Some nuances of Intermittent Fasting

Intermittent fasting (IF) is not a universal panacea, regardless of whether you’re not eating anything at all for a few days each week/month or just restricting your feeding window to a few hours per day.

Some protocols, eg, 20h fasting every second day, significantly improve insulin sensitivity in adipose tissue (Halberg et al., 2005). This is expected to make fat gain easier, and while this wasn’t meant to be a study on body composition per se…


body composition


After just a few weeks, things weren’t changing in a good way (NS).



Exhibit B. And in this study where they fasted every other day, fat-free mass also declined (but at least so did fat mass) (Heilbronn et al., 2005):


fat and fat free mass


From the abstract, “Subjects lost 2.5 ± 0.5% of their initial body weight (P < 0.001) and 4 ± 1% of their initial fat mass (P < 0.001). Hunger increased on the first day of fasting and remained elevated (P < 0.001).”



Diet Advice That Ignores Hunger” 

Further, “As expected, a significant increase was found in feelings of hunger (from 37 ± 5 to 56 ± 4 mm; P < 0.001), and a significant decrease was noted in feelings of fullness (from 43 ± 3 to 23 ± 4 mm;P < 0.001).”



Exhibit C. Reduced feeding window (3 meals per day vs. 1 four-hour feeding window) (Carlson et al., 2008).

Skipping breakfast and ingesting all of their calories in a four-hour feeding window in the evening: “Subjects consuming a single large daily meal exhibit elevated fasting glucose levels, and impaired morning glucose tolerance associated with a delayed insulin response, during a 2 month diet period compared to those consuming 3 meals/day.”

Starting to sound like Dawn PheNOMNOMNOM and Afternoon Diabetes?



To summarize: loss of muscle mass (Halberg and Heilbronn), increased hunger (Heilbronn), and diabetogenic (Carlson).  These aren’t good things; this way of eating is definitely not for everyone.

Can some people benefit from intermittent fasting?  Sure, but best choose your fasting/feeding schedule wisely; keep in line with circadian rhythms as meal timing is an important zeitgeber.  That means eating when the sun is up; frequency is up to you.

I’m not 100% against intermittent fasting and I don’t deny that some IF protocols may work [for some people], but IF is not a universal panacea or necessary to be healthy, and can even be harmful in some contexts.


calories proper


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  • Michelle Grzybowski

    IF has only worked for me since eating early in the day and not at night. My FBG went from high 90s (on a ketogenic diet with optimal protein! and not insanely high fat) to mid 70s-mid 80s since eating early in the day and absolutely NOT at night. Often ending my eating by 4 pm. and the last meal being lighter. Big meal in the morning. Also, I have seen across the board benefits from fasting 2-3 days in a row each week. (at least two sleeps 😉 ) I feel fantastic, more energy, very balanced mood, performance in the gym continues to progress, muscle growth and decrease in body fat, slowly, but surely. My body seems to be liking this rhythm. I workout and feast (quite well!!) all week and fast and do not workout on weekends. When people say IF didn’t work for them, I am always curious what their IF looked like.

    • jasmine johend

      Great work re the 2-3 days fasting in a row; is that a different full fast or is that the IF stopping at 4.00pm, but you eat normal the rest of the 5 days?

      • Michelle Grzybowski

        Hi Jasmine, I typically fast 2-3 days every week, have since about March of this year. That is water only. The other five days I eat completely normal amount of food,(meaning all my calories) ketogenic, optimal protein, but do so in two meals (just because it works for my schedule) done by 4:00 ish most days. does that make sense?

        It should be noted that I worked up to this schedule. Being ketogenic/low carb makes fasting super easy, in my opinion. 😉 I also need to add that I did a 14 day water fast in March, that also brought about a lot of healing! I never want to give the impression that just one day, out of the blue, I started fasting 2-3 days a week. I always encourage people to slowly work their way up to said amount of fasting. I hope all the rambling helps. LOL

  • Woody Payne

    I do 3 meals 4 hours apart. Starrs when I wake. Sometimes I add a fourth meal because I want to gain the weight back I lost on night shifts. So that’s a 12 to 16 hour fast. I feel that’s appropriate. That way I have a robust circadian rhythm. My main concern is the deeper ketosis in the morning and it’s effect on REM. So once I enter segmented sleep I’ll take raw potato starch before the second sleep.

    Never heard of 2 hour eating windows.. I mean why?

  • newbie

    You might be interested in this N=1
    I did IF for a year, am slim to start with, bought into the autophagy, mito biogenesis internet chatter. I loved it, my labs did not.
    Had significant overnight hepatic gluconeogenesis -fasting BS up at 6, A1c prediabetic at 0.60. LDL shot up into the “you need a statin” zone.
    IF was 7pm to noon.
    Did LDL at 8am, repeated at noon prior to eating – level went up from 5 to 6. My theory – cannot substantiate, neither can the lipidologist – liver sent out many VLDL parcels to feed the tissues their energy requirement – TGs – lots of LDL as a result, LDLr could not clear it all.
    Stopped IF, all labs back to normal preIF (no meds needed) levels.
    Just sharing, in case this helps anyone.

    • interesting, thanks

    • juliannetaylor

      That is interesting – did you change any other aspects of your diet?

      • newbie

        No, I am as consistent as a metronome. At that time, I was strict Cordain style paleo (plus kefir). I’ve seen this same phenomenon in some women who severely calorie restrict to lose weight, I assume by the same mechanism. I have read that women and men show different patterns of macronutrient utilization and storage. I posted this comment to give an awareness, maybe to get checked with labwork if you embark on this dietary pattern.

        • juliannetaylor

          My LDL went up into the ‘you need a statin’ zone too. At the time I was having coconut cream in my coffee and not worrying about butter or fat on meat etc. Read the LDL horror stories about Bullet proof coffee and and article by Dr Thomas Dayspring on a woman with a similar story, Dropped all the added SFAs and added more carbs to my diet and it fell back down to slightly high but okay levels. Menopause of course does not help. I eat 3 times a day – I was fasting until late morning at the time, I eat earlier now. Maybe that helped also.

    • FromPA

      Interesting. After about a year of using intermittent fasting (some days, no breakfast; some days, no breakfast or lunch; some time periods, no eating for days), my HDL has increased, my triglycerides are lower, and my TC and LDL are basically unchanged. You have to watch when you get a test done, however, I got a test done on the first day (overnight fast) of a 5 day fast and at the end of the five day fast. The data at the end of the 5 days is much different that the data at the beginning of the 5 days. But since I don’t fast that many days that often, I use the beginning of the 5 days as my reference point.

  • NY

    Nice post Bill, a balancing act as usual. Can’t get my head around this IF bandwagon, PERSONALLY. Low fat is criticised because you have to starve yourself and fight hunger amongst other consequences but starving on low carb for 16 hours or so has become a new “great tool”, really? Yes I can do IF on low carb without hunger but it still sucks for me: energy levels drop and cold sensitivity increases. Remedy to this is: “eat enough calories during feeding window”, which I can’t do without stuffing myself and gaining weight. Sure it works for some, so do high carb low fat diets and eating multiple small meals during the day.

    • some issues i have w/ 1 meal per day:

      stomach volume massive overload, probably actually increases/stretches gastric wall

      energy overload, like 3000 kcals hitting the body all at once — that’s gonna put a lot of stress on your organs… seems like it could be a recipe for ER stress or something.

      But again, it works for some people…

      • NY

        I think these issues equally apply to 2 big meals as well.

  • Tuck

    There are some other things from that Carlson paper. I don’t think your summary as “diabetogenic” is fair. But let’s just go with their summary:

    “Collectively, the available data therefore suggest that meal skipping or intermittent CR diets can result in health benefits including improved glucose regulation, but only if there is an overall reduction in energy intake.”

    As they explained earlier:

    “However, when on 1 meal/d the subjects would have eaten less than those on 3 meals/day if we had not asked them to consume the same amount of food that they normally eat on a 3 meal/d schedule.”

    They also note the increased fasting glucose reversed when they went back on the 3 m/d plan, so it’s likely just physiological, not pathological.

    • “…the subjects would have eaten less”

      sounds like they’re guessing

      • Ketard Aesthetic Bodybuilder

        I don’t think so. The language implies that they had to insist upon the subjects eating. They also reference other studies where this phenomenon was shown. IF is the same “hack” as ketosis, which is energy restriction without trying.

        • “I don’t think so. The language implies…”

          now you’re guessing, too!

          My turn 🙂
          food intake may decline initially because they’re literally stuffed. But once they get used to eating all the food at once [and if not actively trying to lose weight], suspect body weight will float back to set point.

          • Ketard Aesthetic Bodybuilder

            Ok, but you’re ignoring the two citations after “When rodents are subjected to an alternate day fasting regimen, their
            overall calorie intake is decreased by 10–30% and they maintain a lower
            body weight than animals on an ad libitum control diet, and exhibit
            increased insulin sensitivity and decreased blood pressure.”

          • the Johnson study they cite is pretty good: every other day, alternating 20% calorie restriction with ad lib… but context here is pretty different, on ad lib days, they got to spread it out over the entire day (not gorging in a 4 hour window)

  • Jake Jaglarski

    Glad you posted this. This is something I’ve been thinking about lately. Especially since digging back into Dr. Kruse’s work, because he is a big fan of a “BAB” followed by no snacking + an early dinner. Yet, when I was checking some of his citations, a couple researchers he cited – such as Cunnane et al – actually published multiple studies on the BENEFITS of “nibbling” vs. 2-3 meals a day -> IIRC decreased leptin, fasting insulin, fasting glucose, higher thermogenic effect of food, etc.

    I’ve been toying around with “nibbling” but on a ketogenic/mct-oil induced ketogenic kinda diet, and keto sticks are showing ketones each morning – and especially at night – and I can validate what they show since I have mild keto breath and decreased neurological symptoms (which always happens when I’m in ketosis). Now I need to start tracking blood glucose during the day.

    I’m wondering if it isn’t better for some to actually eat throughout the day, even before bed perhaps, yet use a breakfast+light stimulus as a strong circadian zeitgeber. IIRC studies have shown that the first meal (or was it the largest meal?) are the strongest peripheral circadian CLOCK gene regulators.

    • From some rodent studies I posted about a while ago, both meal size and fasting duration are capable of shifting the circadian phase…

      It’s one of the reasons why I think, since light is entraining the central clock in the morning, it’s a good idea to have a long overnight fast followed by a decent breakfast (in the morning) to entrain peripheral clocks at this time, too.

      • Jake Jaglarski

        In that paper published recently about a poly-therapy approach to reversing cognitive impairment/neurodegeneration in 10 people, they mentioned a 3 hour fast from dinner to bedtime being part of the protocol, along with ~12 hrs of fasting per day (not much). Hypothetically, that may be sufficient then, especially if the dinner is moderately light.

        I’ve been wondering how much macronutrients play into this as well, though. If one eats a light dinner at ~5 pm, and normally goes to bed at say, 11 PM, how would consuming a moderate amount of fat in some tea at 7 pm and then 9 pm again negate any potential circadian entrainment, considering protein is the primary macronutrient that impacts gut incretins and orexins and serves as the largest vagal stimulus out of the three macros. From a biophysics perspective, any biophotonic energy emitted from the breakdown of foodstuffs may have some sorta impact, but I’d imagine carbs would break down into high energy wavelengths, whereas fats would not, overall giving a free pass on fat.

        Wonder what Dr. Kruse would say.

        • “I’ve been wondering how much macronutrients play into this as well, though.”

          Good question. Tentatively, I’m thinking it’s calories, because it’s not insulin/carbs/protein, and equally affected by diets with widely varying fat contents.
          (no conclusive evidence for this)

  • Man

    I concur with your article. I went through some IF protocol (sometimes on purpose, sometimes due to poor finances). It never felt like I improved anything health-wise. I usually eat a high carb whole food diets, with some animal stuff now and then but really, the bulk of my cals are carby foods from tubers, legumes, fruits and whole grain (rice and groats). I eat an early breakfast and late lunch, and I will have some light dinner if I feel hungry around 7pm. I am at the bestest shape with this regimen. I make sure to bathe in sunlight whenever there is some. I respect the circadian rhythm and never eat at night. Sometimes, I will skip dinner due to lack of hunger. And I also make sure to move, especially in the morning.

    I can only compare with myself but skipping breakfast and lunch was no fun and made me look rather sick. I know that paleo / primal circles are touting IF and evening feeding (warrior diet kinda style). I think it is really not good and it pushes people into artificial feeding rhythms promising eternal youth but leading them astray in the long run.

    • “I can only compare with myself but skipping breakfast and lunch was no fun and made me look rather sick.”

      I hear this a lot. For some people, it’s the only way they can reduce calorie intake… but not always very pleasant outcome.

  • HughdePayens

    59 years old and eating low-carb since 2011 mildly ketogenic lots of chicken, beef, fish, pork and brussel sprouts, broccoli and hollandaise, wife is an excellent cook. Been skipping breakfast and lunch since 2013.

    Started doing body-weight exercises in 2011, 100 push ups under 5 minutes, handstand press etc. About 6 months ago I started lifting weights. Currently, 1rm 259 squat, 1rm 268 deadlift and 1rm 169 military press. Have built up significant muscle and have gained weight going from 195 to 208. In 2011 I weighed 250 and was weak…not anymore. Since I have been lifting I have added sweet potatoes occasionally and whole fat yogurt with blueberries and a table spoon of honey.

    I think your diet plays a very large role in regards to how you adjust to fasting. Since adding the sweet potatoes, yogurt it is much harder to fast for more than a day. Used to be able to fast for 2 to 3 days without much effort…now very difficult. Carbs make you want more.

    My panels looked great 2 years ago…haven’t done them again since.

    • Sky King

      But once you get over that inertia of starting another fast, it becomes easier by the day. People who eat high quality LC meals find it very easy to start and maintain a fast with very little hunger pangs. But those first starting out or those who have been eating crap for years will have a tough time of it for awhile. They will need a ton of self-discipline and perserverence to stick it out. They’re the ones who will experience a lot of side-effects as the body detoxes itself, and converts over to a fat-burning, ketone-generating machine.

  • Sky King

    Personally, I’ve been conducting all types of fasts since 2000 when I first read Dr. Joel Fuhrman’s book on fasting. I did my first 30 day water/tea fast then (ignored his dietary advice) and thought it was the best thing I’ve ever done in my life. It doesn’t get more Paleo than that! However, the health benefits of fasting (especially long fasts) have been shown to be nothing short of fantastic.

    There are many misconceptions about fasting, especially that of thinking you’re “starving” yourself to death if you fast for such a long period of time. I noticed Dr. Fung, the Diabetes Specialist, has recently blogged on the subject (14 parts thus far) to clear up many misconceptions people have about fasting. It’s a great read for those who are curious about the subject and may wish to try it:

    There are many cancer research specialists, such as Professor Thomas N. Seyfried of Boston College, who believe that fasting may cure/prevent many cancers.

    • Michelle Grzybowski

      I would agree 100% on seeing amazing benefits from longer fasts. My longest has ‘only’ been 14 days, but the changes have been dramatic. I start my next 14 day fast on Sept. 21. Looking forward to it.

      • Sky King

        I try and do a 1 month fast every year. I usually do one every January if there’s no stress going on in my life at that time. Otherwise, I’ll wait postpone it until April or May. I also fast the 1st week of every month for 4-5 days, then every Monday after that, essentially fasting every single Monday of the year. When I’m eating I’ll eat a high protein/fat breakfast, fish (mainly Wild Planet tuna) and salad for lunch, and then a small salad with some meat for dinner sometime before 6pm and no food after that. Works great for me and I totally agree with you that it’s the bomb!

        Happy Fasting, Michelle! 😀

  • CynicalEng

    Varady’s work on alternate day calorie restriction (as opposed to true ADF) is relevant – for example “Body weight was reduced (P<0.0001) by ADF-HF (4.8%±1.1%) and by ADF-LF (4.2%±0.8%). Fat mass decreased (P<0.0001) by ADF-HF (5.4±1.5 kg) and ADF-LF (4.2±0.6 kg). Fat free mass remained unchanged. Waist circumference decreased (P<0.001) by ADF-HF (7.2±1.5 cm) and ADF-LF (7.3±0.9 cm)."

  • This Old Housewife

    Has anybody been looking at the fast that Jimmy Moore is doing right now? He’s on Day 8 or 9–no chewable food at all, and using bone broth w/salt, kombucha, and water. His videos are on Periscope, and he does daily updates. He says his goal is to go for 14 days.

    His blood sugar prior to doing this was cresting over 100 (doing Warrior-style eating once a day w/extra veggies for micronutrients), and his acne had returned, as well as regaining half of his previously lost weight. Now, his blood sugar has reached a low of 64 (Day 6), and is ketones a high of 3 (same day). On Day 7, his blood sugar bounced back up to 80, and his ketones lowered to 2.4. I noticed his face is clearer with fewer breakouts, so I suspect something’s happening with his liver (good or bad), leading to the problems that caused him to resort to fasting.

    Hubby and I instituted a Warrior-like regime here–protein shakes (homemade) for breakfast, small amounts of celery sticks/green beans/nuts for during the work day, and a keto dinner w/reduced protein. As usual, it worked for about 3 days, then returns diminished. Since he now has Wednesdays off as well as weekends, I consulted with him for possibly doing non-chewable food (fasting like Jimmy) on his days off (making the Warrior fasting portion longer than just during the day)–maybe eating once every other day (or thereabouts) could bring the improvements we seek.

    As for getting Wednesdays off: he had a buttload of sick leave he has to use or lose (he’s hardly ever sick any more), so he applied for and got Wednesdays off from yesterday to the end of the year (a major stress reliever, I’m sure). He does this type of thing every year, but he finally got to have Wednesdays–up to this point, he either got Mondays or Fridays, giving him 4 days of hell in a row to still contend with.

    I thought since we’re kinda-sorta fasting, why not make it FOR REAL in the time he’s at home, where I can tend to him if something goes wrong? We start this weekend. I figure what’s good for the goose is good for the gander, so I’m saying WE–I’m in it too.

    • Esmée La Fleur

      I tried to convince him to do just water, but he wasn’t interested unfortunately. Too bad because his results would be better. I have found that when I drink bone broth during a “fast” my glucose rises from 60 to 80 and my ketones fall from 4.3 to 1.8. That is a huge impact and really diminishes the efficacy of the fast. Plus, drinking only water is actually way easier because you are not ingesting anything that will stimulate appetite.

  • This Old Housewife

    BTW, yes I did see the article from Taubes–too bad you didn’t link to it for those who might have missed it.

  • janeyt

    on a true well balanced ketogenic diet, intermittent fasting is not a problem because your body is using fat as fuel. I don’t feel hungry, I have more free time and I no longer follow the big box manufacturers way of recommended eating. who has my interests at heart, big box food manufacturers???

  • HughdePayens

    Hey Bill,

    Where do you stand in regards to John Ioannidis and Richard Horton and their statements about medical research.

    ‘Moreover, for many current scientific fields, claimed research findings may often be simply accurate measures of the prevailing bias.’

    J Ionnadis.

    Richard Horton (editor of the Lancet)
    ‘The mistake, of course, is to have thought that peer review was any more than a crude means of discovering the acceptability — not the validity — of a new finding. Editors and scientists alike insist on the pivotal importance of peer review. We portray peer review to the public as a quasi-sacred process that helps to make science our most objective
    truth teller. But we know that the system of peer review is biased, unjust, unaccountable, incomplete, easily fixed, often insulting, usually ignorant, occasionally foolish, and frequently wrong.’

    Dr Marcia Agnell, who was the editor of the New England Journal of Medicine for two decades.

    “It is simply no longer possible to believe much of the clinical research that is published, or to rely on the judgment of trusted physicians or authoritative medical guidelines. I take no pleasure in this conclusion, which I reached slowly and reluctantly over my two decades as an editor of The New England Journal of Medicine.” Dr Marcia Agnell

    What impact does that have on you when referencing studies?

    • Peer review isn’t perfect, but how to improve it?

      As to me referencing studies, I don’t call foul-play unless there is a clear example of it… can’t just say a study is bad/flawed because it doesn’t agree w/ my personal understanding of a topic — need to be specific.

      I don’t “rely on the judgment of trusted physicians or authoritative medical guidelines.”

      Does that answer your question?

      • HughdePayens

        Thank you for the reply. Well to the layman, the idea that the people responsible for publishing these studies think that many if not most are incorrect is depressing.

        Richard Smith, editor of the British Medical Journal for many years.

        ‘Twenty years ago this week the statistician Doug Altman published an editorial in the BMJ arguing that much medical research was of poor quality and misleading. In his editorial entitled, “The Scandal of Poor Medical Research,” Altman wrote that much research was “seriously flawed through the use of inappropriate designs, unrepresentative samples, small samples, incorrect methods of analysis, and faulty interpretation.”

        Twenty years later I fear that things are not better but worse…

        …The poor quality of much medical research is widely acknowledged,” wrote Altman, “yet disturbingly the leaders of the medical profession seem only minimally concerned about the problem and make no apparent efforts to find a solution.”

        Altman’s conclusion was: “We need less research, better research, and research done for the right reasons. Abandoning using the number of publications as a measure of ability would be a start.”

        Sadly, the BMJ could publish this editorial almost unchanged again this week. Small changes might be that ethics committees are now better equipped to detect scientific weakness and more journals employ statisticians. These quality assurance methods don’t, however, seem to be working as much of what is published continues to be misleading and of low quality. Indeed, we now understand that the problem doesn’t arise from amateurs dabbling in research but rather from career researchers.’

  • weilasmith

    what about eating when i wake up in the dark with sunbox shining on me? hao bu hao?

    • yes. It’s still a bit of a circadian mismatch, but if you have to get up prior to sunrise or in otherwise darkness, this seems like a decent hack.

  • too many variables that can make a difference. a poorly designed IF strategy is (logically) far worse than an IF strategy where you time your meals, time your workout, focus on improving your circadian signaling, consume a clean diet…etc,etc…most of these studies are very (very) trivial.

  • Anastasis Tzanis

    Hi Bill,

    I agree with your main point: IF is not a panacea. My only objection is that IF is best to be done during the day. I think that this holds true for many people (in particular those coming from a hypoglycemic state – getting nausea when skipping meals) but NOT for people like myself coming from a hyperglycemic state.

    Nice article.

    Anastasis (Nutritional Therapist)

  • Esmée La Fleur

    I have done many long fasts (2 to 5 weeks) over the past 25 years and have experienced nothing but good results. I got stared with Herbert Shelton’s Fasting Can Save Your Life, and then read Jack Goldstein’s Triumph Over Disease Through Fasting and Natural Diet, as well as Joel Furhman’s Fasting and Eating for Health. I followed a plant-based diet as all of those authors recommend for the better part of 25 years and do not recommend that, as eating that way did a real disservice to my body. But their knowledge about fasting itself is a goldmine. I recently did a 16-day water fast with my dog who is experiencing some health issues, and the changes in his blood work were nothing short of astonishing. The veterinarian I use was extremely impressed. This was the first fast I did since switching to an all meat diet 8 months ago and it was by far the easiest fasting experience I have ever had. I can tell you first hand that the type of food you eat on eating days has a profound impact on how your body responds during a fast. If you wish to read abou my recent 16-day fast, you can do so here:

  • Ken

    It seems I’ve reverted back to my old habits of eating the majority of my calories at night. I spend all day in the clinic, usually skipping breakfast to get there at 7am, having a small lunch so I don’t crash after lunch and usually not eating till 7-8pm. Would smaller snacks help? I’m generally not prone to snack

    • in general, entrainment of circadian rhythms is stronger with larger meals (arguing for bigger meals earlier in the day), but if that really doesn’t work for your lifestyle, then anything is probably better than nothing.

      also, eating a large meal at night can delay your circadian phase.

  • Jord

    I thought there was significant benefits from alternate day fasting? ie “Every Other Day Diet” from Dr Varady?
    With a protocol like that, maybe better on the fast days to have a small meal for breakfast, fast until next day?

    • I wouldn’t really say “significant benefits;” it helps some people lose weight but can be too stressful for others. Not a panacea.

      The EOD diet is 25% of maintenance calories on day 1, 125% on day 2, repeat… so there aren’t any total full-day fasts. It equates to a 25% caloric restriction.

      Skipping dinner a couple nights per week might be an easy way to see if IF is right for you. Ymmv.