The Sweet Spot for Intermittent Fasting

lipolysis and insulin

Lower insulin means greater fat loss

Intermittent fasting — the practice of going without food for some (undefined) period of time — has many health benefits. It can help prevent heart disease, speed fat loss, and slow or reverse aging.

There are a number of physiological mechanisms involved. It reduces inflammation and oxidative stress, leads to increased numbers and quality of mitochondria, and increases autophagy, the cellular self-cleansing process.

Many of the beneficial effects are entwined with lower levels of insulin.

The function of insulin is to promote energy storage and the growth of the organism. When insulin is increased, fat is stored in fat cells, and other cells take up glucose from the blood.

Most importantly, when insulin is increased, lipids can’t leave fat cells. Since fat loss is all about getting lipids out of fat cells to be burned, losing fat requires some attention to how diet, exercise, and fasting cause insulin to rise or fall.

Take a look at the following graph, taken from a paper by Volek et al. It shows that even small increases in insulin, within the normal range, virtually abolish lipolysis, or the breakdown of fat.


lipolysis and insulin


This is where intermittent fasting comes in, as one of its effects is to lower insulin levels and thus increase lipolysis. The question is, how long do you need to fast before insulin comes down?

Eating causes insulin to rise, the amount of the rise being dependent on a number of factors, such as type and amount of food eaten and the insulin sensitivity of the person doing the eating.

High amounts of carbohydrates and lower insulin sensitivity cause a greater rise in insulin.

Insulin increases and stays higher for several hours after eating – that is, during the “fed” state. The absence of food during fasting lowers insulin.

What duration of fasting lowers insulin and to what extent?

The Sweet Spot for Intermittent Fasting

Ted Naiman, M.D., whose great site is Burn Fat Not Sugar, posted the following graph recently (used with permission). The information comes from a paper, “Progressive alterations in lipid and glucose metabolism during short-term fasting in young adult men”.(1)

Dr. Naiman suggested that “the sweet spot for intermittent fasting” occurs between 18 and 24 hours of fasting, since this is the time period that sees the greatest drop in insulin and increase in lipolysis – the breakdown of fat.

Eyeballing the graph and comparing it to the one above from Volek shows that at an insulin level of about 40 pmol/L, lipolysis should be proceeding briskly.

There has been lots of guesswork as to how long intermittent fasts should last. One very obvious but usually non-verbalized reason is that most people don’t want to fast very long, and after a certain time most people get hungry. But they do want to lose fat.

A very common duration of intermittent fasting, one that I often do, is about 16 hours. A 16-hour fast involves skipping only one meal, typically breakfast, so it’s easy enough. A shorter fast than this wouldn’t involve missing even one meal, so we probably couldn’t characterize it as a real intermittent fast.

But according to the information above, in terms of insulin level, the fast is only really getting going at 16 hours. Extending it further than this ramps the drop in insulin and the increase in lipolysis.

If you can extend your fast into the afternoon, you get more benefits, and a 24-hour fast would do even more.

One thing I would add to Dr. Naiman’s “sweet spot” is that duration matters for insulin level. In other words, it’s not just a matter of achieving a low insulin level, but how long you stay there. Therefore, longer fasts can be of great benefit – though inconvenient in terms of hunger and a normal life.

Fasting promotes autophagy

One of the great benefits of intermittent fasting that I’ve written about often is that it promotes autophagy, the cellular self-cleansing process that breaks down and recycles damaged molecules and cellular organelles.

During the fed state, when insulin is increased, the rate of autophagy is low. During the fasted state, as insulin drops, autophagy increases dramatically, perhaps 5-fold.

Many of the anti-aging effects of calorie restriction and intermittent fasting come from the increase in autophagy – which I discussed at length in my book, Stop the Clock: The Optimal Anti-Aging Strategy.

A high rate of autophagy is characteristic of young organisms; with aging, autophagy decreases, and this allows cellular damage to accumulate. By fasting intermittently, autophagy rates can be reset to that of a younger person.

As we see above, one of the ways this happens is through lowering insulin.

Exercise improves insulin sensitivity, so for any given fasting stimulus, a person who is in shape will see insulin levels drop and lipolysis commence faster than someone not in shape.

Low-carbohydrate diets cause less of a rise in insulin, so probably someone on a low-carb diet who then fasts will also see a quicker drop of insulin into the range at which it promotes lipolysis and autophagy.

Autophagy is suppressed in the presence of insulin resistance and hyperinsulinemia.(2) This may be one of the main mechanisms behind the deleterious effects of diabetes and obesity.

It’s worth noting that the study cited by Dr. Naiman used healthy young men as subjects, and they presumably had good insulin sensitivity.

Fasting as an anti-aging intervention

As noted, by increasing autophagy, intermittent fasting causes the breakdown and clearance of damaged cell parts.

Aging just is the accumulation of damage. As we age, we can no longer recycle damage as readily; cell constituent turnover decreases.

We saw in the interview with Dr. Michael Fossel  that activating telomerase has the effect of increasing cell turnover to youthful levels by lengthening telomeres.

Dr. Fossel roundly rejected my suggestion that, until telomerase therapy comes along and/or it’s shown to truly reverse aging, intermittent fasting is the best way to slow aging.

But, he’s wrong. If the accumulation of damage characterizes aging, and if the aging organism is characterized as being less able to clear damage, then increasing the rate of clearance is the best way to slow aging.

One of the best ways to increase clearance of damage, and hence to slow aging, is through intermittent fasting.


PS: Check out my Supplements Buying Guide for Men, as well as my books, Dumping Iron, and Stop the Clock.


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  1. Crispy says:

    Kiefer says you can achieve the same benefits of a fast, by simply fasting from carbohydrates instead for that window. Comments?

    • P. D. Mangan says:

      I think you can get some, but not all, of the benefits of fasting by omitting carbohydrates. Protein also raises insulin, though not as much as do carbohydrates, and protein completely abolishes autophagy. If you ate nothing but fat, however, you could get most of the benefits. It’s complicated but see here:

      • Crispy says:

        Thanks, so that makes it seem “bulletproof” coffee in the morning to help avoid the hunger would not affect authphagy.

      • Daniel J Antinora says:

        I think whey, eggs, and dairy are even ***more*** insulinogenic than most sugar/carbs but there is no concomitant blood sugar increase.

        I wonder if the liver is getting just as much “signal” not to do gluconeogensis from this type of “low” blood sugar insulin.

        I think you phrase it best when you say that we must make a decision about the growth/aging trade off.

        Muscle is expensive tissue and acquiring it requires elevated insulin levels.

        Excellent work as always Dennis!

    • Dj says:

      Prob need to fast from protein too. Its moderately insulinaemic. Interestingly the population that eats the most animal meat is Hong Kong and they also have the lowest mortality rate. Its only association. No causation links that im aware of.

    • P One says:

      Crispy, no carb only will not promote autophagy. Studies in rodents clearly demonstrate that autophagy is triggered by two simultaneously dietary requirements:
      1) Low insulin
      2) No protein or amino acids

      In experiments, even feeding *singular* amino acids to the animal quickly takes it out of autophagy.

      Interestingly, entering autophagy results in a dramatic surge of free amino acids, and studies have shown that these are the actual breakdown products from the autophagy itself! These free amino acids actually feed gluconeogenesis and paradoxically *raise* the fast glucose level during the autophagy portion of the fast.

  2. Philomathean says:

    A week ago I completed a 72hr fast. I broke it with a heavy meal (carbs and red meat) which resulted in a night of heartburn. The following day, however, I experienced a heightened clarity of thought that can only described as amazing.

    That said: What’s your opinion on breaking fasts? There’s a lot of different opinions on the matter ranging from risking life if broken wrong to no risk at all no matter how you break it.

  3. charles grashow says:

    Have you seen this with regard to TA-65?
    March 2014: Application from K&L Gates, on behalf of Telomerase Activation Science Inc., for cycloastragenol under the Novel Food Regulation (EC) 258/97. Under evaluation.

  4. Ted says:

    I’ve been trying unsuccessfully to treat rheumatoid arthritis with a paleo diet and intermittent fasting with no effect for about a year. A new rheumatoligist two weeks ago suggested I try a vegan diet with no processed foods or oils. He said this would give the liver and kidneys the best chance of clearing immune complexes because otherwise a lot of effort goes into metabolizing and filtering fats and proteins. The diet is designed to mimic areas where rheumatological diseases are almost unheard of. They don’t believe the diet’s effect is genetics either because if the people from non-western countries start a western diet, even a healthy western diet, they develop the diseases at the same rates. I’ve started the diet (desperation) but it’s been too short to judge.

    I was curious about your opinion since you attribute some of your former chronic fatigue syndrome to your vegan diet and your second to last sentence mentions clearance which is one theory behind a vegan rheumatological diet. And in terms of life extension, the diet was based in part on certain rural inland Japanese communities where they are exceptionally long lived. So would it be possible to enhance clearance for life extension purposes by minimizing fats and protein? (I’m assuming removing cellular damage and immune complexes is similar)

    • mike says:

      Try throwing weightlifting into the mix. Calf raises until burnout, squats then pushupts. Diet alone won’t do it. Fasting + diet + weightlifting may help the rheumatoid arthritis

    • Jay says:

      Ted, re rheumatoid arthritis – here’s about the effect of potatoes, grains, nightshade foods:

    • P. D. Mangan says:

      Hi Ted, in my opinion some of your doctor’s reasoning makes sense, but the implementation seems doubtful. I doubt that good fats contribute much to rheumatoid arthritis, but certain proteins, mainly plant proteins, could. Gluten for instance – the other commenters have mentioned eliminating nightshade and starting weightlifting, both good suggestions I think. In the case of nightshade, it’s probably certain proteins in them doing the nasty stuff.

      A vegan diet could be acceptable for short term use, but not long term; I think health problems including fatigue are more likely with long-term use.

      Choose foods unlikely to contain harmful antigens. Besides avoiding nightshades, avoid legumes, possibly milk too. Emphasize good fats: butter, cream, coconut oil, olive oil. No vegetable oils, that’s important. I doubt that meat causes RA, but keeping protein intake moderate may be helpful.

      Clearance in the sense your doctor means and the clearance that I discuss are different. Your doctor means eliminating harmful substances (foreign antigens complexed with antibodies) from your body, the protein complexes etc that cause RA. My discussion of clearance refers to the intracellular breakdown of damaged cell proteins, lipids, and organelles, in other words normal constituents that have become damaged.

    • Max says:

      Ted, you might check out Dr Joel Fuhrman’s book on the benefits of medically supervised multi-day/week water fasting. Longer water fasts and/or strict high-nutrient vegan diets seem to have great success in reversing intractable auto-immune diseases. RA responds well.

      True North clinic in Santa Rosa is a safe place to explore this. MDs on staff. A friend put her lupus into complete remission there.

      The catch is, it seems one needs to maintain the diet to stay in remission. For my friend, at least, no question it’s worth it.

      She did a medically supervised 14 day fast. Think about how much that supercharged autophagy!

      It’s also claimed that during long fasts atheromas (plaques) melt away as autophagy takes hold. The body literally eats itself to stay alive, starting the with the least valuable parts of the organism. Warts and skin tags and miles can melt away. You’d want to stop fasting before important muscles get eaten. That’s why the medical supervision is key.

      Anyway, I highly recommend Fuhrman’s book.

      • P. D. Mangan says:

        Max, interesting. I read Fuhrman’s book on fasting maybe 20 years ago, and it impressed me. I recall the bit about atheromas melting away.

    • julianne says:

      I did a research project last year – interviewed 10 people who went into remission on a paleo diet. Also did a review of diet and RA studies. If paleo doesn’t work – try auto-immune paleo. Some of the group reacted / flared to nightshades, eggs and nuts. It took up to 3 months for some to go into remission.

  5. Tuba says:

    I fast for 12 hours then exercise for three hours before eating at hour 16, or, I do the same thing except for 21 hours then exercising and breaking the fast at 24 hours. I would thing that exercising near the end of the fast would influence insulin levels.

  6. Ben Richardson says:

    As a fellow 16/8 protocol intermittent fast, very interesting indeed. Will this influence your own intermittent fasting protocol?

    I would be tempted to experiment with 24 hour fasts. However whilst I have a Freestyle Optium Neo which I can use to measure blood sugar and ketones, I am not familiar with any method of measuring plasma insulin available outside of a laboratory and I would prefer to do so in order to validate this step-change within my own in vivo. What is your take on this?

    • P. D. Mangan says:

      Hi Ben, good questions. Yes, this is going to influence how I do intermittent fasting. I occasionally, say once a month, have fasted for about 20 to 22 hours, the vast majority of the time, about twice a week, going 16 hours. I have to admit even to going only 14 on occasion, as I get hungry or bored and give in. I’ll now be doing longer fasts more often, maybe once a week. I don’t have a lot of fat to lose, but neither am I shredded, but in any case I’m more interested in the health effects than fat loss. For various reasons, going 24 hours is impractical for me, but 20 hours is easy to implement.

      The only way to measure insulin is through a clinical laboratory. Life Extension has a fasting insulin and glucose test, currently on sale, at $25. That’s much cheaper than testing at a regular lab and doesn’t require a doctor’s order. So, you could test a basal fasting level, then do another at the end of a 24-hour fast. Now that I’m writing this, I think it’s a good idea and I may do this.

      • Ben Richardson says:

        Much obliged and regret I cannot take advantage of that Life Extension test as I am UK based. I will ask the functional medicine practitioner I have recently begun working with about sourcing the same in the UK however.

        I realize the number of internet follow-ups committed to vastly exceeds the number of actual follow-ups, but I commit to sharing findings once I have them!

  7. Arren Brandt says:

    Pity that true fasting/starvation is unexplored by western medicine. Probably because of the clear lack of economic Incentives.
    The Russian fasting-forum Golodanie has some very interesting stories, I’ve read it with a friend who speaks Russian. These people are 40-65 year olds who go for fasts as long as 6 weeks.
    With longer fasts (+5 days and more) re-feeding becomes a critical part of the process, one member died because of intenstinal gas (unsure translation, not a joke) after a sloppy refeeding following a longer faste.
    They are very serious about critical long term DNA changes occurring with longer fastes (14 days and counting).
    Many perform enemas because the intenstines must not be clogged with old debree that stops once the muscles stop working. I’m unsure about it.
    They are angry with western scientists who extrapolate rodent-starvation to humans. Rodents have 10x the metabolism of humans. A rat fasted for 24 hours is like a human fasted for a week or so they say… I have never fasted for more than a week,
    They claim repeated long fastes, 15 days or so, will remove patches of aged skin to an extent that should be impossible according to western medicine. Some note that dental tartar falls of after two weeks or more.

    • Jose Carlos says:

      Interesting post. I have read that the Russians have even cured mental disease with fasts, but I don’t know if it’s true.
      For a longer fast, the golden rule is as follows: if you have fasted for x days, then you need x/2 days before you can eat your normal diet again. That means that for x/2 days you will gradually eat more and an increasingly solid diet, starting with tea, juices, broths, soups, bland food to real dense food. Meats will be your last item in this adaptative process. Also, before you start a long fast, it’s advisable to eat a laxative diet for a couple of days, so as to avoid impacted stools due to the fast.

      • Arren Brandt says:

        I don’t doubt fasting can cure many mental illnesses. Our brain probably gets as fucked as every other organ by western diet.
        Most of the good stuff regarding fasting is written in Russian, a lot about treating mental illness I have heard, little is translated, sadly.

  8. neven says:

    I was wondering if consuming zero-calorie shirataki noodles breaks the fast.
    Is ‘feeling hungry’ necessary for proper hormesis ?

    I appreciate your insightful articles


  9. Haven M. says:

    so here’s the dumb question then. I know when I stop eating for the day but suppose I’m still having a few drinks. Let’s say it’s a vodka soda at 2am? something with zero carbs. Does that drink move my window back a few hours? Or should I just worry about the meal I ate at 10pm?

    It seems like if I drink late at night, I am just going to have to settle in for a long haul fast the next day.

    • P. D. Mangan says:

      Alcohol is actually a 4th macronutrient – it has calories, but differs chemically from fat, protein, and carbohydrate, and doesn’t have the same physiological effects. (They’re better.) But my answer to your question is: I don’t know. Moderate alcohol consumption improves insulin sensitivity, but acutely, it may interfere with fasting.

  10. Mike says:

    so can you give me the cliff notes on how to do this?


    • P. D. Mangan says:

      Don’t eat after dinner, and for breakfast have only a cup of coffee, no sugar. Have another cup mid-morning. Then eat lunch, and you’re done!

      • Rick Duker says:

        This how I fast as well. I think you could extend the fast with a pure fat snack which shouldn’t provoke an insulin response.

  11. Steve says:

    A few comments I would like to make, since I find all this fascinating. Carbs are not the only Macro that causes high insulin response. Whey protein does as well. In the course of a 24 hour day, if one fasted for 20 hours and still ate at a caloric surplus, would end up with more fat (energy) stored at the end of the day. It seems that the real benefit to fasting may be related to anti-aging, as for fat loss, I think energy Balance will always remain the key. Just my opinion though!

    • Richard says:

      Sadly, that opinion is simply wrong. What you have described is a basic application of the second law of thermodynamics, which is true for closed systems, but not for human nutrition. See Jason Fung’s Intensive Dietary management blog on the topic.

      The idea is that a sufficient intermittent fasting program does in the end slightly reduce caloric intake, over-all, but the real benefit is reduction in insulin production. Insulin drives far storage.

      The idea is to quit talking about what foods drive insulin production AND STOP EATING SO MANY MEALS. You’re not going to get leaner by eating. So the idea is to stick to higher fat, reduced carbs, and some protein. Not eating results in production of growth hormone, testosterone, and adrenaline. IF promotes autophagy. Fat does not drive an insulin response, but the idea with fasting is to NOT EAT. Drink water or coffee or tea. do not consume any unnecessary calories: You are not going to die from a few days of missing food, and you are certainly not going to die from not eating for 24 hours.

  12. mike says:

    This is interesting research. It’s tough to tell this to people without them getting angry, but it seems like 36 hour fasts once per week would really do the body good. If older, fatter and in less shape it may be more necessary to do 48 hour fasts once a week.

    Its funny when you talk about the “fed” state. The state the most people are in, all the time. Are “fed” people easier to manipulate? Do they have less drive and determination? Funny how being in constant fed state their body never has a real chance at autophagy.

    People get mad at me when I talk about fasting. They think im some kinda fucked up retard or something.

    Thanks for the invaluable research and eloquent wording.

    • P. D. Mangan says:

      Thanks, Mike. I hardly ever talk to anyone about fasting. Do people really get angry? Why? Maybe they feel guilty about eating all the time and don’t want to be reminded that it’s bad for them.

      • mike says:

        Because the American tradition is “3 meals a day” :carb heavy”, “low fat”. When I tell them about fasting it’s like telling them theyve been wrong this whole time. You can’t unplug someone from the matrix if they don’t want to… they’ll become hostile toward you.

        This is very red pill way of looking at fitness/lifetsyle which is why I can’t get enough of your site. However it’s almost taboo. People think of fasting as some crazy thing muslims do, or what anorexic people with eating disorders do.

      • Bruce J Alldis says:

        I have realized that there is another taboo subject beyond Religion and Politics…peoples food! Telling them to stop eating does make them mad.

  13. ConantheContrarian says:

    The very first time that I fasted, I was in my early twenties. I fasted for three days on water, lemon juice, and honey. It was to rid my body of toxins. For the fourth and fifth days, I only drank vegetable and fruit juices. The purpose of the fast and the liquid diet was to cure my acne, which was cystic and horrible and disfiguring, and it did. Now I fast to burn fat, and I am following Mangan’s suggestion to fast fourteen to sixteen hours from dinner to lunch twice a week. In five or six weeks I have lost about four pounds. Of course, I eat as Paleo as possible, and I exercise with mild resistance training, martial arts (and certain exercises related to the martial art to increase strength), so I am pretty fit. I think that the intermittent fasting has help me lose the weight (and fat) around my waist and derriere. Thanks, Mangan, for the helpful tips. I have been recommending your site to all the men I know over 40.

  14. Joseph Moroco says:

    My question is, does age have an impact on how much one should fast? Should someone mid-sixties be fasting longer than some on mid-forties?

    • P. D. Mangan says:

      In theory it might, since insulin sensitivity declines with age. But mostly that’s a function of increased fat and lower exercise capacity with age, so if you’re in decent shape, I’d say the difference would be trivial.

  15. Joshua says:

    Any thoughts on the influence of exercise during the fasting window? It seems to be that getting some sort of (reasonably intense) exercise might have the effect of speeding things up. I.e. a 16-hour fast where exercise is performed during that time might have the same effect as an 18 or 20-hour fast. But I don’t think I can provide evidence for this claim.

    (Also, it seems that both the comments and the articles-showing-up-way-down-the-page issues are fixed.)

    • P. D. Mangan says:

      Joshua, absolutely, exercise speeds things up. See this: But the exercise done during the fasting window was low intensity, most participants doing “brisk walking”. An intense workout like lifting requires eating afterward.

      I had my web guy do a second go around, and it indeed looks like he fixed everything.

      • JP says:

        Currently I fast twice a week – Tuesday/Thursday – and it is either 24 hours (breakfast Tue to breakfast Wed) or ~34 hours (say, 9 or 10pm Monday night through 7am Wednesday morning).

        However, I just started working out on Tue/Thu as well as MWF. Each time 30 to 45 mins of lifting. So the question is, if I should eat after that, what should I eat? Could I get away with some sort of liquid protein drink? Would that be considered a fast-breaker? Or if I want to exercise MTWTF, then should I fast on the weekend instead?

        • JP says:

          OK, should have read Fed vs Fasted workouts before posting. But how does your week look in terms of exercise days and fast days?

        • P. D. Mangan says:

          Yes, you should eat after lifting, and a protein shake is definitely a fast-breaker. If I work out later in the day, I’ll sometimes fast until workout time; otherwise, I fast only on off days. I always eat after lifting.

    • Arren Brandt says:

      For shorter fastes (1-2 days) you can easily continue with physio.
      For longer fastes (3 days and on) the recommendation from experienced fasters seems to be walking, you can walk a very long way (many km’s). This makes evolutionary sense considering that starvation periods probably coincided with walking to some other place where there is food.
      If you try to speed up the transition to ketosis in a longer faste by hitting the gym hard you are likely to crash and abort the faste out of feelings of misery. Especially when you are a newbie.
      My latest faste was 5 days, sunday to friday. It was the tenth time, the longest time and also the easiest one. I found time for some easy gym stuff but nothing intense.

  16. louis sir says:

    I’ve been IF’ing for a while now and have noticed big toe pain. Today it got worse, terrible even. You know what that means, gout. Can you comment on the association between IF and uric acid build up? Anything that we should do to our diet to stop it? I find it odd that if we have autophagy occurring, then why is this acid building up in my joints?

    • P. D. Mangan says:

      I hadn’t heard of that until now. An article from 1964 mentions it: Uric acid excretion in obese subjects during periods of total fasting

      The mechanisms involved in the renal excretion of uric acid were studied in obese subjects undergoing short-term total fasts. On such a regimen with the caloric needs derived from endogenous fat stores, the serum uric acid increases above normal levels while the urinary excretion of uric acid decreases. A similar effect on serum and urine uric acid levels with diets high in exogenous fat has been noted by other investigators. Probenecid was found to be effective in reversing these changes in the fasting subject, suggesting that the mechanism involved is an increased uric acid reabsorption in the proximal renal tubules. Both glycine and glucose taken orally lowered the elevated fasting uric acid levels and increased the uric acid output in the urine. It is concluded that in a fasting subject (or subjects on high fat diets), decreased levels of amino acids and carbohydrate in the serum result in reduced amounts of these substances in the glomerular filtrate, thereby diminishing the competition with uric acid for the proximal renal tubular reabsorptive pathways and accounting for the increased uric acid reabsorption.

      As to what to do about it, other than seeing a doctor and getting a prescription, I don’t know. Facchini dramatically lowered gout attacks through phlebotomy. As for autophagy, that wouldn’t be involved at all, since that’s an intracellular process and wouldn’t affect serum levels of uric acid, not would it affect deposition of uric acid crystals in a joint.

      • louis sir says:

        Thanks, that is an interesting excerpt.

        I am not obese but I do have a baby gut to go along with my muscles.

        I am doing some research on the matter and it seems that when I break the fast, I go to meals that are low carb etc., which means meat. My point is that what’s eaten during the 8 hour window tends for me to be a little light on roughage focusing on the good stuff. That being said, I don’t have the fructose intake I once would have had bc of IF and LC, as fructose is gout triggerer. There is the alcohol consumption, maybe that is enough of a trigger. I recently switched from red wine to vodka soda to keep calories down.

        I think from now on, I am going to get some tart cherries into the mix along with more veggies when I break the fast. Cherries tend to help clear up the uric acid. So does ACV, apparently.

        Very interesting point being made about “decreased levels of amino acids and carbohydrate in the serum result in reduced amounts of these substances in the glomerular filtrate, thereby diminishing the competition with uric acid” I guess that’s the price being paid if you’re trying to burn fat with a 16-18 fast. I’d take tart cherry juice to offset, but then the fast would end.

        Phlebotomy? Really? Strange stuff.

        • Joshua says:

          I had high uric acid (asymptomatic) for a number of years. Tart cherry juice helped slightly, but what has had a larger impact has been baking soda. Taking it straight, I mean. Don’t try it on an empty stomach, though — it can have a bowel-loosening effect. Start with half a teaspoon with a meal, and maybe go up from there. Bonus: baking soda actually has performance-enhancing qualities if taken before lifting weights. (SuppVersity has had some articles about that.)

  17. louis sir says:

    the best part about ACV is that it wouldn’t break the fast during the day if you took it. Sounds like baking soda on an empty stomach is a bad idea…could u put it in coffee…talk about drano.

    • Joshua says:

      I actually have been using ACV on my vegetables for several years now. I hadn’t heard that it could have uric acid-lowering effects, though. And really, I’m not sure it did. I only noticed a significant difference with the baking soda (which is something I started later than the ACV).

      And baking soda in coffee?! Haha, never ever will I try that. I did a bit of baking soda fasted before, and won’t make that mistake again.

  18. Denise says:

    If you already eat very low carb and are in ketosis you experiencing very little hunger when doing a longer fasts of let’s say 3-4 days.

  19. DJ says:

    Fasting from carbs alone wont have the same effect due to moderate effect on insulin. May be fasting from carb and protein would. In saying that the population that east the most beef is Hong Kong and they have the lowest rates of mortality and best longevity. An interesting association.

  20. T Becker says:

    Great article! I typically go 23/1 Monday-Friday, and then have a bigger eating window on the weekends, so attempting a 24 hour fast is really not a big deal for me.

    I’m wondering how long is too long? I recently did a 72 hour fast and was ready to break it at the end, but I had a few friends who stuck it out for 5 days. At what point is it foolish to continue even if you feel you are able to go on?

  21. What should be the last meal before starting a fast? Lunch? Breakfast? Seems like it should be a morning meal so that you are into the fast by the time you go to sleep and autophagy is maximized.

    • P. D. Mangan says:

      Hi Randall, fasting can be done any way you like. Most people seem to skip breakfast because it’s easiest, but whichever, way, just count the hours from the last time you ate and that’s your fast.

  22. Nick says:

    Right. I’m now 15 hours into my first ever intentional intermittent fast. It’s 10:15 in the morning, and I’m starting to have hunger pangs. Yesterday was nearly carb-free except for a decent load of beer.

    The idea of IF is intriguing, and I thought I’d give it a try. I’m on a schedule of lifting & HIIT, such that IF is really only workable overnight from a rest day to a training day, so maybe 3x weekly. I suppose that’s quite a bit though.

    A fasted workout was impossible for me to imagine, as I work out mid-day. But then this morning, I thought, hey, it might well be possible to go in the morning, say 13 hours into an IF. Might be worth a try, since I have the huge luck of nearly complete flexibility in planning my work hours and stuff these days.

    But not today. I normally work out 3 – 4 hours after breakfast, which is normaly 600 cal of casein, seeds, coconut bits and blueberries. I think it’ll be just a whey shake with coconut & blueberries an hour before hitting the gym for my arms/back/chest/shoulder session today. We’ll see how it goes, if I get hungry and light-headed……

    • Nick says:

      UPDATE: 16 hour fast broken: whey shake with 120 g blueberries, 20 g seeds & coconut, 5 g creatine. A bit hungry, so 12 g Brazil nuts on top of that. Now for some strong black tea & to the gym. (28 g protein, 12 g carb/11 g sugar, 20 g fat, 366 kcal)

  23. Andrei says:

    Hi, the link “Check out my Supplements Buying Guide for Men” at the bottom of the page is broken 404

    Thanks for the awesome work by the way 😉

  24. Nick says:

    What do you make of this post: ?

    Anything questionable there? Obviously, the whole business of carbohydrates and sugar is contentious, though they do seem to point to studies showing benefits of post-workout sugar.

    I did my first 20-hour fast the other day, breaking it with a normal supper of poached salmon & salad, if a bit more salmon than I normally eat. That night in bed, my heart was pounding so hard, if not really fast (didn’t measure my pulse though), that I couldn’t sleep for a couple of hours. It seemed to be over by morning though. I wonder if I should eat less after fasting so long? I’ve fasted 16 hours a few times with nothing similar happening.

    • Joshua says:

      Regarding the pounding heart after the 20-hour fast, I think I might be able to add something there. I’ve noticed that fasting sometimes tends to invoke an adrenaline response. This can get your sympathetic (“fight-or-flight”) nervous system fired up. As a result, that night you might notice your heart pounding a bit and find sleep more elusive than usual. My experience is that eating a larger meal at night helps alleviate this somewhat, rather than hurts. So I wouldn’t worry that you should eat less after the fast. You might also try magnesium or melatonin at night.

      • Nick says:

        Hey, thanks for the quick response! I didn’t have my normal vitamin/mineral “sport” soda tablet that day, come to think of it, so I may well have been lacking some minerals. And it was a pretty low-fat supper.

  25. Joel says:

    So, would five 16-hour fasts, or two 18-hour fasts every week be more beneficial?

  26. Will Mosse says:

    Great article, thanks. Have you written on what breaks a fast? It is probably on your site somewhere, but I haven’t found it. I am currently doing IF between about 16/8 and 18/6, depending on the day. I find having a couple of cups of tea with a dash of skimmed milk during the day helps, but I have read different things on whether this would break a fast or not, particularly from the perspective of autophagy. Could you advise at all? Thanks!

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