Fasting and Lipolysis – Part 4

Insulin is the main driver of both obesity and type 2 diabetes.  The key to reversing both conditions is therefore not “How do we reduce calories?”, but instead “How do we reduce Insulin?”  There are almost no drugs that will do this.  There is actually two classes of medications that consistently reduces insulin – one by a lot, one by a little. Not by co-incidence, they are the only drugs that consistently reduces weight.

But the problem is that they are both expensive and have side effects.  Short of drugs, we need an efficient, effective way to lower insulin if we are to be successful in losing weight.  A diet low in refined carbs and sugar will certainly do the trick for some, but for others it is not enough. The answer, if you haven’t guessed yet, is fasting.Starvation

The classic descriptions of fasting physiology were written by Dr. George Cahill. We reviewed this in a previous post, but here’s a pictorial version. Essentially, fasting is the gradual shift of burning glucose to burning fat.

In stage 1, most of the body is using exogenous glucose.  By stage 2 and 3, glycogen (stored sugar) provides much of the glucose needed. Most tissues are still using sugar, but the liver, muscle and fat cells have started to burn fat.

By stage 4 and 5, glycogen stores have run out. Hepatic and renal (liver and kidney) gluconeogenesis is now providing all the glucose, but only the brain, red blood cells and the renal medulla (the inner part of the kidney) uses glucose.  Everything else has shifted over to burning fat.  By stage 5, the brain has mostly shifted to burning fat in the form of ketone bodies.  Only a small amount of glucose is needed for red blood cells.Triglyceride

You can see that the origin of the blood glucose gradually switches from exogenous (dietary) to gluconeogenesis made from glycerol.  Fat is mostly triglyceride, which contains one glycerol backbone and three fatty acids of varying lengths.

Most tissues in the body are able to use fatty acids directly as fuel. By stage 5, only the brain and red blood cells require glucose. So most of the body is now fuelled by fat, not sugar.FFA

You can see the effect of this in the free fatty acid (FFA) concentrations in the blood in response to fasting (also called starvation). The FFA levels in the plasma just skyrocket from almost undetectable.  Ketones (to feed the brain) are betahydroxybutyrate and Acetoacetate which also show an increase.

The triglyceride is broken down into the glycerol backbone and the 3 fatty acids. The fatty acids are used directly by the body. The glycerol goes to the liver and is turned into glucose by the process of gluconeogenesis. Therefore, fat is able to provide the necessary small amount of glucose for the brain, red blood cells and renal medulla. You do not need to break down muscle for this.

So, fasting does not really ‘starve’ the muscles of fuel.  Instead, scarcely available glucose is replaced with widely available fats as the fuel of choice.  That’s good, because the body is able to store virtually unlimited amounts of fat, but only a small amount of glucose. Mother Nature, again, has proven herself far, far smarter than us.

It’s analogous to deciding to switch from hydroelectric power to solar power in the middle of the Sahara desert. Just smart. If there is no glucose, we will burn fat. That’s really good news because if there is anything we really, really want to do is BURN FAT. For all the miracle cures pushed by Dr. Oz that don’t really burn fat, there is one that does – fasting.

We want to burn fat so that we can look like this guy – Brad Pilon (author of authoritative fasting textbook Eat Stop Eat). That’s actually true, even though this is a blatant and transparent ploy to put a picture of the shirtless man to increase female readership.  But hey! The internet is a dog eat dog world. Dog, mmmm….

Brad Pilon – Poster boy of fasting

One of the reasons why bodybuilders have a vested interest is that their sport demands extremely low body fat levels combined with high athletic performance.FFA2

The brain is now powered mostly on ketones.  This is a normal situation.  This is the way our body is designed.  This should not be confused with diabetic ketoacidosis where excessive ketones are produced in addition to very high glucose levels.

In that situation, there is lots of glucose for the brain to use. However, due to the pathologic lack of insulin, the body also produces lots of ketones.  The ketones are not burned for fuel, but instead pile up outside, like unused logs.

As ketone requirements go up, glucose requirements goes down.  In type 1 diabetes, both are very high and this causes a life-threatening problem.FFA3

Here’s a question I get sometimes. Can my overweight child fast? Seven hells, no. Here’s a graphical description of why. Children simply may not be able to produce adequate amounts of ketones. Even if they could, I sure as hell would not want to take that risk.

In fact, every major religion in the world requires fasting – but ONLY for adults.

In a more recent study of 4 days of fasting, virtually identical results were found. Let’s take a closer lookZauner

There are many interesting details here.  First, you will notice that fatty acids increase 373%.  Blood glucose drops from 4.9 to 3.5 – lower but still in the normal range, maintained by hepatic gluconeogenesis. Beta hydroxybutyrate increases 2527% percent! The brain is powered on ketones and the body is powered on fat. That’s the mythical fat burning – Burn, Baby, Burn!

Second, you can see that over 4 days of fasting, there is a continuous increase in norepinephrine, while epinephrine remains relatively stable.  The increase in adrenalin increases energy and prevents the decrease in resting energy expenditure (REE) or metabolism. REE increases more than 10%.  There is no metabolic shut-down.  Fasting instead revs the body’s metabolism. VO2 also increases slightly indicating a greater capacity of the body for physical exertion.


So here’s a summary so far of what fasting does for the elite athlete, or even the regular person.

1. Train harder – Increased adrenalin, increased VO2

2. Recover faster and build muscle faster – Increased growth hormone.

3. Burn fat – increased fatty acid oxidation.

4. Insulin goes down. This we will consider in more detail later.

This is all available to every person in the entire world, free of charge.  Not only do you NOT have to buy expensive supplements. You will save money because you don’t need to buy food. You will save time because you don’t need to cook or clean up.

If I don't eat, will I lose weight?
If I don’t eat, will I lose weight?

Will you lose weight? Well, DUH. If you don’t eat, you will definitely lose weight. So there is no question that this is an effective treatment of weight loss. There are virtually no circumstances where it will not work. Is it unhealthy?

The surprising answer is that fasting is extremely healthy.  There are a huge number of incredible benefits to fasting. Train harder, build muscle, burn fat. Love it! All legal and totally free! Sounds like a cheesy late night infomercial. Call in the next 10 minutes or I’ll double the price! Read this post today, or I’ll triple the price! (Okay, well this blog is free, too)

This is only the beginning – we haven’t even touched on the benefits to obesity, diabetes, cancer, and even the anti-aging effects.

Start with Fasting Part I

Continue to Fasting part 5

Start with Calories Part I

Watch the lecture “The Fast Solution” – The Aetiology of Obesity 4/6

59 Responses

  1. I am loving this series of posts on fasting.

    I do have a question tho’. If a person fasted for 5 to 7 days, and then returned to a very low carb diet with controlled proteins, how long will the benefits of fasting persist (fat burning, increased TEE, etc) after the fast?

    Thanks again!

    • larry davis

      Dr. Fung,

      Great blog. It appears that most of your discussions are specific to folks just starting out in these type of weight loss programs.

      I am a type 2 diabetic, lost 70 lbs and off all medicine, and on goal. I track my ketones daily, average 2.5, with a net carb of 20 grams per day. Regarding fasting, I have done limited fasting but with me my blood sugars get low forcing me to eat even though I may not be hunger. To be in the “starvation” mode then I believe the keytone levels need to be around 5.0 or higher.

      My questions is can a type 2 diabetic fast as long as you discuss without complications?

  2. Great blog Doc! I’ve done alternate day fasting in the past and had great luck with it – felt great, lost weight, inflammation was reduced. Now I’m considering doing full water fasting for a day. If I can manage that, I may try to extend it for longer. My main concern is how this may affect my gallbladder. I’ve had some pretty intense abdominal/side pain when I first started ADFing, and I understand it can be a common side effect of quickly losing. Is this a valid concern? Any suggestions on how to alleviate those symptoms and lower those risks? Thanks!

  3. Another interesting posting. I find all this fascinating.

    I’ve experimented with intermittent fasting and think it has worked well for me. First a little background. I’ve been on a diet program for about four years. The first 2 1/2 years was a struggle, I was eating too many carbs, things like oatmeal, Slimfast, protein bars, and so on. Then I read two books, the first was “Wheat Belly” and the second was “Grain Brain,” and came to the conclusion I was doing it all wrong. Good books in my opinion, but additionally has gotten out looking around for more information. Since then I’ve read more books and studied some good lectures on YouTube and now am going about this drastically different, including fasting.

    I used to eat breakfast because I thought I had to. I never used to eat breakfast and now I don’t again. I used to eat 5 or 6 times a day, again, because I thought I had to. Eating that much in my opinion is terrible advise, and in my case just made me hungrier. Now I just eat once or twice a day, and strangely, it’s not any more difficult than waiting for my next snack in 2 or 3 hours like it used to eat.

    Last year I lost almost 30 pounds, not bad for the third year in my opinion, and better than year two for me. Towards the end of last year I was eating twice a day, starting at noon and being done by 7:00 at night. Sometimes I had a snack in the afternoon, but tried never to eat in the morning or snack in the evening. Starting in January (2015) I made another change, I began skipping lunch three times a week and ate only once those days in the evening. In seven weeks I lost 11 pounds. Not bad for the final 10 pounds in my weight loss which I expected to be darn near impossible. I have to admit, I was surprised.

    Total to this date is 98 pounds, and only two to go to meet my goal. I’m a believer (I know, it’s an N=1) but for most people low-carb combined with intermittent fasting not only helps with weight but is very healthy. It’s been a process, an evolving point of view for me.

    My point is that I started off following convention dieting wisdom, low fat, eat breakfast, eat 5 or 6 times a day, exercise extensively, and in my opinion it was just plain wrong.

    For what it’s worth.

  4. If a person—because of their own concerns about reducing potential tissue damage resulting from high blood glucose of not yet controlled diabetes or to keep their physician happy—decided to use some insulin for now, would it be a silly protocol to take a little bolus insulin with meals on the basis that it’s short acting and will flush out of the system quickly while periodically fasting to improve insulin sensitivity long term?

    Also, what about longer-acting basal insulin such as NPH or insulin glargine, which many type 2s will be prescribed by their doctors? Are these just a terrible idea, or do they ever have their place when combined with an intensive lifestyle management program?

  5. There’s a lot of controversy regarding fasting not being ideal for females and better suited to men. I know I struggle with it, it’s not physical hunger/discomfort more of a brain deprivation mindset. Probably a fallout from xxxx years of low calorie low fat dieting has screwed my appestat. Anyway I’m slowly working my way towards a nutritional ketogenic diet which is giving me greater satiety and less obsessive re food, but again I read that fasting & NK is too much of a stress on body. I also read that being ketogenic is almost similar to being in a fasting state, so would have the same effects. Just wondering if anyone has any thoughts/experience re this.

    • Hi JW. I’ve considered several different ways to do intermittent fasting myself and have occasionally heard that it may be more problematic for women. One method talked about by Dr. Krista Varady is an every other day diet. I think she calls it time restricted eating, but seems a lot like an intermittent fast to me. There’s a good interview on YouTube by Dr. Mercola and he asks about the effects on women and Varady said most of the people in her research actually were women. I don’t remember any more of the details now, but if you’re interested go to YouTube and do a search for Mercola and Varady, it might provide some additional information.

      • Thank you for your reply Mike. I have her book! It’s a 500 cal fast every day. She has been researching fasting for many years, see Pubmed, and was interviewed in the Michael Mosley documentary. I believe his 5:2 diet was morphed from this as he couldn’t handle 500 cal every other day but could twice a week. I have done Krista’s fast, but for people with possible binge issues (like moi) it created a sense of stress and binging on the rest day. Keto is helping me recover from BED, hunger and obsession with food, so I may be in a position to give the 500 cal alternate day fast or even a Fast 5 19/5 type so at least I eat well every day. Let me explain, binge eating is not overeating, it’s a bulimia type frenzy without the purging. Risk factors are history of dieting 🙁

        • Hi JW, I see you’ve done your homework. I have to admit that on my one meal day I found 500 calories to be difficult. But if I kept my calories to less than 1000 calories I would still lose weight. My normal days (eating twice) I still watched my total calories and tried to keep calories to about 1500 to 1600, so still not eating too much. What I’ve done is just a progression of several years of working at this, little changes here and there, not necessarily what I’d recommend. And yes, I agree, it’s darn difficult at times. Good luck.

        • Thanks, Mike, for pointing out the Varaday interview with Mercola. I see at 10:05 in the video, Varaday’s applied for a grant to study something like the Lean Gains protocol of eating for only up to an 8-hour window every day (that Mercola was also talking about in this interview based on his clinical practice).


          • Mike S

            Great, glad you liked it.

          • Mike S

            Thanks for the link Christoph. I glanced through the “LeanGains on mice” and find it to be very interesting, I’ll be going back when I have more time. I also noticed a few other slides relating to Ancestral Health that look good too, and will be checking those more later. Thanks again.

  6. Oh and I just wanted to add thank you Dr Fung for providing this info for free for everyone. No books, no supplements, just top class information. You are up there with Bernstein in my eyes. Pity my mother isn’t around to take up your recommendations and live a few more years, but hopefully I can delay/stop this horrible disease afflicting me. Thank you

    • He’s writing a book due out next year, which I think is great. It would be nice, if nothing else, to have something to give one’s physician.

      • Yes and to have it all in one place so I can bookmark and highlight! Kindle and computer aren’t the same as a handy book for reference near bedside. Out of all the fasting protocols the window/Fast5 types fit better for me with a time of 2-7pm. That way I have a meal to look forward to. Also some of the best fast days I’ve had are ones that happen spontaneously or if I have a busy day no time to eat rather than a scheduled one. Although I’ve seen a recent study in the last few days, Mark Matson? found ADF fasts better than windows for autophagy, I just can’t find it at the moment, but in any case for insulin I guess any fast would do.

        • Yes, that’s another good video. Do a search on YouTube for TEDx Mattson. He talks about fasting and brain power.

          I also think that this site, Intensive Dietary Management, is a great source of information. Not only lots of good info, but interesting how he ties it all together, different topics like fasting, LCHF, exercise, etc. Excellent. Thank you Dr. Fung.

  7. fascinating!
    Is insulin-lowering drugs, also cause weight loss?

  8. Insulin is the main driver of both obesity and type 2 diabetes. The key to reversing both conditions is therefore not “How do we reduce calories?”, but instead “How do we reduce Insulin?”

    Question, though.

    If the goal is reducing insulin, shouldn’t we eat a whole-food plant-based rather than an animal-food based diet?


    Holt Susanne HA, Brand-Miller Janette C, Petocz Peter. An insulin index of foods: the insulin demand generated by 1000-kJ portions of common foods. Am J Clin Nutr 1997;66:1264–76. Retrieved from

    • Expounding a bit.

      There is clinical evidence that plant-based diets can improve insulin sensitivity, and that has even been done with simple carbohydrates. You doubt that reducing the percentage of saturated fat in the diet can directly reduce the fat within the organs and muscles that you’ve said in some of your lectures are associated with insulin resistance and diabetes (although we agree both Calorie reduction and fasting per se can and do reduce these fat stores in the muscles and organs). You believe that a tolerance to insulin is the main driver of insulin resistance and type-2 diabetes, rather than lipid building up within the muscle, liver, kidneys, and pancreas interfering with intercellular signalling and causing insulin resistance by that mode primarily.

      Assuming you’re right, and given the highly-insulogenic nature of animal protein, isn’t it more likely that a low-carbohydrate protein-rich diet reduces blood glucose and can help with reducing resulting tissue damage, but any improvements in diabetes are likely due to reduced Calorie consumption due to controlled appetite rather than an advantage of this type of diet in reducing endogenous insulin production?

      And that the seeming paradox of why high-carbohydrate diets treat diabetes can be explained, assuming your model is mostly correct and the plant-based physicians’ model of saturated dietary fat causing insulin resistance by the means described above is mostly incorrect, by reduced endogenous insulin production caused by switching from protein to carbohydrate†?

      At least to some significant extent?

      † as well as a reduction in Calories reducing the fat stores in the muscles and organs similar to how low-Carbohydrate diets cause a reduction in Caloric intake

      • I think you have the gist of it. A whole foods plant based diet should have an advantage over an animal based diet based on the insulinogenic effect of animal protein. However, there is the protection of the incretin effect on satiety. This model allows for the possibility of eating a high starch diet, low animal protein diet and still lowering insulin levels. It also allows for the possibility of eating a high animal based fat/ protein diet and lowering insulin, too. The key, is not carbs/fat/ protein but insulin.

        • Joel Furhman is one of the “plant-based docs”. He seems to share your views on insulin whether or not he agrees it’s the primary cause of T2 diabetes:

          Insulin for Type II Diabetes Makes Things Worse

          Out of curiosity, Dr. Fung, do you think medicinal insulin has a beneficial role in treating T2 diabetics, or that it does more harm than good and fasting and one of either a high-fibre or low-carb diet should be used by themselves?

          (Understanding, of course, that one should always make any therapy decisions in consultation with their own physician.)

          • I think insulin for type 2 diabetes is the problem, not the solution. I suspect that Dr. Furhman’s diet works well, if you can stick to it. My guess is that his diet lowers insulin and is therefore effective. But there are other ways to lower insulin too.

          • Thank you for replying, Dr. Fung. I was very interested in your opinion on “therapeutic” insulin for T2s.

            A friend of mine just gave me one of Dr. Fuhrman’s books. I see one huge point he makes, that I think is worth considering, is that the main cause of the complications of diabetes aren’t high blood glucose per se, but by the advanced glycation end-products resulting from high blood glucose. And that a monumental mark in favour of a micronutrient-dense plant-based diet is that the phenols and hundreds of other phytochemicals offer protection from AGEs over and above the mere insulin-lowering effect of the diet, which he fully agrees with you is essential.

            That seems to me a really good point.

  9. Christopher Dollis–one problem with your argument is that while we have a need to take in protein, whether it be from plant or animal sources, on an ongoing basis–not daily, but over the longer-term–we don’t have a need to take in carbohydrate on a regular basis. Carbohydrate is the low-hanging fruit, when it comes to an insulin-reducing diet, and it’s where the calories usually come from on a plant-based diet.

    Personally I think the part of the insulin index study that compares insulin under the curve to glucose under the curve is relatively useless. It serves to point out that glucose is not the be-all and end-all of insulin secretion–that’s all. Showing this ratio makes beef and fish look worse than oatmeal, insulin-response wise, but pointlessly so, This is a misuse of the data.

    Suppose a person needed 60 grams of protein a day, and wanted to get it all from beef. That would be about one and a half of the servings used in the insulin index study. Suppose they wanted to get that protein from oatmeal. That would be about five and a half servings. The insulin area under the curve given for one serving of beef is 7910, where for the porridge, it’s 5093. If we multiplied each of these by the number of servings needed to hit that 60 grams of protein, we’d get 11865 for the beef, and 28011 for the porridge.

    Peanuts have a very low insulin score, but it would take six servings to get 60 grams of protein–so still, about 3000 times six is 18000.

    Eggs, 20 grams of protein per serving, insulin area under the curve 4744, times three gives 14232.

    • Hi Donny,

      I find your analysis very interesting and wonder if you can share the source for the egg data as I have not find any specifically for eggs, and I’m very interested in it as during my journey dealing with IR I have found that eggs are probably the best protein I can have or at least, the one my body likes and metabolizes better, second is salmon. No blood glucose spikes and levels between 95-100 for long periods, even my FBG is much lower when I have salmon for dinner. I have never done eggs, I should try.


      • Donny, please see my above conversation with Dr. Fung, and especially my [first, if there are more than one] comment dated May 7.

  10. Rochelle

    Thank you for mentioning children not fasting. my children know my diet and even though I haven’t actively encouraged them to fast I told them fasting or missing a meal wouldn’t hurt them if they weren’t hungry (possibly the wrong advice) I also told my 15 year old son to enjoy his fast day when he forgot both his lunch box and his emergency canteen money (still not feeling too guilty about this he hasn’t forgotten his lunch again since) My question is how old is a child before they have an adults metabolism and can handle a 24hr fast my kids are a bit older than your example being 12, 13 & 15 years. my youngest is 12 and planning on doing the “40 hour famine” a fast to raise money for children in poverty can I assume that once a year wont actually hurt my child?? and can u do a blog on a healthy diet for children do kids need carbs unlike adults

    • Certainly by 12, it doesn’t hurt to skip a few meals or even a day at a time. I wouldn’t make it a regular weekly event, though. There are no essential carbohydrates, so kids no not ‘need’ carbs.

  11. Thank you for another detail packed post. You answer questions I didn’t even know how to ask.

    I have a question – but first I feel compelled to say something about the fasting program . I have
    been enrolled in the Intensive Dietary Management Program – Long Distance version for almost a
    month now . Unofficially, I was trying to follow what I could figure out about the program , for a couple
    of weeks more – so have been doing alternate fasting for about 6 weeks. My HA1c has gone from
    7.5 to 6.2 – and my weight – what can I say – it’s been great and effective.
    I don’t understand the controversy over the male/ female thing . I think diabetes is an equal opportunity
    offender. I don’t think my metabolic syndrome is any less or more because I am a woman . It simply
    needs to be corrected ( no small thing ! ) if I am to live a happy and healthy life.

    Here is what I AM curious about , however. I have noticed , on an especially long fast – which for me is
    64 hours – that my FBS shot up extremely high ; in fact, higher than it has ever been previously . Looking
    at some of your talks and posts – am I safe to extrapolate that might indicate the level of HGH that has been
    released ( since HGH and glucose seem to be correlated ) ? If so , how should we address this ? I am guessing
    I should perhaps hit the treadmill or lift some weights as soon as I wake up – to take full advantage of
    this HGH surge. Am I following the correct line of thinking – or am I off base here ?

    Thank you for everything . My husband and I both think you hung the moon – especially taking on the
    common conventions of traditional medicine ( and he is a physician ). Takes a lot of courage !


    • Hi Beverlee – To be clear, I don’t mind if people are able to figure out their own diets based on the principles we outline. Some people want more individualized help, and I cannot answer every question that comes up, so we offer the Long Distance Program. The charge covers the salary of our clinical educator. We don’t even break even on it.

      For your individual question, it would be best to post in the discussion forum or ask Megan directly, since it would be best not to have personal medical histories discussed in an open public space. Further, giving such quasi-medical advice on an open forum is very iffy from a legal standpoint, so I prefer not to do so.

      I can say in general terms, though, that HGH is one of the counter-regulatory hormones that would tend to raise blood glucose levels. Also, if you have reduced medications, that may also contribute to increased blood glucose. The raised blood glucose you have noticed is not unusual in diabetics and we see it alot. It does not happen in the normal, non diabetic situation.

  12. Dr. Fung,

    I’m very excited about this new series of posts. I have became a big fan of your website.
    Thinking about the fat burning during fasting, a question came to my mind, what happens with people with insulin resistance but not overweight? I mean lean people. Would it be safe to fast?
    Thanks and regards

  13. I was a bit unclear with parts of this. Is there any particular fasting technique that is NOT good for diabetics (on glipizide, not insulin) due to a buildup of ketones?



  14. HI Dr. Fung,
    Thank you for doing the blog and the videos.

    Is there any data on the safety of intermittent fasting for people who can’t really increase HGH production (no anterior pituitary)? Do you think HGH would need to be supplemented on fasting days for safety and/or to get the full benefit of the fast?
    thanks, Jeff

  15. webgrrrrl

    Well, Dr, Fung, you certainly succeeded re: Pilon. Hubba hubba he is hawt.

    And yet I don’t want to look like him. I hope you don’t mind. Being a girl, I want to look like Scarlet Johannsen. So all your advice on how to look like Pilon is great – for guys.

    When will you tell your female readers how to look like Scarlet? I want the nice body fat percentage she has – and the hormonal profile that tells her body to pack that fat in all the RIGHT places 😉 not the wrong ones.


  16. Dr. Fung,

    Can I fast if I am hypoglycemic? Or is it dangerous?

    • It is extremely dangerous. DO NOT continue fasting if hypoglycemic

      • Thank you for answering but why is it dangerous? Does hypoglycemia go away or is it permanent? I have taken a glucose tolerance test many years ago when I was about 16 yrs old. My parents never took it too seriously so I don’t know anything about it or what it can do. I think the nurse said I have it. I used to have dizziness cold clammy hands sweating blurred white vision nausea cramping shakiness shallow breathing etc. It would only happen in the morning when I was in the shower a few times. Hasn’t happened in years now.

        • Fasting lowers blood glucose into the lower range of normal. If you are already low, it can go dangerously low especially if you are taking medication

          • Wendy

            I don’t take medication for anything and I’m not diabetic. I think my blood sugar gets a little low eating low carb. I always feel like crap going low carb but it could be because I don’t give it enough time to do its thing. It’s difficult for me to stick with it. I wish I could eat fruit but I know I would binge on it. Oh well.

  17. Paul Arena

    Hey Jason,
    If I supplement with JUST branched chain amino acids during a fast will it raise insulin and thus nullify the therapeutic benefits of the fast?

  18. […] fat if it planned to burn protein instead. The answer, of course, is that is does not burn muscle as we discussed in the previous post. It was only a […]

  19. I’m sorry I’m late to the party here. But the following statement reminded me of an outcome of going very low carb as a T1: “By stage 5, the brain has mostly shifted to burning fat in the form of ketone bodies. Only a small amount of glucose is needed for red blood cells.” The outcome is that a T1 can go below 40 mg glucose/dl blood and still partially function.

    My experiences show that I’m definitely fussy and find it hard to concentrate with extreme hypoglycemia. Basically, my mind occasionally goes blank for short periods but then I can force it to function. This has allowed me to find glucose to consume even though I’ve just woke up at 2:00 am, tired and confused. After I’ve eaten whatever, I check my blood sugar and find it is still in the 30’s.

    Many other T1’s have made similar comments on low carb blogs saying they too have found that they can still partially function at very low blood sugars while following a very low carb diet. I know this is a very dangerous situation, but it is a world that I and every T1 lives in every day. So, I do not want this to be sweep under the table just because it is dangerous for the medical profession to discuss. This phenomenon could be a very positive benefit for all T1’s.

  20. Dr Fung,
    From your experience what do you think raises more the risk of ketoacidosis in type one diabetes adults? Being on a high carb diet or being keto-adapted and on a VLCHF diet?
    Thank you!
    Sylvain M

  21. When I have tried fasting my normal 76ish blood sugars rise into the low hundreds and won’t come down even after returning to a ketogenic diet, I’ve only gone two days in the past because of this. Will my blood sugars come down if I continue into the fast? I don’t have a gallbladder and I worry that prevents me from getting to far into ketosis while I am eating but I have had blood ketones up to 2 so figured that would be enough, but is it? I really need some insight into this problem.

  22. “In fact, every major religion in the world requires fasting – but ONLY for adults.”

    I guess that depends on how you define an adult – but I certainly don’t think nine year old girls are adults. I’ve worked as a temp teacher and met Muslim nine year olds fasting (but only girls. Does the boys start later?). They’ve problems to concentrate, and generally feel crappy. Maybe they don’t fast longer than the school day, and maybe they don’t fast all of Ramadan, but the fasting they do is hard on them. 🙁

  23. Dr Fung
    I started reading your blogs a few days ago as I am interested in fasting and CR and today I reached part 4 :). I noticed an error in the claim regarding adrenaline being increased when you fast. In the study you quote ( and table 3 from that study you state that there is an increase in adrenaline whereas in fact there is a gradual decrease in epinephrine (adrenaline ) but an increase in norepinephrine (noradrenaline). They both have an effect to increase blood glucose from breakdown of stored glycogen.
    Would you care to comment on this discrepancy??

    • I also noticed this where you state “Children simply may not be able to produce adequate amounts of ketones.” and you provide the graph showing levels of beta hydroxy butyrates (BHB) in relation to age and the fasting duration. This graph in fact shows that children and neonates can mount a very rapid ketosis state, for the same level of BHB of 2 mM is reached in 12 hours whereas an adult will need 24 hours or more to reach that level. In fact neonates are born in ketosis and the mother’s colostrum does not contain lactose until after several days by that time the ketosis is reversed.

  24. Axel de France

    Hello all
    Sorry to post After so long.
    M’y point of view is that adrenaline should go up as fast is kind of stress for our body.

  25. Nathan Gottschall

    URGENT!!!! I have been fasting for 9 days and still have an evening blood glucose reading of 105. I feel like something is very badly wrong with me. Can anyone provide some enlightenment? Dr. Fung, have you ever seen anything like this yourself?

    • Fung Shweigh inspired by Dr. Jason Fung is a Facebook private group where you can get information regarding blood glucose readings. Good luck

  26. Dr. Fung, I’m enjoying this series enormously but have a question. On the second graph above, relating the legend to the curves, it looks as though it’s the ketones that are skyrocketing, not the FFAs. The FFAs do increase but only approximately doubling. Also, isn’t epinephrine the same as adrenalin, not norepinephrine? Thanks for all you are doing.

  27. Hello Dr. Fung,

    So I heard you on Jenny Hutt’s show Just Jenny. It’s funny, because I was feeling so frustrated. I would do EXACTLY what you were talking about. Restricting my diet (which I am excellent at) and losing SOME weight, but then gaining it back. Now, at 53 even that doesn’t seem to work. I resorted back to a nutritional cleansing/shake program (Isagenix) but found that I gained weight and didn’t have the results that people claimed to have. Even after a 2 day cleanse I felt BAD.

    I think it was due to the Fructose in their shakes and cleanse drink. (I just read your cleanse book, just about all the way through and that’s what I’m guessing.)

    Anyway. I am just done with my day two IF. I fasted from about 7:45pm until 3pm yesterday. I felt pretty darn well. I did have one bulletproof coffee and a great workout! (HITT) Today I didn’t work out… but will tomorrow but fasted from 7:45pm until 1pm today. Do you think If I do that every day, eat during a small window with broth, soups, proteins and healthy fats I’ll lose weight?

    Also, my gym has great protein (vegan, but no sugar and all organic) and makes great shakes, could that break a fast as well? Thanks.

    You talk about not eating too much protein.


  28. […] Fasting and Lipolysis – Part 4 […]

  29. Claudia

    If I am doing intermittent fasting, i.e. daily 18 hrs. of fasting and 6 hrs. eating, when is the best time to exercise? Right before breaking the fast and beginning to eat? Or at some other time?

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