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

Sponsor note:
This post was brought to you by the Damage Control Master Formula, independently proven as the most comprehensive high-potency antioxidant multivitamin available anywhere. With the highest antioxidant per dollar value and a complete anti-aging, stress, and cognition profile, the Master Formula is truly the only multivitamin supplement you will ever need. Toss out the drawers full of dozens of different supplements with questionable potency and efficacy and experience the proven Damage Control difference!

Subscribe to Mark’s Daily Apple feeds

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. Hi guys, I’m pretty new to this primal business, but have been thinking about trying IF for a week or so now. I’ve decided today is the day – only question I have is that I get very shaky, dizzy an headachy if I haven’t eaten for a few hours.. Will this just go away after trying IF a couple of times? Any advice is appreciated!

    Lucy wrote on October 26th, 2011
  2. What is the minimum period of time before a fast becomes worthwhile? Just slipping breakfast? I remember hearing about the magic hour where the mega fat burn kicks in but was it 14, 16 or 18 hours! Personally, I would find missing breakfast to be the most sustainable plan. But do you need to do this everyday or would a couple of times a week suffice? Just finished 18hr fast and tucking into delish tuna salad!

    teresa wrote on November 29th, 2011
    • yes, the benefits are maxed at the 18 hour mark; when I do a full fast I like to get a workout (LHT) in at this point, and I get peak performance. However, I wouldn’t worry too much about it; there are great benefits to IF throughout. Besides, if you factor in sleep time, and skip breakfast, you’re getting over 10 hours fast time (assuming you sleep enough!) which will give you lots of benefits.

      Milla wrote on November 29th, 2011
  3. also just wanted to ask, I have not been exercising – am I going to negate all my efforts and lose muscle while keeping the fat? have been sticking to a largely pb diet with a few strays at the weekend ie junk food and beer!

    teresa wrote on November 29th, 2011
  4. Wonderful beat ! I wish to apprentice while you amend your site, how can i subscribe for a blog website? The account helped me a acceptable deal. I had been a little bit acquainted of this your broadcast provided bright clear concept

    Brenda Kimberley wrote on February 18th, 2012
  5. some people fast because they believe in the Lord and that they are feeding off the Lords spirit. that’s why some people fast, not only to loose weight and things.

    anonymous wrote on February 19th, 2012
  6. I find what works for me is the following: If I’m hungry I eat; if not I don’t.

    For any followers of TCM you will have read that our organ systems operate in a rhythmic fashion. Each day is like a single breath in and out to our bodies – ideally, with the morning to mid-afternoon being an optimal period for intake of nutrients and the late afternoon, evening and nighttime, a period of elimination and rebuilding. Whether it be one or two meals a day, or a series of snacks spaced out over several hours (three concentrated meals seems too much to me personally), consumption of primary protein foods beyond 2pm or so is inadvisable as both stomach energies and available protein-specific enzymes have significantly fallen off by this point in the day, making digestion less than efficient (after all eating isn’t always necessarily about quantity, but about what the body can use). Of course, with shift work and artificial lighting circadian rhythms can be thrown for a loop.

    We as humans are quite flexible and adapted to periods of fasting – as may have been the norm for us in environments where food supply wasn’t plentiful. Such practices can also be beneficial for those who don’t pay attention to their specific needs and find themselves not hungry because their bodies are still in need detoxifying in a period of time where food would generally be welcomed.

    Re: anorexia – it can be due to both psychological disorder and intolerance to specific foods or their chemical components (e.g. histamine intolerance). The consequences of food/chemical intolerance can have physical/psychological consequences that can certainly put one off food. I speak from personal experience. The burden on me as an individual is to determine what foods my body tolerates and go from there.

    david wrote on February 26th, 2012
  7. LOL…. never really thought about it but my normal eating pattern seems to be a cup of coffee with a 1/4 to 1/2 a cup of heavy cream around 9 in the morning or so and a decent size meal somewhere between 4 and 9 pm… would this be considered some form of IF??

    Michael wrote on March 15th, 2012
    • I believe that the heavy cream is a no-no with traditional IF (if you have coffee it usually calls for 1-2tbsp of skim milk). But if this routine works for you and you are staying healthy then absolutely keep at it!

      I would make sure that your single meal does meet your caloric needs for the day and your macros are properly proportioned. Even in a cut, one “decent” sized meal could be too little or off balanced to maintain your metabolism and health.

      Steve wrote on March 21st, 2012
  8. Hi! So I’ve tried to fast a little bit for week now. I can’t say if I’ve fasted long enough yet but I’ve at least have been skipping which means I have been going about 6 to 8 hours during the day of not eating. Fasting has seemed to be giving me good results (I’ve lost 2.5 by doing this just this week!), but since I stopped eating lunch sometimes I feel really good (more energized and better about my body). But then there will be times where I don’t feel so well (when I want to eat I feel like I can’t eat solid food with out puking or very light-headed). Also, I feel like I am really hungry but like I also feel sick at the same time so I can’t eat anything. Am I doing something wrong or should I just do this once or twice a week?

    Amy wrote on March 27th, 2012
  9. Since starting the lifestyle a couple of months ago, I’ve noticed that I naturally skip meals because I’m just not hungry. I am planning on trying a full day fast to see if it will jump start my fat loss. I think IF is perfectly natural and if you really listen to what your body is telling you, your body will tell you to do it anyway.

    Karen wrote on March 29th, 2012
  10. hi,
    I’m currently trying to lose weight. Today Tuesday, is the second 24 fast I do. I did it last wednesday. This whole week I haven’t lost any weight and I’m wondering why that is if I pretty much deducted a good 2000 calories by fasting two days. Has anyone experienced the same?

    Donna wrote on April 17th, 2012
  11. Trying fasting for the first time today!

    David wrote on April 19th, 2012
  12. Nature evolved stomachs and fat because humanity, throughout its development and history has by necessity eaten intermittently. Its only recently that eating has become constant with all the confusion, neurosis and obesity that that has brought. The extent of the intermission depends on how far your hunters have to go, how much is there and how busy your family and friends are prepared to be to grow your own. Sorry to all the clever-heads but its as simple as that.

    dikod wrote on April 20th, 2012
  13. It certainly soufnds like it makes sense. I’ve yet to do any hardcore research, but from what I’ve gathered it seems legitimate. Sometimes mother nature and evolution has things settled, has it all under control and it’s when we try to overstep it that we get f#@%ed. Which really is what happened with humans. We’ve grown complacent now, more so than any species, and food is mostly in abundance. If you’re in a first world country. I know Africa has starving, majorly skinny people but they also don’t have as many animals I’d imagine to hunt as we did thousands of years ago before human expansion.

    I really like it’s premise. Turning on some sort of archaic mindset, a more brutish cave-man body going. Your body gets snapped into a situation where it can’t be prissy. It has to constantly burn fat because it thinks “I don’t know when you’ll get more food, so to make sure you don’t miss your next meal I’ll make sure you’re energized.”

    Definitely giving it a try.

    Cody wrote on April 20th, 2012
  14. I have a question and I’ve looked at numerous places searching for the answer before finally giving in and asking it here. Is it still considered IF if I have creamer in my coffee in the morning?

    Typically what I’ll do is have a large cup of coffee with half & half in the morning but I won’t eat until after noon when I’m actually hungry. I eat my dinner by 7:00 typically and so I have about 17 hours without food. But the creamer is questionable to me and I was wondering if anybody has input on this.

    Yvette wrote on May 4th, 2012
  15. I recently completed a 7 day fast. Before I did it I believed that I would probably die of starvation after missing just one or two meals. I realised though that my ‘hunger’ was a psychological thing more than anything. I felt like I SHOULD be eating, even though I didn’t really need to. After 3 days I didn’t even feel hungry and after 7 days I could have carried on but I felt weak and tired & wanted to get back to my exercise regime. Since then I have fasted for 24 hours once a week and I feel great after it. I don’t do it because I like doing it (I love my food), but it clears my head and makes me feel healthier.

    james wrote on May 7th, 2012
  16. I wasnt able to read all posts here. But in IF.. is it only food not allowed, or you are still allowed to drink water (plain)during fasting? thanks

    ann wrote on May 18th, 2012
  17. Hi Mark, question:

    On fasting days, do you recommend taking a multivitamin supplement, fish oil, etc, or skipping those also? Also considering that most MVMs are supposed to be taken with or after a meal, and that most are poorly absorbed without fat?

    Vince wrote on May 29th, 2012
  18. Does IF get easier as the weeks go by? I’m fasting Monday and Friday 24-36 hours and a healthy diet the rest.This is my 2 week. Does the gnawing in your stomach finally stop occuring?

    Laura wrote on June 14th, 2012
  19. I watched Horizon on TV last week and it covered Intermittent fasting, where on the day of fasting you have to do a reduced calorie day of 600 and then the next day eat basically what you want. This works out that 36 hours between Feasting and I wondered if this was ok? As there is not much literature out there or full understanding of risks. Saying that, I am into day 4 and feel fine, in fact very well indeed. I have only had one hungry moment but that passed as quickly as it came. I am finding that I sleep better on feasting days and my sleep is broken on the Fasting days.It’s probably my subconcious saying it’s nearly Break-fast time.

    Ron wrote on August 16th, 2012
  20. Greetings everyone
    I’ve been reading about Leptin and Leptin Resistance lately. Doctors who believe in IFing(at least in the articles I read)are saying that Leptin Resistant people not IF until they get that under control because,at first, they will lose 10 pounds or so and then completely stall.

    Anyone heard of this? I am IFing and I’ve lost 10 pounds but now I’m anxious. Do I need to be tested for Leptin Resistance? I’m 250 lbs and need to lose
    80 to get to my goal weight. I am type 2 diabetic with sleep apnea.

    Ian wrote on August 29th, 2012
  21. I am trying to fast for about 14an hours everyday. I have a busy schedule being a full time student and have a full time job. Im always on the go and im new to this diet that my friend has had success with. I do go to the gym 3at days a week, but i havent really been getting any weight loss results. I feel better thats for sure but getting frustrated. Not to sure what to do or if i should try fasting on alternate days. But dont see how this could be good for building muscle?

    Rodney wrote on September 5th, 2012
  22. Hey Rodney, if weight loss is your goal, I’ll tell you what I frequently do. But first I warn you that this is bad advice, and I know I’ll get flamed for sure, but that’s okay.

    I frequently fast 23 hours. That means eating once a day. Partially because I go out to dinner with a friend, and it’s near impossible to eat out and not eat excessively, but also because I’m too busy to eat more frequently anyway.

    So last night I showed up late at the bar, and poured a beer from the pitcher. Another patron brought a bag of fresh habanero peppers from his garden, so I ate one, and drank as much beer as I could to put out the fire. Meanwhile, our waitress brought me a big bowl of horseradish, to which I added several drops of Holy F**k hot sauce, which includes plenty of capsacin. A few minutes later my pepperjack cheeseburger arrived, which I promptly covered with the horseradish/hot sauce mixture. Chased that down with lots more beer and a shot of something. And then for desert, another garden fresh habanero, wich led to more beer.

    The beer was light beer (mostly). The peppers encouraged me to drink too much of it, rendering me too full to finish my burger, even though I hadn’t eaten anything else all day.

    In the wee hours of the morning, my gut started writhing in pain like a worm touched with a hot poker. After a few hours on and off the toilet, while drinking lots of water, most of the night’s dinner had passed through me.

    I won’t eat again until I meet him for dinner again this evening, but this time without the peppers (I hope).

    Vince wrote on September 6th, 2012
  23. Pardon the typos.

    Vince wrote on September 6th, 2012
  24. Why are you guys so rude to Rachel????? Calling her names? Does that make you feel better about yourself? This was a perfect opportunity to educate, NOT TO MOCK! What is wrong with you people? Do you feel superior to others? Do you feel the need to make fun of others without carefully considering other options on how to educate? This is a prime example of the infamous mob-mentality. I’m not impressed. And for the record, I support fasting. Again, I’m disappointed at the lack of intelligent responses to Rachel’s original post.

    Lisa wrote on September 17th, 2012
  25. Hi Mark! I was so happy to have found your website!! I have been an advocate of fasting (I call it detoxing) for years. I will go for a day or two here and there to reset my body. I am 37 years old and still have maintained the weight that I graduated from with. ( 2 kids later, I might add)
    Our bodies are truly designed for this, as well as a whole foods style diet. If more people would understand this concept, many of the obesity related diseases would fade away and we would become a much more fit country.
    Much applaud and multiple kudos to you!!

    Meg wrote on October 20th, 2012
  26. I just started IF and I love it. I just do a water/mineral/vitamin supplement on “IF” days followed by dinner some time between 5-9pm. Days I workout in the early morning I will also eat some veggies and Eggs after the workout. Usually about two days a week I workout in the morning and have a post workout “meal” and the other 5 days a week I just drink water and have a vitamin supplement and eat dinner. Thats it.

    Andrew wrote on November 27th, 2012
    • Agreed, except I take my vitamins with a scoop of Primal Fuel instead of just water, because many of those vitamins are fat soluble, so they won’t get absorbed without fat (which is why they say to be taken with a meal).

      VinMan wrote on December 30th, 2012
  27. So if you have a 4-7 hour window to consume the nutrients your body needs to build or maintain muscle mass..then should you consume all of the calories and protein that your body would need in that window?..should i be stuffing my face with chicken and pasta to make up for the fast?. Lets say my body needs 100-150 grams of protein to build muscle when training,do i need to consume this amount of protein in the 4-7 hour window to grow muscle?

    Sean wrote on January 8th, 2013
  28. Iam 72 yrs I have tried every diet known. This works. Iam losing weight, I don’t feel hungry. I have a banana and an apple on my 3 fast days while Iam at work. Its do-able, its free. What more do you want from a diet?

    Christina Mowbray wrote on January 29th, 2013
    • “Its do-able, its free. What more do you want from a diet?”

      Ha! Perfect! :)

      Mina wrote on February 26th, 2013
  29. when you fast it allows the body to heal itself, this is used in some country’s to cure people of certain illnesses, the longer you fast just taking in water and juices the better it is, as the body returns to its natural state and heals itself of illnesses

    sam howard wrote on February 18th, 2013
  30. Hey,

    Was wondering what the consensus is on IF and primal fuel? I ask because I’ve heard of docs who recommend to supplement IF with BCAAs, fish oil, and coconut oil, and the primal fuel really has nothing else besides Amino Acids and MCTs. What do you guys think…looking for some real educated answers here.



    Josh wrote on February 23rd, 2013
    • My 2 cents; any more than 50 calories and the fast is broken. Primal Fuel is 190 calories. I love it and use it but not during fasting. Just fast.

      Beth wrote on February 23rd, 2013
  31. funny, I didn’t know I was actually doing IF, it’s more like a 12-14hr fast, and I was feeling great, losing weight, gaining muscle. I was a bit concerned about that, at the gym they measured total weight, body fat and muscle after 5 weeks I lost 4.5 kilograms (10lbs) and lost only 100grms of muscle (about 3.5ounces) so I was pleased and intrigued….I went from 69kg to 64.5kg on my 1.75mt frame is a lot.
    I eat a huge bkfast (about 450-500cals), a pre workout meal (250-300cals) , and post workout meal (450-550cals), and that’s it, not going below 1200cals a day and never feeling hungry…. drinking more than 14 glasses of water/liquids (I always seem to be thirsty)
    I totally recommend, but how and when you fast I think is a personal discovery… as well as when to train

    lizbeth wrote on March 31st, 2013
  32. HI love IF but whenever i try to sleep on a fast I wake up unable to sleep unless I feed myself.

    Who has experienced the same problem?

    Brooklyn wrote on September 18th, 2013
  33. Sorry to sound ignorant, especially because I’ve tried to read a ton of the comments to find the answer myself, but:

    I would really love to incorporate IFing every once in a while, but I also really love drinking bulletproof coffee every morning. Am I cancelling out the benefits of IFing if I drink one cup of BP coffee during the fasting period?

    Also, does anyone have suggestions for getting through the bouts of hunger I’m expecting to experience around my normal meal times?

    Love MDA; thanks, all!

    Shannon wrote on October 10th, 2013
  34. hi I’m on my second day of IF, doing 16/8 to ease slowly into it. i did not realize all these years, i ate between 12-8 i was doing this. now to learn about Primal eating. Thanks for all the encouragement.

    Dee wrote on November 5th, 2013
  35. it’s true. People eat way too much. My family is constantly hating on anyone attempts to loose weight. They’re very unsupportive and hate it when people loose weight.

    pascal wrote on January 31st, 2014
  36. Awesome post.

    Tyson wrote on February 18th, 2015

Leave a Reply

If you'd like to add an avatar to all of your comments click here!

© 2015 Mark's Daily Apple

Subscribe to the Newsletter and Get a Free Copy
of Mark Sisson's Fitness eBook and more!