Fasting and Ghrelin – Fasting 29

posted in: Fasting, Health and Nutrition | 75

Ghrelin is the so-called hunger hormone. It was purified from rat stomach in 1999 and subsequently cloned. It binds to growth hormone (GH) secretagogue receptor, which strongly stimulates GH. So, for all you people who thought that eating makes you gain lean tissue, it is actually the opposite. Nothing turns off GH like food. Of course, food provides the nutrients needed to grow, so in fact, you need both feeding and fasting cycles to properly grow. Not all feeding, and not all fasting. Life lies in the balance of the two. The cycle of life is feast and fast.

Ghrelin, has also been found to increase appetite and weight gain. It also antagonizes the effect of leptin (in rats at least). Leptin, as you might recall, is the hormone produced by fat cells which turns off appetite and makes us stop eating. Ghrelin turns on appetite. So, if you want to lose weight on a long term basis, you need to tune down ghrelin.

So, how to do that? As we discussed last week, eating all the time sounds like it will turn off hunger and ghrelin. But that’s far too simplistic. Surprisingly, the answer is the opposite – fasting.

Let’s look at this study “Spontaneous 24-h ghrelin secretion pattern in fasting subjects“. Patients undertook a 33 hour fast, and ghrelin was measured every 20 minutes. Here’s what ghrelin levels look like over time.

There are several things to notice. First, ghrelin levels are lowest at approximately 9:00 in the morning. This corresponds to the measures of the circadian rhythm which find consistently that hunger is lowest first thing in the morning. Recall that this is also generally the longest period of the day where you have not eaten. This reinforces the fact that hunger is not simply a function of ‘not having eaten in a while’. At 9:00, you have not eaten for about 14 hours, yet you are the least hungry. Eating, remember, does not necessarily make you less hungry.

Next, notice that there are 3 distinct peaks corresponding to lunch, dinner and the next day’s breakfast. BUT IT DOES NOT CONTINUALLY INCREASE. After the initial wave of hunger, it recedes, even if you don’t eat. Ghrelin shows a “spontaneous decrease after approximately 2 h without food consumption”. This correlates perfectly to our clinical experience that ‘hunger comes in waves’. If you simply ignore it, it will disappear. Think of a time that you were too busy and worked right through lunch. At about 1:00 you were hungry, but if you just drank some tea, by 3:00 pm, you were no longer hungry. Ride the waves – it passes. Same goes for dinner. Further it has been shown that ghrelin spontaneously decreases independently of serum insulin or glucose levels.

Also, note that ghrelin does have a learned component since all these subjects were used to eating 3 meals per day. It is not merely by coincidence that these peaks of ghrelin happen. This is similar to the ‘cephalic phase’ of insulin secretion that we’ve discussed previously.

There was one other big finding of this study. Look at the average ghrelin levels over 24 hours. Over the day of fasting, ghrelin stays stable! In other words, eating nothing over 33 hours made you no more or less hungry than when you started! Whether you ate or did not eat, your hunger level stayed the same.

As we discussed in our last post – eating more sometime makes you more hungry, not less. In the same vein, eating less can actually make you physically less hungry. That’s terrific, because if you are less hungry, you will eat less, and are more likely to lose weight.

So what happens over multiple days of fasting? This study looked at the question specifically. 33 subjects had their ghrelin measured over 84 hours of fasting and they divided the results by men and women, as well as obese and lean. There were no significant differences between the lean and obese subjects, so I won’t dwell on that further. Once again, there were distinct circadian variations.

Over 3 days of fasting, ghrelin gradually DECREASED. This means that patients were far LESS hungry despite not having eaten for the past 3 days. This jives perfectly with our clinical experience with patients undergoing extended fasting. They all expect to be ravenously hungry, but actually find that their hunger completely disappears. They always come in saying ‘I can’t eat much anymore. I get full so fast. I think my stomach shrank’. That’s PERFECT, because if you are eating less but getting more full, you are going to be more likely to keep the weight off.

Notice, also the difference between men and women. There’s only a mild effect for men. But the women show a huge decrease in ghrelin. Again, this addresses one of the major worries that women are not able to fast. Actually, women would be expected to have more benefit from fasting because their hunger can be expected to decrease better than men. Notice, too, how much higher women’s ghrelin level reaches. I suspect this correlates to the clinical observation that many more women are ‘addicted’ to certain foods eg. chocoholics. Sugar addicts. etc. So many women have remarked how a longer fast seemed to completely turn off those cravings. This is the physiologic reason why.

A few other notes about the hormonal changes of fasting. Notice that cortisol does go up during fasting. Yes, fasting is a stress to the body and cortisol acts as general activator as well as trying to move glucose out of storage and into the blood. So, if too much cortisol is your problem, then fasting may not be right for you.

Insulin also goes down, which is what we expect. Growth hormone, as we’ve previously noted, goes up during fasting. I suspect this helps to maintain lean muscle tissue and to rebuild lost protein when you start to eat again.

However, the main point of this post is to show that over intermittent and extended fasting, ghrelin, the main hormonal mediator of hunger does not increase to unmanageable levels. Rather it decreases – which is exactly what we are looking for. We want to eat less, but be more full. Fasting, unlike caloric restriction diets is the way to do that.

75 Responses

  1. Juan Bucio

    If I’m looking at the chart correctly the most benefit on getting GH is on the second day of fasting? How would this be done as far as an eating pattern standpoint?

  2. Dr. Feng thanks for great articles, after practicing your fasting strategy for half a year, I find that many times when I eat is not because of hunger, but because the brain suddenly appears to have a strong idea of eating some kind of food, and hormones are Can not control the idea, which makes me very troubled. Do not know other friends have such trouble. Very much hope you can give good advice, very grateful.

  3. But does the reduction survive in the week after the fast when the patient returns to “normal” eating?

  4. Missing Link

    How do I know if I have a problem with cortisol? I am T2 diabetic, overweight, and have been doing some 14-15 hour fasts (eg 10pm to 1pm) to see how my body responds before trying a longer fast. While hunger does not really seem to be a factor I do have some slight rises in my blood sugar throughout the morning before tapering off around 10 am to what I would consider my “normal” fasting levels. I interpret this as the Dawn Phenomenon and, from what I understand, it is my body releasing glucose from storage in response to the “fright or flight” mode. Does cortisol play a role in this process? I don’t really feel hungry (i.e. hunger pangs in my stomach) during these BSL rises, but I do sense my body asking to be fed (light shakiness, sweating, tingling in the fingers/lips).

    • I think worrying about if you have a cortisol problem will cause a cortisol problem as worrying is stressful. What you said sounds like insulin resistance. Try a five day water fast. It’s all downhill after the 2nd day. That will 1) do wonders for you intra-organ fat and 2) do wonders for you confidence you can handle fasting. If you can do 5 days of water only going 24 or 36 or even 72 hours w/o food (lots of water though) will be a snap.

    • I can’t say about your cortisol but my wife after learning to control her sugars the dawn phenomenon goes away. (at least for her)

      • I think people are confusing Dawn Phenomenon with a bad thing. As described by Fung, it’s perfectly normal and occurs in everyone that wakes up, before they wake up as a prelude to waking up.

    • Missing link… you said:
      ‘it is my body releasing glucose from storage in response to the “fright or flight” mode. Does cortisol play a role in this process?’

      Yes…Adrenaline, Cortisol, Norepinephrine are the three major stress hormones that mobilize your body for action.

  5. Dr. Fung, Thank you for another fantastic post!

  6. If you have high cortisol fasting may not be for you? Blanket statement end stop? Why not post a link to where you know how to control fasting I’ve read your book Obesity Code at least 3 times now and never remember you saying such a thing.

    • I also found this alarming, having read both books! Hope there is a substantive response to this, or at least expanding on what exactly this means.

    • Dr Fung discusses cortisol in more depth in Complete Guide to Fasting. He basically said generally, in his practice, he has not found this to be an issue but in one case it was and it forced ‘changing the strategy”. If you are concerned you should exercise more as that is far more relaxing that watching TV, per Dr Fung. Also try ‘mindfulness’ and meditation, also covered by Dr Fung.

    • I am one with high cortisol, especially at night, and fasting was really bad for this. When pre-menopause hit I wasn’t able to sleep anymore, only a few hours per night. Also I was really “jumpy” and anxious. Last October was a nightmare.

      However, after lots of experimenting, I found that stress and exercise are not my friends, especially in the afternoon, but I needed relaxation (not necessary meditation, which I still can’t do, but crafting, laughing, walking in nature etc). Also, the main supplement that helped with high cortisol was phosphatidylserine (400-600mg before going to sleep). Now I can sleep and I also can fast again, got to 24h fasts without problems.

      • HI Isabela,

        Just wondering what kind of ‘problems’ you had in a 24h fast? What symptoms indicate that fasting was not for you because of cortisol?

        Thanks!
        Danielle

  7. Prashant Gokhale

    Dr. Fung, thanks for the great article. How do you read the terminal spike in insulin?
    Looks like day 2 is flattish. Day 3 falls. And then it spikes on the morning of day 4.
    Is that a case for multiple 72 hour fasts?

    • I suspect that they broke the fast that last morning, right before the end of the study.

    • The spike in insulin on day 4 comes from eating breakfast.

  8. I have never found this to be true: “They all expect to be ravenously hungry, but actually find that their hunger completely disappears.” I do typically experience less hunger over time (in days), but hunger comes in waves, and not always do I experience this. One time of 4.5 days fasting (eat Sunday night, don’t eat again until Friday at lunch), I got famished — and I mean famished — on Thursday night. It was all I could do to make it to Friday.

    Weight lifting also seems to cause more hunger (whether fasting or not, but particularly when fasting). Aerobics doesn’t seem to have the same effect.

    Another thing long fasting times does for me is interrupt my sleep; I usually sleep less, although typically, I’m not as tired as I think I should be. Also, I can get cold at night.

    I’m trying another 4.5 days of fasting next week. I’ll try to remember to report back.

  9. When should you eat relative to exercise (weight training) if you practice intermittent fasting?

    • Luke,

      There are many who recommend working out right before ending your fast.
      Personally, I get my best workouts in while fasted, especially in the morning. My max lifts are usually 10-25% heavier while fasted. I haven’t seen any benefit though to eating immediately after your workout.

  10. the intelligent omnivore

    Another great article and it mirrors my experiments with 24 hour, 48 hour, 72 hour and longer fasting.

  11. I really struggle with hunger and do not experience it in the way described. When my stomach is really empty I have a burning, cramping pain that ramps up and up until I finally eat something. I liken trying to function normally in this state to “attempting to carry on a casual conversation while resting my hand on a hot stove.” I have had this as long as I can remember and really believe that this panic inducing situation is at the root of much of my overeating. The first time I attempted a 24 hour fast I ended up doubled over and crying in pain. I know this all sounds terribly melodramatic, but I actually do have a high pain thresh hold and cope with regular migraines with far less drama.

    I am bound and determined to do long fasts though. I use chia seeds and psyllium husks when the pain hits and this helps to some extent. I recently completed my first 5 day fast and I was really looking forward to the blissful state of not being hungry after day 2. I think I may have gotten a bit of it by the end of day 4 but it remained very tough throughout. What I DO notice is that I eat FAR less than usual during the “Feast” stage. I enter it convinced I will never be sated again and yet I run into a hard stop after a few bites where I find myself unable to continue. So this makes me very happy. However, I refuse to accept that my hunger challenge means that fasting is not for me. It is my only hope at this point. I don’t expect fasting to be pleasant or easy but if it could be a notch or two down from sheer agony I would be most grateful! Is it just me? Anyone have any advice?

    • Monique, the brain is very poor at differentiating hunger from thirst. Even for those eating or eating regularly (no fasting at all) drink 16oz of water 30min before you eat and you’ll eat less. Another factoid, your brain will not signal full until abt 30mins after you actually are ‘full’. This is what leads many to be inadvertently over eating. As it relates to hunger while doing a water fast, drink more water, I’d say two liters or more per day. You may find that reduces your hunger.

      • Stephen T

        Walt, the 30 minute delay from eating to feeling full is important and very good advice. I break my fast with a drink of coconut oil and try not to eat more food for another 30 – 45 minutes. I think this helps to prevent overeating.

        • And folks, don’t forget the salt. Very important to avoid chills and cramping. Broth is a great salt delivery mechanism.

          • Stephen T

            Steve, a good point. I add salt to my coconut oil and add a bit of lemon flavour. I also found magnesium helped with leg cramping.

    • Stephen T

      Monique, I don’t see the sense in putting yourself through all that, although some people clearly like the challenge.

      Bearing in mind the junk-laden never-stop-eating ways of many people, do we have to aim for the extreme opposite end of the spectrum? Isn’t just eating a far healthier LCHF diet with some fasting good enough? It is for me. I admit that I don’t have a problem with my weight and came to low carb for health reasons. I soon found that I had much greater control of my appetite, so I thought I’d try some fasting. I now do 16 hours most days. I’ve never gone beyond 20 hours.

      I see absolutely no reason to put myself through the kind of torture you describe.

    • I found that many times I could not control to eat, not because of hunger, but because the brain suddenly appeared the idea to eat something , and ideas is difficult to control by hormone . Are you the same?

    • You may have a physical reason for your pain, such as an ulcer or other problem that is medical. Perhaps consider speaking to a physician as to the cause. To be honest although I feel fine during a 24+ I have had some reflux and bowel problems (not constipation!) that make it more difficult.

      Also are you taking apple cider vinegar (or any other type)? I have found that makes the reflux worse for me and things have improved since I stopped taking it (during my first 2 weeks would have two or more teaspoons mixed with water).

      I do not believe most of this is emotional. Sure if you are particularly upset, had a major setback in your personal life it is possible or under extreme stress at work or at home but if it is an ordinary day, I personally do not buy it. While I do not agree with everything, I agree that this is mostly hormonal. Years ago when I was pregnant, like some other overweight women instead of being hungrier I became less hungry. Although I ate, food stopped being a priority. I could take it or leave it (which is not the case on an ordinary Thursday, still). By the time the baby was born I had lost weight! This happened more than once and it was all hormonal. My sister in law is an amazing baker (and is a little stressful in other respects) so I am always rushing for dessert when at her house no matter what diet I am on at the moment, it will all go in favor of cookies. Each time I went while pregnancy I would intend to eat dessert and would get so wrapped up in the conversation I would forget about it. Meanwhile under normal circumstances (pre LCHF/IMF) all I would thinking about while having a conversation would be how soon I could politely get more to eat! So there is absolutely a hormone component in general. I think that is much more important than the emotional component which if you have an ordinary childhood and life with no major traumas is not relevant

      I do think Stephen had good advice, if fasting is torture don’t do it! Maybe stick to a LCHF diet and see how that goes.

    • Many thanks for all the responses and some helpful advice. Just a few additional points that may clarify my situation:

      1) Walt: good hunch on the thirst thing. My mother used to suggest the same! However, I drink copious amounts of water and tea. At least 3 litres a day. I am prone to kidney stones so I dare not skimp on this. So I don’t think I am confusing hunger and thirst.
      2) Stephen: Why would I put myself through this torture? Excellent question. I think I have very good reasons – I believe it is the only way to reverse my diabetes and lose weight. I have had reasonable results on a whole food vegetarian diet and exercise up to a point, and then hit a 5 month plateau where I couldn’t lose another gram despite massively ramping up my efforts, and towards the end I started losing muscle and gaining fat. Fasting got the scale and my blood sugar moving in the right direction again. No amount of pain is too great to deter me from achieving what I know needs to be done for my health and well being, and I think I need the longer fasts to tackle my intra-organ fat which is the main culprit in my diabetes.
      3) Why not just do LCHF with short fasts? I am a life long vegetarian – never eaten meat in my life and would rather fast than do so. So I find a strict LCHF vegetarian diet very challenging. The best vegetarian protein sources contain carbs so I just try to stick to whole foods with limited unrefined carbs and hope that the fibre is protective enough. Additionally the pain sets in within a few hours of my last meal so even a short fast is enough to trigger it.
      4) Lori – I have also wondered about an ulcer but if this is the case I have had it since my earliest memories and it seems odd that it would have been with me so long without creating more serious complications. I do think I should find a doctor who will investigate though. For me personally – I don’t think I am an emotional eater. How I know this is if I have the stomach issues under control I don’t eat, whether I am having a good day or a bad one. I do think I have either a hormonal or physical problem that I need to figure out though.

      Thanks again everyone. Breaking a 4 day fast today! Happy Friday indeed!

      • Monique, some more ideas:

        As you see from the article, women seem to have higher levels of ghrelin. This correlates with what I’ve heard from women trying to fast and having a very hard time.

        On the subject of thirst: fasting implies not getting water from food. So if your body is accustomed to 3 litres a day of water plus the water coming from food, it is perfectly possible to “confuse” hunger with thirst. Note that it is not you confusing those sensations, it is your brain sending the hunger signal in stead of the thirst signal because it craves more water. The rule of thumb, thus, is that if you drink and hunger goes away, it was “water-hunger”.

        As for your problems with fasting, I wonder how LC and how HF is your LCHF, and where does protein fit in all this. I say this because it is often hard to overcome decades of learned fat phobia and embrace real LCHF. So many lower their carbs but don’t dare to swap them all for fat, meaning protein consumption increases. Others, starting from classic macro distribution (60% carbs – 15% protein – 25% fat) half their carbs to 30% and consider it “low”. Yet others do both things (so their LCHF is not really LC and not really HF, more like mid-carb, mid-fat, high protein).

        Too much protein will make it harder for you to enter deep ketosis, in which absence of hunger dwells. Same thing goes for not lowering your carbs enough.

        Of course, I just might be dead wrong.
        Anyhow, I hope it helps.

        • Thanks Carlos! I do drink as much as I can when I get the “hunger” pain and it gives momentary relief but I think it is more from having the water in my stomach for a brief time. I think you may be onto something about the high ghrelin levels. My husband fasts with me as he has the same health and weight challenges that I do, and he doesn’t struggle nearly as much. I do have some hope that the ghrelin/leptin situation is improving as this long fast was a little easier than my first one, and my appetite is extremely well controlled on my eating days. It’s just not quite a situation of “hunger comes in waves and passes if you ignore it” but I aim to persevere!

          In terms of my diet – I think I am well over my fat phobia as I eat as much butter, cream, nuts, avo, coconut oil etc as I feel like. I particularly find that coconut oil kills my craving for sugar and baked goods, which has been amazing for me. I try to make fat my go-to when I eat and then add moderate protein and unrefined carbs. If anything my problem is still getting too many carbs but they come from foods such as red kidney beans, chic peas, quinoa, sweet potato etc. Getting enough protein as a vegetarian without getting too much carbs is probably my biggest challenge, but I don’t think we need nearly as much protein as many believe so I try not to stress about it too much. During my fasts I go into ketosis but struggle to stay in it when I eat, so you are probably right about not really being LCHF, with the problem being the LC side of the equation.

          Happy for any and all ideas so once again, much appreciated!

          • Isabela

            Just saying, beans and sweet potato are too much for my own level of insulin resistance. If I don’t keep the carbs to veggies and nuts, I become violently hungry, with hunger pangs, craving for bread, retain water, weight climbs up, etc. However, keeping carbs low is a nice calm place for my stomach, warm tea is enough to help me skip a meal or two. More than that and I can’t sleep at night 🙁

      • Monique, I did not mean you as in a consciously controlled differentiation, rather a very unconscious thing the brain does. But bravo for the 3 litres of fluids/day. What’s interesting, and I had no prior knowledge of this except hunger comes in waves, is the predictability of when those waves occur. So by looking at the above graphs you could discern when to expect hunger to be at it’s worse. Another trick to consider is to eat something of little to no nutritional value just to put something in your stomach then wait 30 mins.

    • Another thought, Dr. Fuhrman claims that hunger is the gut biome wanting carbs and is not always real hunger. He claims it is the bad bugs prompting you to eat sugar and junk.

      While I have no idea if he is correct and I do not follow him, perhaps the issue is your gut bacteria? Certainly worth exploring

    • I once fasted whilst in hospital. 0 kcal for 14 days. I was given chalk-like pills to chew on twice a day against stomach acidity. Maybe that would help ?

  12. I’ve noticed an awful lot of posters asking Dr Fung questions. I used to as well until I realized he either 1) doesn’t follow his blog and/or 2)doesn’t respond to questions. So for those asking him questions, when was the last time he answered you or anyone to your knowledge. Note also, this blog is advertising Diet Doctor, a for profit web site. I believe Dr Fung hangs out there as diet doctor advertises the occasional q&a with Dr Fung.

    I could be wrong, this is just my observation over the last year or so. YMMV

    • I think Dr. Feng ignored the bigger problem of emotional eating , and if you do not solve the emotional eating problem, adhere to fasting is very difficult.

  13. Roger Bird

    Thank you, Dr. Fung.

  14. Wonderful post. Thanks again Dr. Fung. I visited the local library with my copies of Dr. Fung’s books. They reviewed them and ordered a copy of each for their collection. I am donating the cost of these books in hopes others will be able to benefit from Dr. Fung’s generous gift of his time and knowledge to all of us.

  15. looks like fasting works optimally with lower general stress levels which can be achieved via yoga breathing(buteyko breathing method)

    I’ve never been this relaxed in a very long time ever since i started breathing much much slower and allow CO2 to accumulate more in my body.

    Also exercise and cold showers, quick hyperventilation exercises will stimulate your SNS but afterwards you will relax even more deeply.

    U just gotta go with your feeling.

    Fasting is so amazing though im doing it for life now. So convenient as well so side effect is less stressing over making food.

  16. There’s no doubt that one adapts to fasting as far as hunger subsidence and the hormones that drive hunger go down, most notably insulin. The GH remark was interesting insofar as with type 2 diabetics we have too much GH and a lack of the opposite hormone, somatostatin, Somatostatin suppresses both insulin and glucagon and the hallmarks of T2DM are excessive levels of both. However, the good news is that in type 2’s at least, fasting brings up somatostatin levels. and this is actually has a lot to do with the reduced insulin secretion from beta cells in the fasted state. This in my mind may be the main benefit of fasting for T2’s.

    With leptin levels, we need to realize that one may be suffering from low leptin and that’s going to require a different approach, fasting decreases leptin and if you’re hypoleptinemic then you can drive yourself lower here. Most people these days have the opposite though, excess adiposity, low leptin leads to being thin other than a bunch of visceral fat, it’s caused by a lack of adipose cells elsewhere, and when you turn this down then the hypothalamus can go even crazier in its confusion about our blood sugar being low when it is high and command the body to produce more glucose.

    Most people these days are overweight and have an excess of leptin so fasting is perfect to look to turn that down and overcome the hormonal resistance. There can be some real individualization here and we never want to say one approach is going to work for everyone but in this case fasting is a great idea for most people, especially given that they have conditioned us to feed like modern day livestock, fattening us up like they do them, only the trip to the butcher is instead the trip to the doctor’s office 🙂

  17. Although grelin is at its lowest at 9:00, it is also at its highest at 7:00… after the usual longest fast of the day, during the night.

  18. Another question I have regards bone broth. Is there a risk of consuming toxic heavy medals such as lead, arsenic, selenium, and cadmium if this is a regular part of your diet?.

  19. LOL, the data is certainly showing ‘waves’ but 2 hours (for me) is a really long wave. I am happy to have this information, I was thinking (incorrectly) that the waves were much shorter in time. Now to figure out a way to incorporate this new info.

  20. Thanks again, Dr. Fung, for the great blog. In addition to all else, this stuff is simply very interesting! I love the details about how the body actually works.

    I’ve done one four-day fast, water only, thus far. Felt very good – better than I thought I would. No cold feet or hands, only a very, very slight headache once in a while, practically just a hint of a headache. By the second day I had a good, “loose” feeling – I presume from much less water retention and the beginnings of fat burning; being literally less “inflated” is a good thing.

    Hunger – was not a real problem for me. Toward the end of the third day, I did have some cravings for pizza – oh yes, a nice big pepperoni and cheese pizza – but indeed the feeling passed. Stronger, I think, is the tendency to want to return to patterns and behaviors we’ve had in the past. People have mentioned that “emotional eating” is a problem, and that makes total sense to me.

    Rather than go for a fifth or more day of fasting, I decided to eat because I was working the next day, and did feel somewhat sluggish and tired. I did nothing special to break the fast, no broth, juices, etc. Just went right into a low-carbohydrate regimen – it was salad, tuna in oil, sardines and nuts for the first meal. I’ve continued with a very low-carbohydrate practice. Perhaps somewhat high in protein and lower in fat than would be perfect for insulin suppression – as a newly diagnosed Type 2 Diabetic this is of concern to me. Still, the entire process has been beneficial – weight loss and better feelings already. I can *do* this.

  21. @Dr. Fung,

    How is ghrelin affected if you are drinking BulletProof Coffee?

    • Stephen T

      Dawn, I drink coconut oil and find it helps to reduce my appetite.

  22. I definitely agree that hunger during fasting comes in waves that get easier to resist. Honestly I have come to enjoy my fasting days, the mental clarity and high energy are exhilarating! I always wait at least 12 hours after the previous day’s food before a breakfast, and about once a week I fast for 36 hours. I had intended a 4.5 day fast 2 weeks ago but broke it after about 62 hours –as Dr. Fung (and Jimmy Moore) wrote in their book “Complete Guide to Fasting,” you can start and stop a fast at any time, go by how you feel.

  23. This information is life saving for the inconvenience of hunger pangs! I always maintained a normal weight and used to eat a very low fat diet which became a problem because constantly eating resulted in GI problems as well as insomnia. From 2015 LCHF and intermittent fasting became a saviour!

    Since 2015 I would have a high fat breakfast at around 10am and found that I would stay hungry after breakfast in an attempt to do intermittent fasting and to stretch the fasting period to dinner time at 18h00. I then decided to have a bigger breakfast so that I would be less hungry. This strategy sort of helped a bit but with hunger pangs again at around 15h00. So eating did not make me less hungry! I thought it would be better to have my main meal at lunch time but this does not fit our lifestyle.

    The information about ghrelin is very interesting, you are hungry because you eat. I am now in the process of stretching my daily fasting period to 18 hours and break my fast at around 14h00 daily after fasted strength training around 13h00. I understand I will need to establish the new habit and not expose myself to any food to facilitate the process. I started doing this about 8 days ago. I find that my first meal, a normal breakfast, at 14h00 is very satisfying with no hunger pangs until 18h00 when we have our main meal. I now have much more energy during the afternoon and think more clearly. In the meantime it is difficult to get through the morning coping with hunger, even with a fat adapted metabolism, but It does not influence my energy levels.

    My sister is a big inspiration as she has been doing 24 hour fasting daily for the last 5 years, before fasting became known and popular. Of course she was heavily criticised by family and friends. I find it interesting that she was about 6 kg overweight all the time while following this regime and as soon as she adopted LCHF a year ago the 6 kg just melted away! This also shows as mentioned that ghrelin spontaneously decreases independently of serum insulin or glucose levels as well as illustrating the insulin weight set point.

    She now says she has trouble maintaining her weight as she tends to become underweight which she does not like. Initially she had trouble eating fat, her first high fat meal landed in the garden. She then slowly increased her fat intake by about 10g per week until she could eat more fat and replace her carb intake with fat energy intake. She has an early breakfast only on Sundays with her family.

    I am looking forward to not being that hungry during the morning, which I believe is achievable.

  24. Hello Dr. Fung!

    Since fasting increases cortisol, should people engaging in intermittent or extended fasts take extra calcium or other suppliments to offset bone/collagen loss?

  25. SimpsonsFan

    This is intimately familiar to me. My history is that of naturally fasting (as opposed to making a plan not to eat).

    For most of my adult life, I was very thin, without any effort on my part. (My BMI ranged from 15.3-16.2 until some time in my 30s.) And while I’ve always known I had a slow metabolism compared to friends my age/size (my BMI is currently around 800), we got to a point of joking that I must not produce much ghrelin, since I am rarely hungry and can easily go ages without eating. (I have gone as long as 7 days without eating, with ease.) (My long-time best friend, by comparison, was always about the same height/weight as I, yet her metabolism seemed much more active, as she struggled to keep weight on, eating constantly to try to keep up, even resorting to those meal replacement drinks to augment her diet.) (In short, the complete opposite of me, even though, outwardly, we looked very similar.)

    Given my decades of thinness while eating only when hungry (defacto “fasting”; 1 meal/day, on average), I discovered very quickly that eating breakfast, for example (all the rage for the past 10-15 years, telling everyone they must eat breakfast), made me RAVENOUS by about 11 AM, whereas I normally wouldn’t even think about food ’til much later in the day…if at all. This is still the case, to this day. If I eat breakfast, I am crazy-hungry by lunchtime. (My sister once asked me, “Do you ever get to the end of the day, and you’re getting ready for bed, and realize you haven’t eaten anything all day?” “All the time,” I excitedly replied in solidarity.)

    These days, with people noticing how little/seldom I eat, I have often explained about my lack of appetite, possible lack of ghrelin, but usually add that the only thing that gets me to eat more is…in fact…eating. When I do eat, I have more interest in eating, or in food, than I did during the previous (20+hrs?).

    So, this sounds very familiar to me.

    • Stephen T

      Blimey, interesting. I bet you’re popular with the girls eating lettuce and low-fat rubbish in an attempt to lose weight.

      • SimpsonsFan

        Stephen T, I’m pretty sure you should wait until you’re over 13 years old to comment.

        As an accomplished woman with a higher IQ than yours, I find virtually no value in your reply to my comment. You seem filled with hate (and stupidity). But maybe when you’re more mature, you’ll realize that grown-ups attempt to discuss things, share experiences, and learn from each other, rather than immaturely jumping to asinine conclusions and vomiting hate speech in a misguided attempt to make themselves feel superior.

        You’ll get there, though, li’l fella. Just stay in school and keep applying yourself. You can become anything you want in life. Don’t let your current mistakes take you down the path of becoming another ignorant, misogynist a$$hole.

  26. Amotlfoth

    With alternate day fasting (36 h each fast, 3x per week) the hunger was quite strong at the beginning. Drinking lots of cold water during a wave of hunger helped. But I am happy to report the hunger is much much less after practicing alternate day fasting for 2 months. The hunger early on was brutal – now it’s a breeze. It helped that my husband embarked on it with me. I have already achieved my weight loss goal, but continue the alternate day fasting to see where it leads. I had not set a goal of my weight in high school (3 decades ago) but now I think that’s inevitable. That’s happy news, too. So my advice: hang in there – it gets better. Much much better.

  27. Than you Dr Fung for another great post.
    After your posts I started to do 23 hour fasts every day. I must admit that I too have been worried about muscle loss.
    In your book OB p239 you state “5. Protein conservation phase (after five days)”. However, in the last graph of this post the the GH is stable at 1 ug/L until 16 hours into the fast and then rises to 3 ug/L by 24 hours. Does this mean that the rise of GH from 1 to 3 ug/L in the first 24 hours is not enough to prevent muscle loss during that time? Or, that it does prevent muscle loss, but, that it does not reach a maximum until 5 days?

  28. New post by Dr Fung

  29. Hi. I love your posts, however I’ve noticed you only seem to applaud the ketogenic diet, with no regard whatsoever to an high carb low fat diet (really low fat, way less than 20% fat per day). Or even just a plant-based diet. Which means you don’t believe at all that a vegan diet could be healthy. I would like to hear your thought about this, it would be nice to see a well-thought analysis. An analysis not biased by possible misconceptions and prejudices. I’ve seen many doctors and nutritionists saying a plant-based lifestyle is just wrong and that’s just it for them.

    • PlantKeto

      Seline, just purely FYI… I am a plant-based/vegan and am currently doing keto. It is early days, but I’ve had the most success in the first couple of weeks of keto than everything else in the past few YEARS(!), save adding cinnamon (a natural insulin sensitizer) to my diet. (Just as an example, I did the ‘Insanity’ program, which promises “a year’s worth of weight loss in 60 days.” I gained 2 pounds.) Remarkably, addressing my insulin production, reducing carb’s, and adding cinnamon, allowed me to lose 20 lbs in 2 months. Sadly, the cinnamon effect plateaued, and it has not helped me lose any additional weight since that first 2 months of adding it, several years ago. (Maybe it helped me stop gaining weight, though.)

      I did (vegan) intermittent fasting for a few months, without a single pound lost. I started with 20/4, then when that didn’t work went to 44/4 or 40/8. When that didn’t work, I switched to 16/8. (I was already plant-based and following the Insulin Index, with daily exercise.)

      I’m trying not to get too excited about my minor successes in just the first couple of weeks of vegan keto. But I have already dropped 2% body fat. (That could, of course, all be undone very quickly.)

      In my case, I have PCOS (thus insulin resistant), am currently in perimenopause (thus estrogen dominant), and was inexplicably recently diagnosed with a fatty liver. (WT…?!?) That all sounds awful, but I’m really quite healthy, overall. Doctors have attributed my lack of symptoms related to those conditions, and my youthful appearance, to my healthy lifestyle. As such, I have long-known that I have to reduce carb’s as much as possible, so as to minimize the amount of insulin I produce. It’s impossible to burn body fat in the presence of insulin. Insulin is produced primarily in response to carbohydrate (and pretein, to a lesser extent, and almost not at all, from fat consumption). Now that I, apparently, have a fatty liver, the push is on to find some way to lose fat, that simple caloric restriction and exercise has failed to achieve thus far. With 2% BF lost in the first couple of weeks of keto, I’m hopeful. I’m eating virtually zero sugar and low carb, loads of vegetables and greens (which I always have), nuts, seeds, and adding as much fat as I can tolerate.

      TMI, I know. But vegan/plant-based keto is a thing. Wish me luck!

  30. alejandro heredia

    Which foods or drinks can cut intermittent fasting?

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