Marks Daily Apple
Serving up health and fitness insights (daily, of course) with a side of irreverence.
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. I have been fasting for 3 weeks now. My eating window is from 4pm till 10pm. I like to eat in the evening because it helps me sleep. My problem is, Because I am responsible for 5 boys that are in sports and have to tansport them all over the place in the afternoon. My only time to work out is first thing in the morning. Ussually between 6am and 8am. I will drink 8oz. of skim milk preworkout and a 250 cal. 35 grams of protein shake post workout. then I fast untill after 4pm. Am I still receiving the benefits of IFing, or am I ruining it by eating the workout meals. Any suggestions?

    Robert wrote on July 20th, 2010
    • Richard- Based on the IF articles I’ve read as well as Gary Taubes’ “Why we get fat”, you’d be better off getting some fat in your diet for that meal between 6a-8a. A glass of skim milk has nearly no fat but about 12g of sugar and the protein shake is, of course, nearly all protein. You’ll feel full a lot longer if you ditch the skim milk, maybe replace it with about 4oz of cream. A protein shake made with water and cream (or coconut milk) is delicious and highly satisfying, without the pesky sugars to cause an insulin spike.

      If you’d like to hit that peak 18 hour fast mark you could try skipping your pre and post-workout food once a week and maybe taking it easy on the workout that day.

      KateMonster wrote on March 3rd, 2011
  2. My work out is P90X and running for no more than 30-40 minutes. Ussually 3 miles at a 8 minute pace. I am 6’2″ 197lbs. I only run 3 to 4 times a week.

    Robert wrote on July 20th, 2010
  3. I enjoy skipping a meal when I don’t feel hungry. This has been more frequent while being primal!

    Primal Toad wrote on August 6th, 2010
  4. I like juicing carrots for breakfast. Feel great all day, albeit pretty hungry when I get home. And I can do 14 360’s on a skateboard.

    Dave wrote on October 26th, 2010
  5. This seems very interesting. I’m gonna give it a try. 😀

    Tom wrote on November 3rd, 2010
  6. I have been using IF for the last 2 months and have had great success (I’ve lost about 10-12 lbs body fat). I like to keep it simple so I have some loose rules that I follow (you can make your own rules – do what works for you).

    I use a daily “eating window” of “around” 2pm – 7pm (I learned this from the Fast-5 website). I say “around” because I don’t obsess about it. Some days I eat at 12 or 1 and some days I don’t eat until 6 or 7! I base it upon how I feel and what my body is telling me. I do try to stop all food intake by 7pm, but again, I don’t obsess or carry a stopwatch!

    I usually end up eating 2 meals a day using this method, but sometimes I only eat once and other times(rarely)I eat 3 times – it is very flexible and user friendly.

    I try to break my fast with something nutritious – fish, salad, veggies – but I am on the road a lot, so sometimes I eat less than perfectly!! (I had a double double burger “protein style” at In-n-Out a few days ago and didn’t lose any sleep over it!)

    I work out in the fasted state and quite honestly I feel no difference. I was a little nervous at first, but now I actually prefer exercising in a fasted state – I have more energy and my strength has not gone down at all – and I anticipate eating a nice meal afterward. I have eliminated “Chronic Cardio” and now walk, run, and/or play instead (thanks Mark!).

    The number one benefit for me (besides losing the fat) has been proving to myself that I can skip breakfast (ahem…the most important meal of the day!!) and not “lose muscle”. I have never been hungry in the morning, so eating breakfast was always a chore for me. I’d force myself to eat a bowl of oatmeal with protein powder because, ahem… “it’s good for you”. (yeah right!) Then I would time and obsess over my next “feeding” in 3 hours, always sure to add some lean source “protein” to each meal!! I was hungry as hell most of the time. All I could think about was food!! I was really addicted to the Conventional Wisdom that has made us the fattest society in history.

    These days, I have a cup of coffee or espresso when I wake up and I go about my day. If I feel hungry I eat. I don’t worry about the “exact time” or the precise blend of micro-nutrients….I just eat until I am satisfied following the “Primal Blueprint” concepts (mostly!)

    I hope that helps! Good luck!

    Xander wrote on January 5th, 2011
    • I am the opposite. I would rather skip lunch than breakfast. Breakfast is my favorite meal

      Gayle wrote on January 6th, 2011
  7. Hi I like this. I have been primal for about 2 months now. I just came off of a 5 day water fast.
    After I started eating on Wednesday at the age or 46 I realized I eat when I am not hungry A LOT. Why? Well out of habit, because it is ‘lunchtime’, boredom, because i have been programmed to eat 3 meals a day no matter what.
    But now I believe I can “listen to my body” much more and eat when I need to and hopefully this will help break my weight loss plateau. I really like the ideas of ‘eating window’ or an early meal (breakfast for me) and a early dinner.

    Gayle wrote on January 6th, 2011
  8. meant to say ‘at the age of 46’

    Gayle wrote on January 6th, 2011
  9. Humans can go without:

    Air for 3 minutes;

    Water for 3 days; and

    Food for 3 months.

    My PB is one month.

    Noel Victor wrote on January 19th, 2011
  10. Just started doing my first fast in a long, long time. Hunger is my constant companion right now, but thankfully I am going to bed. Hopefully I’ll wake up closer to normal. Haven’t decided how long I want to take this. Being hungry makes you think of breaking the fast in the morning (if not sooner), but I was hoping for another day, up to a week tops.

    From what I have read, a week is nothing, and will give me a chance to see what life is like well beyond the point of hunger.

    I usually have a pretty good willpower so this ought to be nothing, but the desire to eat the last several hours seems more from a strong desire to enjoy the taste of food and not from any physical “need”.

    Dune wrote on January 24th, 2011
    • Made it through work. That made it 41 hours from my last meal until I broke my fast when I got home from work. Last hour of work I had the beginnings of a headache with some jittery feeling which felt like a lack of calcium. I also had a craving for liver. Again today I wanted to eat for the sake of eating and enjoying food, but not as bad as the day before. I will just monitor my hunger and be sure to avoid gorging. Will probably do it again.

      Dune wrote on January 25th, 2011
  11. If you are hungry during a fast it is usually thirst and an ’empty’ stomach not hungry because there is a difference. Since you are burning fat your body will just use your fat for fuel.

    I would like to know the best workouts during a fast and the best food for breaking a fast.

    Beth wrote on February 10th, 2011
  12. So inspired by the research presented here and the email newsletter from a few days ago I skipped lunch today. Well, if the truth be known I forgot to take it with me… Anyway, I figured this is the chance to try skiping a meal.

    I have been eating primal blueprint for about 6 weeks now and one of the immediate benefits is I don’t panic when I get hungry. Todays fast- just skipping lunch- was no big deal. I guess I’ll try this once or twice a week and see how it goes.

    I guess the biggest impact for me is, aside from the effortless weight loss, taking back control of hunger and eating. No longer am I slave to the carb and the hunger panic attacks.

    On a side note some of my friends, family, and co-workers think I am bat poop crazy, so I am taking the Primal Blue Print on the down low. For those who are truly interested in what I am doing I preach it and send them the primer .pdf.

    Mark L. wrote on February 28th, 2011
  13. I was doing a lot of intermittent fasting a year ago. I would go 36-48 hours per week. I went from 270 down to 245 and felt great. The more I did it the easier it got. Once I stopped I began gaining again and now am at 290 and finding it very difficult to fast. I had been eating mostly vegetarian in between fasts but am thinking that this primal diet might make fasting easier for me and eliminate the rebound gaining I was experiencing.

    Honeybear wrote on March 2nd, 2011
  14. hi mark, i been fasting 2 times a week in the past three weeks for fat loss purposes, i was in the pb eating style 1 month before starting, and i look and feel awesome, i want to know if a 36 hour fast represent any benefit vs a 24 hour fast, thank you.

    jorge wrote on March 30th, 2011
  15. Researchers from the Intermountain Medical Center Heart Institute in Utah recently conducted a study to determine the potential health benefits of participation in water only fasting. We wrote about this at

    Hene wrote on April 8th, 2011
  16. IFing is great, saves money and time and is super easy to do,just don’t eat!!!. Also as an extra guys stop eating ANYTHING WHITE!!!! I bet my left testicle the majority of obese/ weight gainer gain weight by eating too much rice/pasta/pizza/bread. Another huge one is DO NOT DRINK CALORIES!! So many people go by drinking coke/beer/martinis/ juices/ sodas/milk. Unless you are drinking a post work-out shake drinking calories is useless as most of what you digest is PURE Carbs. In my case If i drink the night before I do exercise the following morning to counter the carbs and also help my hangover.

    If you find fasting too hard just go with Tim Ferris slow carb method, which imo is more difficult because its not as simple as “only eat once a day”. Btw if you think you can loose weight slowly by calorie counting you are wrong. Yes you might get far, the very moment you eat more calories than before you will gain weight, that is why you must exercise (preferablly HIIT- high intensity interval training) to keep your metabolism up

    Andrew wrote on April 25th, 2011
  17. I am going to start IFing the begining of next week. I have been eating a bit of rubbish after lent, and as I have a holiday until next week, I plan to get it all out of my system.

    i have dabled in the eat stop eat way and found it ok. But just recently I have had a really bad bout of acid reflux (along with having IBS), and tried to stop eating after 5, which really helped me.

    I also remembered that I read a book on fast-5 a few years back and got another copy, so had tried that for a few days as well, 12 til 5, and it was so good. I felt so much better, nice and light.

    Its a bit awkward though knowing what to eat with my IBS, not high fibre because I cant handle it. I was told to eat white stuff.!! Bit annoying, but will have to see how it goes.

    Anyone got any advice? Thanks. Rach

    Rach wrote on April 28th, 2011
    • Rach, check out GAPS. Full expanation of why and how to avoid white foods. Then move on to PB, with the explanation of why replacing grains with nuts (as many GAPSers do) is unwise. Between them, you should be able to piece together where the “eat white” mantra came from but why it’s not going to help you in the long run. Healthyhomeeconomist has an article with a monstrous comments string about this as well.

      Lauren wrote on August 8th, 2011
  18. hi,

    I just started out with Primal Blueprint (well, a mash-up of PB and Robb Wolf’s PS). I’m only on Day 3.

    At what point do you guys think I can add IF to the mix? Does my body first need time to get used to eating differently or can I just try it immediatly?

    Jeroen wrote on May 19th, 2011
    • I used to IF when i was a carb eater. It is just harder mentally because your body will crave carbs and quick energy vs. moving over to burining fat from your body for energy. Once you have been primal for a month it will be super easy to IF and you will find that you are more focused and have more energy when your body dips into its fat stores to fuel your day.

      I would go for it if you want, especailly because you can see how the experience will change over time when you are more fully primal!

      For your first one it is kind of nice to start by eating breakfast (or having a primal fuel shake) and then skip lunch and dinner and go to bed and try to make it to lunch the next day.

      Beth wrote on May 19th, 2011
  19. I worked at a preschool where all we did was feed the children. They arrived at 9am and I always assumed they would have had breakfast already- however I was still required to provide a morning snack (usually crackers or dry toast with jelly). I then followed 2 hours later with a heavy meal . Again 1 1/2 hours later with some type of dessert and a snack again while they waited to be picked up 2 hours later. I was horrified at how much these kids eat all day. I have been fasting one day a week since I was 30(12 years). I find my body responds well to this. I stop eating after Mondays dinner and resume eating Wednesday morning. I guess I am lucky – I never have hunger pains. In fact sometimes I find that sometimes I have to convince myself to eat again- because I do feel much fresher and revived(energetic) when I go a day without eating. I have 3 children and I am a busy active mom who never slows down and fasting has never interfered with my energy level in any way. I guess to each their own.

    Maggie wrote on May 24th, 2011
  20. Mark, I am curious about how biochemistry is being affected by fasting. I am new to primal (1 month) and have for years been eating regular meals to keep my blood sugar stable, which keeps beta endorphins (BEs) from spiking and then leading to a crash. The crash would always lead to cravings for sugar/carbs, but I was still eating whole carbs. But now I am confused. Were BEs not really a factor after all? There are times I feel like I could skip a meal, but am afraid because I really don’t want the cravings to come back!

    All I know is that by eating primal these last weeks, my cravings are almost non-existant…the first time in too many years. And my energy is way up. Maybe this question is too vague, but if it makes sense I’d love to know more!

    Heather S. wrote on May 25th, 2011
    • I don’t know much about BEs but I used to eat to keep from getting sugar crashes. My husband and I used to even call it getting “hangry” hungry and angry.. and it was all about carbs. I used to fast while i was a carb eater and it was just a bigger struggle because mentally and physically my body wanted carbs and would fight it and make it difficult. Now on PB my body is indifferent to the fasting no real issues because your body is now used to burning fat for energy and provided you are not 0% body fat it will access those reserves to keep you feeling full. There is a difference in feeling “hungry” and having an empty stomach AND being thirsty. Many “hunger pains” are actual “thirst” pains and many other “hunger pains” are actually just your stomach feeling empty but you not physically being hungry (weak, tired, lacking energy) just get out of your head and into your body and go for it. Don’t fear cravings, commit and do it. Just skip dinner and breakfast and eat at lunch or skip lunch and dinner (go to bed early) and eat at breakfast. Or just skip one meal and start slow.. just qualify what you feel with what is really going on.. do you THINK you are having a craving because you THINK you should or are you really hungry.. maybe you are thirsty.. just give it the 10 min test. Drink some water and then see how you feel in 10 min!

      beth wrote on June 2nd, 2011
      • Thanks Beth, I hadn’t thought of it that way, that my body is now getting used to burning fat instead of carbs. I have gone long periods between meals and not noticed significant cravings. I have a feeling one of these days I will skip a meal without even noticing! It really is pretty easy.

        Heather S wrote on June 4th, 2011
        • Exactly! That is the best way to do your first IF.. when you notice that you have “missed” lunch because you were working or busy once you notice it just wait till dinner — First IF done! Also a crazy thing happens once you get through a few hours .. you have MORE energy.. I am excited for you and for your first fast!!! Take Care!!!

          beth wrote on June 4th, 2011
      • “many other “hunger pains” are actually just your stomach feeling empty but you not physically being hungry (weak, tired, lacking energy)”

        This right here.

        My very first revelation when I started to get healthier over a year ago was the realisation that hunger does NOT equal an empty stomach and there for should eat, Hunger is when you feel tired and lacking in energy, THAT’S when you should eat.

        Such a simple idea but one so so many people sadly don’t understand.

        jupiter3888 wrote on June 5th, 2011
  21. A lot of people read about IF but end up being confused about where to start – and therefore don’t. I like the way you stress that there is no ONE way to do it. Try what seems practical for you and see how it goes. Great approach.

    Olly wrote on June 4th, 2011

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