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Why Fast? Part Seven – Q&A

Posted By Mark Sisson On April 25, 2012 @ 8:00 am In Diet,Fasting,Health,Self-Experimentation | 96 Comments

By now, you should be caught up on all the benefits that fasting offers. By now, you’re likely either intrigued by the practice, strongly considering taking it up, or basking in the smug satisfaction that your longtime breakfast-skipping ways weren’t destroying your metabolism after all. But although I tried to cover just about everything I could in the last six posts of this fasting series (links at the bottom of this article), I apparently didn’t hit every angle, because I received a barrage of questions from readers via email and comments looking for clarifications, answers, and explanations. I can’t quite answer them all, but I did manage to put together a fairly representative selection of the most common and relevant ones, and today I’ll provide answers.

I would like to IF but I have osteopenia and am concerned about losing bone mass. I have been gluten/dairy free for three years and paleolithic for about 3 months. Would IF be good for me?

Your hesitance is understandable, as caloric restriction has long been associated with bone loss, likely due to the reduction in circulating IGF-1 [7] (insulin like growth factor 1) levels. Since intermittent fasting does not appear to have the same effect on IGF-1 levels [8], however, I’d imagine it’s pretty safe for bone health. Just make sure you’re eating enough calories when you do eat (the IF rodents in the study did not reduce calories overall) and lift some heavy stuff [9] now and then, and I think you’ll be good to go.

There was a study [10] that found in utero IF had a negative effect on fetal skeletal development, but you’re not typing this question from the womb, right? If so, amazing!

Won’t IF induce the body to break down muscle to get amino acids for de novo gluconeogenesis?

Let me hammer this point home: Once you become a fat-burning and keto-adapted beast [11], most of your energy demands will be met by stored fat and ketones, so you won’t need to eat protein to spare muscle. If you are fat-adapted and keto-adapted, fasting (at least IF) is protein sparing. If you DO need to get some glucose for a hard workout, some will come from glycerol [12] (from triglyceride [13]) and some from de novo gluconeogenesis [14]. But you won’t need much from muscle tissue because your glucose requirements have dropped, you are better at burning fats and ketones, and, presumably you are NOT doing a 2-hour blood-letting in the gym.

As I often say, this is NOT the case when you are a sugar-burner. Then you probably DO need some protein to stoke the gluconeogenesis process, and I’d suggest eating a protein-rich meal (see Meat) before you embark on your fast so your body will have plenty of dietary amino acids on which to draw for gluconeogenesis. Of course, this doesn’t apply to all you fat-burning readers out there. To you I say, don’t worry about muscle loss during IF.

Workout intensity? Should I just be a slug during the fast, normal activity (long, slow walks or bike rides), intense workouts? Intense workouts usually make me hungry shortly after.

Long walks are great while fasting. My favorite pastime is an early morning hike on an empty stomach. I typically fast for a couple hours after my resistance training to maximize growth hormone, but then again, these days I’m generally doing bodyweight exercises (sometimes supplemented with a weight vest). Most sources say to end your fast with a workout and eat afterwards. If intense workouts make you hungry, save them for the end of the fast. That way you can derive the benefits of a long fast [15], the benefits of a fasted workout [16], and the benefits of a massive feast after it all. Win win win.

Above all, I would stay as active as possible during the fast. Sitting around like a slug will only make you dwell on food, and the lack thereof in your body. Don’t do that unless you want to obsess over what you’re not eating. Walk, ride a bike, get some work done, do housework, read something [17]. Just keep mind and body active.

I am on a regimented meal/medication plan. I am adopting the Primal lifestyle, but I need to make room to allow for the tasting of these products. Sure, the menu items I can handle, as I just really need to take a couple bites, and that is it. The problem comes from having to taste for quality of the other items, like sauces that an employee makes, for consistency sake. In each, I might only have to taste a teaspoon or two at most to correct for seasoning, but when you have 10 items to test, that adds up.

How would you manage something like this? Would you make the working hours like a fast or something, to account for the tasting?

How does a chef fit the Primal Protocol?

Sounds like a great job to me! Personally, I wouldn’t worry a whole lot about fasting, especially as you start a new job and acclimate to a new schedule. Plus you have a family, which can add even more stress (love you, kids). Intermittent fasting might heap another stressor onto your busy schedule, so keep that in mind.

If you’re dead set on it, though, there are two ways you can incorporate fasting into your schedule, as I see it. First option: don’t sweat the tastings. You’re only doing a teaspoon at a time (and you could probably cut that to half a teaspoon, am I right?), and since fasting is not controlled by an on/off switch, you won’t necessarily be “breaking” the fast. Just consider your work day your fasting period. You’ll be on your feet throughout the fast, so you’ll be staying active and your mind will be engaged with things other than food. Er, scratch that: you’ll be engaged with food, but not necessarily eating it.

Another option is to fast on your off days. Assuming you get a day or two off, just do a full-on legitimate fast for one of them. It doesn’t have to be a full 24 hours or anything, but try to make it at least 16 or 18 hours without eating. Good luck!

Are you suggesting that it really is OK to skip breakfast?

Yes, I am. While epidemiology [18] suggests that breakfast skippers are fatter and less healthy, that’s a correlation, not necessarily causation. It could just as easily be explained by the fact that people are more likely to skip breakfast because they’re overweight and want to lose weight. Or maybe because skipping breakfast is widely regarded as an unhealthy activity (like eating red meat), those who are already healthy are more likely to eat breakfast. See how it works? To date, there has never been research conclusively showing that skipping breakfast causes the metabolism to “slow down” or the skipper to gain more weight. In fact, the bulk of the evidence [19] suggests that meal frequency and timing have no effect on weight gain or health (and it might even be the opposite, as my fasting series suggests).

What frequency do you recommend the average guy on Primal/paleo fast?

It depends entirely on the duration of your fasts. If you’re doing a Leangains-esque slightly compressed eating window, daily fasts are in order and even well-tolerated. If you’re doing longer fasts that stretch toward 24 hours and beyond, once a week is all you “need.” Two would be fine, as well, but any more often might make it difficult to obtain enough calories to prevent the negative effects we often see with chronic calorie restriction – muscle wasting, bone mineral density reduction [20], libido lowering, general malaise.

Can I drink coffee or tea during a fast? How about adding cream or coconut oil to it – will that take me out of the fasted state?

Coffee is actually beneficial for fat-burning, especially during a fast. One study [21] found that an infusion of epinephrine – a hormone which coffee increases – during “starvation” enhanced its lipolytic and thermogenic effects. In other words, fat-burning and metabolism up-regulated in response to epinephrine (more so than usual). Epinephrine also lowers appetite, which can be extremely helpful for people trying to stave off hunger during a fast. Tea, and anything non-caloric, is also fine.

Adding a pure fat source won’t “take you out” of the fasted state, and it may take the edge off the hunger, but it will reduce the body fat you burn by a bit.

One should eat protein and carbs 30-60m post workout to build the muscles. Am I wrong?

If your sole intent is to get stronger, build muscle, and pack on weight – all fine, commendable goals – then, yes, you should eat some protein and carbs within an hour of working out. Of course, this is totally compatible with fasting. Just end your fast with a workout, and feast right after.

I play competitive sports 3d/week. Should one make sure to eat on the days one plays sports? Or is it more important to eat the day after?

Personally, I would eat on game days. It might be fun to try out a few fasted games, just to see how you perform, but the likely optimal way to integrate fasting into competition is to save the fasting days for your training days. By doing this, you’ll be “training low, playing high,” [22] which should result in some beneficial adaptations after training and improved performance in the game (when you’re “high,” or fully replete with nutrients and calories).

Should fasting be considered when you try to GAIN weight?

Usually, no. But there are a couple special cases where fasting might help someone gain mass.

I’ve mentioned Leangains [23] a number of times in the past several posts, and I’ll do it again. It’s right there in the name: “lean” and “gains.” Plenty of people have success gaining lean mass on the 16/8 Leangains IF plan. It’s slower gaining, but it minimizes and sometimes even eradicates fat gain. Of course, you also have to be sure to lift heavy weights and overfeed on training days (most find the two are a natural pairing, though).

I’ve also heard from people who used intermittent fasting to increase their appetite to the point where eating enough calories to gain weight was possible. The constant snacking was keeping them perpetually full, whereas a good solid 18-20 hour fast really ramped up their hunger and allowed them to eat an actual meal.

Can I take vitamins or supplements during a fast?

Sure, but absorption might be hampered without a meal to go along with it. Vitamin and mineral absorption is generally better in the presence of food, particularly fat. For instance, vitamin K2 is absorbed seven times greater when taken with a meal than without (PDF [24]). I personally skip the supplements when I fast.

I’m actually posting this in a fasted state. It’s been about 20 hours since my last meal. Should I keep fasting till I hit the 48 hour mark? I’m not really hungry, but I’ve been doing the one meal a day thing for some time. Thoughts?

Sure, give it a shot. I always say that pushing the limits is healthy from time to time. Plus, this will give you a good baseline. If you know you can fast for, say, 36 hours without doing too much damage or incurring too much stress, you’ll know your limits for the future. People have fasted for far longer and lived to tell the tale, and you seem to be reasonably experienced. Good luck.

Should pregnant or breastfeeding mothers do it?

Probably not. Whatever you do, listen to your hunger signaling. Don’t force yourself to adhere to an arbitrary fasting regimen just because it’s shown to confer all sorts of benefits in other, non-pregnant populations. While I wasn’t able to find any studies on breastfeeding and fasting, there are several on maternal fasting:

There have been studies on calorie restriction and lactation, and it looks like mild calorie restriction (coupled with exercise) has little impact on breastfeeding [28]. If you’re going to do this, make sure your milk quality and quantity aren’t negatively affected. Keep the fasts short (12-ish hours) and infrequent, just to be safe. And, of course, consult your doctor prior to doing it.

Should I fast if I’m trying to get pregnant?

Generally, no. Fasting is a stressor, and if you’re already stressed out over something and cortisol [29] is high (say, because you’re trying to get pregnant and finding it difficult), throwing a fast on top of that will likely compound the problem and make it harder to get pregnant. Cortisol is a potent inhibitor of fertility.

However, if you find that fasting improves your health, reduces your weight, enhances your metabolism, fixes your metabolic syndrome, which can all have negative effects on fertility, it will likely have a net benefit. If you intend on fasting, opt for the “WHEN” method rather than a regimented one, and keep your fasts pretty short. Fertility requires “plenty.” An extended fast does not exactly send that message to your body. A 12 hour fast every once in awhile should probably be the limit, and only if it’s improving other subjective and objective markers of health.

On the other hand, men who are trying to impregnate someone may find it helpful to fast [30].

Should kids do it?

Kids shouldn’t be put on a fasting regimen or anything like that, but they might forget to eat now and again, and that’s totally fine. As a kid, I often spent my summer days in a fasted state from early morning through early evening, simply because I was out running around, playing capture the flag, skipping rocks, and generally getting into trouble. It didn’t always occur to me to eat. I think I turned out okay.

Should seniors do it?

Seniors should absolutely try it. Although we’re talking elderly humans here, elderly rats derive a lot of beneficial neurological effects from intermittent fasting [31]. I see no reason why older folks can’t also enjoy the neurological, life-extending, and health-promoting benefits of fasting, too. It might increase healthspan, stave off age-related cognitive decline, and improve quality of life.

Under what circumstances would you recommend that someone not fast?

High stress [29]. Overtraining [32]. Chronic lack of sleep [33]. SAD dieting. And then there’s my previous take on the subject. [34]

I’m thinking about giving IF a try and am wondering if you have any thoughts on how to track its effectiveness. Would you recommend a logbook? What should I be recording and looking for?

I think for many people looking to track the effectiveness of a given fasting protocol, a logbook can be extremely helpful. Think of it like a training log for your workouts. You can track:

  • Objective measures, like weight, body fat percentage, waistline, blood sugar, dress size, hours slept, plus markers of physical performance, like weight lifted, reps completed, distance run/walked/cycled/rowed. These are easy to track, as they come with numerical figures built-in.
  • Subjective measures, like mood, energy levels upon waking, energy levels halfway through the fast, energy levels during workouts, perceived performance during cognitive tasks. These are trickier to track, so you may want to assign numerical figures to them in order to quantify what is essentially a subjective measurement. Something as simple as rating your mood 1-10, with 1 being “very bad” and 10 being “very good,” should suffice.

And if you’re fasting for a specific health effect, say to boost the effectiveness of chemotherapy, you’ll definitely want to track those specific health markers.

Ultimately, what I hope this series has done is inspire you to self-experiment [35] with fasting. I always maintain that fasting is not essential to Primal living, but it certainly seems to mesh well with it. Whatever you do or don’t do, I want to stress something: don’t stress out over this stuff. If you’re going to give it a shot, do so and do so intelligently – by tracking your progress, maybe even doing so formally – but don’t drive yourself crazy obsessing over the minutiae. Whatever you do, good luck!

Here’s the entire series for easy reference:

Why Fast? Part One – Weight Loss [36]

Why Fast? Part Two – Cancer [37]

Why Fast? Part Three – Longevity [38]

Why Fast? Part Four – Brain Health [39]

Why Fast? Part Five – Exercise [40]

Why Fast? Part Six – Choosing a Method [41]

Why Fast? Part Seven – Q&A [42]

Dear Mark: Women and Intermittent Fasting [43]


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[1] Start Here: http://www.marksdailyapple.com/welcome-to-marks-daily-apple/?utm_source=mda_wwsgd&utm_medium=link&utm_campaign=mda_wwsgd_start_here

[2] Primal Blueprint 101: http://www.marksdailyapple.com/primal-blueprint-101/?utm_source=mda_wwsgd&utm_medium=link&utm_campaign=mda_wwsgd_pb_101

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[6] supplements: http://primalblueprint.com/categories/Store/Supplements/?utm_source=mda_wwsgd&utm_medium=link&utm_campaign=mda_wwsgd_supplements

[7] due to the reduction in circulating IGF-1: http://www.ncbi.nlm.nih.gov/pubmed/15999532

[8] intermittent fasting does not appear to have the same effect on IGF-1 levels: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC156352/

[9] lift some heavy stuff: http://www.marksdailyapple.com/strength-training-women/

[10] study: http://www.mendeley.com/research/intermittent-fasting-effect-bone-maturation-remodeling-young-rats/

[11] fat-burning and keto-adapted beast: http://www.marksdailyapple.com/a-metabolic-paradigm-shift-fat-carbs-human-body-metabolism/

[12] glycerol: http://en.wikipedia.org/wiki/Glycerol

[13] triglyceride: http://en.wikipedia.org/wiki/Triglycerides

[14] gluconeogenesis: http://en.wikipedia.org/wiki/Gluconeogenesis

[15] benefits of a long fast: http://www.marksdailyapple.com/fasting-weight-loss/

[16] fasted workout: http://www.marksdailyapple.com/fasting-exercise-workout-recovery/

[17] read something: http://www.marksdailyapple.com/stuff-that-i-read-or-watch-and-you-should-too/

[18] epidemiology: http://www.ncbi.nlm.nih.gov/pubmed?term=skipping%20breakfast%20and%20obesity

[19] bulk of the evidence: http://www.marksdailyapple.com/meal-timing/#axzz1szpRNTwD

[20] bone mineral density reduction: http://www.marksdailyapple.com/calorie-restriction-bone-loss/#axzz1t0RjjCYZ

[21] One study: http://www.ncbi.nlm.nih.gov/pubmed/2405717

[22] “training low, playing high,”: http://www.marksdailyapple.com/jonas-colting/

[23] Leangains: http://www.leangains.com/

[24] PDF: http://www.eisai.jp/medical/products/di/EPI/GLA_SC_EPI.pdf

[25] Intermittent maternal fasting alters fetal breathing patterns.: http://www.ncbi.nlm.nih.gov/pubmed/16147601

[26] Intermittent maternal fasting alters fetal heart beat.: http://www.ncbi.nlm.nih.gov/pubmed/15526011

[27] Maternal “diet restriction” increases gestational diabetes and induction of labor.: http://www.ncbi.nlm.nih.gov/pubmed/16450268

[28] has little impact on breastfeeding: http://jn.nutrition.org/content/128/2/386S.full

[29] cortisol: http://www.marksdailyapple.com/cortisol/

[30] may find it helpful to fast: http://www.ncbi.nlm.nih.gov/pubmed/3090956

[31] elderly rats derive a lot of beneficial neurological effects from intermittent fasting: http://www.ncbi.nlm.nih.gov/pubmed/21861096?dopt=Abstract

[32] Overtraining: http://www.marksdailyapple.com/how-to-deal-with-overtraining/#axzz1szpRNTwD

[33] sleep: http://www.marksdailyapple.com/the-definitive-guide-to-sleep/

[34] my previous take on the subject.: http://www.marksdailyapple.com/who-should-and-shouldnt-try-fasting/

[35] self-experiment: http://www.marksdailyapple.com/why-self-experimentation-matters/#axzz1t0Irubu8

[36] Why Fast? Part One – Weight Loss: http://www.marksdailyapple.com../../fasting-weight-loss/

[37] Why Fast? Part Two – Cancer: http://www.marksdailyapple.com../../fasting-cancer/

[38] Why Fast? Part Three – Longevity: http://www.marksdailyapple.com../../fasting-longevity-lifespan/

[39] Why Fast? Part Four – Brain Health: http://www.marksdailyapple.com../../fasting-brain-function/

[40] Why Fast? Part Five – Exercise: http://www.marksdailyapple.com../../fasting-exercise-workout-recovery/

[41] Why Fast? Part Six – Choosing a Method: http://www.marksdailyapple.com/why-fast-part-six-choosing-a-method/

[42] Why Fast? Part Seven – Q&A: http://www.marksdailyapple.com/fasting-questions-answers/

[43] Dear Mark: Women and Intermittent Fasting: http://www.marksdailyapple.com/women-and-intermittent-fasting/

[44] 7-Day Course on the Primal Blueprint Fundamentals for Lifelong Health: http://www.marksdailyapple.com/subscribe-to-blog/

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