

          In my opinion, and in practice, based on the I do here plus what I have read, how much (calories)you eat isn’t as important as what and when you eat. I was nearly stalled until I dropped ALL carbs from my diet. Everyone is different in their ability to deal with carbs, and my body just instantly puts them on my fat reserves. Even whole wheat bread, nuts, fruit and veggies….once I dropped them 5days a week, and doing 16:8, the weight started coming off again, in massive amounts.
          Now I eat most protein (meats) and fats. That’s it. One refeeding day and Sunday is like a slow slide back into my fasting. I am 53, have been menopausal for 10 years.

          • For some weird reason, I find it easier to lose weight if I add a little bit of carbs (not refined carbs) like half a carrot, raw plantain, 2-3 tbsp legumes or even a fruit like 5-7 slices of mango when I eat after a 22 hr fast… More protein makes my weight go up and more fat sometimes gives me indigestion 🙁 Is this just me or does anyone else have the same issue?

  8. Dr. Fung, if you’re looking for another topic, consider the following:

    1) This website implies that a low carbohydrate diet does not increase insulin sensitivity. In fact, a very low carbohydrate diet CAUSES insulin resistance:

    Personally, I find this hard to believe, as I was able to lose about 20 pounds following a low carbohydrate (even very low carbohydrate) diet, which I attribute mainly to improvements in insulin resistance. Though it may be due to other effects.

    2) Speaking of testing for insulin resistance, are there tests we can get to track our insulin resistance? The same website says:

    ” While most studies of this nature indirectly estimate insulin sensitivity simply by using a formula based on fasting insulin and glucose measurements (HOMA-IR), which can be inaccurate, Reaven’s group directly measured insulin sensitivity using a gold standard method**.”

    The “gold standard method” is the “Insulin suppression test”.

    Is there a test we can take that would allow us to track insulin resistance? I’ve found this discussion of tests:

    But I’m sure my general practitioner is not going to give me either one of these.

    3) Why does intermittent fasting reduce blood pressure? My systolic blood pressure has decreased about 14 points (mmHg) since I’ve been performing intermittent fasting. My body weight has also decreased about 15+ pounds during that time. Is the decrease in blood pressure due solely to bodyweight?

    • Bob M. — wow— just cam from the and was amazed at what I read. Basically the antithesis of Dr. Fung! I sure hope Dr. Fung can respond to this and give some insight as to this insulin sensitivity question!! Dr. Fung?

  9. Nothing can beat fasting.

    Has anyone come across any study showing the effect of daily hour long aromatic jogging on insulin resistance?

  10. so, i have been doing 18 to 44 hour long fasts since june 6th, … pretty much water or black coffee (or a bullet proof coffee) only
    before starting the intermittent fasting, i was on a ketogenic diet for about 2 weeks
    to date, i have lost 20 lbs in one month 🙂

    i feel great, and my blood sugars are better, i am now off of all insulins as a T2DM, and still using a little metformin / acts when i DO have a meal.
    eating primarily low carb, higher fat, moderate protein when i do eat

    ***i am usually pretty hot natured, but have actually been reaching for a blanket at times, and turning the air conditioner off at times, instead of setting it lower.***

    ??????do i need to be doing something differently???

    my intake consultation for the long distance program is still two weeks away.


    • Jennifer

      Jesse, how many times in that month did you go longer than 24hrs (ie 36-44)?

    • Jesse, one “side effect” I have of fasting is running hot and cold. Normally, I run hot (will have a fan on my while at work), but the days I fast, I go through phases. I’ll turn the fan on, then off, then on, etc. At night, I’ll get cold, pull up the covers, then kick all the covers off later. I’ve done one three day fast, and this side effect seemed to ease after the first day or so. Normally, I’m fasting for 24-40 hours (no breakfast, lunch = 24 hours; no meals at all one day and not eating the next day until lunch = 40 hours), though, so I get this side effect at least the first day.

  11. 44 hour fast started on june 6th,
    42 hour fast started on june 8th, after 2 meals
    38 hour fast started on june 10th, after 1 meal
    28 hour fast started on june 12th, after 1 meal
    16 to 19 hour fasts on june 13th -17th
    24 hour fast started on june 17th
    14 to 22 hour fasts starting on 18th-20th
    38 hour fast started on on june 21st
    36 to 60 hour fast started midnight last night.
    have lost 15 lbs since june 6th
    feel great from an energy level, and concentration standpoint

    • Jennifer

      Wow Jesse, thats hard core. How long are you planning to continue with these many fasts so closely together? I have started a 40h fast (after yesterday’s dinner up until lunch tomorrow) and will do another one starting Sunday, then I plan to take a break for a few days (I always do 16h fast as I dont eat breakfast but i dont really count that as IF anymore). I have 5kg sturbborn fat I want to get rid of once and for all!

      • dunno, i am kinda making it up as i go along

        i’ve had unhealthy relationships with food for a while,
        eating for pleasure, eating out of boredom, eating when feeling blue, eating when irritated, eating past satiety
        i have always a “portions” guy (supersize-me, please) — my wife would always get on to me when i would ask a waiter or waitress : “how big is the serving of fish, compared to the chicken” for example
        for far too long i have derived too much pleasure from eating.

        i am at 36 hours now, and whilst my tummy is growling a bit, i am not “hungry”
        and if i can stay busy till bedtime, (and keep from eating) i know i can push through till tomorrow morning (60 hours) with ease, and maybe 72 hours until tomorrow evening.

        i start three night shifts tomorrow night, and for some reason i feel a little nervous about starting a night shift – 72 hours into a fast. so i may eat then, before work, or i may keep going if feeling fine.

        i think i have read NEARLY every blog post here, and pretty much understand it all. i don’t necessarily “OWN IT” mentally, but it all makes sense, and seems right, except this one thing :

        is it the INTERMITTENCY of the fasting??? in which case i may need to slow my charge.
        the last thing i want to do is slow down my already sedentary metabolism.

    • Exactly what I do. Effortless. Never hungry.

  12. funny,
    I’ve been so busy reading back blog-posts, . . . i am not sure i had read THIS one, – which speaks to exactly my question above.

  13. It is the same conclusion that I keep getting at, when it comes to the nutrition and metabolism part of the obesity equation:
    low insulin -> fat loss.

  14. Deb Griffith

    The way I understand it, and I may be wrong, is that during fasting, your body “eats” your fat reserves. So it is receiving all the energy it needs, therefore, no drop in metabolism. Someone correct me if I am wrong.
    Anyways, I have lost 25 lbs since mid April, so obviously it hasn’t slowed mine down!

    Dr. Jason Fung: That’s exactly right. Furthermore, this is not some unhealthy, unnatural process – this is exactly how we were designed to function.

  15. charlie chambers

    I read part 1-9 last night…. they were awesome…. best discussion I’ve heard in a long time.
    I do have one question though……

    What I got from all 9 posts was fasting and IF is far more beneficial than a low calorie/CER approach’s but I have metabolic syndrome and Type 2, on no meds, eating under 800 calories of meat and fat (I know this is stupid) but I have IR so bad meat causes the least glucose rise during eating.

    In your 9 posts you mention that if IR is really bad that full fasting will help or even reverse IR….. my A1C just a month ago was 8.2 I can’t get it below 110 having not eaten once or twice a day…. IR is out of control….

    So, If I fast with just water and supplements can I have the lipid based vitamins and not hurt the fast… My IR is so bad that using Lipid vitamins raises my BG Level…. this blows my mind.

    Any help would be very much appreciated!

    • Deb Griffith

      Why is eating just meat and fats bad? That’s what I do, 6 days a week. If I eat any carbs (besides what is in the meat), my weight loss comes to a screeching halt! There have been many studies done in the past decades that prove that an all-meat/mostly-meat diet can be healthy.

    • Dr. A.E. Kagal

      This may have something to do with NAFLD…non alcoholic fatty liver disease. Consumption of alcohol may make insulin resistance worse in people with NAFLD. Insulin resistance may not improve until liver function improves. Whether liver function improves with fasting and how long it takes to do so is something I would like to know from Dr. Fung.

  16. What’s the calorie count suppose to be when eating any given meal while Intermittent Fasting
    And should it be LCHF or LFHC, this is not being specified in any of the 9 Fasting Posts.
    Is this information in any other POST on the site?

    • Deb Griffith

      Charlie, he covers diet content (low carb, etc) in earlier posts. If you do a search for “Atkins”, you will find it. But if you haven’t read all of them, I recommend starting at the very beginning. It will open your eyes.

      Some people who fast eat their “normal” diet on non fast days. Others, like myself, eat low carb (or very low carb). The 5:2 plan (fast 2 days…36 hours each), recommends 500 calories during the fast for women, 600 for men.

  17. Barbara

    Dr. Fung, I just came home from a doctor visit. In the last 3 months I lost 24 pounds, my A1C dropped from 9.5 to 8.5, and I feel great! My doctor insists I stop fasting and eat 6 times a day. He wanted me in an insulin study, which I declined because of the eating rules. He insists fasting will ruin my metabolism, destroy my muscle and organs. I see no sign of problems. He is wrong, right? I think he hasn’t been reading up on newer studies, except the ones for drugs he is testing. Any comments? I really believe you and all the studies you quote, but could use some assurance.

    Dr. Jason Fung: Fasting does not cause any of those problems. Those are just myths. If you are losing weight, reducing blood sugar and feeling great, then it seems obvious that you are getting better

    • Your doctor sounds like an unscientific moron, and with a conflict of interest affecting his treatment of you as well. Frankly, he sounds terrible.

      Is there something preventing him from reading any of the multitudes of studies showing clear metabolic benefits to fasting? He ought to be embarrassed! He’s even denying your clinical improvement. What a dolt.

      I apologize if anyone feels I have understated my criticism.

      • Barbara

        Thank you for your reply. No, my doctor is not a dolt. He is a very nice man who just believes what he was taught. And a very busy one. I intend to succeed at this IF/LCHF lifestyle and show him what happens. I’m morbidly obese, have had type 2 for about 25 years, plus high bp, high cholesterol, the whole thing. I don’t expect to be cured overnight, but I will get there. Even if I still have to take metformin, getting the blood sugar under control and the weight off will be a victory! And he will celebrate with me, and perhaps do some research on this website. btw, I am 86 pounds lighter than when I started working on it, tho the first 50 some pounds I lost on a vegan diet. Then the loss stopped, and my blood glucose when UP while on it. Now this is working and I’m thrilled!

    • Barbara

      Thank you Dr. Fung for taking the time to reply to me. Yes, I am getting better and have no intention of stopping. Thank you so much for all the info on this site!

  18. If you mean long term chronic CR, you’re right.

    But on the other hand, short term severe (≤50% of daily average caloric needs) CR … e.g., a modified fast … can and does work, according to widely-published and cited researcher Valter Longo, who is also a proponent of water fasting.

    However, his research shows greater benefits from longer than shorter fasts, with about a minimum of 4 days of at most 200 Calories per day necessary to tap into all the various metabolic systems that food deprivation impacts about in order to get the all the potential health benefits from fasting. However, since many people won’t fast for that long, as well as the fact he believes longer fasts should only be done under medical supervision due to various problems including low blood pressure and accidents, he has designed a protocol that is 5 days in length, repeated every month to every several months depending on the patients’ conditions, and includes more macronutrient intake—with a focus on high micronutrients to macronutrients ratio.

    What are your thoughts about whether it is necessary to fast for a minimum of at least 4 days, less frequently, to gain the maximum possible benefit vs. more frequent, shorter fasts? Do you think this is sound,, or that several 24–36 hour fasts are as good as less frequent 96+ hour fasts?

    Also, do you think relatively severe calorie restriction, which some of the studies you’ve cited have used instead of zero Calories, is close enough to a fast to bring about all the same benefits? Or does going to near zero Calories bring significantly more benefits?

    I’m curious what your thoughts are on both longer, less frequent vs. shorter, more frequent fasts… and also if you see a valid distinction between temporary severe calorie restriction vs. chronic long-term calorie distinction? Evolutionary-wise, It seems to me, in nature, we would have often had periodic “famines” and not only “fasts” (although likely both).

    While not in the title, Longo also talks about the blood-glucose benefits in a presentation here:

    Also, Mosley and Longo were on a BBC documentary together, and Longo’s protocol achieved greater success in favorably altering biomarkers than what Mosley was advocating. Mosley acknowledged this, but said he couldn’t do Longo’s protocol. Which is, in part, why Longo developed the new protocol of severe CR in lieu of a water fast, but long enough to allegedly bring huge benefits.

    As an aside, Longo urges a plant-based, but not vegan, micronutrient-rich diet for longevity purposes.

    • Apology for not closing off the first “b” bold html tag. I meant to close it at the end of “minimum of 4 day”.

    • I’m not clear on the objective of “very low calorie modified fasting” with 200 to 400 calories per day of food, versus plain old fasting in the manner it’s been understood for thousands of years (to wit, no food, only water).

      Regardless, in my own personal experiments and experience, I currently have better results with fasts of 3+ days. Actually, for me, day 3 seems to be the transitional day for the hormonal and metabolic changes that make fasting beneficial. I’m not clear on the personal benefits derived from shorter fasts (16-36 hours) aside from reduction of caloric intake.

      Dr. Jason Fung: The ‘low cal modified fast’ was taken from Dr. Varady’s data of about 500 calories on a ‘fasting’ day. The only reason she did this was because she felt taking zero calories on a fasting day was too difficult. I don’t agree

      • Walter Bushell

        My understanding is that macro composition is important to a caloric fast.
        It’s one thing to have fat calories and quite another to have protein, and worse to have carbs.

  19. I once a page where the diet and fasting was posted.. I can no longer find it. Anyone know where I can find it? It was a downlaod and about 4 pages….

    • it also contained the recipe for the broth.. I have lost my copy of these few pages

  20. Great post! Based on it, the comments, and the views in different forums, it looks like the good old 3 meals a day is a recipe for disaster. Except maybe for Big (processed) Food’s shareholders.

    Anyway. Learn to *appreciate* the variability of your appetites and see the ‘downtime’ as the time when your body cleans house, metabolically speaking. Don’t worry about the process. When your body really needs something, you’ll get a very unique, targeted type of craving (not to be confused with a need for distraction from boredom). Do this for a few cycles and you’ll be amazed by the results of listening to your innate wisdom.

  21. Dear Dr. Fung,

    I’m stopping a marathon reading session of your fasting series (1-9). As a fellow scholar, I must say I’m impressed by your clear, concise, and fully referenced writing style.

    I have a keen interested in fasting for weight loss and health. In my private practice, I use intermittent fasting to help women lose fat.

    It’s refreshing to see your scientific perspective on this subject. A lot of the advice of plain wrong (mainstream nutrition) or somewhat esoteric (naturopathy and alternative medicine practionners).

    Personally, I’ve done intermittent fasting and longer fasts of up to 11 days. I’m now on day 4 of a 30-day fast. I was hoping to find some advice regarding longer fasts in your blog series, but so far I haven’t. I’ll try getting in touch with your through your contact form.

    Best regards from Montreal,

    Etienne Juneau, PhD
    Doctor of Public Health

  22. […] Caloric Reduction vs Fasting – Part 9 […]

  23. Fantastic post, Dr. Fung, Thank you for that.

    What is the maximum amount of time one is able to go without food before GH starts declining again or otherwise it becomes an adversary to the weight loss process?

    What should one eat to break the fasts to make sure the body “catches its breath” so it can be ready for the next high-GH fasting cycle?

  24. Since May I went from 75.7 kg to 68.1, and 17% body fat to about 7%. I’m 53 years old and work out regularly, and had been doing so for years. That extra 10% body fat was stubborn, regardless or exercise. I lost it by using an app on my phone to record everything I ate-and I measured all my food when possible, estimated when necessary. I shot for 1700-1800 calories a day (I am close to 6 foot tall-181cm) and succeeded on about 90-95% of days. I lifted weights and ran, adding about 20% more exercise than usual-more lifting, less running but overall I would say the intensity was up about 20%, as well as time spent working out. This all worked absolutely according to plan. I set the app to get me to 68 kg by the end of August and this has happened exactly as the energy-in/energy-out math predicted.

    I appreciate the arguments made here and don’t underestimate the role of hormones and so forth, but my experience bears out the efficacy of the calorie counting approach.

  25. Dear Dr Fung,
    I have partly read your books and today I started my fast. I have a food sensitivity to cayenne pepper, paprika, red pepper, and cloves (even sensitive to the smell) that leaves me throwing up and somewhat anaphylactic reaction. I noticed that sometimes after an accidental exposure to offending food, when I cannot eat for a couple days because everything causes me to throw up, that I lose weight and it stays off, which is consistent with IDM. I am hoping that trying a several day fast will eliminate these food sensitivities. I also read The Fasting Cure by Sinclair, a hero of mine. Do you have any experience with food sensitivities being resolved. I am 69 years old, 10 pound over weight, and the only medication I take is Synthroid. Thank you for putting all of this information online. What a gift to the world you are!!!

  26. Michelle Uhlig

    Dear Dr Fung (and other participants)

    I have just one questiion… some of the articles explains that you can take in about 200-400 calories in on “fasting days” or periods. Isot then not true that fasting is actually having NO CALORIES at all?

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