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

Calorie 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.


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.


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.


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.


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.


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:

Imagine you’re George Clooney. Take a moment to admire your grooming and wit. Okay, now imagine someone walks up to you and asks, “What’s your name?” You say, “I’m George Clooney.” Or maybe you say, “I’m the Clooninator!” You don’t say “I’m George of George Clooney Sells Movies Blog” and you certainly don’t say, “I’m Clooney Weight Loss Plan”. So while spam is technically meat, it ain’t anywhere near Primal. Please nickname yourself something your friends would call you.

  1. The study presented as showing that IF “even helped cocaine addicts stick to their treatment” is actually about mice, not men.

    Glenn Ammons wrote on February 16th, 2011
  2. I’ve been CRON – Calorie Restriction with Optimal Nutrition (AND primal) for about 3 years (recently participated in CRONA research study at UCSF to help establish CR/anti-aging biomarkers).
    CR and Primal go hand in hand in my book – so not sure why the misunderstandings (on both sides of the table). A great majority of CRers focus on calorically dense real food, low glycemic carbs (and incorporate the various methods of IFing discussed here). Perhaps its the muscle mass issue ( and the impact of protein on IGF-1), as in CR you are trying to down regulate the mTOR pathway (and in muscle tissue at least), you are trying to up regulate it to build muscles.
    At 5″9′ BMI of 19.5 and under 15% body fat (very fit/low fat for a female+ over 50). I’m also an RD and would say CR and Primal are far more alike than different. I just advise my clients how to fine tune to emphasize anti-aging aspects – but for sure weight loss has to come first before you can worry about tweaking/optimizing further. Won’t get my telomere length data for another 10 months when the study concludes…..will know more then!

    deb b wrote on February 16th, 2011
    • deb b, I appreciate your input and comments. Of course, I’m listening through my own biased filters when I hear tales of measuring food by the gram at CR meals or of the mind games involved in overcoming hunger in between. I suspect that a higher fat, low carb CR program might alleviate some of that (much of the CR diet lit still has Conventional % breakdowns of Fat/Pro/Cho). Please let us know when your telomere data comes back.

      Mark Sisson wrote on February 16th, 2011
  3. I tried IF 3 times a couple years ago but experienced some pain in the area of my gallbladder each time at around the 16-18 hour mark. At that time, I didn’t know a shorter fast was okay and was going for 24 hours, so felt discouraged. I will try to do a more strict PB for 3 weeks and then try it again. Thanks for this information.

    Joann wrote on February 16th, 2011
  4. Yes, fasting just feels right. I eat all my calories between noon and 6pm. I feel great!

    I don’t tell anyone though because they roll their eyes and start giving me grief.

    Alison Golden wrote on February 16th, 2011
    • Yeah what is that. My co-workers will ask if I want something for lunch and I’ll say no their next reply is you’re going to get sick and develop stomach cancer. I just laugh because 20 minutes after their lunch break they are good for nothing nodding off at the computer when the bossman comes around checking while I’m alert, energetic and with a clear mind.

      Gorm wrote on February 16th, 2011
  5. what about the 4 hour body cheat day? anyone doing that and IF?

    Tim Carley wrote on February 16th, 2011
    • I am. I lengthen my eating period to about 8 hours and stuff myself. Most of my splurge is fruit and rice. Perhaps a bit of bread.

      The primary reason I’m doing it, along with the reasons stated in Tim’s book, is because it fits my social calendar. I typically go out with friends, visit people, do shopping, and so forth on Saturday. So it is generally hard on that day to maintain as strict a diet and fit my eating hours into the times when my friends are eating.

      David Chunn wrote on February 16th, 2011
    • You’re talking about a one day carb refeed, right? From my experience it can make me feel bloated on that day, but the next day my muscles have a nice fuller look and I feel somewhat stronger than than earlier in the week. I do 24-hour modified IF fasting once a week with lots of protein (whey shakes and canned tuna in brine).

      Jarrett wrote on February 16th, 2011
  6. I have fasted a few times before and was able to pass with flying colors. The longest I have done is about 21 hours… not sure why I did not get to 24!

    It has been months since my last fast but I frequently eat 2 meals on the weekend.

    I have considered doing a planned 24 hour fast once a week or every other week but have not gotten the urge to do so.

    Fasting is very beneficial and if one can handle it then doing it while traveling may save someone – great post Mark!

    Primal Toad wrote on February 16th, 2011
  7. All this stuff about the IF sounds good and I’ll give it a try tomorrow morning before working out (although for a hardgainer like me it sounds like suicidal… I don’t really care), but let’s say I take my vitamins and fish oil in the morning with the breakfast: if I’m on IF should I pospone them too? do they count as a source of energy?

    Ian Benedetti wrote on February 16th, 2011
    • I’m thinking taking vitamins would be a good idea here, although they usually say to take vitamins after a meal. I wonder if the body would readily absorb the vitamins on an empty stomach. 1 gram of fish oil is about 10 calories, similar to chewing gum, so I don’t see why you’d forgo it.

      Jarrett wrote on February 16th, 2011
      • I know right? I mean I understand that IF won’t get screwed up because of those ten calories in the fish oil, but since I’m not really into this I wanted to know if this kind of supplements should be avoided too (I think I didn’t read it explained in this post or the previous ones about IF)

        Ian Benedetti wrote on February 16th, 2011
        • Well, if you want any benefits of the said Fish Oil, you’ll need to be ingesting more than 1 gram of it in one sitting. I personally take 8 caps a day.
          An aside from that, calorie consumption higher than this would throw you out of a ‘fasted’ state into a ‘fed’ state therefore you’d be foregoing any of the benefits you get from an actual fast and effectively ending your fast very early in the day.
          Save your fish oil + vitamins to have with your first meal when you break the fast.

          Clint - Crude Fitness wrote on February 16th, 2011
    • Thank you for your responses guys: now I understand that IF is both about nutrient and calorie restriction for a certain period of time.

      Ian Benedetti wrote on February 17th, 2011
  8. Know quite a few people that practice IF and we want to try. My only experience with fasting is 72 hours of organic apples and water which is a magical experience. Awful day one. Tolerable day two. Radiant day 3. Just ease back in after, because the temptation to binge after a fast is awful!

    Primal Palette wrote on February 16th, 2011
  9. Hear, Hear! I’ve been following the Primal Blueprint in conjunction with Martin’s Leangains protocol. I eat primal, but only during a feeding window from 1pm to 9pm. It’s clearly accelerated fat loss, but I can’t believe the difference it has made mentally. I had a host of stress/anxiety issues before starting the daily 16 hour IF, but there is something about the predictable and rather austere nature of the 16 hours of fasting a day that has set things right upstairs. I love it. I don’t feel hungry and I’ve been setting PRs on the big barbell movements and performing well during 1-2 hour grappling sessions, all in a fasted state – with the addition of BCAAs before and after fasted workouts). I love it, and don’t think I’ll be going back to the old (new?) way of eating any time soon.

    Orie wrote on February 16th, 2011
  10. I also only IF accidentally. I miss about two meals a week. I’ll have to pay closer attention to the mental aspect of it, as I haven’t really noticed it being tied to exceptional clear-thinking states, but it might be a contributing factor.

    About 15 years ago I didn’t eat for eight days just to see what would happen. After the second day it wasn’t particularly difficult, and not all that profound either. I broke the fast with ribs at a friend’s party. If I’d known of the concept, I could have just stayed Primal after that.

    DavidB wrote on February 16th, 2011
  11. This post reminded me that I did something today, and several times before now, that would have been impossible a few months ago. Today, I stumbled into a mini-fast without trying.

    Before, if I didn’t eat breakfast, I’d get the shakes and pretty well shut down. Now, after about 3 months of Primal, I just kept putting off breakfast because I was busy. Then, I put it off a bit more, I was still busy. I never would have been able to do that before. And when I did eat a light lunch, I was totally satisfied with what would not amount to much.

    Just awesome how our bodies, attitudes, and hungers adjust. Love it. Thanks Mark.

    Dennis wrote on February 16th, 2011
  12. I’ve done a couple of IF days since starting to eat primal. My biggest problem seems to be finding a day to do it when I’m not training too much. I can do it on a light exercise day, but not a heavy one or I just get too hungry.

    I know it’s maybe not really in accordance with a primal exercise plan, but I’m putting in some multi-hour days training for my black belt in karate. Training about 15 – 17 hours a week right now (most karate, some Crossfit-style conditioning, a couple swimming and trail running). So finding a day that I can even do IF is difficult. Most days I’m ravenously hungry.

    Today was only a one-hour day as I missed my afternoon session. I haven’t eaten dinner and I’m really not hungry. I can tell a real difference in appetite between light workout days and tough ones. Yesterday was four hours and not eating was simply not optional.

    Robin wrote on February 16th, 2011
  13. Great post Mark. Back when I was taking herbal classes with Dr. Rochard Schultze, he would always talk about “when you are sick, stop eating”. Examples of animals fasting in a sick state etc. would follow. He would quote…”60 % of your energy is used to digest food. Stop eating and you now have 60% MORE energy to fight the bug.” Anyone have the exact figure of how much energy we use to digest food?

    I tell my diabetes clients, “No one got diabetes from eating too little.” Nice to not feel like I needed to snack while reading your post. “STEP away from the food…Step away from the food!”

    Andre Chimene wrote on February 16th, 2011
  14. I have done the Warrior Diet (if you’re familiar with it) for one year, several years ago back in college.

    Essentially, I fasted every day from 18-20 hours, worked out and ate (it was a lot of grains back then)

    Two things I’ve noticed that may help you:

    1. Athletic performance was actually improved when fasting.

    2. “hunger” was purely behavioural. I noticed that the feeling of hunger that I would get were circumstantially psychological. If it was morning, or if I ended class, or if it was the same time I ate all the time before.

    It takes some mental work to get to the point where you don’t feel “hungry” for upwards of 20 hours. Some people went cold turkey. Some would portion their intake and wean themselves off food.

    IF is great accept for the psychological stress it can provide.

    Jamie wrote on February 16th, 2011
  15. Mark,
    While you link to TED above, I cannot find any CR talks via that link. Can you please provide the link to the talk(s) you were referencing?

    Ashley wrote on February 16th, 2011
  16. Great article, Mark!!

    I always wondered why I never felt as bad as what my parents said I would whenever I accidentally went a whole day without eating. In fact, I felt great! Then, as usual, I proceeded to end the day with a million-ingredient salad and glass of wine.

    Now, I definitely don’t feel bad about accidentally not eating at all! I’m still fairly new to primal living – just a few months now, but I definitely noticed that sometimes I accidentally don’t, or “forget,” to eat for a whole day more frequently, about every week and a half to two weeks.

    I’d really like to make this a regular thing now. It makes a lot of sense and seems like a logical component to primal living.

    Apolo Troy wrote on February 16th, 2011
  17. So, about a month ago, I tried to do my first fast… I was going to do a green juice fast cause I am nursing and thought I may not be able to go without calories for a whole day. So I ate my last meal at 6pm and then started the fast, intending to through the next day. The best morning I frank some of l the fresh made green juice and all he’ll broke loose. I started throwing up immediately, and then by lunch, went blind in my left eye and got my first migraine ever! What happened?! Was it the juice?! Also I am nursing, should I not do this while nursing? Gould I try again with nothing but water?

    Erin wrote on February 16th, 2011
    • If you have calories from green juice, it is not the sort of fast being discussed here. I’ve done a juice fast before. Incredibly difficult. Made me hungrier than a straight fast and I felt terrible. Some people say that’s detoxing. I’ve done without and didn’t feel that way.

      In my experience, a one day fast is a lot harder to do than an intermittent fast with an eating window. You should start by eating in an 6-8 hour window and go from there.

      Caloric intake should remain the same on an intermittent fast, you’re just shifting the hours of eating to a smaller window to give your body more time to go through its “cleansing” processes.

      The migraine isn’t necessarily connected to the fast if it only happens once, but personally, I’d be careful. From an evolutionary/biological standpoint, I don’t see how it would impact nursing. However, I am not a doctor and don’t for sure.

      If you’re going to do it, start small. If you’re not going to cut out the calories during the fast time, then I just don’t think it’s really a fast or worth doing.

      You might also be allergic to one of the juices.

      DC wrote on February 16th, 2011
      • Most women store some fat during pregnancy for making milk, but it takes 500-1000 calories a day to make milk. This can come from food and body fat. Hence why exclusive breastfeeding is a great way to lose post pregnancy weight.i lost aLot of weight postpartum. Just make sure you don’t restrict calories too much… You need enough to maintain yourself and milk production.

        Nicole wrote on February 17th, 2011
    • This doesn’t sound like it’s related to fasting. You said that the effects started right after you drank the juice in the morning. That’s not even a fast.

      I fasted on Yom Kippur while nursing and found dehydration affected my milk supply by the late afternoon. I don’t think it was the lack of food because I didn’t really get that hungry, although I don’t know for sure.

      labbygail wrote on February 17th, 2011
  18. I’ve been very strictly primal for 6 months. I have tried IF a couple times, with the idea that I would eat once I was hungry. The longest I’ve ever made it was 16 hours with a post-workout meal breaking my fast.

    Am I doing something wrong? I’m not overweight, so I’m not doing this to lose weight (male, 5’9″ 140, body fat probably around 8-9%). Is my weight/body composition such that I just can’t go as long without getting hungry? While I don’t want to lose weight, I’m hoping to reap some of the other benefits mentioned in this article.

    While this is much better than before going primal (when I would need to eat every 3-4 hours and turned into a total asshole after 5 hours of fasting) and now I can do a fasting workout, something I couldn’t do before w/out feeling drained, I kind of wonder about all the people commenting on this site who say they can comfortably go 24-36 hours w/out eating. I can’t imagine myself doing this.

    Again, am I doing something wrong?

    fritzy wrote on February 16th, 2011
  19. Oops, I meant “the next morning I drank” 😉

    Erin wrote on February 16th, 2011
  20. I naturally have been a faster and didn’t really realize it. I rarely eat breakfast and, due to the nature of my work, often do not get a lunch; usually when I do, I take it super late–like at 4 or 5 PM. I’ve loved going Primal because I seem to feel better during these forced fasting periods; I have plenty of energy, feel light and alert–quick, even–and don’t overdo the next meal. I really think my work performance has improved and fasting might be part of it. I have so far not fasted on a plan or with intention, but I am going to try to see if I can achieve a longer fast more often because I do trust the benefits described above and at Martin’s lean gains site. I am excited to see if I can induce my body to want to fast longer or more often. I am also going to keep a mental note of my eating times. I think the 8 hour window for eating works well for me and I am going to try to stick to that… maybe tweak it a bit to decrease it, even…

    As always, Mark, THANK YOU for such thoughtful blog topics. I love your site and this community!

    obligatecarnivore wrote on February 16th, 2011
  21. I’ve been tip-toeing slowly into a more paleo lifestyle — I’d say I’m at 50% — and already regular eating is becoming less important. As a college student I tend to wind up keeping irregular hours and if I’ve got a bunch of things to do one day, it’s nice to know that there isn’t much of a difference if I happen to miss a few meals. There’s also an odd feeling when hunger kicks in that I’m walking on air and can focus better on work. (And though this blog is not about religion, I can’t resist noting that Judaism, Christianity, Islam, Hinduism, and Buddhism all value fasting.)

    Mitchell Powell wrote on February 16th, 2011
  22. Personally, I find this continual reliance on abbreviations tedious, irritating, pedantic, and lazy. Write the bloody word for heaven’s sake (fhs).

    Sam wrote on February 16th, 2011
    • Agreed – it can make posts difficult to read and smacks of pseudo-science which you don’t need!

      Tom wrote on February 17th, 2011
    • It doesn’t usually bother me except that “intermittent fast” abbreviates to “IF,” which is an actual word (and a commonly used one at that), so it made this post hard to read.

      labbygail wrote on February 17th, 2011
    • I mean no offense, but I think, by definition, you’re being pedantic.

      Keith wrote on February 17th, 2011
  23. I find intermittent fasting pretty easy. Eating a relatively primal, high fat, low carb diet keeps one so sated that it only makes sense to miss breakfast or lunch once or twice a week and fit in some more fun or functional exercise. I quite like it.

    Oh, new funcional wow, loading and stacking pea straw bales. An hour of that and you know you’ve done something for your body and got a job done.

    kem wrote on February 17th, 2011
  24. What if you are trying to build muscle? and gain a little weight?

    Lloyd T wrote on February 17th, 2011
    • Martin Berkhan says more carb on workout days and more fat on rest days.

      Coconut oil is your friend.

      Mo wrote on February 17th, 2011
  25. Primal now for over a year and even at age 59 I’m now recomposing nicely instead of decomposing!

    People who haven’t seen me for a while invariably ask about my ‘reconstruction’… I put them off by saying “Four’Bs’: No Bread. No Beans. No Beer. No Breakfast”

    (But I don’t tell them about the weekly deadlifts or the lovely fat!)

    localad wrote on February 17th, 2011
  26. I am a 57-yr-old woman, one of 4 sisters. 1 of my sisters, age 56, has never been on a diet of any kind and has the same body she had in high school. The other 3 of us have tried every diet in the book and have all suffered from excess poundage for most of our lives. My weight-stable sister? She practiced IF even back in her teen years. It came naturally to her. She was NOT trying to lose weight, as she didn’t need to. But she would say, “I ate a lot for dinner last night and I’m just not hungry today. Besides, I’m going out with friends tomorrow, so I’ll eat plenty again then…..” Very casual. “Just not hungry….” Looking back and what she’d eaten and ahead at what she planned to eat, and then figuring there was no need to stuff herself in the absence of hunger. Smart girl then, and smart to this day.

    Katy wrote on February 17th, 2011
  27. Just two months ago I could barely last four hours without eating, then hypoglycemia would set in (irritability, dizziness, nausea, cold sweats, etc.). After switching to virtually 100% primal it’s reached the point where I can easily go 8+ hours fasting without any trouble at all, even with exercising. Skipping a meal every few days now and it feels good.

    Elizabeth wrote on February 17th, 2011
  28. It sounds from Mark’s post that IF involves/leads to CR. I can easily eat my maintenance calorie level during my feeding window of 5-6 hours, so will this prevent desired weight loss? I have been following the Fast 5 protocol for a week. Still waiting to see the pounds move. I have been PB for a year. Should I be cutting calories too?

    Joanne wrote on February 17th, 2011
  29. I started IF leangains style (~16/~8) a month ago and it gave me terrible gas. It’s not as bad now but I still fart more than usual (and they smell more).
    Anyone else?

    Mo wrote on February 17th, 2011
  30. I’m going to send this post to my brother who believes that he will drop down dead if he dosn’t eat a large (and I mean large) breakfast immediatley on arising in the morning. He tuts and shakes his head if any one tells him they don’t do breakfast.

    Great post.

    kim wrote on February 17th, 2011
  31. Hi everyone!
    Thanks for all the great comments, it’s been wonderful to read! One reply which I hope will settle a few people, is to remember that everyone’s bodies are very different, so try not to compare yourself to those you think are deal tasters! You just may not be programmer like them, and that’s totally fine :).
    I have a quick question I’m hoping someone can help me with; with the nature of many people’s work and social lives these days (mine included), I find it very hard to fast when I’m actually not hungry (when my body is telling me to fast) rather than planning a day (not ideal if my body is screaming for calories). I can definitely relate to having a day where I was just not hungry, and the last time this happened I was scheduled for a couple “meal socials”.
    Thanks everyone :)

    Germaine wrote on February 17th, 2011
    • Uh, I feel your pain!
      From June to October I used to do a 20-hour fast once or twice per week.
      It was extremelly convenient to my daily routine (as I pack homemade lunch and take it to work), allowed to save money on groceries and, most important of everything, helped me to identify and control the so infamous “pseudo hunger” sensation.

      But in November I started working at an small enterprise with rigidly scheduled breaks… and the IF habit was broken. My actual cowokers are totally “common wisdom” and going out for a walk during the lunch break isn’t an option (industrial zone, large busy roads, can’t drive to anywhere else, etc.).

      Anyway, one only has to be flexible and to find a proper alternative plan, after all… there’s no excuse!
      So, I plan to fast during Saturday and maybe skip dinner (or breakfast) a couple of days during the week.

      As a ending note, for me, the most difficult part actually is to start IFing (or re-start). But once one gets used to it, it’s great, indeed.

      Patrícia wrote on February 17th, 2011
  32. I am so motivated by all of the comments and discussion I am going to try my first fast this weekend!

    TonyaL wrote on February 17th, 2011
  33. Primal is totally flawed because meat is highly acidic, if you want to increase your risk of diseases later in life, eat the primal way!

    Sean wrote on February 17th, 2011
  34. Grok did not find much…if anything at all to eat today..OH well.
    We try again tomorrow..THATS PRIMAL/PALEO.
    I recommend you try this..It is an integral part of a primal lifestyle.
    Little or nothing days!!
    Daveman GROK ON >>>

    DAVE PARSONS wrote on February 17th, 2011
  35. Uh, I feel your pain!
    From June to October I used to do a 20-hour fast once or twice per week.
    It was extremelly convenient to my daily routine (as I pack homemade lunch and take it to work), allowed to save money on groceries and, most important of everything, helped me to identify and control the so infamous “pseudo hunger” sensation.

    But in November I started working at an small enteprise with a rigidly scheduled breaks, and the habit was broken. My actual cowokers are totally “common wisdom” and go out for a walk during lunch break isn’t an option (industrial zone, large busy roads and I can’t drive to anywhere else).

    I want to get back to the old habit, though. One only has to be flexible and to find a proper alternative plan, there’s no excuse.
    So, I plan to fast during at Saturday and maybe skip dinner (or breakfast) a couple of days of the week.
    The most difficult part is to start IFing (or re-start); once one gets used to it, it’s great.

    Patrícia wrote on February 17th, 2011
    • Oups. This comment is supposed to be deleted. :)

      Patrícia wrote on February 17th, 2011
  36. The biggest issue I’ve encountered with fasting or in general not eating at the times I usually do is pain from previous meals. For instance if I have greek yogurt with orange juice for breakfast if I don’t eat lunch or some other food I get really acidic pain in my stomach and have to eat something.

    I’m aware that this is likely because the yogurt is acidic (i think? or is it base) and my mother always chided that I should eat something WITH yogurt, but there’s nothing I really can eat – no fresh fruit available to me right now =(

    Daniel wrote on February 17th, 2011
    • If anyone replies, do it to this second comment please! Forgot to hit email notifications…

      Daniel wrote on February 17th, 2011
      • I’ve heard that yogurt can cause problems for some people with acid reflux. It’s PH is usually below 5, yet for some reason certain people just can’t handle it. The orange juice you’re drinking is acidic though, and if you are drinking juice that you didn’t make yourself then there’s also probably a bunch of sugar in it. I would say to break your fast with something like a fat spinach, bacon and egg omelet and see how you feel afterwards. Also, if you incorporate a more structured regimen, such as fasting for 16 hours, then getting your daily allotment of calories within an 8 hour period, it will entrain your hormones better than sporadic meal skipping. Your body will fall into a rhythm, making your fasts much easier to handle.

        Rob L wrote on February 17th, 2011
        • I do not have acid reflux, afaik. I wish I had spinach, bacon and eggs.. I’m at a school in the middle of no where with no grocery stores easily accessible and my meal plan already paid for – the food they offer is disgusting and even the meat dishes make me sick. The salad is all wilted too :/ I graduate soon so here’s to hoping I can land near a good grocery store and get my eating habits back on track.

          Daniel wrote on February 17th, 2011
      • 2 things to consider:

        1) Drinking orange juice with yogurt will cause the yogurt to curdle. Not a good combination. Like a breakfast Cement Mixer. This could invariably cause stomach pain later in the day.
        2) Orange juice is liquid calories (and sugar)

        Keith wrote on February 17th, 2011
        • Both good points. I’ll keep that in mind. I’m not Primal right now, but it’s something I’ll be moving towards this summer when I graduate from college.

          Daniel wrote on February 17th, 2011

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