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Let me introduce myself. My name is Mark Sisson. I’m 63 years young. I live and work in Malibu, California. In a past life I was a professional marathoner and triathlete. Now my life goal is to help 100 million people get healthy. I started this blog in 2006 to empower people to take full responsibility for their own health and enjoyment of life by investigating, discussing, and critically rethinking everything we’ve assumed to be true about health and wellness...

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March 19 2008

How To: Intermittent Fasting

By Worker Bee
207 Comments

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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207 thoughts on “How To: Intermittent Fasting”

  1. are you seriously suggesting people fast? as in not eat? that’s called something isn’t it- oh yeah anorexia! i realize this is one day but you have written a suggestion for people to skip meals, or full days of eating once a week. So which is it MDA- skip meals or eat 5-6 small meals a day? i do understand the point you are trying to make of listening to our bodies, but i think there are much healthier ways of going about knowing when we are hungry and when we are not. and if it was as simple as stopping eating when we are full, we wouldn’t have people on diets and meal plans now would we? and intermittent fasting simply causes us to eat more faster.

    1. you should research before you post, you are completely ignorant on this subject.

    2. Yes you are hanging on to conventional wisdom a bit there. Who says that we need to eat all of the time, every day? What scientific research do you have that suggests that fasting is unhealthy for you? It’s just what you have been told since birth and thought never to question it. Just like in school when it is drummed into our heads that grains should be at the very heart of our diet. Try and keep an open mind when it comes to breaking conventional wisdom. IF is a great practice for health, not just for fat loss, but to give your body a break from constantly loading it up all of the time.

      Also please note that anorexia is a mental condition. It would be foolish to confuse fasting with anorexia as anorexia is the psychological condition which may motivate someone to fast to try and ruthlessly reduce their weight, not the act of fasting itself. Don’t knock it ’till you’ve tried it.

      1. Just a small nitpick to an otherwise good response…anorexia nervosa is a mental condition (and probably what the original comment was referring to) but in and of itself anorexia is a physical symptom, which presents as a decreased sensation of appetite. This can occur as a result of anorexia nervosa or a host of other medical conditions and drug reactions. It is not neccessarily indicative of something harmful…one would need to see what other symptoms were present.

    3. Clearly you haven’t done any research on intermittent fasting! The point of it is not solely to be able to listen to your body and know when you are hungry. Maybe you should do more reasearch or try it yourself before you start arguing against it. There are many doctors who agree intermittent fasting works. Read up a little more before you make such a ridiculous post my friend.

    4. Anorexia is not the same as fasting! Anorexia is a mental condition not physical. It is when a person has mentally brainwashed him or her self into thinking they are fat. They will usually pick at there food and or eat sugary junk and starve themselves in other ways. Fasting changes the body’s physiology and allows the body to dump junk that has been accumulated over time. They are too completely different subjects. If someone refused to eat because they think that the food will make them fat would be considered anorexia. It is the mindset.

      Bulimia refers to mindset as well! Not throwing up. I means the person has an impulsive tendency and is more likely to throw up. They tend to eat 400 and try to run on the treadmill until they burn 400 calories.

      These conditions has nothing to do with fasting.

    5. Yea i agree you don’t know what your talking about.So people who fast for religious reasons are anorexics?Besides that it would be more along the lines of bingeing which it still isn’t so…maybe its quiet time for you now.

    6. Well said…Why the h*ll would you suggest this? Makes no sense to me. Furthermore I am very familiar with up/down regulating as you say and there is no scientific proof that fasting will cause this.

      1. actually, if you look at studies for caloric restriction and its ability to extend lifetimes etc, it makes sense. cr creates beneficial adjustments by putting the *organism* in slightly stressful situations, causing adjustments to be made through up/down regulation. with that said, provided that the person isn’t going to pass out or die of starvation, its quite plausible that hunger would be able to alert the body to make particular adjustments by up/down regulating genes that could be beneficial in terms of weight loss.

    7. Rachel I’ve been caught a few times myself. I’ve posted some bloopers and guess what, they’re on record for all eternity. Now I tend to research before I post. If you wiki “Intermittent Fasting” you’ll get the information you need to clear up the confusion.

    8. most people dont know nothing about fasting, as you just shown here, you have so much to learn, poor you. I kind of hate people like you very ignorant and stupid

      1. But at least she don’t use no double negatives, like you done here.

        Sorry, sometimes I can’t help myself.

    9. A few points:

      1. I just started the Primal Blueprint with my husband a few weeks ago. I was seriously skeptical about the “eat when you’re hungry until you feel satisfied” since I was convinced that part of the reason I gained weight was a lack of willpower. The problem I had was that no matter how much I ate, I never really felt satisfied. Full does not always = satisfied. When I was “full” I could always manage to eat a little more until I was totally stuffed. Even if I stuffed my face until I felt sick, I noticed that about 3-4 hour later I was STARVING. Since I have changed my diet, I have noticed a huge difference. I finally felt something I never had never experienced before; a sensation half-way through a meal–that even though I wasn’t stuffed–I just could not force myself to take another bite. It’s like my body recognizes that it has all the fuel necessary. and the temptation to keep eating is totally gone. My point is that I’ve learned that when you eat highly nutritious food that your body craves, it’s EASY to follow the “eat when you’re hungry until you’re satisfied” guideline… because when you are actually satisfied, you feel hungry less often, or you eat half as much.

      2. From my experience, Intermittent fasting seems to be something I’m doing naturally with my diet. Some days, I just forget to eat a meal because I don’t feel hungry. This happens about every other day. I don’t feel like I’m denying myself at all, because it’s not a conscious choice. It’s just something that happens because without the sensation of feeling hungry, I don’t even think about food anymore.

      Anorexia (an eating disorder, marked by an extreme fear of becoming overweight, that leads to excessive dieting to the point of serious ill-health and sometimes death) and intermittent fasting are not the same thing… not even the same ballpark.

      1. Absolutely!! It’s crazy how I went form being able to eat and eat and eat…and not be able to say no to not even being able to finish a kids meal at the restaurant I work at and not even care!! Sooooo awesome!

    10. “Anorexia”? “eat more faster”?
      What are you talking about?

    11. Actually, you’re last sentence isn’t accurate. I’ve been doing IF for the last month (lost 20lbs)using a 2 day fast, 1 day eat, 2 day fast, and 2 days eat plan and my appetite is significantly less than it was prior to IF. I also tend to crave healthier foods. Salads and meats as opposed to pizza (my former favorite meal). I’m not here to say it’s for everyone, but give it a shot before condemning it.

    12. The ignorance in these comments is almost laughable. Do you even know what anorexia is?
      Just another person using the Internet to be “heard” even when wrong.

    13. anorexia is a disease, in which you cannot/don’t want to eat due to mental health issues. people fast for many reasons, spiritual and for health reasons, and for different lengths of time. did you even read the article? there are many different ways to eat, it is individual. there is not one set way. some people who are “fasting” don’t feel extraordinarily hungry. people can make their own decisions on what they feel is necessary for them, and fasting may be it…or eating three meals a day, or 5-6. maybe read more than one “health” article and form your own opinion.

    14. Just have to say… If this is anorexia, why haven’t I lost ANY muscle since I began eating this way?

      That’s the biggest classic symptom of what anorexia does to you since you are afraid to eat pretty much ANYTHING.

      Agreed with everyone saying that people should research before they post.

      Some people will NEVER accept the Paleo lifestyle. My aunt is a nurse, and one day, she asked me how I kept so healthy and looked so good. When I told her about my lifestyle (hey, SHE ASKED!), she railed on the unhealthiness of all those saturated fats I’m getting, the evils of eating only once a day, lack of carbs, fasted exercising… That was when I was like, “screw it, I’m keeping the Paleo/Primal miracle to myself from now on.”

      1. Drumroll – I have had exactly the same experience time and again – I am asked how I have lost weight/look so good/ look so fit/look so well etc – and I start sharing the Primal Blueprint ethos and get shot down time and again on the spot! Usually by overweight/unfit people who are looking for a miracle shilst being addicted to and wearing the comfort blanket of conventional dietry wisdom – now I just keep it to myself and continue to get compliments!

    15. “Fast to be healthy,” had said the Prophet (s.a.w.).

      I’m a muslim. And I fast. I am not anorexic.

    16. Intermittent Fasting is NOT an attempt at weight loss. People who try it seem to be quite easily able to maintain a very healthy weight.

    17. I have dyslexic aneroxia, I don’t think I’m fat enough.

    18. To the uninitiated it may seem like a drastic and unintuitive step, but there is actually a hell of a lot of research that backs up intermittent fasting. It has been shown in mice (and humans) to improve blood profiles of triglycerides, hdl and ldl levels. Increase insulin sensitivity, decrease abdominal fat (a key indicator for cardiovascular disease), decrease stroke and decrease cancer incidence. It has also been shown to reduce the risk of alzheimer’s, parkinson’s and other brain diseases in susceptible mice. If you consider the typical ‘back-in-the-day’ Homo sapien you would understand how it matches our original lifestyle of long periods without food followed by feasts. It is possible the one single lifestyle change that is most likely to increase your lifespan and later-life quality.

    19. I have been fasting every year since I was 25….sometimes two or three times a year….short water fasts of 3 to 11 days….and the longest was 23 days.. I think you had better do some of your own research before posting ignorantly on a subject that dates back to the begining of time… By the way I am on a water fast now, if anyone would like to join me.

    20. You are seriously reading without comprehension. Before you post a comment. Make sure you understand the subject so you would not seem as ignorant as you are right now.

    21. Chill Out Sistah!
      I’m doing IF for 1 month direct, and ate like 1800 calories a day. And no, it’s not called anaeroxia.

    22. ….and the FDA used to say to eat 12415125 servings of bread a day. Are you still following that? Doctors used to recommend smoking as well, do you follow that? Get with the times, or the times will leave you behind.

    23. Wow, some people really need to stop being so narrow minded and open up to other concepts of living as opposed to the ones that have been drilled into them from an early age by the fitness industry, Government etc.

      I do a 24 hour fast once a week along with skipping breakfast here and there and I am the fittest, best functioning, healthiest and greatest I’ve felt in all my 23 years of living. I’ve also been primal/paleo for the last few years and trying to reach my goal of 7% BF. I’m currently at around 9-10%.

  2. Um, anorexia is far more than just not eating…that’s just the way it is expressed. Abstaining from food for a certain period of time is a common practice that appears to have some health benefits. And the world is not going to end if you are hungry.

  3. Rachel –

    As Katie said, anorexia is a serious medical condition. Intermittent fasting is simply a way to structure your eating patterns in order to potentially receive a variety of health benefits – weight loss not being the main focus. It may not be for everyone. Some people may not care to do it, and others may find it exceedingly difficult to skip a meal. We are simply offering it up to our readers as an eating option that they should, in our estimation, consider trying.

  4. I’ll skip meals a few times a week, mainly breakfast or lunch. I’m usually not hungry when I wake up, so I usually don’t eat until a few hours later, at which point it’s lunchtime. Sometimes I’ll eat an early breakfast, and then find that I’m just not hungry come lunchtime, so I don’t eat. I find this style of eating much more natural and comfortable. I hate being forced to eat when I’m not hungry. It usually just leaves me feeling sluggish and bloated. I’d much rather eat when my body tells me to, not when the clock on the wall says it’s time.

  5. As a recovering anorexic, I really see your point Rachel. However, Anorexia is officially defined as amenorrhea for at least 3 months, refusing to maintain a bodyweight of at least 85% of normal, intense fear of fat or weight gain and a disturbance in the way one views their body. Fasting is certainly a technique that many anorexics use but not all who fast are anorexic.

    I use IF (with the approval of my doctor, even) for religious and health reasons and have seen only positives from it. It has not caused me to go back to my ED’ed ways.

    My only problem now with IF is eating past fullness once I finish my fast – any suggestions on that, guys?

    1. a high fatty meal with a little protein.

      i really enjoy this as my meal back… its almost like a reward to tell you the truth! its dense enough to sustain you and fill you up right good.

      merengue 4 eggs whites to stiff points,
      mix 1 avocado, egg yolks, and baking cocoa powder,
      fold in avo/cocoa mixture in merengue,
      enjoy with some fresh berries 😀

      seriously tho… if you eat half and store the rest for a snack later… (holds for about 8 hours) or just cut the recipe down in half eating it all isnt a huge meal

      1. re: eggs, cocoa powder, avocado snack

        that sounds delicious, but do you cook the eggs at some point? or toss in lemon juice or anything?

        thanks for the suggestion!

      2. Kmac, I am totally stealing that. It sounds delicious. Thanks 🙂

    2. Use your eyes!

      Seriously 🙂 Take a look at how much you want to eat, then cut out about 1/4 to 1/3 of it and only cook the remaining 2/3 to 3/4 of the food. You’ll find that you’re not full, but you’re certainly not hungry either. I usually keep it very high protein, moderate fat, and very low carbs just to keep the fat burning going.

      Depending on how much you usually eat, I’ve found that a good 12oz steak with some veggies is perfect for me. It could be different for you, or it could be more.

  6. I could see avoiding IF if you’re prone to eating disorders or recovering from anorexia, though it sounds like Charlotte has managed it successfully. Psychological health is as important as, and inseperable from, physical health. However, IF itself does not cause anorexia.

    There really do seem to be some health benefits to IF, particularly for insulin regulation.

    Food Is Love

  7. I guess I’ve naturally, unconsciously doing some sort of IF for years. I almost never wake up hungry, so I often skip breakfast. And I find, interestingly, that if I skip breakfast, I almost never want lunch until 1 or 2 pm. However, if I eat breakfast, I’m hungry by noon.

    1. I do the same. When I tell people I only eat when I am hungry, I get statements like, Well it;s linch time. Aren’t you hungry? They just don’t get it.

  8. charlotte,

    Wonder if that’s a vestige of the anorexic days. The sense that the “sacrifice” you just made is worth an “indulgence”. Many people report that they don’t eat as much after a fast as long as they understand that it’s OK NOT to have to make up for the lost calories, that you can stop eating when you are simply not hungry for the next bite (as opposed to waiting for the sensation of fullness – at which time you may have eaten more than is comfortable). One idea might be to take whatever meal you had planned post-fast and divide it into two halves. Eat one half now and allow yourself the option of eating the other half in 90 minutes….but only if you are still hungry. That might train your brain to use the primal signals of “hunger” and “non’hunger” versus having to consciously override a more hedonistic desire to simply indulge until overfull. Does that make any sense?

    1. i get what your saying, i like to use the one bite every 2 whole minutes. just slowing down your eating limits over indulgence after a fast. like mark says its an opportunity to really tell how much it takes to feel full, nad being full. eating SLOWLY is a great way to do it!

  9. Fasting is NOT starving oneself. You can fast..it’s natural and has been done for ooohhhh….couple millions of years. Again, starving oneself with little or no calories is not the goal of IF. The goal is taking in your calories in a shorter time window, or taking a day off eating so your body can do some much needed internal gut cleaning and other health benefits. Most people with serious diseases have found much relief when they allow their body to heal. Healing takes alot of the body’s resources and energies, digestion takes up alot too. You still need nutrients, vitamins, minerals, essential fatty acids and all the wonderful stuff that helps us rebuild our sick cells and detoxify the body.

    If you want some more info, you can also check out a post I did on IF 101
    http://projectfit.org/iflifeblog/2008/02/27/intermittent-fasting-101-how-to-start-part-i/

    I also did one on my own personal reasons on why I choose IF for a lifestyle
    http://projectfit.org/iflifeblog/2008/03/03/why-i-do-if-and-everyone-should-to/

    and here’s one on the benefits for health, cleansing and detoxification on fasting
    http://projectfit.org/iflifeblog/2008/03/05/long-term-fasting-and-healing/

    When you see people with plenty of muscle, plenty of health, living long and fasting…hard to think it is such a bad thing. Just ask Jack LaLanne!

  10. The benefits of fasting and calorie restriction also has some nice little research such as:
    – increased longevity
    – reducing oxidative stress
    – reducing inflammation
    – reduce risk of heart disease
    – improving neuroendocrine responses
    – increasing GH secretion
    – protective effects on heart, lung, brain
    – decrease in insulin resistance
    and other overall disease prevention and life extension factors….here’s about 20 or so studies on it all.
    http://projectfit.org/iflifeblog/resources/

  11. Mike OD wrote: “Most people with serious diseases have found much relief when they allow their body to heal. Healing takes alot of the body’s resources and energies, digestion takes up alot too.”

    Come to think of it, whenever I get sick, I have no appetite whatsoever and can go days without solid food. I guess the body does know what it’s doing.

  12. Personally, when I come out of a fast I eat like a horse. I make up for the calories I skipped, or at least close. But I’m also very active and I don’t think my body wants a long-term calorie deficit.

    On another note, Indians in the Pacific NW traditionally used fasting to treat a variety of illnesses. Fasting and herbs were the first line of defense, and if that didn’t work, it was time to call the medicine man for some good old-fashioned placebo.

    But fasting was also a part of their life even when they were well. The men often wouldn’t eat for a day or more when they were on a hunt.

  13. Mark – thank you for the insight. I think you have a point and I’m going to try the portioning you suggested. I think the problem is that when I stop my fast I feel like I should be able to eat my normal-sized portions but fasting kinda shrinks my stomach and it’s hard to accept that just a few bites makes me “full”. But I like your idea of reminding myself that if I’m hungry an hour later, I can just eat again then. Thanks for the common sense:)

    Rachel – it’s kinda funny. This topic is being discussed all over the blogosphere (something in the water?). Over here everyone is pro- IF, but other sites like The Weighting Game (which I love, btw) are totally anti- IF. Check out the comments over there.

  14. IF can also be used in conjunction with weight lifting to affect dramatic physique changes!

    Check out Martin Berkhan’s LeanGains website for more information and stunning before and after photos.

    http://www.leangains.com

  15. We were not ment to take in tuns of foos evrey day. Even ouer digestive trak needs a rest. Less food is better. Anericans have such a wierd veiw on food. I think people who do this long turm will notice more energey, more vibrent skin, and over all health.
    From a Godly point of view. Its quite nurishing as well.
    Luke 4:4 (KJV)
    And Jesus answered him, saying, It is written, That man shall not live by bread alone, but by every word of God.

  16. I like this idea of IF. I practice it in a small way of skipping breakfast most days of the week. Come weekend time, I’ll eat about two meals a day which tend to be heavier than my weekday meals.

  17. I had a question about IF versus the warrior diet. One advocates not eating at all during the fasting window (IF) and the latter says that if you eat “light” during the fasting period, you’ll reap the same benefits. Which is true?

    1. From what I have learned, it’s all about what your body comes to expect. If your body knows food is just around the corner, it will plan for it. To convince your body to burn fat since food is NOT just around the corner you have to demonstrate that by not taking in calories during the fasting period. Going light will just convince the body to slow down metabolism to “make it through” to the next meal. Also very important to avoid insulin spikes anytime around fasting – before and after especially.

  18. Can someone give me advice. I have been IFing one and off for a year. I try to fast at least 20-21 hours. I find it hard to make it to 24 hours, but I’m working on that. Is 20-21 long enough to be considered a fast? I have found the definition of IF so broad at times that I really don’t know if I am IFing (or IFing correctly). Any advice woudl be wonderful.

    1. 20-21 hours is definitely an IF, as a matter of fact, the benefits of IFing hit their max production at around 18 hours, everything after that is gravy…so to speak.

  19. Travieso, 21 hours certainly counts as a legitimate IF period.

  20. i had a question for mark.. hi i wanted to know if i have been intermittently fasting becausebfor years i eat only one meal a day between 9am and 3pm and before 3 i will have a snack. I lost weight this way awhile back and ive kept it off ive had a clean bill of health for a long time and my cholesterol is low and everything has been pretty much normal for a awhile . So all i wanted to know if what ive been doing is the same regimen youve mentioned on your website?

  21. tracey – Yes, you’re eating patterns could fall in to the realm of intermittent fasting and is perfectly healthy. There is no reason for anyone to be eating 3 regular or 6 small meals everyday. If you’ve found a formula that works for you then stick with it. Just make sure you are eating right otherwise (enough calories/healthy fat, low carb, high-density vitamin/mineral/antioxidant foods etc.) and you’ll be fine.

    1. Mark – isn’t the point of IF to break the routine ?
      It would seem that consistently eating one meal a day is a routine and by definition is not IF (nothing intermittent about it).
      I am not disparaging the eating pattern – whatever works. But it can’t be really called intermittent.

      I have done IF way before learning about primal anything usually starting with dinner and ending with breakfast so over 24hrs. Amazingly in the morning i would eat very little and feel very full. That was the main benefit for me – shrinking stomach -> shrinking portions for about a week after.

  22. hello mark i just wanted to say thanks for the reply but i also had one question . Why is it so hard for me to get back to IFing if i make a mistake and start eating after 3oclock? it almost feels like im starting over for the first itme and the cravings for whatever i was eating will come back at the same time everyday and its like im in a battle with my body to start eating clean again.I usually wind out gaining 15 pounds if i dont get back on track.Tonight im struggling again but so far im doing better.How do i stay disciplined no matter what outside stresses im dealing with that make me want to eat when i dont want to.

  23. hello mark i had another question for you. I have been reading the book about the fast-5 lifestyle and my question is as follows if the 5 hour window is good no matter what window you choose, then why is the 5pm to 10pm window so widely perferred? my 5 hour window is between 9am to 1pm nowdays and i keep feeling that if i suddendly change my window to 5pm to 10pm that i will start to gain weight and i dont want that.

  24. Tracey, there’s no real magic to the 5 hour window in my opinion. Just do what works. As for your other question, if you are IFing and you decide to eat, you embark on a whole new set of hormonal changes, which include added hunger. If you are only eating one meal a day every day, you may be reducing the value of IF. You might try two meals a day for 6 days and then one meal on the 7th for a while.

  25. hello mark thanks again for your reply, i have been eating one meal a day for many years but its usually what some people eat for dinner like baked chicken and vegetables and maybe sweet potatoes and a glass of orange juice. Afterwards i will go walking or if i feel like i’ll go jogging at the park near my house and on the weekends i go hiking in griffeth park. Ive never felt weak or lacking in energy its just i have had a problem craving sugar sometimes and if i eat at night at least in the past i would gain weight. This diet is a way of life for me the only thing that caught my attention was the focus on nighttime eating even though i usually get hungry only in the early part of the day and that may be due to the fact that i conditioned my body to expect food in the early part of the day. So far so good. Also i think i do eat about 1000 calories in the meal i have between 9am and 11am thats the new approach ive adapted since the first post i printed and when i first started this in 1997 i thought i had thought of this on my own, it was just an experiment…my friends thought i was crazy. Anyway thanks for reading my post i really appreciate it a lot .

  26. Your body does this naturally anyway when you get sick or injured. I can remember not eating for a couple DAYS when I got the flu. And far from getting worse, I got better. And came out the other side minus a couple pounds of bodyfat. I wonder about losing muscle though….

  27. Hi,
    I think every one is different. If I ate anything at all like my hubby, I’d weight 300 lbs! Every year, it changes too… with age (currently 38) I just find it harder to stay in the same size clothes. I have to restrict my calories. It no longer matters that I lift and run and cycle and work out (sometimes a couple times a day.) If I want to keep the belly fat off and keep from getting chub-rub on the long runs (ouch!) I simply have to restrict my calories. It doesn’t matter that I don’t eat grains (I don’t). It wasn’t always this way… But, a combination of genes, job and age mean that I must have fasting periods, or slowly, but surely…a little muffin top appears and I have to slip a notch on the old brassiere. I want to fit the same size of clothing for my whole life. I don’t think aging = getting soft and flabby. But – if I told people how little I actually eat, they’d think 1) I’m lying or 2) I’m losing it somewhere along the line! lol. I’m not. It’s my body type and my desk job. I never eat at work – that’s 4 days per week, no calories for 10-12 hours a day. When I do eat, I eat like a horse…but, similar to what a horse eats (with protein) – a massive salad with all the fixins. I would not recommend this to everyone – but, some people have propensities that set them up to be fat. I happen to be one of those people. I find that fat makes it hard to hike to the beautiful places and fit comfortably in my clothes, so…I’m thrilled with IF and happy not to see an old practice getting some credibility thanks to research and people on this site.
    Our genes are not our destiny and a desk job =/= heart attack or diabetes…
    🙂

    1. Working out twice a day (even if only on occasion) is probably too much. Your body needs time to recover from a workout.

      By not letting it recover you increase the secretion of cortisol. While some cortisol is absolutely necessary for life, and even healthy, too much causes the body to hang onto fat. This may be thwarting your ability to drop body fat.

      I’ve read that people who workout solidly three or four times a week often see more muscle built, and fat lost, than people who do so every day. The rest time and lower cortisol levels probably explain this. More muscle is built while resting than when you are actually working out!

  28. 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

  29. 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

  30. 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.

  31. 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!

    1. 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 – http://bit.ly/7HseGe.

      1. 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!

        1. 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.”

  32. 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.

    1. 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! 😉

  33. 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: http://you-fat-bastard.blogspot.com/

  34. 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

  35. great idea, get your muscles into a catabolic state with no protein to feed them… let us know how it goes!

    1. 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: http://www.leangains.com

  36. 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!?

  37. 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.

    1. 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.

  38. 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

  39. 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!

  40. 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.

    Anna

  41. 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!

    1. 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!

  42. 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!

  43. 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!

  44. 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!

  45. 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?

  46. 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

  47. 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.

  48. 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.

  49. 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?

  50. 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!

  51. 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?

    1. 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.

  52. 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.

  53. 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.

  54. 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!

    1. I am the opposite. I would rather skip lunch than breakfast. Breakfast is my favorite meal

  55. 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.

  56. Humans can go without:

    Air for 3 minutes;

    Water for 3 days; and

    Food for 3 months.

    My PB is one month.

  57. 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”.

    1. 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.

  58. 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.

  59. 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.

  60. 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.

  61. 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.

  62. 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

  63. 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

    1. 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.

  64. 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?

    1. 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.

  65. 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.

  66. 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!

    1. 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!

      1. 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.

        1. 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!!!

      2. “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.

  67. 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.

  68. Warning: blood glucose. The brain uses most of the glucose in circulation. In between meals the liver has to look after the brain. It converts protein to glucose. This protein comes from your lean body mass–chiefly your muscles. A tiny snack of a biscuit or even a couple of grapes every couple of hours is all you need for adequate blood glucose levels.

    1. I have just read up on blood glucose, and it is important to note that even when starving blood glucose remains the same…but the body actually needs a little more glucose than it makes under duress, so there is an argument for eating a few 100 cals of rice ( good starch ) to enable good brain function. Check out the “Perfect Health Diet ” blog on glucose.

  69. I wish I could IF…but ever since going primal the foods just taste SO DARN GOOD.

  70. This is ideal for me. Eating when youre not hungry is not natural because hunger is the signal that you need food, and, well, if you’re not hungry, don’t eat. Sometimes I have a whole ton of nut butter before a workout and just dont eat anything for the rest of the day until late dinner because I’m simply not hungry. Sometimes I do a conscious fast, but most of the time its pretty natural!

  71. I’ve almost completed my 24 hr IF and I feel great. I’m thinking clearer than I have in a long time and not hungry at all.

  72. Okay, I’ve been doing the diet thing for about 6 months, jumped on the workout plan about 4 months ago and I have to say it has been working. But I am now down to 15 to 16% body fat and would like to get down to 10%. Yes I’ve been guilty of eating to many carbs. Yes I’ve been guilty of cronic cardo. But it doesn’t seem to matter how strict I am I just have hovered at the same weight with no change in fat for the past two months. Today is my first day trying IF, how often will I need to do this to break the cycle. Will once be enough to start seeing results.

  73. I am interested in trying IF and would like to know what is the best time of day to start IF? I work from home and sit for 8.5 hours and I also exercise and watch my calories and have been stuck at a Plateau and think that this would help break it. If you can send me an email or comment I would appreciate it. Thanks

    1. I do a daily fast starting at 8am and not breaking until 12 noon the next day.

      Also if you want to do a full on 24 hour fast (which I also love) it is easiest(in my opinion) to skip dinner go to sleep and eat a late lunch the next day to go a full 24 hours. Some days I am not hungry for lunch during my daily fasts and so i just skip it. On the weekends I try to get in a long bike ride or jog under 75% of my max heart rate before breaking the fast so sometimes that means i am not eating until 2pm… just take it slow and go with the flow. If you are primal already it will be easy since your body already burns fat for fuel and so you will not have the same hunger cravings as non primal people. You will get to a point where your stomach is “empty” but the “empty” feeling is NOT hunger, it is just empty. it is fun when your mind starts to make that distinction!

    2. One other good idea about plateaus.. cut out nuts if you are eating them.. i tend to eat more than i want to admit so I had to stop having them around…another one to cut out is dairy. Just try it for 3 weeks and see if you break your plateau…oh and make sure to get 8hrs of sleep each night!

      1. Well I rarely eat nuts so thats not an issue but i do eat 1 Chobani yogurt everyday and I use 2% milk when I make my replacement shakes or protein shakes. Ive just started replacing 2 meals a day with replacement shakes. So by not eating/fasting what do you drink during that time to keep you full? And how many days before you see pounds lost?

        1. I mis-typed my daily fasting window it is from 8pm-12noon the next day. Not 8am-12noon. When I fast I do not drink anything except water and coffee.. check out http://www.leangains.com/ for a lot of information on fasting. I do not a lot of meal replacement drinks unless they are really a meal replacement and then i mix them with water and only use Primal Fuel to keep it all in the low carb/good fat area. I cannot tell you how many days it will take for you to see a loss and if you are really close to your ideal body weight you might not ever see a loss on the scale but just notice a difference in how you look/measurements. At some point you are replacing fat with muscle and that is when the scale can mess with your head. I put mine away in April and have not taken it out.. I could probably stand to lose about 10 more pounds but the scale was making me do silly things to try to see a loss/difference like not drinking water in the night so that the next morning I could weigh in at less. Also when you are losing fat sometimes your body holds onto water while it is transitioning the fat away so it will reflect differently in the scale. I would start skipping the 2% milk, eat real food most of the time vs meal replacements, keep your carbs under 100 or try to go for 3 weeks under 50 carbs per day and kick your body into ketosis and then judge your progress by measurements or a before/after photo for 3 weeks… and then if you want validation get on the scale. And again you should really check out http://www.leangains.com/ truly the definitive guide to IF.

      2. Great advice beth… all three of those things are my downfall! I do fast every day, for about 22 hours (I take weekends off…).. but dairy, almonds and 5 hours of sleep are my nemisis!

  74. 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!

  75. 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!

    1. 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.

  76. 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!

  77. 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

  78. 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.

  79. 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.

  80. 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??

    1. 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.

  81. 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?

  82. 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.

  83. 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?

  84. 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.

  85. 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.

  86. 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.

  87. 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.

  88. 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

  89. 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?

  90. 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?

  91. 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.

  92. 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.

  93. 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?

  94. 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).

  95. 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.

  96. 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!!

  97. 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.

    1. 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).

  98. 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?

  99. 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?

    1. “Its do-able, its free. What more do you want from a diet?”

      Ha! Perfect! 🙂

  100. 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

  101. 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

    Josh

    1. 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.

  102. 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

  103. 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?

  104. 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!

  105. 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.

  106. 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.

  107. Are you able to follow this way of eating if you are vegetarian?
    What would you substitute for meat? Tofu and the like?

  108. Can the condensed IF be maintained daily? Is adding “fatty coffee” during the fasting part break the fast? I have been sort of following the condensed IF method for about 3 months now. I pretty much don’t eat breakfast anymore, but I drink a cup of fresh coffee with organic butter and MCT oil during the “fast”. During the eating part, I pretty much follow the Primal approach to eating. I lost 22 lbs without much exercise in the first 2 months. Now it seems I am stuck at the same wieght. I want to start incorporating the exercise recommended and not sure if I can maintain the IF daily anymore if I am exercising. Thanks for the replies.

  109. Quick question, may I drink water with Himalayan sea salt when I get up ? (I am following the “skip breakfast” method) Thanks

    1. Hi Joanne
      The rule of thump is you don’t go over 40 cal and don’t drink anything that will cause an insulin response… so i pretty sure you’ll be safe.

  110. Fasting is a great way to cleanse your body from toxins and stay healthy and live with health. Very cool article, Thank you for sharing