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

Is Intermittent Fasting Healthy?

If only I weren't so skinny!

One thing is certain in the field of health: what is common wisdom today can easily become “misapplied science” tomorrow. What’s “in” this year may be “out” next year. Often it’s hard to arrive at the right answer.

For example: Oily fish is good for you because the Omega-3’s are so healthy, but oily fish is bad because it can be contaminated with heavy metals, but oily fish is good because recent tests prove it’s not actually very contaminated, but oily fish is bad because the fishing industry paid for those tests…you get my point.

The Fats vs. Carbs argument is another. So when a reader recently asked about regular fasting as a means of maintaining good health, I had to re-evaluate my point of view slightly. What I found surprised me and convinced me to add a new twist to my ongoing health-and-anti-aging regimen. It’s called Intermittent Fasting – or IF.

Twenty years ago, as I was first forming my Primal Health point-of-view (based on a model of how humans evolved), I found it very easy to embrace the concept of “grazing” that seemed to represent the collective conscious of the weight-loss-and-health movement at the time. After all, eating several small meals a day – grazing to maintain even blood sugar and to avoid having your body go into starvation mode and start hoarding gobs of fat – seemed to fit my picture of early humans roaming the plains of Africa foraging for roots, shoots, nuts, berries, grubs and the occasional road-kill leftover from a hyena feast. The explanation that we in the weight-loss business gave the public was that by maintaining this steady supply of protein, fats and carbs throughout the day we would never experience a wild swing in blood sugar due to rapid rises and falls in insulin, therefore we would be less inclined to store fat and more inclined to burn off our existing fat stores. Heaven help us if we skipped breakfast, overate or starved ourselves periodically. That would surely wreak havoc on the delicate hormonal systems keeping us in homeostatic balance.

Well, maybe not.

The truth is, many people have succeeded in losing weight and keeping most of it off using this simple grazing method, which consists of eating 5 or 6 small meals or snacks spread evenly throughout the day, with no single meal exceeding 600 calories and where each meal or snack contains a little protein. This grazing method is the ultimate in portion control: take the 2400 (or more) calories you might otherwise scarf down in 2 meals and simply spread them evenly throughout the day. I think it’s reasonable to project that many more have avoided or postponed getting type 2 diabetes using the same method.

But like many behaviors in the fitness and health world, there comes a point where the benefits decrease and we find ourselves on the dreaded plateau.

The first thing most people will tell you about their attempts at grazing is, while it usually works well if you are diligent, it’s pretty difficult to stick with, since you need to be near a source of quality food every few hours. If you work at home most days as I do, it’s not a problem, but it can make life difficult if you work in an office setting or happen to be a road warrior.

The next common issue is that after a few months of progress, you arrive at a frustrating point where the weight stops coming off, the initial high energy levels decline or you stop building muscle. That makes sense from an evolutionary perspective, since the body is so well-tuned to adapt to any situation – including a perfectly even flow of nutrients. In this case, the body’s reaction to this steady supply of nutrition is to actually decrease insulin sensitivity. It “knows” there will always be food, so it “down-regulates” insulin receptors, and probably down-regulates other metabolic systems as well.

In my Primal Health articles here at MDA, I am always looking at ways we can harness our DNA blueprint to maximize health. I like to see how we can shake things up a little and trick the body into burning more fuel, creating more lean muscle, repairing cell damage and staying injury- and illness-free. So when my 79-year-old buddy Sid at the gym started raving about his weekly 24-hour fast over a year ago, and my friend Art started writing about his own fasting experiences, I decided to look into it further.

The results were surprising and impressive.

Numerous animal and human studies done over the past 15 years suggest that periodic fasting can have dramatic results not only in areas of weight (fat) loss, but in overall health and longevity as well. A recent article in the American Journal of Clinical Nutrition gives a great overview of these benefits which include decreases in blood pressure, reduction in oxidative damage to lipids, protein and DNA, improvement in insulin sensitivity and glucose uptake, as well as decreases in fat mass.

How can you argue with results like these? And it all makes sense from an evolutionary perspective, because our predecessors almost certainly went through regular cycles where food was either abundant or very scarce. The body may have established protective mechanisms to adapt to these conditions by sensitizing insulin receptors when it was critical that every bit of food be efficiently used or stored (as in famine), or by desensitizing them when there was a surplus, so the body wouldn’t be overly-burdened by grossly excessive calorie intake.

Beyond insulin sensitivity, it appears that caloric restriction and intermittent fasting may “turn on” certain genes that repair specific tissues that would not otherwise be repaired in times of surplus. One could surmise that this adaptation serves to allow certain cells to live longer (as repaired cells) during famine since it’s energetically less expensive to repair a cell than to divide and create a new one. That might help explain some of the extended longevity seen in animal studies using caloric restriction and/or intermittent fasting (read about here, here, and here). Intermittent fasting has also been shown to reduce spontaneous cancers in animal studies, which could be due to a decrease in oxidative damage or an increase in immune response.

So, what are the practical applications of this research?

It depends. There’s probably no right answer (remember what I said at the beginning!) Art suggests mimicking the experiences of our ancestors, which is to say don’t plan any fast, just surprise your body every once in a while with 24 hours of little or no food. My friend Sid does his fast every Tuesday like clockwork, so he has a light final meal on Monday night and doesn’t eat again until Wednesday breakfast. He does drink water and a little juice on his fasting day. Some fasting programs suggest you take a two-week “cleansing” approach where you eat regularly every other day and fast (or eat 40% of normal) on alternate days for two weeks twice a year.

One thing that is most interesting about the intermittent fasting studies is that slightly overeating on the non-fasting days (to make up for the lack of calories on fast days) yielded similar results, so it wasn’t so much about total calories as it was about the episodic deprivation.

As for me, I’m going to try the once a week deal, but I’ll start by no longer agonizing over a skipped breakfast or late dinner. What I used to think was the end of the world might just be the beginning of a new one!

Let me know of your own fasting experiences.

UPDATE: See this post on Women and Intermittent Fasting.

Further Reading:

My Carb Pyramid

Healthy Recipes

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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. I fasted for 6 days the first time over 30 years ago but I didn’t do it right. Now I started fasting again but for only 24 hours once a week. I start with my last meal at 6PM on Thursday and start eating again on Friday at 6PM. I drink only water and as much water I feel that I need. I missed one week of fasting but I picked it up the next week. This is my 3rd. week at fasting. I plan to make it a way of life. I heard it was very healthy and also starting to eat more vegetables like apples and celery. I love it.

    Kitty Peterson wrote on February 5th, 2011
  2. A 24 hour fast isn’t when you have a final meal one night and then not eat until breakfast the day after the next.

    It is (for example) having your final meal at 7pm one night and not eating until 7pm the very next day – which isn’t difficult to do at all.

    Matt Orb wrote on February 28th, 2011
    • True…

      Patrick wrote on February 28th, 2011
  3. Hey Mark,

    Your post on IF has enlightened me! I have been experiencing dizzy spells for the past couple of weeks and thought something was going wrong with my body. Now I know why! I was too lazy to pack a big lunch to work so I would constantly graze and the result was dizzy spells if I skipped a snack. I am definitely going to start practicing IF. Have a couple of questions!

    1. Can I skip lunch to start off with?
    2. What is the point of drinking coffee during a fast? Isn’t caffeine bad for the body?
    3.Can I have fresh fruit juice / raw veggie smoothie during that time?

    Appreciate your response.

    Sindhu wrote on March 9th, 2011
  4. Hi everyone,

    Great article and comments! I just started the IF lifestyle one week ago and have been very happy with the results. I’ve lost 4 pounds in the first week. I have 7 more pounds until I reach my goal weight and although I intend to stick with IF most days of the week once I reach my goal, I will probably give it up on weekends.

    Here’s my one big concern and I haven’t been able to find a true answer to this question. Will fasting for 20 hours/day slow my metabolism? I worry that if I choose to give up the IF lifestyle that I’ll blow up like a whale. Does anyone know the answer?

    Wendy wrote on March 25th, 2011
    • Wendy,

      Research shows the basal metabolic rate slows after 48-72 hours of fasting or very low calorie diets. This is the problem with juice “cleansing” fasts that last for 3 to 10 days. It’s just another yo-yo diet. You lose water weight and lean muscle mass quickly, but the water also comes back on quickly and the metabolic set point has been raised so the same amount of calories eaten before the juice fast now get squirreled away as fat since the body has learned to be more efficient with what comes in.

      There are human studies of intermittent fasting showing NO decrease in metabolism from 24 hour fasts. Lean muscle mass is also preserved. You can safely IF for 24 hours without concerns about negatively affecting your metabolic rate. I can provide references if you like – I have them.

      Best of luck with a healthy IF plan!

      Kathleen Lea Summers, MD, PhD wrote on June 2nd, 2011
  5. IF has opened my eyes to metabolism. Wendy, you lost weight because your metabolism was kicked-up. We all fast so if IF causes a cessation in metabolism then we could not sleep or, as some suggest, stop eating at 7:00 PM.It is the fasting period, the time between dinner and breakfast, that I believe makes any diet work in the first place. Prolonging that period of time does not diminish metabolism. As a matter of fact I am planning to extend my fasts from time to time. I do IF everyday.

    mary titus wrote on March 25th, 2011
  6. I wasn’t sold on fasting but but I think I am now.

    I am 44 yrs old, about 275 lbs and 6 ft tall.

    I have lost dropped to about 207 in the past and then rebounded after about a year.

    I have recently started a hard regimen of cardio and weight training again, because I am so tired of wearing size 41 pants. When I am at 207lbs I was wearing 33s. any way after I started loosing it always seemed pretty easy to continue once I was in shape and I didn’t intend to fast but it seemed like I did it without trying I am not very hungry when I am running 3-5 miles 5 days a week. so I think in retrospect that I lost easier because I was fasting, it seemed I could almost feel myself loosing weight for 24 to 48 hours after the workout. especially when i would take a day off.

    I had always tried to maintain a low carb diet and eat many small meals a day but just didn’t have time. I was always worried I would start burning muscle when I didn’t eat regularly but never saw any sign of that. Now I am going to fast regularly and I am positive the pounds will fall away, especially since I quite smoking after a pack a day for 28 yrs and I am not drinking at all at least for the first 30-60 days, then just socially maybe once or twice a week.

    I love this site, I just came across it and it is very informative. I would love if other people would give their specific stories and make sure they give specifics ie; age, height, size etc. Thanks

    Troy wrote on March 25th, 2011
  7. I am 5’10, male, weighed 219 when I started, about one month ago. Now, I weigh 112, am doing slim in 6 everyday with my class and have been thinking of fasting, because my body is kinda telling me due to growing up a runner and athlete. It wants to run. I did a 40 day master cleanser and dropped 40 pounds, I was running 3 miles a day, loved it. Gained all back because I did not know that my body was allergic to carbs, but now that I have found “The Secret” I want to do a water fast, about a week would be good, and fasting 2 days a week. I have noticed that my body does not need that much to eat, so in the future, I think I can eat one, 2 days off and my body would like that. Problem is (why I am posting) that I smoke, a lot. I have read that it is not a good idea to fast and smoke, but I have done so. I know that the master cleanser covered some of the effects of smoking during the fast, but with a water fast I know it will be different, so I must stop, and I figure that during my first 2 day fast this week, I can dump all the nicotine out of my body. Any hints as to how to deal when I get a nicotine itching?

    Peter wrote on March 25th, 2011
    • You know quitting smoking is very individual. You might try the gum. It is good for acute nicotine withdrawl onset. I’m not a doctor but when I stopped, it helped to imagine myself inside a coffin and never seeing anyone I loved again.
      Or hold think of when you get done sprinting and trying to catch your breath, now imagine if that feeling never went away like when you have late stage emphysema. That worked for me. My father died from Lung C. at 55 and I am 44 and recently felt short of breath just going up stairs. I guess there is nothing like fear of loosing your life to really make you think.
      Good luck and remember usually a cig craving only last for about 1-3 minutes at a time so what I do when I get one is drink green tea and after about 7 days the cravings come less and less. Plan on not putting yourself in situations that you would normally smoke for at least 2 weeks, the IF should help because one of my times was after a meal.

      GOOD luck :)

      Troy wrote on March 25th, 2011
      • It doesn’t matter when you do the 4 hours off IF, it is up to what works out for you.

        Troy wrote on March 30th, 2011
  8. Sorry, to second post, I live abroad and am used to using K, so I started at 119 Kilos, now weigh 112 Kilos, need to get down to 100 Kilos before running, or even more, I will know when to run, when while walking my body will want to take off, my mind wants to do that, now.

    Peter wrote on March 25th, 2011
  9. Hi Mark,

    Thanks for this great post. And, wow, what a load of comments!

    I for one am a big fan of intermittent fasting, but done as per recommendations given by Martin Berkhan at

    I find that I have more energy when I follow this protocol, I have lost fat AND gained muscle and strength over the last 3 months, very happy with that.

    I have just written a post about the potential benefits of Intermittent Fasting and the Ageing Process. I hope you or some of your readers find it interesting.

    Keep up the good work,

    george super boot camps wrote on April 4th, 2011
  10. I have struggled terribly with my weight since I was about 20 (now 53). I yo-yoed 40 to 80 pounds, year in year out, on every fad diet program that came out. I have lived my whole life being told that if I stopped eating I’d end up in an even deeper hole than I was already in. Then, on April 1st of 2010, I had an ah ha! moment. If you want to lose weight eat less. I know, to most, this doesn’t seem like a real epiphany but turning 52 and back up to 220 lbs what did I have to lose? I started eating 1700 calories day from 2 pm until 6 pm 7 days a week (20 hour fast). One year later I’m now 170 pounds and from size 42 to 34 pants. I do walk. I have been for the last 6 years my wife used a cattle prod for the first year to get me away from my desk and walking. Even that only helped me to maintain my weight rather than gain anymore. Not until I started fasting did the weight start dropping off dramatically. I was losing so quickly friends and family actually secretly asked my wife if I was sick. It’s now become a lifestyle. Amazingly, I am now one of those people I have envied all my life that can eat as much as they want of whatever they want. To prove my point I didn’t walk at all from November to March and gained just 2 pounds. If you’re(seriously) tired of being overweight do this! You’ve got nothing to lose but the fat. Right?
    Oh btw, fasting means water only, black coffee or tea, no juice. The moment you take in any calories (and juice is *loaded* with calories) you’re on a low calorie diet not a fast. Good luck!

    Faster4life wrote on April 9th, 2011
  11. I started reading the first reply page and stopped after that. Seems to me that most of you that stumbled upon this blog are vegetarians?

    If you have to literally PLAN your IF then you’re not well nourished.
    I am so filled with nutrition that my hunger signals are completely turned off. Even the one for appatite…regardless if I smell the food or not.

    IF happens…automatically without you even noticing…when your body is so well nourished that it shuts the door for a certain amount of time on it own.

    I’m on a 80% carnivorous diet…no grains or legumes, no sugar, no juices ever, not even honey. If you have ANY kind of cravings before starting IF you’re not ready to starve. You’re missing minerals. When you force IF upon yourself for the sake of weightloss you’re depleting your mineral reserve = your bones.

    Good Luck to all playing the starvation game for vanity reasons.

    Suvetar wrote on April 16th, 2011
  12. Your way of doing IF makes perfect sense and should be the goal of us all. But as for me, I have not achieved that yet. I do eat primarily animal protein so I am quite far from being a vegetarian. Your appetite is suppressed because your body is producing many ketones that make sure that nutrition is absorbed thoroughly.Ketones are natures method of maintaining, protecting and even strengthenin the human body which proves that there is no need to eat constantly. There is no need to diminish anyones method of doing IF nor why. I do it for health reasons and of course, I don’t want to turn out being as fat as my great grandmother. I have been doing this for 5 years so I know the benefits of IF.

    mary titus wrote on April 16th, 2011
    • I am 44, working out really hard, alot of weight training and cardio every time i lift to start, usually 3 mile run or 3 min on the eliptical, then I hit the weights for about 5-6 sets of 3of 10 each supersetting without much resting.

      Anyway I am trying to loose weight I weigh 275 was, 285, and 6 ft tall I have been doing this hard for 4-5 weeks and eat a big fn salad everyday and if still hungry just protien like chicken. I am starting to loose weight took awhile because my muscles have been getting big again, like they used to be. My waist has lost about 4 inches but my question is I am starving some days and others not at all. but when I get done working out I am just shot, like I don’t have enough food energy. So I basically just try to eat in a 4 hour period everday and fast for 20 hours, any suggestions on what I should be doing?


      Tpattison wrote on April 16th, 2011
      • I would guess that you are almost certainly not getting enough nutrition from the amount you’re eating, especially on your training days, if you’re ending up shot once you’ve finished.

        If I remember rightly from reading Martin Berkhans site, he would recommend that you eat for an 8 hour block, and focus more on protein with your salad, especially post training, which if you’re doing a lot of you will be needing more protein. How many days a week are you training?

        Martin also recommends varying your calorie intake so that you eat more on the training days and less on the resting days. About 500cals either side of your BMR, if I remember right.
        See for more about Martin’s approach to I.F.

        I also remember something Lyle McDonald wrote on his site about not losing weight as quickly when calories are severely lacking AND doing lots of exercise. Check his site out, it really is superb.

        Hope this helps,

        George wrote on April 17th, 2011
  13. Author: mory
    been fasting three days a week for three months– maybe lost a pound. on my eating days, it was maybe 1300 cals of very healthy foods. I run about 10 miles week. I’m about 190 at 5’4″ 34″ waist (rolly polly) very healthy, never get sick— just meant to be chubby I guess? before doing three days a week I was doing two for nine months– didn’t loose then either. I started two years ago with Tuesday fasts and daily 1200 cal days. over two years lost maybe 10 pounds? I’m close to 60, so maybe that’s it? people say I look early fortys, and that’s the way i feel— just thought by now I’d be.., maybe, 170?

    In response to this comment, I would guess that one of two things might be going on:
    1/ You’re not recording calories effectively and therefore eating more than you think you are.
    or 2/ You may be low thyroid, but borderline, in a way that normal docs tests wouldnt show up. You could read the work of Broda Barnes and do some baseline temperature tests, that’s what recommends, and you can also read this by Ray Peat;

    Either way, good luck

    george wrote on May 18th, 2011
  14. H, I been working out everyday for the past 3 1/2 months without missing a day, counting calories no more that 1200 and i have successfully lost 33 pounds, but now my body is in total denial about lose any more weight the last month or so I haven’t be able to lose a pound, this is really frustrating, so reading all this about Intermittent Fasting that is new for me, I was wondering if you think is something that would jump start my weight loss? you think is what I should do at this point of my weight loss goal? I m planing on do 1 meal a day winch will be dinner around 5:30ish to 6? all my meals through the day are healthy, so should I consume my healthy 1200 cal in that hour, or should a lower the cal intake in that 1 a day meal? please help!!!! thank so much

    Gaby wrote on May 24th, 2011
  15. Here’s my experience: Fasting one day a week for two years, maybe lost one pant size. Started fasting two days a week, 9 months ago, have not lost much at all… Then at the end of Febuary of this year started fasting 3 days a week— think I’ve gained slightly over the last few months. I know my calories don’t exceed 8000 for the week. All i know, I feel great, little chubby, saving money.

    mory wrote on May 24th, 2011
  16. You can lose weight on IF, but I would not begin IF to kick up weightloss. You might be dissapointed.I wanted to lose 10 lbs the first year of doing IF. I not only lost 10 lbs…I lost 12 lbs. It took the entire year and I was fine with that. But I find many people are not happy with losing so little over such a long period of time. I was happy with my results and I continue doing IF even though my weightloss eventually slowed.Fasting will not cause you to drop a lot of weight unless you do it for a long time. Be willing to do it and yes, you just might lose a little weight.

    mary titus wrote on May 24th, 2011
    • I’m so glad to hear this. I, also have not lost allot, and so many have– which rasied the possibility of thyroid issues… I think I lose about a pound a month too. I am now fasting Monday and Tuesday, eating Wednesday, and fasting again Thursdays. 3 days a week for at least 3 months now; love the psychological and physiological aspects, but was surprised that I didn’t lose. Although, it feels like I lost a tiny bit over the last few months, but three days a week, and maybe a couple of pounds!! this kinda shocked me. I should be about 20 pounds lighter– so maybe a few years down the road? In the end, it doesn’t matter, I’m feeling good and NOT GAINING!

      mory wrote on May 26th, 2011
  17. I have been fasting twice a week for 24 hour periods and trying to restrict my daily calorie intake to between 1200-1600 a day in between. If I know I am going out to eat in the city and having a huge meal with an appetizer and desert I prepare for that by having that be my only meal for the day cause its easy to pack away 1200 calories in that one meal when you do that. I started last June and now its going on a year later. I was 215lbs and now I am 154. Lean, Abs and the thinnest I have ever been and all of my lower back pain I used to get now and then, is GONE!:) Never have it anymore. The beauty is, I hardly ever workout except pushups and pullups every week or couple of weeks. Gonna start hitting the gym again though when my schedule slows down which will be in September. Good luck everyone. It WORKS!! I have been on every diet and had results with them all but not like this.

    Jeff wrote on May 25th, 2011
    • This is what I do. Today is our anniversary and I plan to eat like a fool but not until our “date” tonight. I have been trying to do a little lifting but that is it. I hate exercise but my body needs it.

      Mary Titus wrote on July 15th, 2011
  18. Just remember NOT to fast right after an intense workout and do give your body a chance to recover completely before start on a fasting program.

    I agree with some of the users in here that drinking juice on a short fast is NOT ideal since your body will think you are on a low calorie-diet instead of really fasting.

    I fast on water/herb teas once a week on a Sunday for 24 hours starting after lunch until noon on Monday. Again, the reason for Sunday since it is a quiet day for me and I have done my intense workout during the week, which my body completely recovered by then.

    I alternated between drinking hot water with lemon and herb teas throughout the day. The kind of herb teas I drink are detox teas like kidney cleanse, liver cleanse, artichoke leaves etc.

    I break my fast with a vegetarian protein shake, which consist of two tablespoons of organic brown rice sprouted powder (85% protein digestibility), two cups of coconut milk, one tablespoon of wheat grass, a large ripe banana or pear and a handful of baby spinach.

    Cheers from Karl :-)

    Karl Roberts wrote on May 27th, 2011

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