Power: Fasting vs Low Carb – Fasting 26

What’s the difference in power between fasting and LowCarb High Fat (LCHF)? Sometimes it feels like arguing whether Batman or Superman is more powerful (Superman, of course). But they’re both superheros, and the point of both these dietary superhero regimens is to lower insulin. This stems from a rational examination about the causes of obesity and type 2 diabetes. You need to understand the aetiology of obesity (the underlying cause) if you are to have any hope of treating it.eatwell%20plate%20377%20sized

For decades, we have laboured under the false assumption that excessive calories caused obesity. However, overfeeding and underfeeding studies clearly proved this hypothesis wrong. If calories caused obesity, then overfeeding calories should cause obesity. It did, but only in the short term. Long term, weight went back to normal. Underfeeding calories on the other hand, should lead to permanent weight loss. But it did not. The failure rate of this Caloric Reduction as Primary strategy is an abysmal 99%.

Using a more rational model of obesity as a hormonal disorder (mainly insulin, but also cortisol) leads to the hypothesis that increasing insulin should lead to lasting weight gain. Decreasing insulin should lead to weight loss. And guess what? It worked just as advertised. (See the Hormonal Obesity series for a full description).

So, if we understand that excessive insulin causes weight gain, then the treatment is quite clear and just really damned obvious. You don’t need to decrease calories, although there is some overlap. You need to decrease insulin to cause weight loss. Both LCHF diets and fasting accomplish this goal. Refined carbohydrates are the biggest stimulus to insulin, so reducing carbs reduces insulin. Protein, especially animal proteins also raise insulin, so keeping protein moderate and fats high is another way to keep insulin levels down. Fasting, by restricting everything, also keeps insulin down. A ‘fat fast’ ie. eating nothing except pure fat, may also accomplish the same thing, but studies are sparse. So ‘bulletproof coffee’ may certainly achieve the same goal of lowering insulin without lowering calories, but the data are simply no there to say for certain.Nuttall1

But which diet is better? LCHF or Fasting? A comparison of power shows that fasting wins every time. In this study of a carbohydrate free diet vs fasting in type 2 diabetics, you can see that carb-free does extremely well. If we compare the glucose response of Carb Free versus a Standard Diet, you can see that blood sugars come way down. But fasting does even better.

If you are trying to lower blood glucose, nothing really beats fasting. After all, you can’t go lower than zero. Even then, the carb-free diet does remarkably well – giving you 71% of the benefits of the fasting, without actual fasting. The standard diet was 55% carbohydrate and 15% protein, and 30% fat – not far off of what most dieticians and Dietary Guidelines recommend. You can see how shitty it is for actual blood glucose control.

The carb-free diet is <3% carbs (that is ketogenic or ultra-low carb), 15% protein (moderate)  and 82% fat. LCHF pretty much says it all. The calories delivered were 25 kcal/kg (1750 calories for a 70 kg man) in 3 meals – this was the same between the standard and carb-free diets. So the benefits of carb restriction on blood glucose were NOT simply due to calorie restriction. This is useful knowledge, considering how many ill informed idiots doctors and dieticians keep saying ‘It’s all about the calories’. Actually, in this study, it had nothing at all to do with the calories.

Anybody who still believes that ‘It’s all about the calories’ despite 50 years of unrelenting failure of the Caloric Reduction as Primary (CRaP) model either has not thought about things very hard or is simply not all that intelligent. Yes. If a strategy such as CRaP fails for 50 years, we should be changing our strategy. It doesn’t take Albert Einstein to tell us that is the very definition of insane.

This graph is pretty sobering. Looking at the Standard Diet (ADA recommended), you can see how high those peaks of glucose really get. You might rightfully ask yourself, if the good folks at the ADA knows that their diet sends blood sugars skyrocketing upwards, why on earth would they recommend it? Are they trying to kill us? Unfortunately, the answer is yes. They are trying to kill you. Not intentionally, but with their ignorance. All that money showered upon them from Big Food and Big Pharma have something to do with it, too.Nuttall2

But what is carb-free just isn’t enough? I have lots of patients who limit their carbohydrates but still have elevated blood sugars. How do you get more power? Sorry, Batman, it’s time to call in Superman. (Don’t bother about the Wonder Twins – they were always useless. One of them would turn into a dolphin or something.) In a word, we need Fasting.

The study results are even more impressive when you look at insulin levels. This is very important because blood glucose levels are not the main driver of obesity and diabetes. Insulin is the main driver. The entire strategy of weight loss hinges upon lowering insulin.

Looking at total area under the curve, you can see that carb free diet can reduce insulin by roughly 50% but you can go another 50% by fasting. That’s power.

This makes sense, of course. A carb free diet will still contain some protein which will increase insulin. The only way to get lower would be to eat 100% fat – which is largely an artificial construct. That is, we don’t generally eat pure olive oil as a meal or pure lard. Bulletproof coffee is certainly a great ‘hack’ but it’s hardly been tested by thousands of years of human history and millions of people. Fasting has survived this test of time. It is Anti-Fragile. How? The more we eat processed and ultra-processed garbage and pretend it is food, the more we need to fast. If you eat a lot of fast food (foods that are ultra-processed and send insulin skyrocketing) the more you need to fast (bring those insulin levels back down).

And NOTHING beats fasting for bringing down insulin. It is simply the fastest and most efficient method of reducing insulin. Luckily, it’s also not as hard as most people believe it to be.

What about glucagon? Remember that glucagon is sort of the opposite of insulin. One of insulin’s main physiologic role is to suppress glucagon. Dr Roger Unger did much to explore the biological role of glucagon and often considered it the most important. However, in this study, it had no clinical relevance at all. In dealing with patients, glucagon also plays little or no role.

Let me explain. Insulin causes weight gain – so giving insulin causes weight gain. Does reducing glucagon cause weight gain? Not really. Does increasing glucagon cause weight loss? Not really. Sure, glucagon plays a primary role in rat livers, but I don’t really care. I care about humans.

The bottom line of this study is to reinforce what we knew already. Insulin is the primary (but not the only) driver of obesity. Therefore, for most people, reducing insulin is the best method of treating obesity. Carb free diets are a powerful method of reducing insulin. But if that doesn’t work, then intermittent fasting offers an even more powerful strategy.

In type 2 diabetes, you can reduce blood sugars by 50-70% by carb free diets. You can reduce it another 30% with fasting. So, if we already know how to reduce blood sugars in T2D with dietary strategies – why do we need medications at all? Here’s the answer, of course. You don’t. Type 2 Diabetes is an entirely reversible disease.

97 Responses

  1. Rickard Hökros

    Hi Jason!

    Thanks for the interesting post! 🙂

    I have a question I’m wondering about which I really cant explain why it’s happening…
    I’m on a LCHF diet and I’m also doing a 24 hour fast twice a week.

    My first meal every day is about 13 o’clock and I always eat a bulletproof coffe with 4-5 raw eggs.
    Usually I’m going to the gym between 11:30 to 12:30 and practising quite hard.

    The days when I’m eating lunch my blood glucose is always lower than when I fast.
    Usually it’s between 4.9 – 5.5 when eating and when fasting it’s about 6.
    Do you have any explanation why my body reacts like this?

    When I’m doing a long fast for five days then my blood glucose goes down to 4.5-5 during the last days of fasting.

    Best Regards

    /Rickard Hökros

    • That’s interesting. When are you measuring your blood glucose levels, relative to when you are eating?

      Overall, you’re getting higher blood sugar levels than I am. After fasting 4.5 days, I’ve had levels of 63 (3.5) and 74 (4.1), and “normal” 12-hour fasting levels of 97 (5.4) or less. However, I don’t have a machine to test and these results are from blood drawn from my arm and sent to a laboratory.

      I am also not diabetic.

      • Rickard Hökros

        Hi Bob!

        I’m a type 2 diabetic.

        Usually I’m taking the blood sugar before I’m having dinner, about 6 PM.
        By that time I’ve been fasting 24 hours if it’s been a fasting day, otherwise it’s about 5-6 hours after breakfast/lunch.

        • Hi Rickard,

          So, your blood glucose is lower after 5-6 hours after eating than it is after 24 hours? Are you using insulin (or other drugs)? If so, when do you take the insulin (or other drugs)?

        • My guess: Fasting is mildly stressful, raising cortisol levels which in turn raises blood glucose. Eating a low carb meal will mean that your cortisol levels fall and so does BG and the low carb meal does not raise BG much.

        • Jason,
          I have a gout condition which I take meds more. I have done 24 hour fasts and my uric acid spiked.
          Is this common?
          Is there a remedy to avoid uric acid increases?

          Thanks for your help… John

      • I am not a diabetic, but my experience is very similar to yours. I tried a 72 hour fast just to see how the ketone and glucose levels changed. The glucose fell to a low point after about 36 hours; I think it was in the upper 50’s and the blood serum ketone level spiked to just over 6 mmolar. At 72 hours the glucose had come back up into the 60’s and the blood serum ketone level dropped to just under 5. I guess in my case 3 days is long enough for things to come to some kind of steady equilibrium. It is too bad that I cannot measure insulin levels without having blood drawn, and paying for the test. It would have been very interesting to see the insulin variation over the 72 hour period.
        As usual my doctor has absolutely no interest in any of this. In fact, I now refer to the healthcare industry as the medical business because in the majority of cases it has little to do with human health,

        • Samuel, I took an insulin test after fasting 4.5 days, and it was <3 uIU/mL; a previous test with a "normal" 12 hour fast was 3.8 uIU/mL.

          I had to pay for both of these tests. My doctor, like yours, is uninterested in this and would rather proscribe a statin to me. Unfortunately, this test is too expensive to have done daily.

    • You are training hard. Do you measure your BG within hour or so after training? It spikes your BG.

    • What’s bullet proof coffee?

      • It is regular coffee with added fat…

        Here’s the recipe I use:
        2 cups freshly brewed coffee (can be green tea too)
        1 Tbsp MCT oil (this is derived from coconut oil, but contains only the smaller fatty acid chains C8 & C10)
        (you can also use Coconut oil – your choice)
        3 Tbsp Organic Coconut Milk (the canned variety with full fat, 11%) You can use full fat cream – that’s whipping cream 36% fat.
        1 Tbsp Chia Seed
        1 Tsp Vanilla Extract (non alcohol) or Vanilla Bean Powder
        Avoid adding any sweetners – this is tasty and sweet enough with the coconut oil and cream.

        Throw everything into a blender and blend on High for 1 minute – Enjoy.

      • Bullettproof coffee, as originally designed, is black coffee with 1 – 2 tablespoons of grass-fed butter (Kerrygold is good) whipped into it. You can also add coconut oil or mct oil.

        Jenny’s recipe sounds delicious,, but she uses Coconut Milk and/or chia seeds both of which add carbohydrate to the coffee, which is not original Bulletproof coffee. The idea behind Bulletproof coffee is to have only fat and 0 carbohydrate in your coffee throughout the morning up until 2:00 when you might then break your fast, if you’re doing, say a 16 – 18 hour IF regimen. If you are doing a fat fast, it is still recommended that you refrain from coffee after 2:00 p.m., but you can drink decaf tea with butter/coconut oil/mct oil mixed in. Bulletproof coffee was designed with the idea in mind that by having 0 carb, and 0 protein in the coffee, insulin would not be stimulated. Dr. Fung said in his last post that the research on this is still not clear. Nevertheless, Bulletproof coffee fits in well with a LCHF diet.

        • So is high fat coffee (bulletproof or with heavy whipping cream) allowed during a fast?

          • The short answer is “no”. Foods that contain fat are not allowed if you are doing a true fast.

          • Kelley Spada

            However Dr. Fung in the Obesity Code says some cream in coffee doesnt break the fast.

        • Butter is churned cream. You can buy a container of cream, empty some out to make room in the container, shake it for 15 minutes or so, and out comes butter. Why go to the trouble of using butter in coffee rather than just adding cream?

          • Ermias

            The milk solids that remain in cream will add some carbs, whereas butter has zero carbs. That’s the major difference for those concerned with keeping carbs as low as possible.

            I’m also curious: in what way is butter more trouble than cream?

        • seebrina

          I hit my mid 40’s and was gaining weight even after being low carbs for many years. I watched the doctors kill my mother with diabetes ‘treatment’ so i knew then atkins was on the right track. then i started menopause continued to gain and couldnt lose a pound. Started a keto diet and bought a glucometer. i carry about 40 extra pounds alot of which are on my trunk area so i know i have alot of visceral fat which concerns me greatly. I am VERY insulin resistant also very inflammed and i couldnt figure out why and the next step would have been diabetes. And my fasting bg was around 115 and i’d like to see it come down under 90 or so. No weight loss on keto which led me to dr.fung and i started 22 hour fasts everyday. very little weight loss and my numbers rose to 125 fasting which he explains happens in the beginning. I am very impatient to get this weight off since i’ve been fighting it for years which has led me to the Bulletproof rapid fat loss protocol. which is bulletproof coffee only for 6 days and then a refeed on the 7th day. repeat until… Theory being the fat doesnt raise insulin and actually helps the body burn your body fat. Today is day three and iam doing well and have lost 9 lbs in 2 days While not being hungry . I know its not all water because i already went through keto and a horrible keto flu for 2 weeks and my hands stopped swelling finally. Would i like to eat? Yes, but i want this weight off more and its more a mind thing than actual hunger. So tired of this losing battle. My fasting was 117 this morning so moving in the right direction. I know its extreme but ive tried everything else and need to get this visceral fat off and my numbers down immediately. And then i i will stick with keto intermittent fasting as a life style. Just thought this might help someone especially us women who have a much harder time losing weight.

          • Patricia Richker

            Hi, Seebrina —
            I have read hundreds of posts and yours is right-on for me. I am 77 years young, have to lose 125 pounds. Been on every diet, had surgery, etc. I know LCHF is the way to go. Have read/listened to everything on Diet Doctor and Dr. Fung. I was doing the LCHF for a month and gained a couple of pounds. Long story short, I started 24-hour fast today. I was going to do it for a week and then every other day. I was looking specifically for the answer to my main question and you answered it: “Theory being the fat doesn’t raise insulin and actually helps the body burn your body fat.” And you lost 9 pounds in two days. I do NOT have diabetes, a miracle in itself. I am very healthy, take no medications.
            Since this is working for you, what is your plan, i.e., how many days fasting and then LCHF? And when you do eat, what exactly do you eat?
            Please forgive my lengthy response. I don’t mean to impose on you, but any response would be appreciated. Thank you so much!!!!

          • I can so relate. I gained 40lbs when I turned age44 in about 6 months. I had no clue about blood sugars, insulin etc.. I am 52 now and taking the slow road. Keto worked short term for me and I stalled out after a 15lb weight lost and felt horrible. After a hysterectomy I am doing low carb but not keto. I am fasting from Sunday dinner to Tuesday dinner each week and losing 1lb per week. Slow going but it is working where as nothing else ever worked.

    • Dr. A.E. Kagal

      This is due to “Reactive Hypoglycemia” which is a well known phenomenon in pre diabetic people.

    • Rickard, I experience something similar when I fast often having higher blood sugars than when I’m eating lots of vegetable fiber with my LCHF eating. That can be discouraging, especially since I don’t feel all that great when I fast (42 hours, haven’t gotten beyond that before my stomach hurts too much for me to want to continue.) I’ve been doing this program for 3 months, so I figure it just takes time… perhaps my organs are releasing fat at a faster rate when I fast, and that’s causing the (modest) increase in blood sugars…. and those blips in my fasting blood sugar levels might be a sign that I’m healing.

      I have a rather severe case of type 2, and in general the blood sugar numbers are coming down, way down, just not at ‘perfect’. I wonder, why don’t you get a blood glucose meter and testing strips? Without being able to monitor my blood sugar several times a day, I don’t know how I could have made these changes! While it’s extremely annoying if you have to pay for these supplies yourself, you get so much more information for your buck : ) or pound : )

    • Rickard, I have T2D, and recently attended a group nutrition class for diabetics, and one person in the group brought up a very similar issue. His blood sugar was always higher in the morning prior to eating. The answer we were given was that when the body is in a fasted state, the liver automatically releases glucose into the blood stream until we begin to eat again. When we eat, the liver stops releasing glucose, and our blood sugar may actually decrease temporarily.

  2. Wow, I realized fasting was more effective than carb restriction just from my own experience with each, but TWICE as effective?

    Now that’s amazing !

    p.s. – I love your latest video on youtube (therapeutic fasting), one of your best !

    • Bernadette

      There is a new video on YouTube? Yay! Loading it now. I also appreciate Dr. Fung’s link to the Anti-Fragile book — interesting stuff.

    • I wasn’t quite sure how to process that info.

      Does that mean that it’s just as effective to eat carbs and fast every so often? Or is he reccomending a fasting period in addition to a low carb plan?

  3. honeycomb

    Can’t wait to read your book .. it’s on the way (all 3 copies) .. should’ve got it on kindle at the same time .. good stuff as usual.

  4. Laura Joan Day

    thank your Dr Jason Fung–“you”— are a super Hero , thank you for all that you do to educate us.

  5. Thank you once again Dr. Fung. Straightforward, understandable information – no membership required… I appreciate your work!!

  6. Wenchypoo

    You might rightfully ask yourself, if the good folks at the ADA knows that their diet sends blood sugars skyrocketing upwards, why on earth would they recommend it? Are they trying to kill us? Unfortunately, the answer is yes. They are trying to kill you.

    Thank you for the confirmation and having my back–I’ve been saying FOR YEARS that they were trying to kill us!!

    The more we eat processed and ultra-processed garbage and pretend it is food, the more we need to fast. If you eat a lot of fast food (foods that are ultra-processed and send insulin skyrocketing) the more you need to fast (bring those insulin levels back down).

    Garbage in, garbage out–right?

    In type 2 diabetes, you can reduce blood sugars by 50-70% by carb free diets.

    However, carb-free diets (also known as Zero Carb) employ a hell of a lot of meat, and lots of meat = protein overload = gluconeogenesis and mTor problems. The only no-carb, no-protein, and no-gluconeogenesis substance I can think of (besides fat) is water. So to get 100% control of our blood sugars and insulin response, we should live on fat and water in between bouts of fasting?

    • @Wenchypoo, you don’t need to cut out protein or even eat a lot of meat on a super low-carb diet. Sure, you mustn’t overdo protein, but there’s a big range between not overdoing something and cutting it out completely. Plus, low GI veggies are needed as well, so it’s not just fat and water. I think Dr. Fung’s book should explain more (I should get it today), but another good source of food/exercise recommendations is Dr. Ted Naiman.

      • There are essential amino acids and essential fats, but there is no essential carbohydrates, or it is a completely optional nutrient in the human diet.
        That says science.

        • Super Hans

          And yet, complete carb elimination leads to deficiency-like symptoms.

    • When you are not eating any carbs, you have a bigger leeway for how much protein you can eat without raising fasting blood glucose. My minimum requirement for protein is about 50 gm, but I can easily eat twice that without it affecting my fasting glucose. How much a person can eat without negative repercussions depends on their degree of metabolic damage when starting a Zero Carb diet. The best way to determine your personal limit is to test your fasting blood glucose. If it is over 90, then you are likely eating too much protein for your particular metabolic situation.

      • If you have a full-blown case of type 2 diabetes, you cannot extrapolate that a fbs of over 90 means you are eating too much protein. I started with a fsb of 268. With LCHF eating, it immediately (within 36 to 48 hours) dropped by over 100 points. That was a little under 3 months ago. With continued LCHF eating and intermittent fasting, it is slowly coming down from there, but the progress, even when I fast completely for 42 hours, is slow. To say from this that I am overeating protein (I don’t have a big taste for it, and my consumption is moderate) is not only wrong, but it’s discouraging and could make it more difficult for someone eating LCHF to continue with this way of eating. Please be careful about doling out proclamations beyond your own personal situation! It’s damaging towards many of us who are dealing with a more severe situation.

        BTW, all of my diabetic complications have been greatly reduced through this way of eating, including the debilitating neuropathy in my legs. And my morning blood sugar has rarely been under 130 during this time.

        • thank you for your words of wisdom!! my experience is very similar.

    • I’ve discovered that low carb does NOT automatically mean one has to overdose on protein to feel full. I use a lot of low carb veggies as my “filler” in a meal, about a cup or more, then moderate protein (a small palm-sized), and a reasonable amount of fat. Say, a small wedge of cheese, or good oil in a salad. Just saying, low carb doesn’t mean one has to eat ridiculous amounts of protein.

  7. Dr Fung I love your blogs – thanks Darren for reference to therapeutic fasting. I just watched it. I have been working with Megan and new to fasting having joined your remote program since mid Jan – no question it is effective with IMMEDIATE results. Can’t thank you and Megan enough for all your efforts to educate and support people like me through your blogs/videos and IDM program.

    Question 1 : In reference to the slide you presented by Zaunder 2000 (min 23:49 on video) with glucose levels dropping and insulin dropping but levelling after 4 days of fasting, is there a “target” glucose level where you can be assured that insulin is low enough ?
    Question 2: this graph suggests the you need to fast beyond 2 days to get insulin to drop. I know you advocate longer fasts but how can intermittent fasting ( 24 hrs or 36 hours fast) result in the same drop in insulin after 4 days? I am measuring BG level and assumed insulin level was coming down but really don’t know what insulin is doing.
    Thank you Heida

  8. This is great information. I can’t wait for the day my diabetes is gone!

  9. So, what about the High Carb, Low Fat (HCLF) option? The three options you discuss here are SAD diet, LCHF, and fasting. Do you plan to ever discuss the 4th and easiest option? Or have you already discussed this in a separate article that I may have overlooked?

    My understanding of the HCLF theory is that the root cause of diabetes and obesity is really insulin’s ineffectiveness when intercellular fat keeps the locks jammed and keeps cells resistant to insulin. If one can eat whole food high carbs like rice and potatoes to satiation as a base of the diet, with low amounts of whole food fats like avacados & nuts, and non-animal proteins like beans, legumes, nuts & seeds, with plenty of good healthy mineral-rich greens and some fruit, why in the world would one want to fast!? or to eat so little carbs as to be tired and depressed all the time?

    • Rickard Hökros

      Hi Michwoo!

      What do you mean when you say that you will get tired and depressed on a low carb diet?

      Personally I feel at least ten years younger and full of energy.
      My immune system has never been as good as it is now when eating lots og vegetables, fat and proteins.

      • I think individuals have varying tolerances for carbohydrates. I, for one, lost weight on a calorie-restricted low fat diet but it was a struggle to resist hunger and cravings. I didn’t have a particular carbohydrate target at first but the calorie restriction meant that I must have been eating less carbohydrate than before.

        When I experimentally reduced carbs a little my glucose levels dropped a little. When I began intermittent fasting, glucose levels dropped a lot and I lost more weight without even trying. By then I was still averaging 100g of carb a day with wide variations.

        Over the last three months I’ve got down to a more consistent 50g or so carb a day and my glucose has dropped even lower and become stable around 4mmol/l (=72) except when I stray on special occasions.

        Every time I saw an improvement I thought I had gone as far as possible, but I continued to surprise myself whenever I tweaked things a little more. There is so much information and wisdom in Dr Fung’s blog and lectures that I couldn’t have absorbed all of it at once. Megan’s online guidance in the Intensive Dietary Management Program has given me the confidence to continue trying new things. I have followed their insistence on discussing all my changes with my own doctors who have monitored my blood results to ensure I’m not harming myself.

        Thanks Jason and Megan!

    • Michwoo,

      I find fasting to be by far the easiest option (I do 18/6 IF), and low-carb actually helps it. If I try to fast after eating a lot of carbs I feel sick, but if I have kept my blood sugar steady with low GI foods, it’s a snap. Not having to worry about meals is much easier for me and frees up time and energy for other things, and I feel fine.

    • Because we have Type 2 Diabetes and LCHF leaves us feeling amazing. No more expensive and possibly harmful medications. Rarely feel hungry. No more IBS. I feel happier and more positive not eating carbs and sugar than I did on the suggested diet for Diabetics which is CRAP! and always made my BGL too high even when on medications.

    • sten Bjorsell

      Hi Michwoo !

      If you read an earlier article from December last year by Dr Jason you will find a completely different explanation of “root cause of diabetes” that puts the whole thing in a different perspective. Here is a link: https://intensivedietarymanagement.com/insulin-resistance-good-t2d-7/

      Diabetes-1 causes cell glucose starvation as you state. Jason Fung argues that in Diabetes-2 cells are instead overloaded with glucose. See article at the link. This agree well with long term diabetic damage as blindness and neuropathy. Failed studies with stricter glucose control also supports this, showing shorter life span instead of expected longer. But I cannot find any research that supports the main trust in the article. Links, anyone?

      • Diabetes is mainly uncontrolled fatty acid flow out of adipose tissue. In other words severe adipose insulin resistance. This directly causes elevated hepatic gluconeogenesis, so what other cells see is both an overabundance of fatty acids and glucose.

    • I also find it was exactly the opposite: going on a low carb, high fat diet cured my tiredness. In fact, when I was on a low fat, high carb diet, not only was I hungry all the time, with huge mood swings (bordering on depression), but I got seriously tired at 3pm/1500 every day. That’s not been the case for years, since I’ve been on low carb for almost three years now. I’m literally never tired, never have mood swings/depression, and have tons of energy. Intermittent fasting has helped even further with this.

    • I ate the diet you describe for 15 years Michwoo, and it very nearly killed me, both the starch-based version and the 80/10/10 raw version. All I did was get sicker and sicker. A diet high in plant foods is not ideal for many people like myself. And a diet low in fat, especially animal fats, creates deficiencies in fat soluble vitamins. Read Deep Nutrition by Dr. Cate Shanahan to gain a full understanding of this. I love fasting and employ regularly. I have tasted anywhere from 1 to 26 days in length. It is the single pay powerful therapeutic modality I have every encountered. Eating the low-fat, plant-based diet you described does not do anything even remotely similar to a water-only fast. I know because I have experienced both approaches side-by-side. Zero Carb, practiced in conjunction with water-only fasting, is a dynamic way to improve one’s health. I know this as well because I now practice both approaches side-by-side. There is simply no comparison, Zero Carb and fasting win hand’s down.

      • I agree with you, Esmee. For me, nothing beats zero carb plus fasting. Have never felt better or been healthier. I’m so grateful for the work & effort of Jason, Andreas, & you – your site is a wealth of information, as well.

      • ” I love fasting and employ it regularly. It is the single pay powerful therapeutic modality I have every encountered.”

        Well stated mon ami–à votre santé. I agree completely.

    • Sorry for the typo’s, no way to edit my comments. Hopefully, you can figure out what I meant.

    • I am glad that Mitchwoo raised this question. The boyfriend of a patient of mine completely rejected my suggestion to try a LCHF diet (he is obese and a Type 2 diabetic) and decided instead to go with the recommendations of another doctor. I took a look at the recommended diet and in summing up:
      Total 2000 calories per day of which 240g carbs ( pasta and or rice and some veg.) , 200g protein and the rest , some PUFA fats making up the difference. Also, 30 minute of walking per day.
      After one month on this diet, he has lost 5 Kg and she tells me that his blood glucose is 100 and he is off of his insulin.
      So is there any value at all in this HCLF diet or are these results just a fluke.

    • See Dr. Fung’s post of Oct 22, 2015, “Thoughts on the Pritikin Diet.”

      He discusses HCLF vs LCHF

      The key: insulin

  10. Great movie picture! Really appreciate the graphs. So glad I heard about Dr. Fung through Jimmy Moore’s Livin’ La Vida Low Carb podcast! Weekly 24 hour fast and almost daily 16 hour fast have put a spring into my step! Thanks Dr. Fung!

  11. Excellent
    And remarkably simple when explained & you think about it.

  12. […] Power: Fasting vs Low Carb – Fasting 26 […]

  13. I sometimes think Dr. Fung’s definition of intermittent fasting is not the same as many Americans would define intermittent fasting. Here intermittent fasting means 16/8 20/4 22/2 etc..

    • In the interest of clarification, what makes you think that, Wolf? As an American, I recognize *intermittent* fasting as being intermittent, and *fasting* fasting as extended, as in of the sort practiced by some religionists and some political protesters, as in Ireland in the 70s. I am quite sure that I do not speak for every American, but I suspect that the majority would define those terms similarly to how I do. That said, I am often surprised to learn that in some groups, several fellow Americans at any given point do not realize that veg fall into the nutritional category of carbohydrates, or, if they do realize that, see no nutritional distinction between a wedge of cabbage and a bowl of refined pasta.

  14. Jude from Australia

    Being leptin resistant seems to add another obstacle to losing weight even with intermittent fasting and low carbing. I’m finding it virtually impossible to shift any weight at all. 🙁

    • Hi Jude,
      I’ve had a lot of difficulties too in shifting weight, esp after an initial 12kgs drop in the first 4 months starting LCHF. I’m now into 15 months of LCHF. I sat at the same weight for 7 months. I refused to revert back to hclf, so kept at ‘it’. After reading and listening to Dr Fung I realised that I was doing a short fast every day by not eating breakfast, as I wasn’t hungry in the mornings. My hunger kicked in circa 11am -1pm and I also had a small dinner that night. Realising that a lot of my hunger at night was ‘head hunger’, I started to drop off the night dinner most evenings. Therefore increasing my fasting hours. Slowly but steadily my weight loss started to move agin, albeit slowly, but it’s happening. I feel much better too, less tired, clearer mentally and overall quite happy in myself. I see all the ‘time’ I’ve been eating LCHF as a ‘healing process’ and in doing so allowing my body to do ‘it’s thing’ to work with my daily needs where food is concerned. I’m learning to make food work for me rather than, I need to get the food into me because I just can’t do without it – cravings. So I feel that a lot of my problems one of them- leptin resistance is quietly being resolved. I’m learning by living this LCHF way of life- it takes time.
      Thank you Dr Fung. Cheers Jen.

  15. Dr. Fung, thank you very much explaining the science so well. Loved the Superman-Batman analogy.

  16. Peter Polvi

    My diet is LCHF and it has been so for 4 months, I exercise a lot, not overweight and IF 16/8. I follow my blodglucose with a dexcom G4, never under 6.7 and also never over 9.7, I will do a 24/h fast and see where the numbers end, my mother and her sisters has Mody 2 and I think maybe I have it too. The rise or the drop of my blood glucose is very slow, no spikes.

    • sten Bjorsell

      The high blood sugars after months with LCHF do not indicate strict LCHF. But do try the fasting and write again! I found when I took a brisk walk in the middle of the fasting day the blood sugars rose just after, but dropped considerably an hour later, with maintained energy as fat was burnt. I like the idea with autophagy through fasting to clear out waste and rebuild.

  17. Thanks Jason for this excellent post.

    When I look at the Nuttall et al. paper I see a noticeable glucagon rise after the high CHO meals. Perhaps this wasn’t significant because of individual variation and sample size, or wasn’t the measurement of glucagon they were looking at.
    But, assuming it’s there, this is going to produce post-prandial glycogenolysis, which has been noted in other studies in T2DM and which is suppressed on a carb free, high fat diet.
    This doesn’t seem to require adaptation to the diet – like the dietary input of glucose, it seems like a low-hanging fruit of carbohydrate restriction for control of serum glucose

  18. […] intermittently. A low-carb diet is very effective in minimizing insulin response but fasting is even more effective. Nothing moves the dial in terms of my weight or waist measurement like fasting. Remember […]

  19. Dr. Fung (superman), yes! And Amen! This is so true and I was able to reverse diabetes by means of LCHF/Fasting. It works! I used to take several medications, my A1c was 8.5 and began high blood pressure meds due to my diabetes. My liver enzymes were elevated as well. My last A1C after a yr of LCHF/Fasting was 5.1 can’t wait for my next test. No more Blood pressure meds or diabetes meds. I’m healthy, my lipids are amazing. So, thank you!

  20. Your comparison is only over a 24 hour period. It feels like an unfair comparison because the fasting group is not going to fast every day where the LCHF group is eating that way every day. What would the results look like if you compared fasting to a LCHF diet over a longer period of time? For the fasting group, the reduction in glucose and insulin is going to be 100% for one or two days a week, but the other five or six days they will have no reduction. This makes the weekly average of only 14-29% reduction. By contrast, the LCHF group is going to have a 50-70% reduction every day which puts the weekly average in the same range. So in light of this, which is the better plan? Is there any idea of how long the beneficial effects of a single day fast lasts?

    • Hmmm, Etai, I along with the others I know who fast, do so every day. I fast for 18-19 hours, and eat in a 5-6 hour window. That is seven days a week, week in and week out. For me that is only three weeks so far, but I have peers who have done for months and onto years now.

      • I get that, but you’re not fasting for a 24 hour period like the data in this article is referencing. This article is trying to compare no eating to being on a LCHF diet which is what I have problems with. There are many different eating patterns that fall into the umbrella of fasting and what you’re doing is not the same as in this article. Depending on what you’re eating you could be spiking your insulin levels on a daily basis. So my question still remains, how long do the benefits of fasting last once you starting eating again?

        • sten bjorsell

          I think that you after having seen later posts about waist measure see that the benefits will not last that long as long as the metabolic syndrome remains. It depends on how much visceral fat is left, or the waist/height measure, the measure of the extent of the metabolic syndrome. See the March 24 2016 post .

  21. Andrea Chang

    Hello, I’m on my 6th day of fasting. My starting weight was 83 kg (around 183 lbs). I started with juice fasting for the first 2 days and then changed to water. I got my weight today (on another scale) and it showed 83kg! Am I doing something wrong? I’m on birth control pills for my polycystic ovaries, would that have somthing to do? Also, my hunger hasn’t reduced.

  22. Andrea Chang

    At least I hope my insulin level has gone down a bit. It’s within the normal range but on the higher side. My sugar levels are good, though, so I have no problem with it. It’s always between 85 and 90

  23. Thanks. Fasting has worked for me. Combining it with low carb diet is even better.

    Some validation recently for the reversal of DMII:

    Very-Low-Calorie Diet and 6 Months of Weight Stability in Type 2 Diabetes: Pathophysiologic Changes in Responders and Nonresponders


  24. Artificial sweeteners:

    Hi Jason, have just been enjoying your new book. Was intrigued tolerance that artificial sweeteners raise insulin levels, even though they may not raise glucose levels. My question is, if insulin goes up, wouldn’t you expect to see blood glucose levels driven down?, ie further. Leading to hypoglycaemia?

    • sten bjorsell

      TeeGee, Interesting!
      The insulin rise is probably why it is often claimed that A.S. makes people hungry and craving food resulting in that they do not lose weight. Without knowing, they compensate for the lower blood sugar. A fruitless battle.

    • Axel de France


      In my understanding during normal homéostasie if blood glucose goes down with higher insuline level pancréas Will turn off insuline production and start glucagon production in order to compensate (gl this lowering (glycogénolysis or gluconeogenese)

  25. I wish we had a Reddit forum just for Dr Fung.

  26. John Hart

    I’m being pressured by both my endocrinologist and cardiologist to increase my insulin levels without restrictions to bring my BG down at all costs. I’m on LCHF and attempt IF but am discouraged by lack of results so will try Dr Fung’s suggestions. I appreciate his hopeful outlook

    • sten bjorsell

      John Hart!
      In my experience BG in mornings often goes up for DT2 with fasting. Search this Blog for Dr Fung’s explanation!
      You need to keep at a water fast at least for a week to see morning BG coming down. But add in daily Bone Broth also to avoid complications! Faster result with a walk every day to reduce glycogen in liver stores. Good Luck

    • Hi John, I’m not a doctor nor a medical expert, but I can share my own experience with T2D and IF. I’d read several sources that state that IF can help restore your body’s sensitivity to insulin. This is important to me, since T2D is basically due to one’s body becoming resistant to insulin. So I integrated IF into my routine, and have been doing so for nearly 3 months. My personal experience has been quite positive. I do 16/8 fasting 3-4 times a week, I don’t take meds, and I feel great. I can’t promise it will work for you, since everyone’s body functions differently, and I can’t say whether my insulin levels are higher. What I can say is that my body is more sensitive to the insulin it does have, meaning that my insulin is more efficient, even if the quantities have not increased. To me, it seems that increasing your body’s sensitivity to insulin would be more important than increasing the amount of insulin, but as I’m not a medical professional, this is something I’d encourage you to speak to your doctor about.


  28. lena, 6 lbs in a month isn’t bad. one pound a week is considered a serious target! nothing is wrong with what you’re doing. stick with it.

  29. David Wynne

    I have found LCHF difficult because I have to count carbs so carefully; and it’s hard to stay under 20g., but my loss has accelerated with IF.
    I have found IF easy. I fast 24 hours (dinner to dinner) twice a week. I do a 16-8 on two or three other days if I feel like it. IF works so well. I donthave to worry about undoing my progress like you do with LCHF.
    I never abandon LCHF but I don’t count. I keep to above ground veggies, no flour or sugar anything, no fruit; well, I do have dark chocolate if I want it. For others with ‘resistant’ bodies, don’t give up; follow DQ advice and use IF.

  30. I am a type 2 diabetic my blood sugar readings are 275-290 but I don’t take medicine. I am 45 and weigh 270 pounds and stand 5’6″ tall. I am wanting to fast but does anyone know the proper way to do it? i drink at least a gallon of water daily.

  31. Hi Dr Fung

    I was diagnosed as paediatric (with PCOS) 10 years ago. Nothing I did made it better, but luckily it never got worse. I have been doing LCHF for 4 months and I was so excited to go for blood tests, convinced that all my levels would be better. Got my results yesterday and I was absolutely mortified. Again, not better, not worse. It is as clear as day that IF, and probably extended fasts, are the only way to go. Thanks for all the perfectly clear expositions. You make biological science accessible!

  32. Hahaha, thanks autocorrect! PREDIABETIC!

  33. Hello, guys… I never limited alcohol but doing the Low-carb for a year and still lost 27 kgs /was 117, now 90 kg/, I am male 185 cm, 37 years old.

    Maybe I somehow managed to do it because of fasting – I never knew about it but somehow felt it is good, especially after a tough weekend with overdrinking…

    So after drinking if you fast for let’s say 36 hours… it explains my progress, right?

    And another question – if on 18/6 fasting, I am on it all weekdays, am I doing it wrong squeezing half a lemon in mornings with 400 ml of water? It surely gives me a carb or two but it do you think it is breaking the fasting period as I am usually only having lunch at 12 and dinner at 6pm.


    • 1. Test your blood sugar before and after the water.
      2. Run water/weight loss tests before and after 36 hour fasts with and without the lemon or any small meal.

  34. Hi!

    I’ve been fasting now for 42 hours and my goal is 21 days or as long as I feel fine. I’ve done longer fasts before up to 4 days and when I break fast I will just eat a small meal of what ever I want to eat. But if I manage to do 21 days how do I break the fast? I don’t want to eat fruits or juice, I want to start with LCHF right away. So can I eat a small meal of say pork and some broccoli?

  35. Great article. I utilize both HFLC and Fasting. My insulin resistance has been well under control for the last 5 years and after stopping the use of Metformin and Glimeperide I am no longer “sick” and got to stop worrying about blowing out my Beta cells. I have passed this info along to everyone that suffers from all forms of Blood Glucose issues. Most are firmly entrenched (brainwashed) in the “Allopathic Approach.” Personally I have little use for Allopathic Medicine.

  36. Dr. Fung, I am hoping you will respond as I want to make sure I can continue my fast. I am perfectly healthy, almost 54 y.o. and not on any meds. Never diabetic or any health issues. (Menses stopped in Jan of this year.) I have been eating ketogenically for years and testing both blood glucose and blood ketones regularly with Precision Xtra. I had about a four month period this summer where I wasn’t keto and gained back some weight (about 15 lbs. I was about ten to 15 lbs to goal when I took a break.) I restarted keto ten days ago and have been back in ketosis for about 5 days now. (Dropped 6 lbs. in 5 days then stayed same to now.) My morning BG is usually in 70’s when just low carb and in low to mid 60’s when keto. This mornings reading was 60. I decided yesterday after finishing my one meal at 6pm (I naturally IF all the time and usually only eat dinner, though lunch a few times a week) that I would try a 5 day fast. I only had a cup of black coffee this morning and water with pink Himalayan salt in it throughout day. I just tested my BG (usually don’t test at night) and it was 40! (Ketones this morning were 1.5. Running out of strips so didn’t retest tonight and know it is usually higher at night anyway, but used my ketonix and it was blinking red twice.) In the past I’ve done fasting but never saw BG under 45 and that was after 4 or 5 days and always after being fully keto adapted too. So should I be concerned? I feel perfectly fine, alert, etc. and know what outward signs to look for in that respect as to when I should end my fast. How low is too low? Is there a number I should watch for to know if I should end my fast? Ok to continue if I feel ok? Thank you so much in advance for your professional opinion.

  37. Can we all stop with the B******** Coffee? That guys products and ideas are worthless and usually taken from others.
    Put 1-3 tbsp of heavy whipping cream in your coffee, it blends with coffee, oil and butter does not.

    Also, having some broth for sodium or whipping cream really is not going to stop a fast.
    Test your blood sugar and water loss before and after a 36 hour fast using whipping cream and or broth and let me know when you see some large variance. I have not seen it.

  38. The Glucose Response Graph says it all. No food (fasting) and still the blood glucose remains low, level and steady. Insulin Response, same. I am convinced. Thanks.

  39. Does stevia break a fast?

Leave a Reply