Fasting – A History Part I

posted in: Fasting, Health and Nutrition | 124

Fasting is a time tested and ancient tradition.  It has been used not only for weight loss, but to improve concentration, extend life, prevent Alzheimers, prevent insulin resistance and even reverse the entire aging process.  There is much to talk about here so we begin a new subsection “Fasting”.

There is nothing new, except what has been forgotten – Marie Antoinette

So the forgotten question of weight loss is “When should we eat?” We don’t ignore the question of frequency anywhere else. Falling from a building 1000 feet off the ground once will likely kill us. But is this the same as falling from a 1-foot wall 1000 times? Absolutely not. Yet the total distance fallen is still 1000 feet.


All foods will increase insulin levels to some degree. Eating the proper foods will prevent high levels, but won’t do much to lower levels. Some foods that are better than others, but all foods still increase insulin. The key to prevention of resistance is to periodically sustain very low levels of insulin. If all foods raise insulin, then the only answer is the complete voluntary abstinence of food. The answer we are looking for is, in a word, fasting.


The answer to this vexing problem lies not in the latest and greatest diet trend, but in the tried and true. Instead of searching for some exotic, never-before-tried diet miracle, we should focus on ancient healing traditions of the past. The waaaayyyy past. Fasting is one of the most ancient healing traditions in human history. This solution has been practiced by virtually every culture and religion on earth.

Whenever fasting is mentioned, there is always the same eye-rolling response. Starvation? That’s the answer? No. Fasting is completely different beast. Starvation is the involuntary absence of food. It is neither deliberate, nor controlled. Starving people have no idea when and where their next meal will come from. Fasting, on the other hand is the voluntary withholding of food for spiritual, health, or other reasons. It is the difference between suicide and dying of old age. The two terms should never be confused with each other. Fasting may be done for any period of time, from a few hours to months on end. In a sense, fasting is part of everyday life. The term ‘break fast’ is the meal that breaks the fast – which is done daily.

Fasting is one of the most ancient and widespread healing traditions in the world. Hippocrates of Cos (c 460 – c370 BC) is widely considered the father of modern medicine. Among the treatments that he prescribed and championed was the practice of fasting, and the consumption of apple cider vinegar. Hippocrates wrote, “To eat when you are sick, is to feed your illness”. The ancient Greek writer and historian Plutarch (cAD46 – c AD 120) also echoed these sentiments. He wrote, “Instead of using medicine, better fast today”. Ancient Greek thinkers Plato and his student Aristotle were also staunch supporters of fasting.

The ancient Greeks believed that medical treatment could be observed from nature. Humans, like most animals, do not eat when they become sick. For this reason, fasting has been called the ‘physician within’. This fasting ‘instinct’ that makes dogs, cats and humans anorexic when sick. This sensation is certainly familiar to everybody. Consider the last time you were sick with the flu. Probably the last thing you wanted to do was eat. So, fasting seems to be a universal human instinct to multiple forms of illnesses. Thus fasting is ingrained into human heritage, and as old as mankind itself.foodcoma

The ancient Greeks believed that fasting improves cognitive abilities. Think about the last time you ate a huge Thanksgiving meal. Did you feel more energetic and mentally alert afterwards? Or, instead did you feel sleepy and a little dopey? More likely the latter. Blood is shunted to your digestive system to cope with the huge influx of food, leaving less blood going to the brain. Result – food coma.

Other intellectual giants were also great proponents of fasting. Philip Paracelsus, the founder of toxicology and one of three fathers of modern Western medicine (along with Hippocrates and Galen) wrote, “Fasting is the greatest remedy – the physician within”. Benjamin Franklin (1706-1790), one of America’s founding fathers and renowned for wide knowledge in many areas once wrote of fasting “The best of all medicines is resting and fasting”.

Fasting for spiritual purposes is widely practiced, and remains part of virtually every major religion in the world. Jesus Christ, Buddha and the prophet Muhammed all shared a common belief in the healing power of fasting. In spiritual terms, it is often called cleansing or purification, but practically, it amounts to the same thing. The practice of fasting developed independently among different religions and cultures, not as something that was harmful, but something that was deeply, intrinsically beneficial to the human body and spirit. In Buddhism, food is often consumed only in the morning, and followers fast from noon until the next morning daily. In addition to this, there may be various water-only fasts for days or weeks on end. Greek Orthodox Christians may follow various fasts over 180-200 days of the year. Dr. Ancel Keys often considered Crete the poster child of the healthy Mediterranean diet. However, there was a critically important factor that he completely dismissed. Most of the population of Crete followed the Greek Orthodox tradition of fasting.

Muslims fast from sunrise to sunset during the holy month of Ramadan. The prophet Muhammad also encouraged fasting on Mondays and Thursdays of every week. Ramadan is the best studied of the fasting periods. It differs from many fasting protocols in that fluids are also forbidden. In addition to fasting, they also undergo a period of mild dehydration. Further, since eating is permitted before sunrise and after sunset, recent studies (27) indicate that daily caloric intake actually rises significantly during this period. Gorging before sunrise and after sunset seems to negate some of the beneficial effect.

So fasting is truly an idea that has withstood the test of time.  Arguable, the three most influential people to have ever lived agreed that fasting is beneficial.  If this was a harmful practice, do you not think we would have figured this out, oh, say 1000 years ago?

There are certainly people who don’t want you to fast.  There’s this happy fellow….


There’s also this lovely mermaid who doesn’t want you to fast…



And don’t forget this lovable Tiger….


So the question comes down to this.  To fast or not to fast. With regards to your own health, who would you trust?


Start here with Calories I

Continue with Fasting part 2

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

124 Responses

  1. I haven’t tried fasting yet, but I have been stretching out the time between meals — basically, not eating until I am truly hungry. That’s almost a bigger change for me than my low-carb, high-fat diet. I’ve always been a “clockwork” eater. I let the clock tell me when I should eat. Now I can see myself trying a fast. I do believe it would give me a sharper mental edge. In my high-carb days, I’d never have considered fasting. The thought of it was almost painful.

    • Bernard P.

      Jim, I can report on my own experience. I have done the 24-hour fast a number of times and it is suprisingly easy. The first time, I was a bit afraid of being too hungry or having headeaches, but the day passed easily.

      I only had a good cup of coffee after getting up (no sugar!), and the day went by pretty fast until it was time again to eat at 6.30 pm. I didn’t even feel the need to calm my hunger with water, tea, or bouillon.

      My wife has had the same experience. We are pleasantly surprised by how easy it is to fast for 24 hours.

      The following times were even easier because we knew it would be easy. We have even gone grocery shopping while fasting.

  2. I suspect it would be easier to fast if blood glucose and insulin levels were stable.

    • I went from 3 meals a day, to 2, and eventually to one. Now my blood sugar seems to be much more stable (I think I was pre-diabetic about 15 years ago). These days, I know that hunger will go away if I wait 30 minutes, and my stability is much greater. I have even missed eating a whole day before because I was distracted (so approx. 48 hours between meals).

      Bottom line. It can be difficult to change to fewer meals, but once you do, then you have more freedom (I can go from eating multiple times a day one day to just one the following days without having to adjust again).

  3. I am an American in Crete now. I can assure you that this is NOT a healthy culture even though the food is wonderful. The young are vibrant and healthy, but by middle age folks look quite tired and inflamed and the elderly are very ill, often quite heavy, have shrunk and lost their height, are often bent over, limping, etc. Maybe it was different in the past but not anymore. This is a wheat intensive diet here, all imported. I suspect the historic diet did not include as much bread, but I’m just speculating.

    We eat beautiful real food Med diet daily sans grains. They do have a lot of spectacular food. Thus the poor health we see here daily is troubling to see.

    Finally, the Greek Orthodox priests we see here (tomorrow is their Easter so they are out a bit more) are mostly obese even with whatever fasting is going on. So Lesson learned: get the diet right first, then incorporate fasting.

    As for fasting I do 16-18 hours fast 5-6 days a week and really have seen powerful value in LCHF with the iF. I am 64 and 100% free of symptoms of any sort. -john

    • May you have many years of a healthy and satisfying life. I am 81 and I have fasted 24 hours at this point. Yesterday was my first fast and today I feel so good and energetic I’m going to continue another 24 hours. I do not have any medical issues that concern me, although the doctors might find something that needed “treating”. I feel confident that I can treat myself. So, with any luck, you may have a lot of years left to live.

    • I am not from Crete, but my heritage is Orthodox. I can assure you that the fasting that is done during the fast is not healthy. A strict Orthodox fast involves no meat (beef, pork, chicken, sometimes no fish) or animal products (eggs, butter, milk, etc..) During the fast, those foods tend to be replaced with lots of grain products (bread, crackers, jam/preserves), fruit, vegetables (depending on the time of year). Salad/lettuce is rarely eaten. My parents still do Orthodox fasts & usually gain weight during the fasts due to all the grain-based carbs.

      • Christina

        My husband’s family is Coptic Orthodox and that’s exactly what I’ve observed too.

  4. Wondering if there is an optimal fasting pattern seen in your IDM program for adherence or compliance and improved insulin sensitivity; e.g. alternate days (24hr food allowed w/ 24 hr. no food only non-calorie liquids), Partial days – food w/in 6 hr. period no food – liquids only for 18hrs / day (24hrs), etc.- the patterns could seemingly be endless. So is there an optimal way to start?

    • Thats the million dollar question. It looks like we are on our own to try and determine the ideal protocol. Unfortunately, I found experimenting with different protocols very tiring and more like yo yo dieting to the point where I am ready to give up on this fasting bs

      • I will cover different routines in an upcoming blog. There are many different variations, and some do better with longer fasts less frequently and others better with shorter fasts more frequently.

        • I find that I do ok with fasting but then something hits and I am very very bad. I am just not consistent. Any suggestions

        • I have been doing the one meal a day /24 hr fast every day for about 5 weeks and am finding that I seem to be hitting a plateau. I am not counting calories during my meal. I am worried that my metabolism is slowing to match the drop in calories of only eating one meal a day. Could this be true? Should I not be doing this everyday? Also, while I am far from my goal, I’m concerned if eating one meal a day every day causes me to stabilize does that mean I will only eat one meal a day for life? While I believe in the benefits of fasting and plan on incorpoeating it in some form, I didn’t think it would be a daily thing of 1 meal a day.

  5. Along the same lines (fasting is not starvation)

    Starvation occurs at the end of a long-term water only fasting, when body-fat levels become so depleted that your metabolism starts burning muscle and organ tissues to survive. During fasting the body focuses on healing and repair. When fasting ends and starvation commences, it is the point of no return. Consequently, even the leanest person may be able to water-only fast for a couple of dozens of days without ever going into starvation.

  6. What are your thoughts on a “fasting regiment” like Eat stop eat by Brad Pilon? Basically he advocates fasting for 24h once or twice a week. Breaking the fast after 24h with a normal meal.

  7. Jill. My own experience is that blood glucose and insulin levels became stable after I began fasting.

  8. Hi Jason. Great job with these posts. I lost 50lbs going LCHF for over two years. I have reached a stable weight and have managed to stick to the diet easily and without problems. However, I plateaued about 15 lbs higher than I would like to be and stayed their consistently for about a year. All in all, I was happy because I was still relatively lean, muscualar and in pretty good shape. However since reading your posts I have been convinced to try intermittent fasting. So far, I have definitely lost weight and it has not been super difficult, although it’s not effortless. I will keep you posted for futher updates.

  9. After viewing Dr fung videos I now fast, in fact I’m less hungry when I fast, and more hungry when I eat which is a bit odd, but it is what it is. The best side of fasting is that it really pulls the weight off you, and thanks to Jason I now know how to diet properly…..

    • Susan Parker

      It’s not odd Stuart. I do the same. When we fast, blood sugar and insulin are low. I am hyperinsulinemic which means I produce lots of insulin coupled with insulin resistance and do uptake it properly, so eating after not eating for a long time makes me more hungry as well. Chemistry. I am confident this will heal over time with fasting and the ketogenic diet.

  10. Cassandra

    Thank you for your blog; I’m learning a lot about the three components of dietary management (what, how much, when) that I definitely need to address to lose lbs finally (49, female, yo-yo dieter, glucose intolerant with familial history of diabetes).

    For now a quick question: what is your position on so-called fasting regimes that allow for consumption of up to 20% daily energy needs, usually 400-500 cal. as a “modified” fast (Varady and that shyster English journalist who beat her to press) or “down day”(Johnson)? Is there any use in this, let’s say, limited to a short eating window, or is it better to aim for 0%?

    • Good question, I’m wondering if the doctor is not responding because of the limited scientific data related to your question. If that is the case, maybe, looking at some n=1 data would help.

      In my limited experience with IF (I’m guessing 50 or 60 days total fasting days), I normally have my coffee or tea with some heavy whipping cream. Also, as a diabetic, I’ve needed to consume a few grapes or raisins to maintain my blood sugar above the normal 83 mg/dl of blood. So, my ‘fasting’ days have always included about 5% to 10% of my normal calories. Even so, I’ve always felt positive results.

      My guess is that the more insulin resistant you are the closer to 0% calories you will need to be to get positive results, especially if those calories are carbohydrates.

      If you are so inclined, careful self experimentation (n=1) may be worthwhile.

      • Cassandra

        Makes sense. Will try set that goal for next 24 hr scheduled fast. 20% isn’t doing much for me though it’s only been a week.

        • MarianeC

          Cassandra and Nate this answers the questions I had. I am wondering about the heavy whipping cream too. It is probably trial and error with it. I am going to try fasting with 2 T total whipping cream in 2 c. coffee/tea today (I am fasting) and see if that works better than just having 0 food for 24 hours.
          I think everyone is different and what works for me might not work for you.

    • There are really no head to head studies so I can only give a clinician’s perspective from my own experience. I think that those fasts that allow 20% of cal or 5:2 style diets still work but slower than a full fast with 0 calories. I think that the most efficient fasts are close to 0, but that is not alway feasible for some. However, I think (only my feeling) is that eating 0 calories is easier, especially for extended periods than eating a small amount. I think the body ‘switches’ to burning fat and the 500 calorie/day diet stops that from happening. We always recommend eating nothing during fasts, but vary the durations according to personal preference.

      • Cassandra

        Thank you Dr. Fung for this reply. You used to have a resource page that included a sheet of fasting tips, and if I remember correctly you OK’d coffee with small amounts of milk (cream) and bouillion. Is that accurate?

        I’m trying 24h of 0% today…if you don’t count the HWC in coffee 2x and bone broth 2x.

        To concur with what you wrote, it does seem that on days that I try to compress eating into a 4-6 hour window it is hard to stop once I begin eating.

        I’ve contacted your office via the form regarding your distance program to get some further guidance and hope to hear back soon.

  11. I have fasted several times and it does indeed stabilize my glucose and insulin levels. I would not wait for that to be corrected to undertake a fast. I once did a 92-day green juice fast, and as a result I was then able to maintain stable levels, as long as I ate consciously. It is not easy to begin, but after a few days you feel better and your appetite diminishes.

  12. Thanks for the history lesson. I especially liked the part about Crete and the Greek Orthodox Christians. It reminded me of one of my favorite Rumi poems. Rumi wrote the following excerpts in his poem, ‘Fasting’, in the 13th century Turkey, a neighbor of Crete.
    This translation was by Coleman Barks:

    “There’s a hidden sweetness
    in the stomach’s emptiness.
    We are lutes, no more, no less. If the soundbox
    is stuffed full of anything, no music.
    If the brain and the belly are burning clean
    with fasting, every moment a new song comes
    out of the fire. The fog clears, and a new energy
    makes you run up the stairs in front of you….

    But even if you’ve lost all will and control,
    they come back when you fast, like soldiers appearing
    out of the ground, pennants flying above them.

    A table descends to your tents, Jesus’ table.
    Expect to see it, when you fast, this table
    spread with other food better
    than the broth made of cabbages.”

    • Cassandra

      Lovely, Nate–thanks for sharing. The Sufi orders depended (and depend) on the heightened consciousness achieved via fasting for their religious rituals.

    • Wonderful! Thanks a lot for sharing.

    • Kat Lakie

      I love that Poem thank you for posting.

    • Linda Martin-Peoples

      Awesome…Thank you, Nate!

  13. i find it takes 3-4 days of fasting for my blood sugar to fall into normal range. I have done one 4 day fast and one 9 day. I wanted to get to 10 days but my blood pressure dropped and I got lightheaded. In a supervised setting a longer fast may be ok, but I was ‘on my own’ with it.

    For me, fasting for a few hours or even a day or two doesn’t actually acheive anything. I can only lose unwanted weight when water-fasting. Even very low calorie doesn’t shift it.

    I have systemic worms that I have been grappling to overcome. Because they hijack a lot of my nutrition (and I am convinced they are almost certainly the cause of the diabetes), my body continually thinks it is starving and holds on to the fat. If I knew it could starve the beggars out I would gladly fast for weeks……

  14. Johnny D.

    I’m diabetic if I start to fast with my meds will I develop low blood sugar? I would really like to be off the meds I think there bad for you. Of course my doctor is not real keen on natural fixes.

    • Kat Lakie

      Johnny D.
      I guess I’m lucky my doctor is fully supportive of my efforts to get off my T2D meds and so far I have managed to ditch the Glycazide ……I’m still taking Metformin, but Doc has said if my Hb1Ac tests are low in 3 months I’ll be able to halve that and in another 3 months, still maintaining low readings, I will come off all medications and could consider myself to have reversed my condition. I have spoken with my Doc about fasting and he agrees I can delay taking the Metformin until I eat, but this is only on a 16 – 18 hour fast…….he said I can try for the 24 hours, but to monitor my blood sugars closely so that I don’t have a hypo.
      I would try to convince my doctor if I were you, site the studies, the doctors doing this research ……etc., and try to get him on board.

      • Kat, you are extremely lucky to have a physician who is supportive of you IF protocaol. I am so tired of doctors telling me, “you can expect to be on insulin for the rest of your life.”

  15. If the basis of our lifestyle is evolution, then let me repeat, fasting is a fail for women, as it reduces fertility. This has been proven in animal models. Since inability to reproduce is an evolutionary fail, I continue to be confused why LCHF & Paleo people insist on fasting for women. Do you really want your wives to be infertile? Most women want to have children, and as men, I believe your evolutionary success lies in your wife having kids. Jes’ saying. 😀

    “In the luteal phase, insulin concentrations increased notably in the fasted group. The number of recovered embryos per female and the speed of embryo development were reduced in the food-deprived group. Acute fasting altered both metabolic and endocrine markers and embryo development.”

    High insulin in the luteal phase is basically the disease known as PCOS. While some fasting reduce insulin for grossly obese women/insulin-based PCOS women, thus bringing them toward “normal” ovulation, for women without these conditions, fasting clearly reduces fertility by impacting the hormonal environment that allows eggs to implant, harms embryo development of those that have implanted, and increases the likelihood of miscarriage.

    Ladies, if you want to be preggers, or could be preggers – if your fertility is important to you – carefully research the effects fasting will have on your fertility if you don’t have PCOS or metabolic syndrome. The majority of women will experience reduced fertility and increased miscarriage risk, as proven in animal models.

    Advice that works for men doesn’t always work for women. 😀 Best wishes.

    • Actually my experience was the contrary. Losing excess weight helped me get pregnant. And if fasting helps women lose weight, it should be considered beneficial. Before losing all that weight (10kg), it seemed impossible to get pregnant for over 6 years and there was no detectable problems with either my husband or myself. Of course, once pregnant, fasting is not recommended.

    • Linda Martin-Peoples

      Ohhhhh, webgrrl… I am almost 70 years old and 50 pounds overweight. I also have a 48-year-old daughter and a 22-year- old granddaughter, so I’m going to just take my chances on not being able to ‘get pregnant’ on this wonderful WOE… (down 21 pounds and counting! YAY!) I’m not picking on you, sweetie….it’s just that this WOE is a Godsend to so many of us who are no longer in our child-bearing years, or who are not interested in conceiving. The need to properly nourish our bodies during pregnancy goes without saying, of course.

  16. […] Start with Fasting Part I […]

    • “Since inability to reproduce is an evolutionary fail, I continue to be confused why LCHF & Paleo people insist on fasting for women. Do you really want your wives to be infertile? Most women want to have children, and as men, I believe your evolutionary success lies in your wife having kids. Jes’ saying.”

      Are you serious? While fertility is an issue for some, being obese is an issue for all.

      Your statements regarding husbands not wanting infertile wives and “most” women wanting to have children show a rather limited view of the overall picture. I really can’t get over this “do you want your wives to be infertile,” comment. I’m not sure what century you’re from with that mindset. Perhaps wanting a healthy wife matters more than wanting a brood mare. Or perhaps women are perfectly capable of deciding what’s most important to them on their own. And maybe husbands don’t get to dictate to wifes what, how, or when they eat anymore.

      I won’t say that you’re wrong regarding the potential for impact on fertility, and the issue does matter for many people – but I do take issue with the overall tone and gerneralizations included in this statement.

    • hi Robin,

      Let me make some comments on the type and need for fasting that is being discussed here. It is for those of us who are struggling with insulin resistance or diabetes. I can tell you for sure that for us, not fasting is leading to infertility because of all the problems associated to high insulin levels. I’ve been dealing with infertilit for about 2yrs now and no doctor of all those I consulted was able to find the root cause which is insulin resistance, and just because I’m lean none did ever suspect of insulin. Then in cases like mine fasting might be a good appproach or even and hopefully the solution.
      I would say fasting is not for everyone but, cannot state that fasting will inevitably lead to infertility and high insulin will always lead to.


      • I don’t disagree with you – my comment wasn’t really about fasting impact on fertility. I think that the blanket statement and tone of the comment that I replying to was off and frankly, insulting. And that’s what I was responding to, the, “men do you want your wives infertile?” statement. Just a bizarre mindset to bring to the table and insulting to women.

  17. Christine

    I have been following Dr Fung and intermittently fasting for about a month. I am in a steady weight loss and no longer taking my insulin (Lantus and Humolog). I feel great and even got my doctor on board.

  18. What is the most common frequency for fasting? Is once a week 24 hr a good start?

    Is it advisable to fast when you are fasting to be involved with intense physical activities like playing a game of tennis, hike or gardening?

  19. Hi Jason,
    What about patients with ulcers and IBS and all other digestive issues, how can fasting help dont they experience symptoms while fasting. Combine that with diabetes

    • That is a separate issue entirely. Some will feel better, others worse.

    • therese

      Would suggest reading Dr. William Davis and the for good info on gut and many other issues. Have had tremendous response to these dietary changes.

    • Richard B

      Joseph, I noticed you had IBS. I suffered from that for years along with diverticulosis. I read MSM and high doses of Vitamin C heal these conditions. My wife is from Brazil so, while there, I cut an aloe leaf and drained off the green fluid about 15 minutes, (the green juice can cause kidney ailments), cut the leaf into small bits and added one piece per day with ascerola cherry pulp, a cherry from Brazil known to give about 1000% daily vitamin C from a glassful. Blend it in blender with stevia and I drank one with aloe and 2 without for about 6 weeks. My IBS and soreness in guts is completely gone now. Store bought MSM and vitamin C is supposed to give same results.

  20. Ernest Sebastian

    Hi. Dr. Jason
    I have diabetes 2 for more than 25 years. Having read and listened to some of your notes
    On fasting relating to diabetes I have begun with my LCHCD diet and intermittent fasting
    for a couple of months now and seem to be having good results : generally between 3.5 to
    6.5/8 on a couple of days. I started with 45 units and gradually reducing to 25 units now.
    What would be the best approach to reduce the possibility of reducing my insulin further.
    I am 77 yrs old and feel so much better now than I have ever been for many many years.
    Thanks for the good work you are providing and if you have the time like to hear your comments.
    Thanks and regards. Ernest

  21. Dr. Fung. I stumbled across your YouTube talk. Can you please give some guidelines to start fasting, daily, weekly, what kind of fast, water only, green juice, etc. please too let us know how to become your patient. Having diabetes troubles here. Thanks.

  22. Barrie Walsh

    Dr Fung, My problem is the other way round. I’m 77 and a type 2 diabetic but with the LC diet my weight has dropped to 50 kilos. Fasting I know works, but I’m worried about losing more weight by fasting, but i want the benefits! Can you please help. Thanks

    • You can simply use shorter periods of fasting, say 16 or 20 hours and if weight drops too much, to increase food during eating window.

  23. I have type 2 diabetes and when I fast, it always raises my blood sugar. Is fasting always recommended? I was just diagnosed a few months ago but had done IF for a while doing a primal diet (Mark Sisson highly recommends IF). Am I doing something wrong or is it possible fasting doesn’t work well for some?

    • No, this often happens. The increase in growth hormone and adrenalin increase gluconeogensis which increases blood sugar. It is neither good nor bad.

    • Fasting is only one way of controlling diabetes. It does work for the large majority of people, but not all.

      • If your blood sugar goes up when you fast, is that something that could change over time with fasting? Will your body correct itself so that it doesn’t happen? Or should you just not fast at all?

  24. You don’t mention Jewish fasting. in several moments of the year.

  25. I am a type 2 diabetic for 22 years. Before finding Dr. Fung’s website and watching YouTube videos, I was up to 50 units of Lantus once a day and 16 units of Novolog after each meal (usually eating twice a day) plus 2g of Metformin a day. I started fasting March 26, 2015 and today I’m off all my insulin and only I’m only taking 2g of Metformin a day. My question is when should I stop taking Metformin or should I just cut my dose down by half. My sugar is running between 110 and 130.


  27. […] Start here with Fasting I […]

  28. Hello Dr. Fung
    I am reading this for the first time and I’m highly impreesed with all the comments. I heard of Dr. Fung from a friend who is a medical student who had a life experience with her patient that went on the fasting diet, she told me to try it which is why I wanted to know more abot the diet hence here i am. Please how do I go about this? Is there a specific food I should be eating during the eating period? I am diabetic but my blood sugar is under control as I try as much as posibble to control my eating habit and portion, and also do 10000 steps every night. Fasting will not be a problem for me for I do fast for religious purpose before. Please advice on how to go about it

    Dr. Jason Fung: I generally advise a Low Carb High Fat diet. has a number of good posts and videos about how to do it.

  29. […] valt zo’n beetje samen met het begin van de ramadan, 18 juni. Toeval ?  of niet. Volgens Jason Fung  in het eerste lesje over vasten, bestaat vasten al heel lang:”Fasting is one of the most […]

  30. […] watching Dr Fung’s videos and reading his blog series on calories, hormonal obesity and fasting has turned out to be life changing for […]

  31. […] Start here with Fasting part 1 […]

  32. First I want thank you all your helpful advice 🙂
    I am doing 18:6 3-4 days per week and 24hr fast the remaining days to help with blood sugar/insulin dysregulation & general overall health benefits. I have lost 72 lbs lchf and want to lose 75 more to reach maintenance/goal. Wondering if adding bone broth (grass-fed sourced) for my mid-day and 5pm “meals” on 24hr fast days would hinder/eliminate any of the benefits/results I am seeking. Thanks in advance for your kind response; I know your time is very precious and I am most grateful & appreciative 🙂

    Dr. Jason Fung: I think bone broth is quite beneficial and will not hurt fasting efforts.

  33. […] Start here with Fasting part 1 […]

  34. […] Start with Fasting part 1 […]

  35. […] Start here with Fasting part 1 […]

  36. Richard B

    Dr Fung: I just started the fast today and ate some eggs, cucumber, green olives and cheese at 9:30 pm, or approx 30 hours since yesterday’s last meal. I’m DT2 with blood sugars going into 200’s from dawn phenomenon. I was on sulfa drugs but they were not doing much good so I am taking some Metformin er 1000 mg x 2 a day that I had at home. The metformin gives me terrible stomach problems with diarrhea , nausea, so I left metformin off until after I ate tonight and then took 500mg now and will take another at bedtime. I take some adrenal formula called Drenamin 3 x day my chiro gave me for weak adrenals. Will I see good results from fasting even though I’m skipping some metformin to let my guts rest? The metformin does help lower BG, today at 5:30 am was 147. Thanks for your blog and info on youtube, you are a real champ for helping people!

  37. […] Start with Fasting part 1 […]

  38. […] Start with Fasting Part 1 […]

  39. I had to laugh out loud when I read the end of this article! Who are you going to trust, Jesus, or Colonial Sanders? Lol! I’m going to go ahead and side with Jesus, thanks!

  40. […] I am a nutrition geek and proceeded to read everything I could on water fasting.  I came across Dr. Jason Fung’s blog and all the pieces started falling into place in my […]

  41. Bruce AIken

    I was wondering how to get the broth to the more gelatinous consistency. Beef seemed thicker than the chicken. Any suggestions?

    • Use lots of bones, maintain a slow cook for at least 24 hours, really minimise the amount of water you use. I normally after I strain the stock boil it to reduce the liquid. There are heaps of websites with recipes of great broths.

  42. […] Start here for Fasting Part 1 – Historical Perspective […]

  43. […] Start here with Fasting Part 1 […]

  44. Awesome article, I’m off to read the rest now but first I had to say thank you! I’m an intermittent faster and I eat the LCHF way, I found this article helpful and educational. It was also refreshing to not have to skip the caveman/millions of years ago junk and just call on people from our real history! Well done! One thing I struggle with when learning about all of this from my new teachers (not the current health care system I was raised on) is that it’s hard to respect these great fellows when they start including people that never existed in years that never existed! The written history is much more interesting then a monkey we call ‘uncle!’ Way to go Doctor, greatly appreciated.

  45. […] Start here with Fasting Part 1 […]

  46. Thanks to Dr. Jason Fung.
    I started intermittent fasting about 5 weeks into my 6th, with LCHF diet. Sometimes I fast between 18 – 22hrs. I exercise even on the day I am fasting. I can without a doubt confirm what Dr. Fung is commenting on. My Cho has reduced from 310 to 192 i.e. overall and still getting lower. My Tri has reduced from 180 to 117 latest result 78.
    My Glucose reading started off at 237 today its between 80 – 110. Off course I’m not on any meds. Just went based on Dr. Fung’s Videos and Advice and amazing results. The best part is, in 6 weeks I have reduced from 300lbs to 265lbs, 35lbs lost and still losing weight, every week with fasting, LCHF and Exercise. The best weight loss advice I have ever gotten and I’m loving the side effects. Keep doing what your doing doc, thanks for this life changing advice, truly appreciated. Looking forward to getting your new book.

  47. […] early as 400 BC, Hippocrates championed the practice of fasting, telling his patients that eating will only feed […]

  48. […] For Fasting series start here – Fasting Part 1 […]

  49. I am aType 2 Diabetic since2008. Recently I found Dr Fungs U tube videos re Fasting to try to reduce my Hba1c which was 58 in August. I commenced Fasting 2days each week and did that for 8 weeks
    24 hrs from my meal one Eve until my meal the next day. On the morning of my fast I did not take my
    Metformin or Gliclazide I took them when I broke my fast! I lost 7 lbs in the 8 weeks
    I then had my Hba1c checked at the end of November and to my disappointment discovered it is again 58
    My GP is blaming the fasting as She maintains that when my blood sugar is low on my fasting days.
    my liver will release sugar into my body which will be reflected in my Hba1c result even although my home
    testing is fine. I still feel I could lose another 7 lbs and find fasting no problem.However I am now unsure what to do.

    Dr. Jason Fung: If you reduce your medications, your blood sugars will go higher. That is expected. However, where did that sugar come from when you fasted? It could only come from stored sugar from within your own body. So, you are moving sugar from the body back out to the blood. I don’t think that is necessarily a bad thing.

  50. My GP is saying that on my fasting days with no food and no medications my blood sugar is low and therefore my body tries to correct that by releasing sugar and raising my Hba1c. My problem now is that because of that result my GP now wants to raise my medications and is predicting that I will eventually be on Insulin!! She is also stating that the fasting is causing this to happen.My BMI is 25.8 so not too far off course.However I am 76 yrs old and she thinks I am too far along the progression of Diabetes!!

    Dr. Jason Fung: If you are not eating, where is this sugar coming from? It can only come from stores inside your own body. So, this is normal. Insulin will only force the sugar from the blood into the body, where it will damage all your organs. It will make your doctor feel better, but will not help you in any way.

  51. […] also recommend you read the following blog posts on fasting by Jason Fung over at Intensive Dietary Management.  This is a great series which goes in depth into fasting and is a must-read if you are considering […]

  52. I was just diagnosed with type 2 diabetes, and am obese. Immediately I was put on metformin and told I would have to take it for the rest of my life. I am a Christian, so I began praying about how to cure this. I felt led of God to fast, and then go to a low carb, all natural food diet.

    So excited to find you and read your suggestions, it is confirmation from Him, that I heard Him correctly!
    I start Jan 1st, and will eat this way the rest of my life. It is true wisdom! Thank you for sharing truth!

  53. […] insulin, the best way to lower it is to fast. Seriously, if you haven’t yet, I suggest you read Dr. Jason Fung’s series on fasting, obesity and diabetes. Or you can check out his lecture.  Plus if he’s fasting the hubby’s IBS symptoms […]

  54. I’m doing this for weight loss. in about 10 days, i was lost 3kg. and about 1 month, i lost 10 kilograms. I feel great! I’m fasting for 18 hours, start to eat at 12pm and fasting at 6pm

  55. […] Start here with Fasting part 1 […]

  56. Will I lose weight if I do high intensity interval exercise after 12 -14 hours fasting if I have insulin resistance ? Will this access the fat or will it just raise cortisol and break down muscle ? I have been given conflicting advice and want to know how to access the fat to burn so I can lose weight which is hard to do when you are insulin resistant.

  57. Hello, I have been T2 diabetic for more than 15 years, high bp and high cholesterol. Medicated for all for 15 years. Diagnosed after transient stroke. 15 years later heart attack with stent inserted. 30kgs overweight with extreme difficulty losing the weight until losing 18kg with HCG diet – couldn’t maintain and put it all on again. Quitting smoking and exercising daily has helped and now off all mess except for metformin and one other (bsl went to 22 so had to go back on these Meds, now bsl averages at around 12 (higher on waking). Also have horrible gut issues with pain and bloating (looks like 9 months pregnant)…. Atkins diet sent bsl levels soaring even with mild ketosis. Any advise from anyone resolving the issues with IF on low carb using 16:8 or should I do gut repair first? Poo tests are expensive so don’t want to go to the expense if IF has been shown to help. Also should I go off the metformin whilst I experiment with the low carb IF.

  58. […] started intermittent fasting after reading Dr. Jason Fung’s blog series. Rarely do I eat 3 meals a day anymore. Typically I fast for 18 hours before eating my first meal […]

  59. Wow Dr Fung. I was simply enthralled by the information provided in your blogs, so much of it reflected personal experience with calorie reduction based dieting, reducing energy levels and subsequent weight return (plus a bit more). After dedicating the best part of three days reading almost all your blogs and YouTube clips I decided to attempt a 5 day fast straight up. I purchased a glucose meter (for companionship through what I thought would be a feat of human endurance beyond the capacity of a normal human) and commenced with the recommended “out” in mind… FEEL BAD just EAT.

    Background – 47 year old male, 105.5kg, 172cm (a middle age, short, fat fellow). A lot of weight around the gut. I had relatively good blood sugar levels, no medications, not a diabetic but a family history of diabetes from age 50 onwards … I knew where I was heading.

    I was shocked, the fast for me was so easy! As other posts have indicated a low carb diet leading up to the fast I think really helped (I had coincidentally commenced this diet 4 months before. I went through 2 days of bad headaches and tiredness when I moved to a low carb diet but this did not occur at all with the fast. I assume since my available easy accessible “body” sugars were already limited and I was already moving to ketosis regularly. Note, I had lost 8 kg while on this low carb diet). As each hour and day passed through the fast I keep thinking surely I’ll get hungry soon, but apart from isolated brief periods of very mild hunger there was nothing. I thought I would test this after day 2 and went out to the pub with mates a few times over the subsequent days. While they drank beer and ate I had a good time with no hunger – not eating or drinking (except water). As the fast progressed my energy went up, I went for daily 6km hike, no issues. During the fasting period I increasingly felt stronger and “tighter”. I could not believe it. Average glucose from Day 1 though Day 5 dropped from mid 5mmol/L to mid 3mmol/L. Only passed a poo on Day 1.
    I keep everything as simple as possible. I consumed lots of water, some black or green tea (no milk) and one coffee (espresso with a few tablespoons of milk). I found I could not have any more coffee as this single coffee shot had more effect on me then 3-4 shots would normally. I also had magnesium citrate powder as I was experiencing some mild leg muscle spasm before the fast and apple cider vinegar daily ( I read about this stuff and was not sure if it would make any difference but thought it could do no harm – except mate, that stuff tastes so bad). I forgot about the salt until Day 5 and had a few litres of mineral water that contained some sodium – probably not enough as in the last 1/2 day of the fast I had some localised muscle cramping in my hand of all places (not bad)
    My weight dropped to 100.5kg in 5 days, a loss of just over 5kg (very close to the advised average loss of 0.9kg per day for this fasting duration). I broke the fast with a few tablespoons of tuna in olive oil ( there must have been something special about that tuna as it tasted soooo good). An hour later I had a medium sized meal of slow cooked dead cow and greens. No issues, slept soundly and was rewarded the next day with a wonderful poo.
    A day after the fast my weight was 101.5kg (it has not fluctuated more than 0.1kg from this value for almost a week). I have maintained a low carb diet and typical a 14-16 hour fast (missing breakfast as not hungry)
    I LOVE FOOD, but it is wonderfully empowering not feeling somehow obligated to eat food all the time. I don’t feel hungry at lunch but typically I still have something light to eat to enjoy socialisation and to get out of the office. It’s a form of freedom that I have not experienced before. I don’t feel guilty if I have a big meal, I just watch my carbs and make sure I don’t snack.
    I plan a few shorter fasts over the coming week or so and then will complete another 5 day fast. I will be eating bone broth this time on the longer fast. As advised it will be an easy way to consume salt and get some minerals. I hope it does not increase my hunger but I think it will help with mental strength/health to maintain the fast. Still very early days but I feel better then I have for more than 10 years. I’m hoping that I continue to improve and look back on my first fast as the start of a body/mind transformation. Only time will tell.
    I am in your debt Dr Fung, I do not have the words to express my thanks

  60. […] think about what is happening here (you may also want to refer to my 26ish post series on fasting). As you fast, there are a number of hormonal changes that do NOT happen with simple caloric […]

  61. Fascinating information.

    I’ve been fasting myself on and off, and the wellbeing I experience the following day is amazing. A 36 hour fast really is not all that hard work either. Just needs self-discipline.

    Great article! Thank you!

  62. […] i svälttillstånd? Jo, fasta. Man kan se detta i studier på fasta, eller överviktskirurgi. Se Fungs artikelserie om fasta. Hormonerna håller aktivitetstillståndet uppe eftersom man förväntas gå ut och jaga för mat. […]

  63. Liliana Diaz

    Does clear broth interrupts the fasting process?

  64. […] Another wealth of info by Dr Jason Fung:- […]

  65. Hi, other practice of eating by the prophet Muhammad is “eat while you are hungry, and stop before feeling full”. I hope you can share (if it does exist) the physiology of this practice too. Thanks

  66. That last question is a really. I guess I would take the cornel.

  67. […] Eating less often has many benefits on our health, as brilliantly explained by Dr. Jason Fung in his articles about fasting. […]

  68. I’m really looking forward to reading your series on fasting. Although, as a scientist, I would resist relying on sources like Jesus and other historical figures with respect to who I should trust about medical information. It’s a little off. Just because they were important in some cultural or even scientific area doesn’t mean they knew anything at all about the subject.

  69. […] Fasting – A History Part I […]

  70. […] (nov 16) as well as massive youtube based lectures on and…/ as well as a key contributor to […]

  71. […] I have written an extensive series of posts on fasting starting with part 1, a history, and lasting 26 parts so far. All that information is completely for free, if you can put up with […]

  72. […] I have written an extensive series of posts on fasting starting with part 1, a history, and lasting 26 parts so far. All that information is completely for free, if you can […]

  73. […] interested then it is available here. I highly recommend that you read it. Dr. Jason Fung has an invaluable series on Fasting where he discusses the need for fasting, its effects on your body and how to […]

  74. Love your blog, excited about fasting, my first one today of 17 hours, I feel so great combined with HFLC of 3 weeks. I hope to loose more weight , slow so far. I have the metabolic syndrome , obese sugar levels on the high side , not diabetic at this stage.
    I thought I have to join your blog because I feel so good with hope in sight to loose my weight. I have been on every diet with some effect,resulting each time with more weight gain. I am 71 years of age my weight was increasing ,Doctor threatening me with Diabetic medication. if I do not loose weight. I am on thyroid medication for Hypothyroidism and Blood Pressure.. I do hope I can decrease all of these soon. I finally understand my problem with the help of Dr. Diet .com. and your great explanations in video form. I really had given up hope for my condition.I thought this is the end of life for me… This is a new lease of life thank you so much… I will help my family members and others with my new Knowledge I received by you and the Diet Dr. It is wonderful that you help so many with all your information

  75. Can I drink a cup of beef broth made from powdered beef bouilion during my fast and not break my fast??

  76. Susanne Maron
    This is THE way to get weight off and be healthy,I’m convinced!!Have been a ‘yo yo dieter’ for years but think I’ve finally found the real answer to how to get weight off n keep it off.Started this way of eating August 26th 2016 @ 257.4 # and now weigh 215# on November 20th !!!I’m nearly 69 and only 5ft., 2 “.also,so,feel this is quite an accomplishment!

  77. […] early as 400 BC, Hippocrates championed the practice of fasting, telling his patients that eating will only feed […]

  78. Dr G Shashi Kumari

    Hi Dr Fung, I am 47yrs old female, 87kgs, Ht 167cms, T2D ,htp .Hypothyroid, elevated Triglycerides .
    My Dr here in Vizag India doesn’t believe in fasting.I wasrecently put on Lyxumia 20mcg and Lantus 30 u with 2g Metformin daily.
    I have recently started intermittent fasting and my fasting and predinner blood sugars are around 250 with all the above medications and fasting.
    Should I also take mixtard to control my blood sugars or do I wail. I started fasting 5 days ago.

  79. […] Fasting – A History Part I […]

  80. Greek Orthodox fasting isn’t ‘nil by mouth’. Here are the things we abstain from on most fast days: meat, oils, dairy, fish, alcohol. My grandmother always filled us with pulses/beans, sweets/breads and vegetable soup. I feel like our fasting traditions (my family is originally from Crete – so our traditional diet is exactly what you’re talking about) is actively working against your argument.

  81. Dr Fung,

    Thanks for your wonderfully informative blogs. There is a religion called Jainism (which has many similarities to Buddhism). Fasting is a well known, though not common practise and a number of different kind of fasts of varying length and eating restrictions are described. (

    My grandmother on my mothers side, had type 2 diabetes for 40+ years and she kept it very well controlled by following what you essentially describe as alternate daily fasting with a strict vegetarian diet. She did it for religious purposes, but it did have fantastic side effects of controlling her diabetes without medicine.

    Clearly, many religions and communities have known fasting is immensely helpful. Thaks for highlighting and explaining the mechanism of working so lucidly.

  82. omar nuri

    Hi, i am new here, this is my first time. I am so very happy to have come here by coincident. This is the month of Ramadan( I am Moslim) and I was searching on Google to sea if fasting reduces Cholestrole. That is how I got here, and I have been reading all of the above material and comments about the benefits of fasting for the last hour. ( I started around 4:30 am, breakfast time during Ramadan) and its almost 6:00 am now. I stopped eating at 4:30 am. I am not a religious person but always exited about coming of Ramadan since I lose 20 pounds during Ramadan. As for as I remember, I have been a food addict and overeater, even now( I am 67) still struggle with controlling amount of food I put in my mouth. If I like it I will eat a lot of it, or all of it. I do not know the concept of: I am full, that is enough! I believe it all started with emotional issues in childhood. Stress has also a lot to do with it. I am working on it! I am planning to continue fasting in any shape and form even after Ramadan, now that I know so much more that fast can do for me. Thanks all.

Leave a Reply