Marks Daily Apple
Serving up health and fitness insights (daily, of course) with a side of irreverence.
16 Feb

The Myriad Benefits of Intermittent Fasting

intermittentfastingCalorie restriction is all the rage in anti-aging circles. A few mice and worm studies seem to show that drastic reductions in food intake over a long period of time have the effect of prolonging life – although I’m not sure I’d call it living. For one, these animals are actually restricted. There’s no ad libitum access to food. They’d prefer to eat more, but are prevented from doing so. I guarantee you they’re unhappy and, if they could put (cartoonish high-pitched) voice to physiological state, would say they’re starving.

Anyway, humans have picked up on this calorie restriction stuff. You might have seen one or two CR gurus giving TED talks; the exposed rib cages, gaunt faces, and complete lack of lean muscle mass are dead giveaways. Okay – that’s a bit unfair. CR is a legitimate way to improve many health markers. I’m just not convinced actively restricting your calorie intake through sheer will is the true path to enjoyable longevity. I’d rather be robust, vibrant, and full of zest. I want to eat big strapping meals of steak and veggies smothered in butter without counting calories. On occasion, I like to devour an entire roasted chicken (yeah, yeah, chicken has more omega-6 than most animals, but I’ll live). I want to maintain muscle mass and have enough energy to go on long hikes and have the legs to still leap for high passes (over the young guys) at the end of Ultimate games. And as I appreciate the neuroprotective and autophagy-promoting qualities of calorie restriction, I’d rather not expend the mental energy and fortitude required to maintain such a regimen day-in and day-out. Nor would I willingly subject myself to forced calorie restriction, a la the lab mice. No human-sized rat cages for me, even if they include a salt lick and a running wheel (don’t get any ideas, Blaisdell). Based on the science, I don’t think all that is necessary. I’ll just IF instead.

Fasting is one way to have your cake and eat it too. Beyond the already proven benefits of a Primal Blueprint low-carb lifestyle, fasting once in a while seems to offer many of the same benefits of calorie restriction – you know, stuff like increased longevity, neuroprotection, increased insulin sensitivity, stronger resistance to stress, some cool effects on endogenous hormone production, increased mental clarity, plus more - but without the active, agonizing restriction. You just eat Primally, focusing on meat and vegetables with plenty of animal fat, and skip meals on occasion. A sixteen-hour fast is on the low-but-still-effective end (you could easily maintain a daily sixteen hour IF regimen, giving you an eight hour eating window, a la Leangains), or you could opt for longer, more intermittent fasts – say, a full twenty-four hours once or twice a week. When you’re done with the fast, eat as much as you want (which usually isn’t an issue, once you’re PB-adapted). It essentially turns into “eat when you’re hungry,” because let’s face it: eating the types of foods we evolved eating induces powerful satiety and makes eating the right amount of food a subconscious act. Fasting becomes a whole lot easier (and intuitive) when you’ve got your food quality dialed in. And I’ll come back to that little caveat at the end here.

“Fasting” was the top search term for MDA last week, and I hadn’t done a big post on it in a while, so I thought I’d do a comprehensive rundown of all the benefits (some conclusive, others prospective) you can expect to obtain from IF.

Longevity

Everyone wants to live longer, but I find longevity pointless if you’re not enjoying yourself. Otherwise, life becomes dreary. Consider the plight of the vampire – he lives a long, lonely life, never really connecting with anyone, never really enjoying all the time he has at his disposal. If the suggested longevity benefits of fasting pan out, I think we can enjoy the vampire’s longevity (and perhaps even some of his incredibly immune and restorative properties) without the downsides. Oh, and we’ll eventually have to die, but we have the option of sunbathing.

The popular c. elegans worm enjoys increased longevity with both twenty-four and forty-eight hour IFs via signaling through a gene that we all have.

One study (full PDF) from the 1940s found that varying amounts of twenty-four hour IFs (every other day, every fourth day, every eighth day, etc) prolonged the lifespan of rats without retarding or stunting the growth (as occurred with calorie restricting them). Female rats responded best to every eight day fasts, while males responded best to every other day fasts.

Reductions in brain insulin signaling have been shown to increase lifespan in animals, either by calorie restricting or actively knocking out brain insulin receptors. Fasting also reduces brain insulin signaling, at least in rats.

Blood Lipids

Going in and pharmaceutically manhandling your cholesterol synthesizing equipment is one thing; eating real food and exercising, resulting in possible alterations to your lipid profile, is another. We don’t set out to force your blood lipids into submission, but lifestyle changes that happen to change them for “the better” are usually a good thing. Fasting brings potent changes to blood lipids in an “organic” way – you’re just letting your machinery do its thing on its own – and this is probably a very good thing.

IF is as or more effective than calorie restriction in improving metabolic syndrome markers in overweight women, and it’s a whole lot easier to stick with.

Alternate day fasting improved cardiovascular risk markers, including lowered triglycerides and LDL-C numbers (although it’s unclear whether the improvements were related to the weight loss alone or something unique to fasting).

I discussed this last week, but it can’t hurt to mention that short-term alternate day fasting wrought improvements in LDL particle size and distribution in obese adults.

Compliance

A dietary regimen is useless without compliance. In fact, that’s what we’ve always said about the low-fat, low-calorie diet advice we’re inundated with: sure, they might work, but they’re impossible for most people to maintain. Eating Primally solves this problem, because it’s simple, easy, delicious, and satiating (you just have to enjoy cooking, or learn to), and IF is another compliance-breeding regimen that blends quite nicely with the PB. A lot of Primal eaters find that fasting just kinda happens without them setting out to do it, so it’s not even a conscious struggle. Check it out:

The obese (read: the ones who need the most help and often have the worst time sticking to a diet) were able to “quickly adapt” to alternate day modified fasting, which meant on fasting days they’d get 26% of their normal caloric intake. They were also able to maintain physical activity despite the fasting.

Heck, intermittent fasting even helped cocaine addicts stick to their treatment and rehab program. Not bad.

Cancer

The notion of IF reducing cancer incidence and improving survival is compelling, but little evidence in humans exists. Ketogenic diets may also offer exciting potential for cancer patients, and both IF diets and ketogenic diets share something: fat (either dietary or from your own adipose tissue) as primary fuel sources. But, while ketosis isn’t exactly desirable or optimal as a lifelong dietary regimen, IF is sustainable, simple, and can be integrated into your current diet. As of now, most of the evidence for IF’s protective effects against cancer exist in animal trials, mostly using mice. Still, fasting seems to confer so many other benefits that working it into your life for its anti-cancer potential is probably worth it. Some of the evidence:

Calorie restriction is proven to fight cancer cell proliferation in mice, but researchers found that intermittent fasting was just as effective. In fact, here’s a review of most of the animal anti-cancer evidence. It’s quite compelling.

Some researchers are speculating, based on substantial evidence, that fasting before and during cancer treatment should result in reduced morbidity, better tolerance of chemotherapies, and higher cure rates. This is refreshing news. A preliminary study in human cancer patients found that fasting during chemotherapy reduced the negative side effects of the treatment. The authors are quick to point out that the results are in no way a prescription for fasting in chemotherapy patients and that controlled trials are needed to change official recommendations, but that doesn’t mean you – the individual – can’t experiment.

Growth Hormone

Aging humans “normally” experience reductions in growth hormone. While it’s true that unchecked growth hormone can lead to unwanted cell proliferation (like, ya know, cancer), growth hormone therapy can really help stave off the doldrums of old age. Luckily, short-term fasting induces growth hormone secretion in “normal men.” I’m not for mainlining GH or anything, but I’m all for amping up my own production. Furthermore, a recent study found that resistance training actually blunted hunger for an hour. I’ve found this to be the case for me. If the body “needs” food right after a workout, why would hunger be blunted? This is why I tend to hold off on the eating post-workout. Every little bit helps, especially as you age.

Neurological Health

Fasting doesn’t cause your brain tissue to waste away, contrary to what some people will tell you. It’s actually good for brain health. Any dietary restriction tends to increase neuronal plasticity and promote neurogenesis, but it was IF that had the greatest effect (with the fewest downsides). Another study of mice found that meal frequency impacts neuronal health. That is, mice who ate larger meals more infrequently saw greater increases in brain and overall bodily health. Still another study found that IF was beneficial for peripheral nerve function in mice by promoting the maintenance of the neuronal pathways responsible for locomotor performance. It’s almost like this stuff just puts your brain in repair, or maintenance mode.

Autophagy

Fasting turns on autophagy (most studies nowadays treat this as common knowledge), which is the process by which cells recycle waste material, eliminate or downregulate wasteful processes, and repair themselves. Why is autophagy so important? It’s required to maintain muscle mass, and inhibiting it induces atrophy of adult skeletal muscle.  It reduces the negative effects of aging and reduces the incidence and progression of aging-related diseases. In fact, researchers have determined that autophagy is the essential aspect of the anti-aging mechanism of fasting. Without the autophagy that fasting provides, you would get very few of the benefits. Fasting even increases neuronal autophagy, which aids in maintaining mental health and function. Short term fasting, too. No marathon thirty-six hour fast required.

Fitness

You’ll hear that you should never exercise on an empty stomach. You’ll hear that fasted training will burn your  muscles and cause you to waste away. You’ll hear that performance will surely suffer. None of these things are necessarily true – and they are even less so if you are well-adapted adapted to a low-carb eating strategy. Fasted training can actually result in better metabolic adaptations (which mean better performance down the line), improved muscle protein synthesis, and a higher anabolic response to post-workout feeding (you’ll earn your meal and make more muscle out of it if you train on an empty stomach). Studies on Muslim athletes during Ramadan show no effect on performance while fasting, as well as better lipids in those who exercise and fast rather than just fast. When you train in a fasted state, glycogen breakdown is blunted and more fat is burnt, leaving you more glycolytic energy in the tank for when you really need it and less body fat. Those are just a sampling of the benefits to fasted training; there are dozens more. Check out Martin at LeanGains (linked above) for more information on fasted training. It’s his specialty.

Mental Well-being and Clarity

You’ve heard this “advice” before, probably from an expert dietitian in some copy-and-paste article on healthy living on Yahoo! Health. It’s the mantra of the high carb crowd: failure to eat something every few hours will cause mental fog and sluggishness, so keep a banana or a granola bar on your person at all times. Of course, this is all based on an assumption that we need to supply exogenous carbs on a regular basis to properly fuel the brain. This notion that fasting is only the province of anorexics or “those crazy caveman dieters” has kept many people from experiencing the myriad benefits.

I maintain that one’s comfort in handling IF effortlessly does increase dramatically when you’ve reprogrammed those cells (and genes) to predispose your body to derive most of your day-to-day energy from fat, as opposed to constantly dipping into glycogen stores (as happens when we rely so much on refeeding carbs every few hours). It’s also why I recommend that you eat according to the PB for at least three weeks before you really start incorporating IF on a regular basis. I’ll be discussing this detail more in upcoming posts on IF and what I am calling “the Metabolic Paradigm Shift”.

Overall, fasting just seems right. It’s like a reset button for your entire body, presumably across a large spectrum of maladies and dysfunctions. It puts your body into repair mode – at the cellular level – and it can restore normal hormonal function in the obese or overweight. Now, you don’t have to fast, but it’s definitely something to consider. As I said, I don’t plan my IFs – I let them happen. I prefer to fast when it’s forced upon me, like when I’m traveling or under a deadline. Once you’re acclimated to the Primal Blueprint diet, give it a shot and report back. Obviously, you won’t know if you’re fighting budding cancer cells or turning on autophagy in your brain, but if you can tolerate fasting and even derive some subjective benefits, those potential long-term benefits make it a worthwhile addition.

Have you tried IFing yet? Did you have a great, transcendent, middling, or perhaps even awful experience? Let me know how intermittent fasting has worked – or hasn’t – with your lifestyle in the comment section!

UPDATE: See this post on Women and Intermittent Fasting.

You want comments? We got comments:

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  1. Great post. I have recently gotten into the idea of IF, though I have found that, like stated above, it kind of just happens on its own. There was a post about a month ago that said, “Today, you’re going to skip your next meal. I took this as a personal challenge from Mark, and never looked back. I usually don’t eat till around lunch, and usually don’t even notice it. It works wonders in shedding unwanted body fat, while really clearing my head. If you haven’t tried it yet, well, what are you waiting for.

    Joe wrote on February 16th, 2011
  2. I fast on Mondays (no food between Sunday night and Tuesday morning), but I always have trouble sleeping on Monday nights. Anyone else experience this? Perhaps the problem is that I do drink some coffee (no more than other days) which may be more potent without food in my system?

    M Miller wrote on February 16th, 2011
  3. Interesting stuff. Thanks.

    Phil wrote on February 16th, 2011
  4. Ironically I just started IFing last week. I do 2 24 hour fasts. One on Mondays and one on Thursdays (I stop eating at around 6-7 the night before and then start eating again the next evening at 6-7). I was a little scared at first that I’d be overly hungry, but after going Primal a year ago it’s really not that bad. It was actually quite easy.
    At this point in my life I really don’t care about losing weight (I went from 208 last year down to 175 due to going Primal, and that was in a matter of 3 months without even working out). I care more about lowering my body fat%. My goal is to completely get rid of my post college beer gut. :)

    Adam wrote on February 16th, 2011
  5. Eating protein, fat and low carb vegetable ONLY when one is hungery will most likely result in reduced calories compared with what most people eat. That would result in ‘calorie restriction’ without trying.

    Josea wrote on February 16th, 2011
  6. I fast on a daily basis. Actually we all fast…what I do is I do not eat my first meal of the day, or my fast-breaking meal, until 3:00. Sometimes I eat later. Eating at 3:00 opens up my 4 hour “feasting” window. When I eat later than 3:00, I eat just one meal for the day. The only reason eating 3 -4 square meals a day plus in-between snacks seem necessary is that is what we’ve been taught. I am pre-diabetic and my blood glucose levels rarely go above 100. Now that being said, my glucose levels are usually in the 80s. I am not athletic but I do walk regularly while I am in my fasting mode. This is something that I do at least one hour before I break my fast. I am planning to run in a 5K dash just to see if it can be done while fasting. I am willing to wager that it can be.

    mary titus wrote on February 16th, 2011
    • That sounds like a great idea all around. I might have to give it a shot – I’m quite a foodie I’m afraid, but the problem is that I can be fairly mindless about it, even being primal. Having a time window seems like a good idea.

      Marni wrote on March 18th, 2013
  7. I can definitely relate to the increased mental clarity upon fasting. I find that after about six to nine hours of IF I get way more alert and rise into a state of much more relaxed awareness. Only thing is I tend to binge hard on the next actual meal I eat.

    Nicky Spur wrote on February 16th, 2011
  8. don’t we all kind of IF anyway? if we eat dinner/last snack at 8.00, then eat breakfast next am at 8.00, that’s 12 hours right there. Not that far from 16 hours IF? what is so speacial with 16 hours vs 12?

    tuscany wrote on February 16th, 2011
  9. I eat breakfast and lunch and IF until breakfast again. From reading these comments (and others on IFing) everyone skips breakfast and eats lunch/dinner. Is there a reason that this is the pattern and not breakfast/lunch skipping dinner?

    Darlena wrote on February 16th, 2011
    • I would venture to guess it’s that most people like to go to bed on a full stomach. That’s why for me anyway.

      Uncephalized wrote on February 16th, 2011
    • i am wondering the same thing. is it really considered fasting as your sleeping?
      i skip breakfast most days, but i never considered myself an IF.

      i also have a question…i was talking with a nonprimal coworker about this and she mention some about your body going into “starvation” mode when you skip meals. I realize this is CW but I’m just wondering what your thoughts are on this and why its made to sound as a bad thing.

      jennifer wrote on February 16th, 2011
  10. I’m recovering from an eating disorder. I like the idea of IF but whenever I do it my eating disorder seems to re-ignite and be fueled by my hunger (which I can’t stop). I’m lean 13.5% BF 31 yrold female. Is there any way I could incorporate IFing into my healing process?

    Meg wrote on February 16th, 2011
  11. I have done and still do Dr. Johnson’s Alternate day with 600 cals one day and my regular 1800 the next especially when I have inflammation issues and the diet helps with the pain and swelling. My lower back pain improved, too. It’s not a total fast but has helped me and if I am experiencing a plateau it helps break it,too. I still have 125 to lose(already lost 212) so I can afford the fasting some days.

    Amy wrote on February 16th, 2011
  12. FINALLY!!!! It feels so good to have what I’ve always known validated!!People have been scolding me for years for skipping breakfast! They insist one must eat within the first hour of rising in order to “get your metabolism going”. I began skipping breakfast when I was in high school just because I wasn’t hungry in the mornings (my Mom allowed it because she was the same way). Then, a couple years ago, I started eating first thing in the morning, and continuing with the “6 small meals”. I have to say, I felt sluggish, gained weight, and have been depressed. I’m back to eating MY way (no breakfast), and have much more energy and sleep better at night.
    Back in my 20s I fasted every Monday as part of my weight-loss program. It was the best I’ve ever felt!! I’m about to try it again. Thanks for a great post!

    susan wrote on February 16th, 2011
  13. geez mark, I was so interested in this article I burnt the almonds I was roasting.

    How dare you!

    On a serious note, WHY is IF good for you? These tell me why to do it, but not exactly why it works.

    Is it, fundamentally, autophagy? If so I’d love to read an article on that specifically

    College Caveman wrote on February 16th, 2011
  14. I see no other way to live.
    Eat like a starved animal once a day, enjoy it thoroughly and stay full until the very next day.
    Not to mention weight loss is a breeze.

    NSWM wrote on February 16th, 2011
    • Are you fasting every day? Are you eating just dinner and then, dinner again the next day? You say weight loss is a breeze. Can you be more specific about what kind of IF you are following (# of hours and eating window). Thanks.

      Claudia wrote on February 16th, 2011
  15. Great post, Mark! I’ve been doing IF 16/8 per the leangains approach as well as throwing in one to two 24 hour fasts a week. I’ve only seen benefits and have never had problems with energy or clarity. It also helps me stay lean and I love setting myself up to be able to listen to my body when eating to find the right satiety level. I’ve always had trouble trusting myself in how much I eat and IF has really helped that. I do miss breakfast sometimes, though. I don’t break my fast until lunch at the earliest. IF is great and I recommend giving it a try!!

    Ryan wrote on February 16th, 2011
  16. Just love reading these posts, Mark!

    Call me a crazy caveman or cavewoman dieter if you want… but this stuff really works. I used to be one of those crazy SAD people who constantly had to have a piece of fruit or a protein bar handy… When I didn’t eat every couple of hours, I would get the shakes, couldn’t concentrate, etc.

    Did my first 16 hour IF about 3 weeks in learning to be primal. Didn’t feel any ill effects so I decided to try a 24 hour fast this week. I ate lunch, then didn’t eat until lunch the next day. I never really felt hungry until about 23 hours in. The salad I ate never tasted so good!

    Loving the primal life!

    Maryann wrote on February 16th, 2011
  17. It is good to read that so many people have luck with IFing. I have tried to psych myself up for IFing but I keep psyching myself out. I also used to do it naturally before college, I was just too busy to eat.

    However now that I have made the switch to primal I feel preoccupied by food trying to make the “right” choices throughout the day.

    I am excited to give it a shot. I think I might just need to “let it happen,” to get over my mental block.

    Great encouragement to read all the positive experiences!

    Meredith G. wrote on February 16th, 2011
  18. Have been IFing for 12-16 hours easily, but am now thinking of trying longer IFs to help with torso fat. Thanks for the great info Mark, as always.

    I, too, have sworn off nuts, hoping this will help with the body fat.

    Sun is shining…..rare for here, so must get outside, even if it is cold.

    Dragonfly wrote on February 16th, 2011
  19. I’ve been fasting according to the Leangains protocol for 2 months with some very favourable results. I’ve dropped a few kilograms, have started to lean out rather nicely all while gaining lean muscle. You’re right, Mark, fasting just happens now and I’m no longer bothered when in the fasted state but do enjoy the 8 hour feeding window :)

    Eddie wrote on February 16th, 2011
  20. I just started planned IFing at the beginning of last week. Prior to that, I’d accidentally IF’d several times. Last week and this week on the days when I work out in a group setting, I have skipped breakfast, resulting in a 15-16 hour fast. I feel slightly hungry right at the time I would usually eat breakfast, but then that feeling would go away till lunchtime. My workouts are at least as effective as they were before. I feel lighter, I don’t need to drink water all the time. It’s rather good.

    For years, I joked that my son seemed to play soccer better if he hadn’t eaten anything that day. I had no idea it might actually be true!!

    Liz Chalmers wrote on February 16th, 2011
  21. I do not necessarily notice a smaller appetite after going primal, I’ll basically clear my plate regardless of how much is on there. If I make a whole lot of food, I’ll finish every bite and be satisfied. If I just make a light salad with a hard boiled egg, still satisfied. If I fast for a day or two I def. feel it and get hungry, but in a good way -not debilitated by hunger pains.

    Anders wrote on February 16th, 2011
  22. I eat however much my body feels it needs at the moment.(in reasonable way)Going hungry on purpose dosent come across as very bright,so your going to tell your body theres a famine,so your matabolism slows down.Yes ive heard of this,folks from life extension magazine are into calorie reduction.each to his own.

    ron wrote on February 16th, 2011
    • Your body is not stupid enough to think that going less than a day without food is a “famine”, Unless your insulin response is totally out of whack from SAD. If you eat low-carb, going without food for even 24 hours at a time is pretty effortless.

      Uncephalized wrote on February 16th, 2011
    • I’m 44 hours fasted right now (experimenting to see what it is like and to kind of hit the reset button). I’ve seen it other places but Leangains notes that your metabolism goes up initially while fasting and doesn’t start to drop till around 5 days later.

      Jonathan wrote on March 1st, 2011
  23. As a menopausal woman I’m finding that IF is good medicine to lose weight and reduce inflammation.

    I prefer 24-hour fasts but occasionally add a couple of boiled eggs or very small LC snack, keeping it under 500 calories. Usually I get through the fasting period OK but if I do it more than twice a week I need to watch that I don’t eat too much on the eating days. I also drink coffee with cream on the fasting days but try not to overdo it so I don’t get too buzzy.

    It’s the only thing that’s helped me lose weight and really helps with arthritis and other inflammation-related problems.

    There are challenges though:

    – I do have problems with concentration and focus sometimes on the fasting days. On days where I need to get a lot of work out I find it’s best to not schedule a fast. (Going VLC or doing IF is great for my body but sometimes affects concentration and mental sharpness. I need to tweak when needed, I often need to find a balance.)

    – I also need to stay LC on the eating days and watch that I don’t psychologically feel a need to eat a lot more because I fasted the day before.

    – I also find that the longer fasting period (18 to 24 hours) works better for me than just not eating most of the day then having a large dinner, which sometimes makes me feel sluggish and bloated.

    When I was younger I felt lousy and spacey if I skipped meals and didn’t eat throughout the day; this is much easier for me to handle now at midlife.

    Also, even going VLC didn’t result in weight loss; the alternate-day fasting has helped me lose weight again and feel much better which is such a boost at midlife when (quote from one of my favorite TV shows) it feels like I have the metabolism of “a hibernating bear in menopause.”

    One thing I also pay attention to is drinking mineral-rich herbal teas (as hot infusions, letting them steep longer than regular teas) like dandelion leaf, nettle, etc. A lot of people don’t pay attention to this but you get a lot of minerals that way, especially important for hormonal changes.

    elegans wrote on February 16th, 2011
    • I am also a menopausal woman and would be interested in hearing more about the mineral-rich herbal teas you mentioned. Are there any that are supposed to specifically ease hot flashes? I’ve been experiencing flashes for about 6 weeks now, almost always in the evenings (between 7-11pm), and they’re driving me (and my husband) just a little bit crazy.

      susan wrote on February 17th, 2011
      • Susun Weed is a good source for info on herbal infusions; here’s a start:

        http://www.susunweed.com/Article_Mineral_Rich_Herbs.htm

        Local Harvest is a good source for dandelion, nettle, and other herbs from small growers, most do mail order with reasonable shipping fees.

        elegans wrote on February 17th, 2011
  24. IFing really works for me too. Breakfast is generally my favorite meal of the day so on my IF days I usually have lunch as my last meal around noon and then enjoy a wonderful primal breakfast at around 9 or 10 the next morning…I do this usually 1-2 times per week. Most weeks I also do a 24 hour fast as well, Mondays work best for me…great way to start the week!

    Andrea wrote on February 16th, 2011
  25. Awesome. Been doing Martin’s Leangains IF for well over a year and a half. Loving it.

    I’ve tried longer fasts (36-48 hours) and those are even better. I’m still trying to get my family on the fasting bandwagon, but it’s a pretty difficult task when they aren’t health geeks like me.

    Rhys wrote on February 16th, 2011
  26. Intermittent fasting is great I do it from time to time but just don’t get so caught up in it, it becomes the answer to all weight problems. I see people becomes so fanstatical they start fasting during the day every day.I mean everybody loves to eat.

    Bodybuilders who are ‘shredded’ you see every minute detail of their muscles and they eat 6 times a day, the longest living folk in an island in Japan don’t fast! … so I.F. is a simple way for most of us to eat less but you can also do it a number of other ways ..its another tool to use.
    Raymond

    Raymond-ZenMyFitness wrote on February 16th, 2011
    • Have you seen bodybuilders in the off-season? They are not shredded, they are covered with a nice layer of blubber. They get shredded by fasting and using diuretics and other drugs. They eat 6 times a day precisely because they know they are going to lose muscle mass while leaning out pre-contest.

      As for the Okinawans, I’m guessing that traditionally, like most people, they did IF. Farming the old fashioned way is a lot of work–just based on the fact that you have to work sun up to sun down as a traditional farmer (and that is what most Okinawans did), you’re going to not eat most of the day. Also, all those old Okinawans did go through a lot of extended fasting during WWII. I mean if you can show us that Okinawans typically eat a bunch of small meals a day, I’d love to see evidence of it.

      On a related note, I found Mark’s comment about Muslims during Ramadan particularly interesting–I remember years ago when Hakeem Olajuwon was playing in the NBA and winning championships, he would go on these tears during Ramadan. And people would be amazed he was playing so well when he hadn’t eaten in 16 hours or so. But there he was, fasting and clearly the best conditioned athlete on the court.

      RobG wrote on February 16th, 2011
  27. I’m new to the primal movement, but not new to IF. I’ve used IF in religious settings and more recently for the health benefits. Overall, my experience has been nothing but positive. The benefit I enjoy the most is the awareness I’ve gained. That first meal to “break the fast” is a great time to eat mindfully and really feel the food’s effect on your body!

    I’m glad to have found a community of folks who are on a similar path!

    jdperkins wrote on February 16th, 2011
  28. I’m a huge advocate for IF and lean gains in particular.
    I had great results with it prior to Xmas last year (results on my website).
    It’s something that’s EASY to stick with and combining that with stellar results and the ability to eat awesome meals that may in fact be bad for you on a regular basis, equals a WIN for me.

    Clint - Crude Fitness wrote on February 16th, 2011
  29. What an awesome and timely article! My question is…what constitutes “fasting”? I’ll skip dinner every now and then and feel great the next morning. Reading this article and some of the linked resources, it seems that fasting means not eating for extended periods of time – as in L-O-N-G! I once fasted for 36 hours for a colonoscopy and thought I was gonna die. Maybe I’ll try a 24 hour fast and see how I handle it. It seems the health benefits are certain.

    Vince N. wrote on February 16th, 2011
    • In Eat Stop Eat, Polin claims that the research shows the majority of benefits from fasting come between the 16th and 32nd hours of the fast. As such, your fast should probably be at least 16 hours and no longer than 32 hours, with 24 hours right in the middle.

      Personally, I fast from dinner to lunch ( at least 16 hours) pretty much every day, but take a dinner to dinner fast (about 24 hours) once a week. I don’t plan the 24 hour fast; I just go for it if I’m not feeling hungry around 3 pm or so.

      Once you’re used to 16 hour fasts and eating a high fat diet, 24 hour fasts will happen almost by accident.

      ASmitty wrote on February 16th, 2011
  30. This is simply an excellent summary. I find IF is easy after only 1 or 2 days of being hungry during times you normally eat.

    john wrote on February 16th, 2011
  31. I fast 5-6 days a week (leangains style so 16 hours fast followed by 8 hour eating window).
    My fiance even does it now (but does 14/8 due to being female ;)).

    We find it VERY easy (may take a week or so to get used to however)

    Clint - Crude Fitness wrote on February 16th, 2011
  32. “Leangains” has some great info on Ghrelin (sp?) which I believe is the hormone that tells us we’re hungry just because it’s 7am and that’s when we usually eat.

    FWIW – I’ve been IF-ing for about a month now and after an initial period of adaptation I actually feel like my energy levels are more consistent with eating less often.

    FWIW II – I think one of the biggest advantages I’ve seen is in my digestion. No more cramping/bloating. It’s almost like my guts need the break each day.

    I do the 18/6 Leangains approach (shout-out to Lean Saloon as well).

    p-if-lg-me.blogspot.com if you want to read some of my ramblings…

    Dan wrote on February 16th, 2011
  33. I am new to Primal eating, I began about 6 weeks ago. I note the following changes so far: I am far more satisfied with the food I am eating, and consquently am eating less food with no increased hunger or cravings. I always work out for 20 min. every morning on an empty stomach, after at least 8 hours of (far better since going Primal) sleep. After working out I often don’t want breakfast for about an hour, with no ill effects whatsoever. I think that IF will come very naturally to me given more time eating Primally. I now feel that I can “hear” what my body needs and wants without all the “static” of conventional eating habits. I have given up eating unless I am hungry, and I eat when I want to rather than 3 X a day. Thank you Mark for your generosity of Knowledge and Spirit. I have learned so much. Choosing to eat Primally feels intuitively right for me, and has changed my life for the better.

    tootsie wrote on February 16th, 2011
  34. Are the benefits of IF the fact that the body has to dip into its fat stores for energy and this creates some kind of favourable biological environment for anti-ageing and other benefits OR when people IF are they limiting calories as in caloric restriction? I’ve heard some say they eat the same amount of calories they normally would in a day but in a shortened window. Do most get less calories when doing IF?

    Sue wrote on February 16th, 2011
  35. Amazing post! Love all the research links!

    I do an intermittent fast with a 4-6 hour eating window, usually 5 hours. (I don’t stress out on the exact times as long as it’s in that range.) I eat about 80% primal.

    And I do high intensity workouts with weights every 4-6 days.

    For the last two months, my workouts have occurred 3 hours after the eating window has closed and I don’t eat again until the window starts again, as normal.

    In that time I have added 6 lbs of body weight, obviously lost bodyfat unless the mirror lies, and added 1.5 inches to my arms, chest, and legs.

    So all the panic over eating within an hour of a workout that you see or you’ll minimize your gains, I don’t buy it. Some people seem to almost go into a panic about it.

    Your body can store amino acids and use them when needed. Otherwise we’d never have survived as a species. Otherwise, vegetarians couldn’t survive. It can also wait until new food comes in the next day.

    Besides which, I’m just not hungry immediately after a workout and feel a little sick if I workout with food in my stomach.

    David Chunn wrote on February 16th, 2011
  36. I haven’t tried IFing yet. I plan to in the future but I’m still cleaning up some of my diet. Up until a year ago, I was eating six meals a day for about 10 years. I’m almost at 3 meals a day. The six meals a day were during my high carb days. It’s nice to to be away from the mental fog.

    Trevor wrote on February 16th, 2011
  37. Mark or somebody, what about fasting with adrenal fatigue? Is this absolutely contraindicated as most “experts” suggest?

    Stephanie wrote on February 16th, 2011
    • Stephanie, some people (many?) have incurred some pretty severe metabolic damage over the years, adrenal fatigue being one manifestation of that damage. For people who are coming off serious health issues, it might be best to acclimate to the PB style for a longer period of time (longer than three weeks, say). Then start to experiment with shorter IF periods until you are confident you can handle longer fasts.

      Mark Sisson wrote on February 16th, 2011
      • Thanks so much for your reply. I actually tried my first planned IF last Saturday, but only for about sixteen or seventeen hours from Friday dinner to a late Sat. lunch. I felt a little bad (shaky) Sat. morning, but had wonderful energy Sat. night. Will keep experimenting. Just being able to go 5-6 hours without a meal or skip lunch is amazing for me. I used to get a little crazy if I missed a meal :) Primal is awesome and is changing my life. Thank you for your body of work which is greatly helping my body :)

        Stephanie wrote on February 17th, 2011
      • Mark, Thanks for your response. That’s sort of what I did. I’ve been primal since late November and stopped snacking and skipped a meal here and there with ok results. I have fasted once for 17 hours and today I broke my fast after about 23. i did feel a little shaky at times but I’m curious whether this will help or hinder. I’m going to keep experimenting and see what happens. It seems like it gets easier for me over the duration of the fast and I’ve had some really productive days these last two weekends which coincided with the fasts. Hope to be a success story soon! Thanks for everything!

        Stephanie wrote on February 20th, 2011
  38. I agree Mark. When you are eating primal and getting a good ratio of healthy fats to proteins to carbs fasting seems to just happen.

    When you are eating a primal diet you just don’t have the same cravings that force you to eat often and eat regularly.

    Dr Brett Hill wrote on February 16th, 2011
  39. I do LeanGains 16/8 fasting (from the comments it appears I can no longer consider myself a special snowflake), sometimes up to 20 hrs. It’s the best way to take advantage of my college meal plan; I have fewer weekly meals than average, so I just eat twice a day, usually ~12:30 PM and then again around 6 or 7.

    Richad wrote on February 16th, 2011
  40. Is eating clean protein (no fat or carbs) a bad idea when IFing? I’m thinking not whey protein, do to the insulin response, but why not canned tuna (packed in brine)? I hate the thought of losing precious muscle tissue if I’m not eating anything, especially protein. I’m a hardgainer, so I had to bust my hump to put on this muscle and I aim to keep it! ;) Any thoughts on this?

    Jarrett wrote on February 16th, 2011
    • I do IF and I eat the same number of calories as I would if the meals were spread over 18 hours instead of 6. Assuming you’re doing that style, I don’t see how you would have a caloric difference.

      If you have bodyfat and you’re working out and building muscle, your body will burn fat instead of protein on IF. Your body prioritizes. If you aren’t using your muscles, it will burn them. That’s how I understand the process at least.

      David Chunn wrote on February 16th, 2011
      • Right, I’m not worried about calories as your body can burn body fat to get all the energy it needs to keep you going, but your body uses protein to build and maintain muscle, right? So where does the protein come from when IFing? The only source is muscle, isn’t it? If that’s true then IFing would eat muscle much like catabolic hormones, which would suck. Please correct me if my understanding is off here.

        Jarrett wrote on February 16th, 2011
    • Jarrett, the whole idea IS to spare muscle (and increase repair) through short fasts. This is not an issue for those who have become fat- and keto-adapted by eating according to the PB. That’s that three week adaptation/acclimation period. OTOH, it can be a big problem for those who are still living in the carbohydrate paradigm (like the 80-10-10 crowd)and whose muscles expect to be fed more glucose every 3-5 hours.

      Mark Sisson wrote on February 16th, 2011
      • Thanks for the reply and writing this interesting article, Mark :)

        Jarrett wrote on February 16th, 2011

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