Fasting Makes You Active

It’s a familiar image we might attribute to stereotype: a sluggish, maybe portly individual lying prostrate on the couch, his/her front littered with Dorito crumbs. Could there, however, be truth behind the picture? Is there indeed a connection between incessant snacking and chronic slothdom? Or considered another way, is there a connection between fasting and being active? As a long-time fan of intermittent fasting (and a believer in the research behind it), I’m convinced. A study out this month sheds even more light on the relationship between lethargy and continuous eating.

For decades now, conventional wisdom has told us that we should eat regularly throughout the day to keep our blood sugar steady. With three regular meals and at least two snacks, we’re counseled to keep our bodies in a perpetual postprandial state. However, newer research, including this month’s study from ETH Zurich, questions this assumption. Scientists focused on the opposing relationship between a transcription factor, Foxa2, and insulin. Foxa2 is found in both the liver and the hypothalamus, the central command for hunger regulation. It has a hand in the expression of two eating and physical activity related neuropeptides, melanin-concentrating hormone (MCH) and orexin. When insulin is present, as it is during and after eating, Foxa2 and the related MCH and orexin are reduced. However, fasting mice showed consistently high levels of Foxa2, MCH and orexin. The researchers then found that “hyperinsulinemic, obese” mice showed reduced Foxa2, MCH, and orexin, regardless of whether they had eaten or not. When the scientists bred mice with continually active Foxa2 (immune to the counter effect of insulin), these mice showed high levels of MCH and orexin – and a correspondingly high level of physical activity whether they had eaten or not. The specially bred mice had low body fat as well as higher muscle mass.

Consider this study another nail in the coffin of conventional wisdom. (It also goes a long way in explaining the snacking couch potato association.) Fasting, even short, between-meal breaks, promotes the activation of Foxa2 and the resulting formation of MCH and orexin – as well as their activity-inducing effects. A simple survival principle explains this: a hungry animal needs to get up and move to find food. On the other hand, if we are constantly swimming in the insulin of eating and post-eating states, we’re undermining our own motivation (and biochemical stimulus) to get up and burn off what we just ate.

CW encourages us to never skip breakfast, bring along a mid-morning snack, make time for a good lunch, grab a mid-afternoon nibble and then have a good dinner. Oh, and if you can’t sleep, you’re supposed to have warm milk and a banana before bed. Our bodies are either eating or processing what we ate. There’s never a recovery period. Nary a resetting opportunity. We’re so focused on the hobby horse of “stable” blood sugar that we’ve forgotten that there’s more to the biochemical story of balanced energy. We make ourselves feel perpetually full to the exclusion of feeling anything else. (How about light, energized?) We continually raise our blood sugar and insulin levels and, in doing so, turn off the body’s chance to activate or upregulate other key substances that promote energy balance – and as this study shows, the physiological motivation to be active. Simple advice: skip the snack. (Besides, dinner never tasted so good as it does on a healthily empty stomach.)

Let me know your thoughts. IFers – have you found this principle to be apparent in your own experiments? Thanks for reading.

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

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145 thoughts on “Fasting Makes You Active”

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  1. I find that when I fast I am more likely to curl into a ball and do nothing – no energy to do stuff.

    1. probably because you are not yet adjusted to the process. I’m a regular now and I can last quite a while (up to 3 days) without serious hunger pangs or drops in blood glucose. you could just be… weak.

      1. IT fasting is a great time for the body to rest the digestive system … if you are new to fasting of any kind, I have found that eating my last Primal Meal of the day by 5pm and going to bed feeling a bit hungry helps me sleep better and feel alive and energized in the morning…. practising this as consistently as possible you might find fasting a joyful pleasure rather than an unpleasant experience…

    2. I was the same before switching to a [more] primal eating style. I haven’t tried a full day IF or longer yet, but the single skipped meal IF brings zero loss of energy, zero mood swing (from decreased blood sugar) and a feeling of intensified alertness/awareness. My brain (not my body!) keeps trying to tell me it’s “meal time” and therefore I should eat something – despite the fact that I’m NOT hungry – so I sometimes walk or cycle just to distract my brain 🙂

      1. this subject intrigues me. for several years now, i’ve noticed my body go through cycles of hunger and not-hunger. i’ll be eating normally and then randomly (at least, to me) for a week or so i won’t actually feel hunger and have a hard time reminding myself to eat. then after several days of this, i’ll swing to the opposite end where i’m hungry all the time. i’ve never noticed energy changes with the swings. only when i try to mess with it, like, make myself eat regular amounts when in the non-hungry phase or not eat when in the hungry phase. and it seems to work to go w the flow – ‘binging’ when in the hungry cycle seems to trim me up, counterintuitively.

        1. I find this has a lot to do with my cycle. The week before my period I double my caloric intake and the week after I eat almost nothing.

  2. Great post! I used to be one of those who was under the influence of CW. I thought I had to eat every 2 hours. It was a struggle because I was hungry all the time and I never could get my body fat % down. Now that I follow a PB I never worry about the next meal and I’m happy with both weight and Body%. Thanks Mark

    1. I also used to eat every two hours (prior primal) and NEVER loss weight lol, or body fat. Ever since the primal diet I noticed my calorie intake is fine, and I don’t get so hungry and so I got curious about fasting and came accross Marks wonderful posts, and will start my first fast tomorrow 🙂 I am actually excited. BTW since primal I have lost 17lbs and dropped 7% bf to a wonderful point of 125lbs and 20.6% woo hoo. I find this so amazing.. I too never stress about my next meal and don’t binge crave… I love the experimenting of awesome refined carb free recipes… very fun. LOVE IT. Can you tell I have mega energy, and at the end of the day AND caffeine free!!

  3. I really want to believe that when I skip the between meal handful of dried figs, coconut and or handful of almonds that I am helping my body regulate insulin properly. However I struggle with fasting even between breakfast and lunch (about 4-5 hours). This morning I did eat 1/8c steel cut oats with flax, 1 pear, and 2 eggs cooked in bacon fat at 7am. Its 11:30am now and I am so hungry that I am afraid that lunch is going to be a gorge-fest on more grains (pregnant wife loves 1 slice of Roggenbrot per day). As a matter of fact, yesterday I had to perform magic on myself to give an illusion that I was not hungry by drinking so much water because I decided that after dinner [7pm] until 7am I was not going to consume anything. I did, but I was awake all evening, I had trouble sleeping and my dreaming was so lucid I thought I was reincarnated as bear and ate my dog.

    Mark, I really want to subscribe to IF, really, but I note that my sprinting, strength training or any real deep interval training suffers.

    Could I not be eating enough at my normal B, L, D meals? Should I step up more fat?

    1. Daniel,

      Could be that the 35 +/- grams of carbs in your breakfast are causing the problem. If you had had 4 eggs and no oats and/or pear, you might reduce insulin and, hence, the hunger that accompanies. As I say here, it takes about three weeks of steady low carb eating to “reprogram” the genes to preferentially burn body fat. When that happens, hunger subsides and energy stays even and balanced.

      1. Weird, 2 days of oats (we’re talking 1/8c dry) and I am beginning to notice a scratchy throat and a bit of the sniffles. So crazy because I don’t feel like a cold or anything. I have been really off the grains for a long time now, but thought I’d change things up as long as I keep the carbs under 150ish. Time to re evaluate. Thanks!

        1. Daniel, I would definitely say increase the protein and fat, with or without the carbs. In fact, with the carbs the protein and fat will slow down digestion and prevent blood sugar swings, so you may be able to go longer without eating. But if that still doesn’t work you might want to cut out some carbs as Mark suggested.

          It does take time to get used to, though. I was a chronic eat-eight-small-meals-a-day person about a year ago. I’ve finally got myself down to 2-3 meals a day, and in the past couple weeks I’ve been dabbling in IF as well.

          It takes some adjustment to consume the right amount of food in fewer meals. I like the idea of an “eating window” of a couple hours or so. It makes it less of a strain to consume enough food to keep hunger at bay for a longer period.

        2. Daniel, I concur with what Elizabeth and Mark both said. I’d only add that you really should try increasing your consumption of saturated fat. Many, including myself, have found a hperlipid diet to be incredibly satiating. I usually go about 15-17 hours between dinner and lunch with nothing in between each day. I eat a lot of FAGE Total yogurt, eggs, bacon, full-fat meat, cheese, etc., and this satiates me for a LONG time. Before starting lacto-paleo, my breakfast was whole grain cereal. I was ravenous by 11am and remained irritable and cranky until my lunch fix. And so on throughout the day. The idea of fasting was a complete turn off. After going lacto-paleo, and now that my body is in ketosis, I find fasting is a breeze. A few times a month I’ll go 24 hours like it’s no big deal. I did so on ThanksGiving day this year. I drove down to San Diego to visit my cousins, and hadn’t eaten since the night before. TG dinner was at 4pm. When I arrived at 1pm my aunt asked if I wanted anything to eat and I said that no, I hadn’t eaten since the night before but wasn’t very hungry so I’d wait for TG dinner. She was shocked and thought I must be ravenous, but to her disbelief I repelled the snack foods she waived in front of my face.

          I wouldn’t have believed this about myself just a year ago. Now it’s second nature. Go true primal (lacto is okay if you tolerate it, and fermented full-fat lacto is great!). You’ll probably find your energy levels increase dramatically, especially when well fasted.

      2. I so agree!! Fruit especially seems to be a trigger for me. Berries I can handle, but even those have to be kept to a small portion. Oatmeal and a pear for breakfast and I’d be starving within an hour….adding the eggs might allow me to last 2 hours. But give me a couple of eggs and a few strips of bacon and I’m good for at least 4-5 hours!

    2. Daniel,

      I don’t know how long you’ve been going Paleo, but I’d recommend not forcing the fasting issue until it becomes easy for you.

      My wife, for example, took about 6-8 months of Paleo eating before missing breakfast was realistic for her. It just takes some of us a long time to restore our bodies ability to mobilize fat and regulate blood sugar.

      Eat lots and lots of fat, avoid crap, and only eat when you’re hungry. After a while, months to years maybe, fasting will happen naturally.

      Don’t force it or you’ll turn yourself off to IF forever and miss out on the great benefits!

      In answer to MDA – I find I’m jumping out of my chair all day when I fast, I’m doing one right now!


      1. I absolutely agree with this, Bryce. It took me nearly 5 months on the PB (at near 100% compliance) before I was ready to IF. When I was ready, it happened almost by itself, without effort.

        For me, it was a combination of learning to trust my body not to go into chew-my-arm-off-hunger mode if I skipped a meal, plus learning to identify (and wait for) genuine hunger rather than eating “because it’s mealtime,” plus understanding the science behind IF.

        I started by stretching out the time between dinner and breakfast to 12-15 hours most days. Then, the day before Christmas Eve, it happened…I had a late lunch at 3:00. Worked out in the evening. Wasn’t hungry, so didn’t eat dinner. Slept well and woke up early, worked out again, and didn’t eat until company arrived for brunch at 10:00. Totally easy.

        Give it time. Let it happen. 🙂

        1. Another thing — learn to accept hunger. It’s okay. All the world’s food will not evaporate if you wait half an hour to eat…but likely as not, your hunger WILL evaporate.

          This only works for me when carbs are low and grains non-existant, but it’s wonderful! I just now went through an “I want dinner” phase that lasted about 20 minutes. I’m hungry, but not starving. I’d rather wake up tomorrow with that wonderful, light, fasted feeling than indulge in a snack tonight. So, I didn’t eat…and now the hungery feeling in my stomach is settling down.

          This is very cool, Mark. Thanks so much for helping me get off the carb carousel!!

    3. My own experience is that it’s all about adaptation. I don’t follow PB explicitly (although now reading about it with interest) but I’ve been practising daily IF (anywhere from 19/5 to 23/1 schedule, usually after 6pm) daily for most of the last decade. I’m also a regular exerciser (mainly Heavyhands and bodyweight) and hill-walk, bike and ski, mostly without the need or desire to change my usual feeding schedule.

      Nowadays I associate fasting with energy and clarity, for work, play, or exercise of whatever level of intensity is needed. Eating, by contrast, is followed by a noticeable (though not necessarily unpleasant!) post-prandial period of relative sluggishness, and poorer performance should significant exercise demands occur at these times.

      I assume that numerous changes have occurred in my physiology over time that account for these effects – not being expert in these matters, I can’t claim to know exactly what they are. But I suspect that we can’t know what our bodies (or psyches) are capable of under any particular circumstances until we have had time to adapt to them, and this makes such matters impossible to assess over the short term.

  4. Great post Mark. It certainly makes sense and I am sure everyone here can attest to having more energy when in a fasted state. People who eat all the time, or as many call them, grazers, don’t stimulate those processes that tell them to get up and move to food. Their bodies think food is and will always be around.

    I am currently bulking and trying to get all my calories in a 4-6 hour window. It’s nice being able to feel hungry, prepare and gorge. I’m also not convinced about pre and post workout nutrition leading to higher gains.

    1. Has anybody heard of the warrior diet? seems to comply with fasting all day and having one meal at night time.

  5. I have been experimenting with fasting and I find if I eat breakfast and lunch I can skip dinner. I usually try to eat between 9 am to 2 pm and not eat the rest of the day during my work week and 11am to 4pm on the weekends. I feel great. I have found that dinner seems to be superfluous and I eat it out of habit or boredom. Most intermittent fasters seem to skip breakfast but I get up a 530am and there is no way I could work all day and last until dinner.

    1. as far as I understood it you’re not really reaping benefits in full from the fast unless it’s around 24hours w/o caloric intake. someone strike me down if this assumption is incorrect.

      1. [quote]Fasting, even short, between-meal breaks, promotes the activation of Foxa2 and the resulting formation of MCH and orexin – as well as their activity-inducing effects.[/quote]

        From above. I’ll trust that Mark did his research 😉

        1. I find it hard to believe that you quoted the article above… actually I’m flabbergasted.
          Perhaps it wasn’t in the article? {Wink}

      2. The 24 hour fast is the least prevalent form of fast. The most common is the eating window fast (fast 19 hours, eat in a 5 hour period), or the one meal a day (23 hour fast, eat in a 1 hour window). You reap the full benefit by just giving your body enough hours to process and reset. 36 hours is also great, beyond that and while there is still some benefit, the law of diminishing returns sets in. I believe 72 hours is where metabolism really slows down and your body starts preparing for famine mode.

        The point is any break you give your system is beneficial, and you will notice that you don’t need as many calories as you thought you did. You sh*t most of the overage out anyway. You’ll notice less frequent bowel movement when IFing, as your body extracts more of what’s needed without rushing to evacuate.

        Big IF fan here.

      3. As a diabetic who test blood sugar hourly when making dietary changes, I can confirm that a 12-hour fast makes a difference in my blood sugar levels. I’ve been eating breakfast and dinner with no lunch for only about a week and there is a noticeable difference in my response.

  6. I have stated this prior to finding your website as well as the benefits of IF. There would be days I would be laying tile, building cabinets or some other type of work only to find it becoming dark outside and realizing I had skipped all meals that day. At the time, I attributed it to a micro-calorie diet, and rather then eating well and properly, I simply ate less. It gave me loads of energy, but was probably not that healthy.

  7. Hm…I do IF, but I find that the only reason I move around more during fasts is to keep warm.

  8. I think you’re right on… although I don’t have enough IF experience to say definitively.

    I felt better and was more energized when I was IF’ing, but then I got the flu… so I don’t know if my loss of muscle was due to IF or being out of the gym – or both.

    I’ve always liked the higher activity level I have when I’m fasting, and as long as I’m eating clean, I don’t have any energy swings or cravings… and that’s with an 18-19 hour fast, on average.

  9. Great post and it totally reinforces my experience. I eat twice a day, once around 10am then dinner 6-9 ish depending on the convenience of it. Also do 2 24+ hour fasts per week. I’m quite active and feel fine energy wise. I do occasionally succumb to the hunger and snack on some nuts and cheese, but not too often. I am still carrying 15# of spare tire fat and wonder if by my body having a ready energy source to tap into that keeps me going and all the sluggish folks are skinny little punks?
    Thanks for all the effort.

  10. I’m replying to Daniel Merk’s post — Daniel, maybe you’re very carb-sensitive. I am too and I would find that quite a carby breakfast, with the oats and the pear (tried to eat a pear last month and found it too sweet). Dried figs are also very sweet. Maybe eating just protein and fat for breakfast…?

    1. Interesting. For 4 months now I had been eating uncured bacon, and 4 eggs for breakfast. By noon I was not hungry and noticed I would not eat again until dinner. I thought that if I went back to doing “some” oatmeal I would change things up a bit but I think you are pretty much spot on– I am carb sensitive.

      1. I think 150 g. of carbs a day is a lot for anyone. If you do have insulin sensitivity issues then its way too much.

      2. Carbs at evening, or every few evenings. By morning, you’ll be in ketosis again.

        Protein, fat, and low-starch vegetables in the morning.

    2. I responded directly to Daniel, but I would definitely agree with Anne. Unless you have restored your insulin/carb sensitivity, I’d avoid oats and starches for a while. If you are hungry three hours after eating starches, then you are not adapted to them, and should give yourself a break for a while.

      An occasional piece of fruit, or weekly sweet potato, won’t derail your efforts to restore carb sensitivity, but dried fruit and oats in the morning will.

      Good call Anne.


  11. When I’m active (which is pretty much all the time) I’m ravenous. Three meals a day don’t cut it for me; I’ve gotta have snacks.

    I gave IF a try once, and all I wanted to do was sleep.

  12. I work out fasted, I’ve played a day long tennis tournament in a fasted state with no drop in energy….only enhanced “senses” if you will.

    IF is much less scheduled for me know. Most days I eat only 2 meals a day. First one around noon or 1. Second anywhere between 6 and 8.

    As anything new….. START SLOW.
    Happy new year everyone

  13. When I eat consistently throughout the day, I get really panicky. Maybe I’m crazy (ok I’m definitely crazy) but my anxiety is non-existent when I fast. For the last few months I’ve been thinking that “snacking” is sort of like an assault on the body. It’s helping me think twice before eating between meals.

    1. I had incredibly bad mood swings when I was eating higher carb, so it definitely makes sense.

      1. I had major anxiety and panic attacks for years, on drugs and everything. They all vanished with low carb. It was amazing. We’re not alone.

  14. I find this to be absolutely true. I typically eat only breakfast and dinner, sometimes just dinner. I find I have more energy than when I have 3 squares. Not to mention when I fast for any duration I’m more apt to break into a run rather than walk. Even if it’s from my car to the front door.

  15. IF makes everything easier throughout the day. I always take my midterms and finals fasted because I feel much more awake and alert and I always try and go to Crossfit fasted between 12-16 hours. Granted, eating primally I never really feel sluggish. Even when I overeat I still feel like I could go sprint if I needed to.

  16. Today I did 5 x5 sets of military presses followed by 10 rounds of deadlifts (about 50% of my max) followed by 10 burpees at 6 am. It’s now 9:30 am and doing an IF til noon. Will this have a negative effect on muscle gain? I am trying not to lose weight but am trying to gain muscle mass (I’m 56 years old-have lost some muscle mass)and lose BF “love handles”.
    Will IF or longer fast after a workout help me reach my goals (gain muscle and lose BF?

    1. I wouldn’t worry about losing muscle while IFing. You would need to fast for up to 72 hours for that to happen. Make sure you are eating a lot of fat and a lot of protein when you do eat. Going IF and Primal is like going on a ketogenic diet. hell yes you’ll lose body fat! Just maintain your training and you will maintain and even grow your muscle.

      If you can, I would recommmend the book eat stop eat and it will explain how the idea of negative effects on muscle growth is falls. Body builders routinely IF for weeks before competitions (the bad ones starve which is stupid, but whatever).

      As always though, listen to your body, give it a chance to adapt. Once it frees itself of decades of bad programming you will see the difference. The only thing you’ll notice is, like everyone else, you get colder, but heat up fast when you get moving.

      1. Thanks for the reply. I am in my mid – fifties and have worked on gaining muscle the past 2 years. But, no muscle gain. So, following PB religiously has been very productive with muscle gain. Been told to eat more protein but feel too stuffed and lethargic. So, maybe fasting can help me gain the HGH needed for muscle growth??

        1. Ooops. Following PB outline for gaining muscle has not worked for me, waaaah!

      2. About the getting colder thing. I am low in carbs (<100), but high in calories. What does it mean to be cold?

    2. According to Art Devany, you will be better off not eating until noon — his theory is that eating after a workout will reduce the growth hormone response. On the other hand, many studies indicate that eating some protein and carbs (some say before, some say after, some say both) enhances muscular development. Supposedly, thirty grams of protein is the maximum needed, more than that provides no benefit, for a lighter workout, 20 gms would likely suffice. Myself, I prefer some protein/light carbs before a good workout and my body tells me whether it wants a booster afterwards.

  17. I agree with Meeses. I don’t really notice much difference in energy level (usually not a problem). However, I definitely feel colder – esp. in the a.m. Perhaps “enhanced senses” as Marc puts it?

  18. I am new to PB. I have been doing well but wonder if I am esting too much fruit. I do berries once or twice a day, a grapfruit and then an apple or banana? Any help would be appreciated. Thanks!

    1. That’s a hard question to answer because everyone is different, but what you mention doesn’t sound like too much, as long as you’re not loading down your diet with any other carbs, and as long as you’re eating plenty of fats and proteins. It’s important to listen to your body and see if you can tell how it’s reacting to what you’re eating.

  19. So hunger pangs are good? I want to try IF, but I’m nervous. In the past whenever I go too long without eating, my stomach gets bloated and hurts like crazy. Can that really be good for you?

    1. Hahaha, I had those problems at the beginning too. But you have to realize there in lies your answer. Hunger pangs are not real hunger. Hunger pangs are muscle contractions. It is muscle memory. You have been eating a certain way for years, decades even. If you pay attention, the worst hunger pangs always hit at the time you were statistically most likely to be eating a meal. Your whol system starts working, stomach acids churning, before it realizes there is nothing coming.

      If you drink a cup of tea and then find something to do to keep you busy, you will quickly realize that the pangs do not last long. The bloating happens because your system is used to being stressed and it has mobilized all your internal chemicals out of habit. Think of that as withdrawal. When you see someone in drug withdrawal, how bad it is, is a good measure of how bad the drug itself is.

      Have you ever been so busy with work or having fun that you missed a meal? Congratulations, you have IFed. Where were you hunger pangs then? The pangs have nothing to do with hunger, they are just a ghost of your body trying to conserve energy by setting a schedule based on an inflated schedule you gave it.

      Give it a try, feel miserable, feel a headache, feel cold. I assure you after you feel the triumph that first time, the hunger pangs won’t feel that bad again, and after a few weeks, you won’t even remember what hunger pangs feel like. I haven’t felt a hunger pang in almost a year. And I do the most extreme form of IF. I eat 3500 calories each day, and then eat nothing the following day. One day on, one day off. According to conventional wisdom, I should be starving, lazy, racked with migraines, losing too much weight (I’m maintaining a steady 2 pound down a week), and losing muscle (I am actually gaining muscle size and definition).

    2. I actually used to be the same way. I was severely carb addicted and if I did not eat breakfast, I would get incredibly nauseous and nearly throw up. I’m not kidding!

      All of that went away when I found my appropriate carb level (which is very low) and “real” hunger took over. I think all those horrible drops in blood sugar were to blame for the nausea. When I am going to IF I usually eat a very low carb meal before I do it, so I don’t set myself up for failure.

  20. Im not sure if your familiar with the book “lights Out” Sleep, Sugar and Survival. I recommend it to anyone who wants to start “IF”. Make sure you have your diet down and get plenty of sleep (9 hours) and then through in a “IF” period. I try to run with a 15 hour fast before i start eating.
    Great as always Mark! Look forward to 2010.

  21. Jamie, that does seem like too much fruit, at leat it is for me. I keep my fruit intake to a minimum, maybe every other day or less, and I restrict it to berries only, and just a half a cup at that. Treat fruit like a dessert that you imbibe in on an infrequent basis.
    Apples and bananas are very high in sugar…

  22. James-Try to limit your fruit intake, its like “candy” if your down with a low carb paleo diet, Try to stick with veggies, i run on about 50 to 70 grams of CHO a day since i switch to a low carb deal and cut of the fruit. Fruit also tends to give me GI problems so i treat it like a “cheat” and limit my intake to post work out meals.

  23. Hi Mark,

    I’ve been IF-ing for about a month now after reading about it on your site and doing some research on the benefits of IF and calorie restriction. I essentially skip breakfast, eat lunch at noon and dinner at 5 or 6pm and then don’t eat until lunch the next day except for some green tea in the morning. I am much more energized and am not constantly thinking about my next meal or snack- my appetite has decreased tremendously. I didn’t think I would be able to feel greater than when I started eating low-carb about 6 months ago, but IF is even better!

    This is a timely post for me, considering I was just home for the holidays and was unable to resist all of the delicious temptations- while I tried to stay relatively low-carb, I got completely off of my IF schedule. Since then I’ve noticed a remarkable drop in energy. I feel like I have some sort of food hangover. I couldn’t bring myself to go to the gym last night and could barely wake up for work this morning.

    So, after dropping IF for a week and experiencing such incredible difference in energy level and overall well-being, I think I am living proof of the theories presented in this article. Thanks for the post- it’s always interesting to learn about these biological mechanisms.

  24. I have found a significant decrease in musculoskeletal aches and pains with IF.Granted it’s a n=1 but I am pretty observant and smart(also cute for an old guy.Even if you are sketchy on the scientific merits, IF is worth doing just to observe your relationships to food,desires,rituals etc.Brad Pilon’s ebook Eat Stop Eat is worth reading.

    1. I’ve tried to locate Brad Pilon’s book, but it seems to only be an e-book, correct? Can you get a print copy anywhere?

      1. n=1 is just a scientific way of saying that the statement is just based on personal experience. N is the number of whatever is being studied, such as 6,543 men and women in a study is written as n=6,543. In other words the commenter is saying the comment isn’t based on any large scientific study, just their own personal experience.

      2. “n” is the unknown cause that equals the known result of “1.” So, OldDude is saying that he aches less (the known result, or “a”) and, due to correlation, he suspects that IF (a possible solution to “n”) is the cause. 🙂

        1. NO. In statistics, “n” denotes the sample size and there was 1 person in his sample. He is just speaking of personal experience.

  25. Thanks for the input. I have been very strict. Coffee,eggs with bacon for breakfast then eat thefruit while at work. Dinner has been a large salad w/almonds,cheese and chicken or steak and green vegatables. I also snack if I get hungry on almonds. I found fitday yesterday and I was in the 50-100 range ofr carbs. What are other snacks I could go toduring the day of I cut fruit down. Carrots and celery get old pretty quick. Any ideas would be appreciated. By the way, I am really enjoying this site. I feel so much better since going primal.

    1. As far as the celery goes, It can get old, but I try to make it a bit more appetizing with Almond butter. Take some raw almonds and put ’em in the food processor until they turn to butter. It can take 5-10 minutes for a cup. I add one teaspoon of extra virgin olive oil. for more creaminess. Then I add one tablespoon of 100% cacao powder, and a few drops of Stevia. Spread in your celery stick. Tasty and good for you.

      1. Boiled eggs, cold roast beef, cold chicken, all lovely snacks at work. I make mayo for chicken salad to go with crunchy veges sometimes as a treat. Add in some pine nuts, yummy.

  26. My first swing at PB and within 10 days of starting, I was off of work and putzing around the house/running errands. The entire day went by, my family came home and was wondering what was for dinner! I had gone about 28 hrs without eating and never even missed it. And I got a lot of stuff done!
    I say first swing because I fell off and got run over by the wagon. Back on it again now and my simple goal is to make it thru today eating primally!
    Thinking I like accidental IFs!

  27. I IF as a matter of lifestyle–I don’t like to waste time eating if I don’t have to–but I find that in colder climates (Korea, mid-west) it is hard to keep warm. When I was in Iraq in the summer, I was the only one who didn’t think it was hot and I also didn’t get as thirsty when I was fasted.

    I also spend less money on food, since I’m not eating all the time. I don’t know how this impacts anything, though it hasn’t made me less fit. I think the reduced heat production is evidence of less waste.

  28. This is a very timely post for me. Working with a trainer right now who’s got me on a short but hard exercise plan very similar to PB. She has also gotten me to reduce my daily calories to 1600. At first this was hard. She kept saying, “I want to see what this does to your energy”. What I thought she meant was, am I getting enough calories at 1600? It turns out she meant the opposite: are you bouncing off the walls? Once I got good at keeping myself at 1600, I couldn’t fall asleep at night! She said, “Now that is what I’m looking for”!
    She said to me just the other day: “learn to accept a little hunger – not too much, just a little”.

    1. Just make sure you’re getting enough good food for your body. I like IF because it’s a temporary lull in calories that you can make up for. Skipping meals and eating less than you need triggers the release of adrenaline and cortisol (so does exercise) – that’s what gives you that energy surge. That’s all right for the short term, if you make up for the spent hormones with a good diet. But if you spend very long on a low-calorie diet (for most people 1,600 is low-calorie) then you risk adrenal burnout. At least in my own experience this has been true.

  29. I’ve done 10+ mile runs, heavy weight lifting sessions, and 2-hour basketball games all on 12+ hour fast with only water. I experienced no ill effects, and continue to get stronger and faster. I’ve done the eating windows, the Eat-Stop-Eat method, and the alternate day fasting. ESE seems to suit me the best, but I LOVE working out fasted. Eating primaly with plenty of fat helps me go all day, even as long as 36 hours, without much effort.

  30. I love this. Years ago, the conventional wisdom said three square meals a days and that’s what I grew up with. I never get hungry between meals if I eat every 5-6 hours and my meals are “clean” (no starchy carbs).

  31. I clicked too fast. I meant to add that I used to fast all the time for a day of too and have done juice fasts in the past and always felt great. I think it’s a great idea and good research!

  32. Strangely enough oats are the only cereal that doesn’t give me the munchies, I can eat a bowl of porridge with fruit and not suffer from hunger pangs for hours. This may be because I am a Scot… 😉

    PS No I’m not eating oats at the moment, I’m trying for the full 30 days free of any cereal.

    PPS I eat 4 times a day, and feel like I have good energy levels, even during this -12C snowy weather.

    1. You know, Eat Fat Lose Fat mentioned a woman who experienced less hunger on soaked oatmeal than eggs and bacon (though the book promotes the eggs and bacon!). I would imagine that’s the exception rather than the rule, but it’s interesting to hear someone else had a similar experience. I know it wouldn’t be the case for me!

  33. What amazes me is that we, as thinking, rational animals, often fail to examine, consider or even imagine what might have been the natural gustatory patterns of our ancestors, or at least the need for the gut to take a break.

    Even more odd is our insular belief that eating small frequent meals is the right and healthy habit, even though the French and Spaniards hardly ever snack yet don’t suffer the obesity epidemic that continues to grow in our country.

  34. I too am very carb sensitive. I noticed that over a period of two days I seemed to be retaining water. It corresponded with a soup that I made from 3 pounds ground beef and one pound each of green beans, spinach, and carrots. I figured it was probably too carby for me to be having one bowl per day.

    I ditched the soup on the third day and had chicken and olive oil for lunch, and a small handful of almonds for dinner. I didn’t eat until lunch today after that. I felt much better and broke through the weight loss plateau I’d been on. Yay!

  35. Anyone have any experience or know of any research about IF while lactating? How does it affect milk production?

    1. I don’t know from experience but I thought I’d throw my two cents in. I think it’s most important to be sure you’re getting the proper nutrients in – plenty of saturated fats and fat-soluble vitamins. Think eggs, cheese, butter, meat, coconut oil, etc.

      I really don’t know if IF affects milk production, so I won’t specifically give advice on that part. But unless you hear of a valid reason why not, maybe you could try easing into it? If you’re used to eating three meals a day, try delaying breakfast for an hour and eating normally after that. Then after you get used to it, try eating a really good breakfast and see if it can hold you till dinner. However you do it, just work into it gradually.

      If you feel comfortable and satisfied, if you’re consuming enough healthy food and your milk production stays up it might be all right. But I would really listen to your body to make sure it’s a positive thing.

      I’d certainly love to hear if someone else has personal experience with this, or know someone who does.

  36. First off, I love the MDA website and am a big fan. I really want to like the IF/MD lifestyle but have some concerns that I was hoping you could help answer.

    I am an ex-jock and division I two-sport athlete. I have spent much of my life in the gym and at the training table. However, now in my early 30’s, the main reason that I train at this point is for aesthetic purposes (I admit it!) and trying to stay lean and fit. The science behind your concepts do make complete sense. However, at the Olympia this year in Vegas, I met several of the “big wigs” of paleo/crossfit/IF lifestyle who’s stuff I had been just began to read on the internet. After meeting them, I left thinking “I already look better than them doing more traditional stuff.” After meeting several die-hard crossfitters who subscribe to the IF/Paleo diet principals over the past few months…it confirmed what I saw at the Olympia. Most folks out there who are participating in what I would term as non bodybuilding type workouts and diets really do not have impressive physiques….they just look skinny….not fit. Of course, yourself and Arthur Devany are two notable exceptions.

    My wife is an IFBB professional figure competitor and model and eats 6 times a day and does traditional bodybuilding splits and long cardio sessions. She looks fantastic year-round. Everyone that we have ever met in the fitness modeling/ bodybuilding industry eats 6 times a day and includes carbs such as oatmeal,yams, and brown rice into their diet.

    Do you see where I am coming from? I really want to get off the traditonal bodybuilding concepts. The science makes sense but besides a few examples, I don’t see the proof. Help?!

    1. I have the same questions as Jeff S.
      I used to be in the Obese category – adopted a bodybuilding lifestlye got down to 9% BF and stayed healthy. I like what IF has to offer and I love the idea of not thinking about food all day but I do get foggy and tired if I go longer than 4-5 hrs without food.
      Can someone speak to Jeff S. concerns?

  37. Sorry to point out that the French now have a rising obesity epidemic. In the five years that we have lived here, we are seeing increased obesity on the streets.

    This corresponds with the huge updrive of junk food now available…all for convenience…

    The original French food pattern in our area was two small meals (breakfast and goute -afternoon tea) and two large meals per day (lunch and dinner).

    1. Is the increased obesity with the “native” French people? Or is it the increased immigrant community to France who are the ones who are obese?

  38. Perhaps I just need to let my body get used to it, but I’m the exact opposite. I’m lethargic until I eat my breakfast, but once I do, I feel a burst of energy.

    Also, while trying to gain weight right now, I doubt I could fit 4000 calories into a tiny window of the day, especially while trying to cut carbs. Over half my calories come from carbs: rice, pasta, and oats. My calories would be less than 2000.

    1. Hey Allen. I tried I.F. once back when I ate a “standard” diet, and then recently again after I had adjusted to the primal-type of diet that Mark advocates. I found I.F. MUCH easier when eating very low carbohydrate, because my body was more efficient at using fat (dietary, and in my body) for fuel. I was doing 24 hr cycles (ie: eat dinner, breakfast, lunch, then not eat again till the next dinner).

      If your body is expecting to be able to use easily converted carbohydrates, then it’s no wonder you feel lethargic, and then a burst of energy after eating them.

  39. I fall into the same trap of overdoing it on the fruits. Also, I find IF much more manageable when I eat a ‘late lunch’ around 3 or so and then fast through the evening and night. When I wake up the next day I actually am quite energetic and usually do a workout, wait an hour or two and then have a nice big breakfast (late around 10 or 11AM).

  40. “I find that when I fast I am more likely to curl into a ball and do nothing – no energy to do stuff.”

    “I gave IF a try once, and all I wanted to do was sleep.”


    That makes at least three of us.

    1. Me too. It felt like a sick day. Just AWFUL. I’m on board with the science, but in practice I had a hard time with it. I couldn’t wait to get up the next day and eat.

  41. I fast at least once a week (24 hours), or sometimes 2 or 3 times a week.

    At first my energy levels were low and I was ravenous when I ate (something I soon discovered you don’t want to do!).

    Now after over a month of IF I find I do have more energy like this article indicates. I workout heavy too and love it.

    For me, fasting has been the magic bullet to weight loss, more energy, and control over my body. Love it!

  42. Mark,
    Today is day 5 of my primal diet program. I have ordered your book on amazon but I have been reading your blog for a while now. Based on that, I have been sticking to a very basic primal diet with no grains. I can tell you that I after my first meal (4 eggs, 1 cucumber, 2 strips of nitrate free bacon, 1 tbsp walnuts and 1tbsp olive oil), I don’t feel hungry till 3-4 pm. Even that hunger is very manageable and I seem to have more energy. During this time (just before meal time, I seem to be more active) My strength seems to have remained the same.
    My weight has dropped from 168 to 163 pounds. My ab circumference seems to have remained the same. Can anyone explain this? I definitely don’t want to be losing muscle!

    1. Well, it’s just a thought, but if you just started the diet 5 days ago the weight could be water or glycogen stores. These usually distort weight loss during the first week or two. If your strength is the same, that’s a good sign. Keep your saturated fat intake up, too – just fry those eggs in coconut oil or butter (or bacon drippings). It’s healthy and it tastes great, too. 🙂

      1. Thanks. I am eating a decent amount of saturated fats. I guess I’ll see if there is a change in a week or two.

        1. you eating saturated fats are crazy! that’s why you’re the fattest people on earth! Eat tons of palmitic acid which interferes with the feeling of satiety in the hypothalamus and causes insulin resistance. Food manufacturers have known this for a long time and feed you to palmitic acid all day and you eat all day, fast food, butter, milk, sweets and lots more is all full of palmitic acid (palm oil and animal fats) ! I’m not a terrorist, I would like to save millions of people from obesity and premature death that all these related diseases it carries. If you really want to lose weight healthy without starving continues ban oilio the coconut palm oilio and everything it contains, Ninte butter bacon bacon! Eat in the evening at 20:00 and then complete fasting only water until 11-12 days after protein meal with no saturated fat as olive oil, mayonnaise, eggs, fish oil also, light ham, dried fruit but no carbohydrates now! 20:00 to eat more carbohydrates you can. pasta with tomato sauce with Italian olive oil and fried onions found the rivets on the net! pizza bread with lean meat or eggs etc.. then stop until the next day .. 11-12 IF this diet is a cyclic dinner 20:00 – 15 hours fasting – 12:00 Lunch – 8 hours fasting – 20:00 dinner with low saturated fat and low simple sugars.
          TRY ONE WEEK, you lose weight without hunger forever is a promise from an Italian friend.

      2. Elizabeth, I’m really impressed with your replies, very much agree with your ideas. been to your website, read all the book you recommend. very impressed!

  43. IF rocks… I can go trough the day without any brain fog, mood swings, sleepiness feeling, even anxiety… My energy is on top and i feel really free..

    I think in the psychological aspect the fact you don’t have to put any attention to the eating and post-eating process gives you heap of time to get so many stuff done, it definitely makes my day longer so i can finish everything I’m supposed to.

  44. I always feel more active on fasting days. At times I am almost wired. I think the advice about not missing meals applies to carb hounds only. If you have access to your fat you have the opposite, more active effect.


  45. Jeff and Jenn,

    I eat pretty paleo, do intense lifting/calisthenics and plyometrics twice a week, and sometimes yoga. I’m pretty muscular. I’m 183 lbs and 6 feet. If you click on my profile, you can see my physique.

    I used to eat 6 or 7 times a day, but found that I look and feel better eating once or twice a day with high fat meat and leafy greens only. When I was downing smoothies and starches, I was in the 190s and less chiseled-looking as well as always feeling bloated.

  46. I’ve been dabbling with IF ever since I began the PB lifestyle about 8 months ago. It started as a couple of skipped breakfasts to a couple of 24 – 36 hr fasts here and there… It seemed to really spark additional fat loss and I didn’t find it too difficult to do. Then over the past two months, I’ve notice that I just don’t get hungry much anymore for breakfasts,.. and my lunches were getting pushed back further and further to a point that i just wasn’t hungry until about 4-5pm… at which point, i just decided to just wait til dinner around 6-7ish when I got home for dinners… basically i started to follow “just eat when hungry” type of mentality. I realized that I’m able to perform 19-24hour fasts during the weekdays, and eat brunch and dinners during the weekends when I’m with the kids more at home. I’ve felt no noticeable change in energy levels one way or the other… Probably a bit more active when fasted, but I can’t say for certain that it’s really elevated it that much more, as to when I was just eating 2-3 primal meals. I’m still able to work out intensely with weights, sprinting and playing intense sports, and feel pretty good overall. There are some days that I do get hungry around 2pm or if there’s an occasion at the office where people are going out to eat,.. then I just eat. I don’t really force the issue of IF, but it seems perfectly natural to just eat whenever you get hungry. I have noticed that I do feel a bit colder while fasting,..but wearing warmer clothes seems to get rid of that. From what I’ve read, I fast more for the added convenience of not having to eat all the time and the added benefits that come along with it.

  47. I’ve always just eaten one meal a day, really. Big dinner with raw milk and a few egg yolks mixed in with it for breakfast. Since going low carb the thing that is somewhat concerning is how few calories I consume. I’m somewhere around 1500/day and I’m STUFFED.


  49. I think that when you eat mostly fat, your body gets used to converting its fat stores rather than relying on the constant doses of insulin-spiking carbs. So you can go quite a ways without eating and feel great. I base this on Gary Taube’s book as well as my personal experience. You have to eat this way for a while for your body to learn it. I’ve never purposely fasted; never set out to say “I’m gonna fast today” or “I’m gonna skip this meal.” Usually I am trying to gain weight, as my body does not digest carbs well and I really have no choice but to keep it at about 125 grams per day, almost no grains at all or sugar or dairy, and this level of carbs along with my level of activity makes it a bit hard for me to keep on weight. I eat when I’m hungry. But I’m almost never hungry until I’ve been up and moving for many hours. When I’m engaged in strenuous physical pursuits (mountain bike rides with thousands of feet in elevation gain, rock climbing, hauling heavy packs, etc) I’m often satisfied with just a bite of food here or there…and then I will power down thousands of calories later that evening. Sometimes I’m just not hungry even doing day to day stuff. But I usually end up with about 3,000 calories a day on average, for my 120 lbs 5′ 4 frame. A lot of times I scarf my meals standing up. CW says, very bad! I’ll bet Grok ate this way, and Ms. Grok too. I think this is more natural than 3 meals a day–even though people will treat ya like ur a freak for eating this way! I have no doubt that I can go for a long time on fat stores but sometimes I do wonder about hard anaerobic work when my carbs get low…the burst of power, limit-strength type of work. I think I biff sooner on that sorta stuff when my carbs are low, racing heartbeat and bonk. Muscle glycogen is critical–I’m still tinkering with how much I need and how to get it without my small intestine freaking out. Fat stores are not inert blobs, you know if you’ve read Taubes. Fat is always circulating through your system. Some of us have trained our bodies to use it. Some of us eat pears and oatmeal, and then the body uses those carbs instead and begs for more, stores the extra as fat, which eventually cannot be retrieved when the pancreas tires of squirting out all that insulin, then arteries harden from the excess fat, people are hungry all the time and have no energy. That’s the “too many carbs” negative spiral. PS I love a little bit of steel cut oats once in a while for a special treat, just 1/8 a cup with lots of cream and olive oil and blueberries.

  50. I have been IFing for 2 years now and it is my preferred approach to eating. My wife and I have just built a new house with a long period of moving furniture plus lots of landscaping. We have had plenty of people help out over this time. When a scheduled lunch break or whatever is taken – people have noticed I don’t stop and take a break. My answer – I will go to sleep and lose motivation to keep on moving and working. For me not eating during the day means a full day of endless energy where I can get plenty done. No peaks and valleys – just constant energy. But you can be rest assured that at the end of the day there will be plenty of eating in a primal manner to be done.

  51. I lift weights (intensely) during a 20 hour fasted state all the time… I have never, ever had energy problems. And there’s nothing better in this world than stuffing myself after it. :]

  52. Egads! I’ve did a 24 hour fast last Thursday, IF Sunday 15 hours, and IF for 15.5 hours today. I’ve taken 1 day off from Crossfit. On the fasted days i eat two full meals but am running short of my protein amount, eating 80 to 100g, trying to reach my supposed lean body mass of 138 lbs. I weigh 154lbs.Tonight I did a visual check of my BF. Yikes! I noticed more BF around my waist. Have not gained more than 1 lb. the past 6-7 days. Eating good fats (70-90 grams a day) avocado, nuts, almond butter, olive oil. Consuming good carbs, 99% vegetables…low starch or no starch veggies. Do use olive oil and other dressings on salad. Also, sleeping 6 – 7.5 hours a day.

    I am puzzled :(?? Thought fasting would help lose unwanted fat and by eating the PB way, would not lose muscle nor energy.

    Mark, or anybody else. Do you have an idea how I can reverse the BF increase?

  53. Even though I’m a skinny guy (Octomorph) I still find myself eating sometimes just for the sake of it. I’m gonna skip some snacks today and see how I feel. It’s true about constantly eating not letting our body regenerate itself too.

  54. Here in France, having snacks isn’t part of conventional wisdom. Advertisements for several kinds of non-primal products are even required to warn people against eating between meals.

    (Now, not skipping breakfast is part of the local CW).

    I am personally used to skipping meals, typically breakfast and/or lunch.

  55. Jeff S and Jenn,

    To elaborate more… since eating primally, I’ve leaned out and still stayed muscular. Granted, I’ve lost some mass (probably fat and muscle), but from a purely aesthetic standpoint, everyone has commented that I look better. I know I feel better as for as not feeling bloated when I ate six times a day.

    Also, I never really wanted the bodybuilder look and when I was near 200 pounds, I noticed a decrease in my functionality (mobility and flexibility). I still do heavy lifting at times. I switch it up though. I never isolate body parts and always do total body, compound movements. I also use kettlebells and do a lot of body weight moves.

    By no means am I skinny-looking. I’m not sure why the paleo/CrossFit adherents you met were “skinny.” Maybe they’re not doing a fair amount of resistance. Did you happen to see them shirtless or in shorts? Maybe they looked “skinny,” but were ripped under their clothing. Seriously.

    When I first leaned out from eating strictly paleo and IFing, one of my friends thought I looked “small.” (ironic since I still weighed more than him at 183 to his 170, but I;m more muscular than he is so that makes sense sort of), but then when he saw me changing as we prepared to go for a workout, he remarked that I looked ripped and muscular and very defined. Also, he along with others have remarked that my face now looks more chiseled and my features more defined and masculine (not that they were effeminate before)

    All in all, I find that I feel better physically living this why, and that’s what’s most important. When I ate starches dairy and overabundant fruits, I was always hungry yet bloated and felt compelled to eat 6 times or I’d “get skinny.” Still not skinny, but have noticed that my body has dropped superfluous mass. Then again, superfluous is relative. Like I said though, when I start approaching bodybuilding dimensions, I note how mobility and flexibility suffer. I find a I like a balanced state of being aesthetically muscular and lean and svelte, but highly functional. Almost ever bodybuilder I know has zero functionality with their proportions.

    1. Thanks for the detailed reply….it is helpful to hear/see your experience. Jeff S.

  56. Until recently I was a dyed-in-the-wool, dedicated FatBoy. (I’m still fat but every day dawns on less of me.) I worshipped daily at the altars of the great gods of Cheeseburgers, Pizzas, Cookies, and Ice Cream. I state, unequivically, that eating all day definitely slows one down. Eating several small meals does the same thing. As Mark notes, the body has no rest time, it is continually working at digesting the constant influx of food.

    I did my first fast almost two years ago. After the initial killer headache which are withdrawal pains, I believe, due to the sudden lack of refined carbs, everything has gone swimmingly. I managed to kickstart my weight-loss and I haven’t had even a single ounce of man-made carbs since. I now do two two-day fasts per month at random times. I always notice an increase in energy during and after the fasts.

    My job entails working 24-hour shifts. Usually taking three or four short naps during a shift is no problem but when I anticipate a tough shift with little likelihood of getting a nap or two, I start a fast before the tough shift begins. Staying awake for the 24 hours is still a bit difficult but not any where near as difficult as it would be if I had food in my stomach.

  57. Any time, Jeff. If you do decide to fully jump in, I’d be curious to read how your experience goes. If you continue to do explosive total body movements (lifting, plyometrics, intervals as well as some suspension training with things like TRX, elite rings and straps), I think you won’t get skinny.

  58. Mark’s post fully confirms my experience of the last month. I started IFing somewhat sceptical of my own ability to take to it, and now, four weeks later, I am fasting 23-24 hours every other day. The days when I fast, I have as much if not more energy and clarity than the days when I eat. But unfortunately, you can’t not eat EVERY day…:)

    I am sure, based on previous, far more negative experience, that eliminating most cereals from my diet for a month before starting IF helped me adapt to the practice easily. (I still take oatmeal porridge with lots of almond butter and fresh cream on the days I eat, which I guess I must be adapted to, as it gives me perfect bowel movements and leaves me uninterested in sweet foods for the rest of the day).

    But the greatest gains for me from IF have been psychological. I realised quite quickly that I just don’t get hungry when I fast, not even after 24 hours (tho anticipation of food will make me look forward to it, physilogically as well as mentally). So for the past 45 years, most of the time, I was eating out of fear of being hungry, rather than from hunger itself. I find it hard to exagerate just how liberating this discovery has been.

    Thanks to Mark and all the other people whose exposition of the benefits of IF and the paleo diet helped me realise this before it was too late!

  59. Who really understands the interactions within the human body (transcription factor Foxa2?). It is just far too complex and changing one thing affects many other downstream signalling factors. We do not really know all the compounds in the food we eat, etc.

    So many people “sold” on PB use logic. How did we evolve – that makes sense to me. And common sense says if you are active all day (tacking animals for example) – you didn’t take a granola bar with you! And here is another thought – it is 11-am on the West Coast, my 10-year-old has been up for a couple of hours. Is she at all interested in eating yet? Not at all. I think if you just let kids eat when they are hungry many would be surprised at the patterns they would adopt. Most of the way we eat is a learned response.

    OK that is my thought – now I have a question for experienced IF’s. Do you have tea or coffee or anything when you skip breakfast? I do find I need a cup of tea (admittedly a learned response – being brought up in England).

  60. Hey Mark, LOVE the site, heard you on CrossFit Radio and have been training my clients (I own a healthclub) using crossfit and paleo (and readings on your site) for some time.

    If I may, I’m going to play devils advocate about fasting. I recognize that we’re talking about intermittent fasting but, indulge me.

    I’m I’m Grok, and I leave my cave in the morning to go hunt, if I walk past a bush with berries on it, I’m going to grab a handful. If I pass a tree with nuts or apples on it, I’m likely to grab some of those too. All of this as I’m spending my day hunting. That sounds, to me, like numerous small meals a day. Just wanted to add my 2 cents worth.

    Hope to hear back from you!
    -Hugh MacEachran

    1. Actually Hugh what you described is “undereating” which indeed is a form of Intermediate Fasting… which is fine to do because the amount consumed is and should be far less than the evening meal.

      Much of WHAT our Paleolithic ancestors ate is known, but WHEN is only speculated; however can be understood to be more logical to my recommended protocol. Of course one can deduce that they did not water fast every day and when they had a little bit of something they at it.

      One way to tell is by studying the cultures who still practice this lifestyle. Indigenous people in South America, Australia, and Africa still eat this same way even today. They don’t have the cancer, diabetes, high blood pressure, and high cholesterol as the Western World does. Of course they have other issues because they’re all inbred, but that’s another article topic altogether for another time.


  61. Yes Mark I do believe there is wisdom in your post. Though I eat very primal I know my problem is grazing as you and I both call it. Healthy foods but all day = no BF loss. So it’s a New Year and Decade time to go with out in between meals. Should work great at work sense dinner break is at 9:30 pm and I get out at 2am (hey some times Grok had to stay up and guard the camp at night) if I go to bed a little hungry I think that will be a good thing. Let you know how it works out.

  62. You don’t need breakfast or lunch. Once you eat it you’ll engage the Parasympathetic Nervous System which will lower your GH and Testosterone levels and spike insulin. You store fat and get tired.

    What If I Can’t Daily Fast?
    No problem, but keep in mind that this might simply be an excuse moreover an actuality. In reality you can do whatever you decide to do… as long as you have a plan. Some people believe or strongly feel that they absolutely need to eat during the day. This stems from years and years of doing this due to food being so convenient for us to acquire. I wouldn’t recommend going cold turkey on the water fast protocol unless you are the type of gung ho person who can do that. If that is not you then don’t force yourself to water fast. Eat small pieces of fruit such as berries and fist size fruits. If eating berries is what you want to do then go ahead.

    Whenever you eat something- even protein- you get an insulin spike and thus store a little or a lot of fat depending if you have excess blood glucose after breakdown. We want to minimize all insulin spikes by advocating only one primary insulin spike a day and that is in the evening. Therefore you use your body’s fat stores during the day. Instead of spiking insulin when eating you will have your glucagon spiked and thus using stored fat. Then eat when your body actually needs and uses the nutrients for repair and recovery. That is at the end of your day.

    There are two environments where the body increases its fat burning hormones and therefore uses its fat stores as fuel. That is while exercising and while fasting. If you can fast for 18-20 hours per day as well as exercise during your fasting period then you will experience amazing results very quickly.


  63. Since really going full-on paleo, I noticecd that I didn’t need breakfast anymore. I could go until about 1:30 or 2:00 before eating lunch. And I was like buzzing with energy… no slumps. I think it depends a bit on what I ate the day before and how early I had dinner though. If I was carb-heavy then I seemed to get hungry for breakfast. It’s great for travel though. I’m not afraid of my sugar dropping suddenly anymore because it doesn’t.


  64. The whole IF topic interests me greatly considering I am a Strength and Conditioning Coach and involved on a daily basis with fat loss clientele. I personally have used IF for about 8mo with fantastic results. After an injury I came down from a stubborn weight of 245 to my more comfortable weight of 225. I also finally managed to get rid of my protruded gut! I’m convinced this was a direct result to the years of following what I was taught to do, eat every 2-3hrs!

    What’s interesting to me is that I believe that many “over fat” americans are over-fed and under-nourished. Then there are those others I’ve consulted with that under eat, are “over fat” and are essentially using an IF way of life and not knowing it. Why are these under eaters/non practicing Intermitent Fasters still fat? I honestly believe it’s because of poor macronutrient intake. I believe it all comes down to quality of food and there may be too much emphasis placed on frequency (5-8 small meals) of food.

    Now back to the macronutrients issue… Conventional wisdom and the mainstream push low fat dogma. Let’s not forget that the majority of bodybuilders use low fat and this is where Americans originally adopted the concept of eating every 2-3hrs. Why? Because when you eat low fat, you’re always hungry! Eating a low fat diet not only forces you to eat at regular intervals throughout the day it also causes people to crave simple sugars and poor quality carbohydrates. By switching to a Paleo/lower carb type of lifesyle your macronutrient ratio’s switch from a hyper carb (high sugar) to hyper fat (high satiety). This not only elliminates the need for multiple meals it more importantly elliminates sugar cravings, sweet tooths, balances blood sugar and allows people to choose foods of higher quality when they do decide to eat. Let’s also not forget the benifits of better insulin sensitivity, lower risk for ALL degenerative diseases, increased vitality and improved quality of life…

    In conclusion it’s probly safe to say that eating less and moving more works after all but… It all DEPENDS on what type macronutrient ratio’s you’re consuming. What’s funny is that you’re really not eating LESS calories, you’re eating LESS frequently! I guess it all just depends. Food for thought.

  65. I found out about IF from Brad Pilon’s Eat Stop Eat. I started immediately, doing one 24 hour fast on tuesday and one on friday. At that time I was also switching to PB. The first couple of weeks were a real slog, I was so focused on food and where my next meal was comming from, not surprising considering I had been following a 6-8 meal a day body building diet for years. Around about week 3 it got a lot easier and I’ve become more active (in fact I usually now workout only on my fasting days) and each week that goes by it becomes easier and more enjoyable.

  66. Why not make it MUCH simpler!

    Ask, act
    Ask, act

    Am I hungry? No (don’t eat)

    Am I hungry? No (but you ate anyway.. ask why?)

    Am I hungry? Yes (eat the correct food for YOU)- not for the next Grok.

    Forcing ANYTHING is never good.

    That’s easy.

  67. I have been doing IF for over 2 weeks 6 days a week. Eating only in a 4-5 hour window. I feel a lightness to my mind, more focused and on task for my day. I started this after coming off of a 3 day fast of water and tea only. During that fast, I split wood at a cabin, had no issues of needing a nap. I have lost 10 pounds and feel great.

  68. To Matt, Hypoglycemic Question:
    I have been myself. Many days waking up at 49 to 70 on the glocometer years ago. After simple carbs it would drop a few hours later. The secret for me is protein, with fat. If I eat them before going to bed, I have normal sugar levels in the morning.
    If you are really resistant, you may need more time to get adjusted. My wife is diabetic and is no there yet herself.

  69. This is so cool. I fast typically for three days at a time for religious reasons and I’d always thought it curious that I was never really zapped of all my energy until about the third day. Then I could expend energy but couldn’t recover as quickly. Great Post!

  70. It’s funny how when the word “fast” is mentioned most people immediately go into this brain fog that says “OMG, I’m going to be hungry. Or I’m going to starve until my next meal.” That’s what CW mind control has done to us.

    Have you ever been so busy that you didn’t have time to eat or even think about eating? You’ve run around doing this, that or the other and never really feeling starved or hungry.

    Guess what – you were fasting. Did you notice how much energy you had while doing all those things? Did you notice how much clearer your thinking was and when your body finally was ready, you noticed, now it’s time to eat.

    Of course if you don’t practice PB you might have eaten a little too much or not but the point is you went hours without any harmful side effects.

    Until I discovered IF and the science behind it (sorry Mark, Brad Pillon turned me on first), I was eating six meals a day and eating even though I wasn’t hungry because I believed what the “norm” was suppose to be.

    Now with PB and IF I am totally liberated and happier. No calorie counting or clock watching and I truly eat food (minus grains) that I love.

    I am even switching, I mean suggesting to clients how wrong I was and how the benefits of living a PB life and IF can be more beneficial.

    I even started to switch up the regimented workouts for my boot camp. We played kick ball last Saturday (plus I’m still in recovery) and I never saw such a happier bunch of people. Watching them “sprint” around the bases, run down balls and dive for them was just amazing.

    Can’t wait to play with them next week. 😉

  71. My first fast was 3 or 4 months ago and it was hard. Headache, feeling shaking, etc. The 2nd one a few days later was so much easier and I have been doing IF once or twice a week now regularly. It has gotten to be so easy. I am so much more in tune with my hunger levels.

    I love lifting heavy on the days I IF. I have tons of energy. There may be one hour during the day when my body expects food and I feel kinda “hungry” but it passes soon and I feel amazing the rest of the day.

    I seem to have one problem though: I love breaking my fasts with a good beer (like an IPA). I am not trying to lose weight, so I can afford the carbs. And I don’t drink more than one or two, but boy, I just crave a beer at the end of the fast. I don’t drink a beer everyday either, usually just when I fast! Weird?!?

  72. Hi all,
    – I have I have been zone paleo for about 1 year solid now,

    – I am a moderate gainer,

    – My Body fat % is never any more than 8ish and never lower than six.

    – I am training pretty hard at the moment and i keep reading more about fasting.

    Do you recommend it when training?

    If so when should i fast?

    I really would appreciate you impute and advice.
    Thank you

  73. IF takes a bit to get used to, I got used to it in college when I had work/class 2 days a week solid from 8:00a-5:00p. Since I was so busy I would fast without wanting to, but after a while I stopped getting hungry. Now if I have to skip a meal or eat late it is no biggie. Its a real bonus.

  74. Mark — weren’t you on CW’s side when they recorded the DVDs for Tony Horton’s “P90X?” You were the supplement consultant on that workout/diet program and you recommended that we make sure to eat six small meals a day so our blood sugar doesn’t drop. When did you change your mind?

    1. I knew I’d seen Mark somewhere before! Haha I wonder what Tony Horton would have to say about the PB’s defiance of conventional wisdom? He seems like the kind of guy who’d take a fit if he saw what I ate in a day (or lack of things on an IF lol)

  75. I have been living primally for somewhat less than a year.
    Two weeks ago, I rode my bike 40 miles on one cup of coffee and 3 pints of water and did not feel like eating for at least 12 hours afterward with no Ill effects whatsoever and felt wonderful.
    I’m a 70 year old male.

  76. I have been living primally for about six weeks now. I do find that I feel satiated for longer periods than ever before, though some days I still get hungry between meals. I’m trying IF (whole day) for the second time, and I find I feel good, plenty of energy, no issues, except I’m really hungry. I know the advice is, if you’re really hungry, eat so you don’t stress yourself. Does this mean I’m not cut out to fast?

  77. Hi, I’m new to IF – going on my 2nd week. I do struggle with hunger occasionaly, but I find when I drink water with a splash of lemon and a dash of cayenne pepper (for kick), I’m good until my window at 5:00. I feel incredible! So in control, and knowing that I am no longer controle by food. This is the longest I’ve stayed on a “diet”. I still have to incorporate better food into my diet, right now I’m eating pretty much what I want, but I know this has to change in order to be at my optimum health, and not to mention my ideal weight. I have about 73 lbs. to loose to be at my desired weight. So far I have lost 6 lbs. and I truly believe this time, with IF, I will reach my goal. So glad to have found this site! If anyone would like to “buddy-up”…I’m all for the support and encouragement!

  78. Now THIS explains why Jack Bauer can go 24 hours without eating! If he DID eat, he wouldn’t be able to go 24 hours at all!

  79. Just started training at Crossfit about a month ago, and trying to get used to this whole Paleo/Primal thing. I fasted for the first time in my life yesterday, went 20(ish) hours, worked all day just drinking water and even golfed after work and felt fine.


    Here’s my issue: Say for example my in-laws are having us over for dinner and they’re serving lasagna, I’m not going to be one of those a-holes and say, “Nope, sorry, not apart of my diet, won’t eat it…” I’m going to be polite and eat what is being served. Primal is good in theory, but when you’re eating as a family, it really hinders you (or your family).

    So what do you do when the family is eating something “non-primal”? Anyone else running into these very real problems?

    I can get away with the primal thing for breakfast, no one takes offense if you don’t eat pancakes or waffles.

    But when it’s a family meal/dinner, how do you say no?

  80. I came across fasting while working as a weekend security guard. The security handbook manual, specifically mentioned that guards on duty, must not eat or drink anything. Since I was working a full weekend shift…that meant 48 hrs. of a complete abstinence fast. What I found, was that my mind became very clear and alert, and was able to respond to any emergencies quite effectively. Going without food for a few days is a small price to pay, considering the enormous physical and mental benefits resulting from such a dietary practice.

  81. I’d have no problem telling family, hey guys, I trying a new way of eating, please don’t be offended if I don’t have the lasagne. Eat their salad and use the opportunity to tell them how much weight you’ve lost/healthier you feel/etc etc.

    If family don’t understand then my gosh you are in a bad way.

    If you eat it then suggest an after dinner stroll to deal with SOME of the pasta?

    Ive been known to pick out the pasta in a dish and simply say Im sorry I dont eat pasta anymore.

    They might surprise you and ask why!

    Makes for interesting dinner conversation!


  82. I’ve been trying to read all the posts connected to IFing (love saying IFing–smile). And I have to tell ya, Ifing is amazing for energy for me. I’ve posted earlier, I fast Monday, Tuesday, eat Wednesday, and fast Thursday. Three days of water/week. Tuesday is by far my best day of energy, sleep is incredible on Tuesday night, Wednesday morning I don’t want to ruin by IFing buzz, but I do by noon. I eat pretty normal on Friday through the weekend, you know–beer the whole bit. I have to tell you, I’m really considering going total health nut diet during the weekend, I hate that I ruin my f-ing buzz by eating and drinking– yet, I still am tied to to the sociology of “going out– havin a good time”. It’s just that I’ve never felt this good. Maybe I’ll become a non-drinker…

  83. I began fasting about 3 years ago. I eat once or twice a day although I do take in calories while fasting. These calories are in the form of fats that in my opinion supports the ketogenic aspect of fasting. My diet is strictly low carb which also supports the ketogenic aspects. I am pre-diabetic and I keep my fasting glucose levels under 100. That being said, I can keep my fasting glucose levels under 90 with little effort.Supplements I take are ionic magnesium, vitamin D3, krill oil. If what “they” say is true, regarding the need to eat constantly throughout the day,there would be no way I could eat this way. I plan on going a day or two without eating to increase my fasting window.