Marks Daily Apple
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19 Mar

How To: Intermittent Fasting

After the great discussion last week following the 1 Meal vs. 3 Meals news post, we thought it was a great opportunity to follow up and delve into the nitty gritty of IF. Practically speaking, what does IF look like? Today we’d like to focus on the “window of eating,” a dimension of IF that got people talking last week.

Any brand of fasting can already seem a little daunting for the newcomer. (But for those whose impressions of fasting involve hunger strikes or gaunt figures sitting in meditation, we think you’ll be pleasantly surprised.) Reading about some options, and knowing your efforts will indeed be rewarded with true health benefits, makes the leap a little more inviting.

Let’s first put this on the table: there is no one way to do IF. The only real guideline is that, as always, the food you eat should be healthy. (It’s pretty clear how we choose to characterize that.) In addition to the substantial health benefits, the simplicity and flexibility are what draw people to IF.

As Mark said, he enjoys mixing it up beyond the use of one approach by missing meals naturally or on an unplanned basis in addition to full day fasts. Let your choice(s) fit with your personal/family schedule, natural rhythms, and your personality (some of us are meticulous planners and some are more spontaneous – “and that’s O.K.”). The point of IF is this: episodic deprivation takes your body “off the track” for a while and allows systems to reinvigorate and recalibrate (also known as up-regulating and/or down-regulating gene expression). Check out Mark’s previous post on IF for more info on the research and nifty benefits of fasting.

Here are a few ways to IF (in unofficial terms):

Skipped Meal:
As Mark alludes to in his comment in the 1/3 meals post, he likes to miss meals naturally or on an unplanned basis. When we listen to our bodies rather than blindly follow routine we find we’re not always hungry when mealtime comes around. Let yourself skip a meal when this happens, or plan a meal skip during a convenient time.

Condensed Eating Window:
As shown in the comments from last week’s post, this is a popular option. The day’s food intake is condensed within a set number of hours, often somewhere between four and seven hours. The timing of this window varies depending on the individual’s schedule and preferences. The time since you prior meal or until you next day’s meal becomes the fasting period.

Early and Late:
For some, this option is more easily managed than the condensed eating window. The day’s food intake and nutrients are balanced between an early meal and later afternoon/early evening meal.

Single Twenty-Four Fast:
Most people choose to have a normal dinner and then fast until the following evening. Others choose to extend the fast until the following morning. For many people, this can be a weekly routine. Others may integrate it on a monthly basis or as an occasional event based on their sense of progress/plateau.

Alternating Day Fast for Week (or more):
This approach is often credited with a deeper “cleansing” character. Some people do it once or twice a year. Others make a seasonal commitment. You can choose to drink only water or include teas/small amounts of juices during fasting days. On the alternate days, some people choose to eat normally, and some opt for reduced caloric intakes.

One tip: During your “window of eating,” however long or brief it is, don’t feel that you should eat more than you might be hungry for. It’s a unique opportunity to listen to your body’s signals. It also serves as a way to “prove” to your conscious brain that you can survive quite nicely on smaller amounts of food and that you don’t need to “make up” for those temporarily lost calories. Of course, eating according to the Primal Blueprint at all times whether fasting or not means that you are constantly refining your fat-burning skills. This, in turn, means that you are not so dependent upon regular meals to sustain normal blood sugar levels, physical energy and mental acuity.

Interested in trying IF for the first time? We’ll highlight the “condensed eating window” approach (one option among many) to get you started. This approach, particularly with a fairly extended window, is very doable and can seem less daunting as you get started. Choose your own timing and length of window based on your schedule and preferences. If you can’t decide, you can consider condensing your eating between the hours of eleven and 5:00 p.m. Look for a corresponding IF menu in this week’s installment of “Eat This Today, Feel Good Tomorrow” later on today.

Be sure to send your feedback. We’d love to hear your results!

*Florian Flickr Photo (CC)

Further Reading:

Post Workout Fasting

Modern Forager: My IF Success Story

Conditioning Research: IF Reduces Inflammation

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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. hey,
    I’ve been IF’ing for about 2 months now, 18-22 hours, twice a week, always Tuesday and Thursday. By keeping a constant schedule of fasting, am I reducing the benefits? I’ve read in several places on this site that part of the point is that your body has to adapt to changes. Occasionally I’ll skip a meal in addition if I’m just not hungry for it, but for the most part, it’s Tuesday and Thursday.
    Thanks for the advice

    Andrea wrote on June 16th, 2009
  2. Andrea, Are you doing the Eat Stop Eat diet? I have gotten great results as a diabetic with the Warrior Diet- also never hungry. Soildly based in Mark’s Primal and Atkin’s low carb. I would vary the days off ala tricking your metabolism. I do it with taking extra Fat or extra carb days or extended IF on various days. I like to keep the body wondering what the next bit of food will be

    pjnoir wrote on June 16th, 2009
  3. Nope, I don’t have Eat Stop Eat. I just added IF to gain some of the benefits that are seen with CR, without the crankiness.
    It seems that 3 days normal, 1 day fast, 1 day normal, 1 day fast (repeat the next week) would be mixing it up enough, but I wanted Mark’s opinion anyway.
    Though my body might not mind a random schedule, I don’t like it, I’m an engineer, we tend to be picky.

    Andrea wrote on June 18th, 2009
  4. I’ve recently been looking into the whole IF program as well as Brad Pillon’s “Eat Stop Eat”. I’ve read and understand the beneficial and cleansing aspects to it, however I’m wondering if I would be a good candidate. I find that if I go more than 3 hours without eating, I start getting really shaky and irritable. Because of this, I always have a bag of almonds or a banana in my purse. Also, I simply cannot function without breakfast. I tried this the other week when I had to go in for a blood draw and almost fainted. So, I’m a bit dubious as to whether this is even doable for me. I’d love to hear from others about this!

    Karen wrote on November 13th, 2009
    • Karen, when I started Brad Pilon’s ESE the same thing happened to me. I had to do a few mini-fasts before doing a full-blown 24-hour fast, and even then my first few 24-hour fasts were hell. H.E.L.L. But each one got significantly easier and I felt better on each one. By around fast 3 or 4, I felt great. Perhaps there was some de-toxing going on, I don’t know …. Brad talks about the dizziness factor a little here –

      Karen wrote on November 23rd, 2009
      • Thank you for the response and the link. It was very helpful. I know that just the anxiety of not eating is going to be hard on me. I get anxious just thinking about it!! I like my food :) I think the idea of doing mini-fasts at first is a great idea. Thanks again!

        Karen wrote on November 23rd, 2009
        • Hi Karen,

          I’ve been fasting off and on for several years. There are times when I want to fast and I run into the same issue that you do. What I’ve learned along the way is to prepare my body. If you are eating meat, start to minimize the amount you eat, and at times it takes me between 3-7 days before I start. I fast every other day. I don’t usually do it for longer than 4 weeks at a time. Basically, I eat one day and not the next. I drink only water with a little bit of lemon. It’s worked wonders for me. I have a clear mind and I feel much healthier. And when you feel like you can’t do it, I tell myself, “I can always eat it tomorrow.”

          jen wrote on January 29th, 2010
  5. Thanks Jen for the comment. I still haven’t tried to fast yet. I know that just starting it is the hardest part for me. I think if I could avoid food altogether, at least initially on the fasting days, it would be easier. Unfortunately for me that is not possible since I have a husband and two young kids to cook for.
    I appreciate your comment though. It makes a lot of sense.

    Karen wrote on January 30th, 2010
    • I think it also helps to tell yourself you’re going to ENJOY the experience. If you think of a fast as a negative experience, or have doubts you’ll stick to it you won’t succeed. You have to BELIEVE you’ll stick to it before you actually do. I say things to myself the day before like “I’m going to enjoy my fast tomorrow and enjoy the time it provides me to be productive.” …which is actually true! When I’m not cooking, eating, and constantly thinking about where my next meal is coming from I can get a lot of things done! 😉

      Fixed gear wrote on February 1st, 2010
  6. I just completed a week of alternate day fasting. …sort of. It went like this M-W-F, I fasted. On Tues, Thurs, Sat and Sun I ate primal like I always do. Not in excess to make up for the fast days, just a regular amount of food. The results? In a week I dropped 4 pounds! AND I got stronger in the gym in most of my lifts. And I’m starting pretty lean already around 12% bf, so I’m pretty stoked on how well it worked. I wrote about the whole experience on my blog:

    Fixed gear wrote on February 1st, 2010
  7. Oh man this stuff is retarded

    BB wrote on February 2nd, 2010
    • Way to bring up the level of discourse.

      John wrote on February 2nd, 2010
  8. Hi Mark and fellow posters,

    Just wondered what is recommended in terms of exercise while fasting?
    Im going to start IF with 18-24hr fasting periods every 2/3 weeks to ease me in, should I be exercising on these days? and if so should I go for resitance exercise, or something more like sprints/tabata training?
    What have other people found works best for them?

    Thanks all for the help!

    Phil wrote on February 5th, 2010
  9. great idea, get your muscles into a catabolic state with no protein to feed them… let us know how it goes!

    BB wrote on February 5th, 2010
    • What evidence do you have that this is the case? Fasting releases HGH and if used sporadically (cutting calories too long causes prolonged metabolic slowdown) it can work to build muscle.

      Have a read:

      David wrote on February 5th, 2010
  10. Sarcasm…very witty

    I was asking the question to see a) if exercising was recommended (I’m guessing from your response you think not!), and b) what other people do.

    People ask questions on here to get help
    and advice, unless I’m mistaken that’s the idea!?

    Phil wrote on February 5th, 2010
  11. fasting is great and eating is highly over-rated in north america. People think somehow that eating more will help them increase muscle mass.

    Before I joined the infantry I ate like a horse and remained a thin 147 lbs while working out 5 days a week at highschool (19 yrs old).
    Then I joined the army and felt hungry ALL THE TIME. I cannot remember a time when I wasn’t hungry, even right after a meal because they fed me so little. BUT, after my first 3 months in basic training, CONSTANTLY exercising, doing push-ups etc. and getting fed less than ever before, I was up to 172 lbs. (and I’d never been able to gain weight before.
    We’ve still got alot to learn about food….most of us eat WAY more than we need.

    andy wrote on February 10th, 2010
    • That’s interesting Andy. I do Ironman and I burn (depending on the day of the week) between 1000 (easy day) and 4000 (hard day) calories a day, 7 days a week, training. I am also vegan so I don’t eat meat, dairy, or eggs. Some days I am very hungry and some days I am not. I am a 5’10” female. 135lbs. Pretty lean. I wonder if IF would have any benefit for me. Or if it would compromise my ability to train.

      Blaine wrote on August 3rd, 2014
  12. Phil,
    I do Crossfit and started the Condensed Eating Window IF.
    So far its been business as usual with my Crossfit WODS with little or no difference as it would relate to energy.
    I say, do what you always did, and don’t worry about the fast. Its going to be part of your primal system, right?
    Best of luck!

    Jeffer wrote on February 10th, 2010
  13. I just want to thank you, Mark! IF has really helped me. I had heard of fasting before, of course, but I really needed to re-adjust my perception of it. I think a part of it was trusting my body enough to know that if I miss a meal, that I’ll be ok. Once I found that I could do it, it’s been a great help. Thanks!

    Rachel wrote on February 24th, 2010
  14. Mark, completely agree that we don’t need to “make up” for those temporarily lost calories. For me, small amount of food works fine. At the beginning, I was thinking ‘eat only when hungry’ but didn’t seem to work for me because I seldom feel hungry. So I switched to ‘eat only when I want to’. I have been doing one meal a day. So if one day I have lunch, the next day I have dinner, my fasting hour is longer than 24. But sometimes it’s shorter when I have dinner one day and followed by lunch the next day. No matter how my IF window is, I just eat normal amount of food and never feel a need to compensate for the lost in calories.


    Intermitten Fasting Success wrote on March 8th, 2010
  15. This has just been amazing! I started the eating window exactly a month ago. I am a number geek, so I kept a journal of weekly body fat and weight based on the window I had chosen.
    First of all, I had to tweak my windows on the weekends and on busy days. I completely lost the desire for the typical “3 meals a day” mantra and would completely forget to eat! I went two 24 hour periods last week when I was just too preoccupied to eat.
    So my window starts for 7 hours after I first eat. (Mark is that okay?) Sometimes I eat frequently in that window, sometimes not.
    Secondly, I have lost atleast a pound and BF% per week since I started this! I was not over weight to begin with, so having these extra pounds just fall off has been amazing!
    I look forward to summer bikini season! Hee hee!

    Jeffer wrote on March 9th, 2010
    • Jeffer, way to go. There is no right or wrong here – just what works best for you. Sounds like you have it dialed in. Now just tell everyone you know!

      Mark Sisson wrote on March 9th, 2010
  16. fasting has always been a part of hindu culture. traditionally people fasted once a week – different days were designated for a different god, and people picked their favourite- during certain phases of the moon, or on certain festival days.
    these fasts could be either skipping one meal, being on liquids all day, eating only a certain kind of food, or a complete solids and liquids free day.
    didn’t do anybody any harm, in fact we, even as children were encouraged to do the ‘skip one meal once a week’ fast to give our digestive system a rest.
    a lot of what passes off for hindu ritual is based on long forgotten scientific fact, and now it seems like the science behind it is being discovered again – good for the world!

    magicalsummer wrote on March 22nd, 2010
  17. Hi Mark
    Just a quick note to give support to IF been fasting for the first time now since Lunchime yesterday (approx 22 hrs) and feel great full of energy and no fatigue as a x-fitting alpinist I feel this is a real positive knowing that I can still feel full of energy and alert without constantly re-fueling on long hard climbs. Keep up the good work!

    Trevor Marrs wrote on March 30th, 2010
  18. I’ve just started reading the Primal Blueprint. I have been eating Paleo/Primal for 6 weeks now and I love it! I feel great and I look better than ever, but I must admit, the idea of fasting is something I’m a bit wary of. I look forward to reading about it in the book, but I will admit – I LOVE EATING. I’m not overwieght and don’t struggle with my weight. If I go longer than a few hours without food I can’t think of anything else until I eat – even with full protein high fat meals. My carb intake is below 150g a day sometimes even below 100g….how hard is this for peopel like me! I’m sure I will try it – not afraid of new things – but I fear for those around me!

    Stef wrote on April 19th, 2010
  19. I know this is a stupid question but does having a couple cups of coffee with cream in the am and not “eating” until lunch count, kind of?

    kat wrote on April 22nd, 2010
  20. Hi, Been reading this post with interest. I have been following the Eat Stop Eat programme for a few months and been totally fine with it. Although still want to lose a few more lbs and its also a good way to keep healthy. Just wondering about doing it the window way.

    How many cals are you supposed to eat in the window? Say its between 11 and 5, do you have to eat all of your calories you are supposed to in that day, or eat as normal, but obviuosly cutting out the before 11 and after 5?

    thanks Rach

    Rach wrote on May 1st, 2010
  21. Well, I have never “purposely” fasted before but I am finally going to give it a try. A mini fast that is…

    I finished eating my large breakfast just before 8. I would usually then eat a lunch around 12 or 1. It is 1:01 right now and I am truly not that hungry.

    I am going to go till at least 4 and if my stomach isn’t growling then I will wait till 5 or 6 and eat a regular meal.

    I am not intending to lose weight… in fact I want to gain weight – muscle that is. But, I know I still have some fat to lose so I am giving IF a try. If I go till 4 feeling fine, then I will probably fast more often and simply eat less or not eat when the food that is available is not that great.

    Primal Toad wrote on May 12th, 2010
  22. For we planners, is there an optimal fasting interval for fitness? I would imagine that one would see diminishing returns if one were to fast too frequently and not get the most out of its benefits if done too infrequently.

    freddy wrote on May 18th, 2010

      Ben wrote on May 18th, 2010
  23. I have been IFing for couple a years…one question I have always had is how do you take your vitamins on an empty stomach?

    Sheila wrote on May 18th, 2010
  24. Does it still have the same benefit to protein powder, as a replacement for meals? I have been doing this recently as I want to make sure I only use fat not muscle, and so that I can do light exercise whilst fasting.

    Do you only get the same benefits when your stomach is screaming at you? because I did this by necessity when travelling in Peru, and I lost 7kg, and all my muscle with it. I came back a wreck, and now I have carb or fat cravings all the time, even after putting the weight back. IF with protein really helps me to stop binge eating. I think it’s the lack of addictive carbs.

    But I don’t think I could fast for long on a totally empty stomach with no protein, I wouldn’t have any energy to move!

    Richard wrote on June 1st, 2010

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