Marks Daily Apple
Serving up health and fitness insights (daily, of course) with a side of irreverence.
15 Mar

Why Fast? Part One – Weight Loss

“When a person has nothing to eat, fasting is the smartest thing he could do.” – Herman Hesse, Siddhartha.

I like that quote. It’s making (non-caloric) lemonade out of lemons, and for all the transcendental insights contained in Hesse’s book, this line strikes me as a really cool, no-nonsense way to make the best out of a bad situation. No doubt about that. But how useful is it, really, to today’s readers? Very few of us ever have “nothing to eat.” On the contrary, food is ever at our beck and call, with very little effort required to obtain it. Actually, that’s not completely true. Processed junk and fast food is readily available, while the good stuff – fresh meat and veggies, actual, you know, food – requires prep work, cooking, time, and the doing of dishes. But the main point stands: we rarely go without.

That doesn’t mean the quote is useless. In fact, with a few slight modifications, it becomes extremely effective weight loss advice. Check out my version:

“When a person has had too much to eat, fasting is the smartest thing he could do.” – Mark Sisson, Mark’s Daily Apple.

If that sounds harsh or even unrealistic, consider the story of the Scotsman. Back in 1965, an obese Scotsman of 27 years and 456 pounds came to the Department of Medicine in Dundee, Scotland, with a problem. He needed to lose weight. A (1/8 of a) ton of it. The doctors suggested maybe not eating for a few days could help. It was just an offhand recommendation, but our Scotsman (known only as “AB”) really took to it. He stayed at the hospital for several days, taking only water and vitamin pills while undergoing observation to ensure nothing went wrong. When his time was up, he continued the fast back at home, returning to the hospital only for regular monitoring. After a week, he was down five pounds and feeling good. His vitals checked out, blood pressure was normal, and though he had lower blood sugar than most men, he didn’t seem particularly impaired by it. The experiment continued… for 382 days.

Yes, AB fasted for 382 days, drinking only water and taking vitamin, potassium, and sodium supplements. All told, he lost 276 pounds, reaching his target weight of 180 pounds and maintaining the bulk of his weight loss. Over the five following years of observation, AB regained just sixteen pounds, putting him in excellent, but underpopulated territory (at least 80% of dieters eventually regain all the lost weight). Other doctors paid attention. Maybe it was the fact that it was the 60s, and all sorts of crazy stuff was going on – rebellion in the air, good music being made, a war in Vietnam, Ken Kesey and his Merry Pranksters blazing across the U.S. in a beat-up school bus, spreading the good weird word, Kevin Arnold and a young Marilyn Manson coming of age in Anytown, USA – but for whatever reason, placing obese patients on extended and short-term fasts became relatively common practice.

But could this work for the average person looking to lose weight without submitting to constant medical observation?

Absolutely. Study after study shows that whatever you want to call the protocol – intermittent fasting, fasting, alternate day fasting, or alternate day caloric restriction – it works very well for weight loss. A few recent ones:

So, yes: it works. But does fasting work solely through caloric restriction, or is it doing something special?

That’s the real question. There’s no question that fasting causes weight loss through caloric restriction. Obviously, when you don’t eat anything, your body turns to its own stored energy reserves, reserves that take up physical space and have mass. Depletion of those energy stores reduces mass and thus weight. Total and absolute caloric restriction. That’s elementary stuff and the studies from the 1960s show that.

To dig a bit deeper, let’s look at how weight loss occurs during a fast. I’ll stick to research involving humans only (sorry, rodent personal trainers).

Secretion of growth hormone, one of the premier fat burning hormones, increases during a fast. In a five-day fasting protocol, men experienced increased GH secretion on day one and day five (the only two days where GH was measured). A later study showed that during two-day fasting sessions, growth hormone secretions increased in both frequency and intensity in men. They experienced more frequent GH bursts and each burst secreted a higher mass of GH. A more recent study found that 24-hour fasts increased GH by 1300% in women and almost 2000% in men.

Fasting decreases fasting insulin levels. The presence of insulin inhibits lipolysis, the release of stored triglycerides (body fat). Without lipolysis actually releasing stored body fat, it’s rather difficult to, well, burn that body fat for energy. During a fast, fasting insulin decreases and lipolysis increases. This insulin-blunting aspect of fasting quite literally allows the fast to be successful, because without the ability to access stored body fat for energy, making it through a period of zero caloric intake will be nigh impossible.

Fasting improves insulin sensitivity. 20-hour fasts were enough to improve insulin sensitivity in men.

Fasting increases the catecholamines, both adrenaline (epinephrine) and noradrenaline (norepinephrine). Both catecholamines increase resting energy expenditure during a fast, and guess where your fasting body finds the energy to expend? From body fat. Catecholamines activate hormone sensitive lipase present in adipose tissue, spurring the release of said fat. This makes intuitive sense, doesn’t it? If you’re hungry in the wild, you need to hunt (or gather, or fish, or somehow procure food) and you need energy to do it. The catecholamines help provide some of that energy while burning fat in the process.

Hmm, notice anything? All those mechanisms dealt with fat burning specifically. While there may be some weirdo out there who’s interested in reducing bone mineral density and muscle mass while maintaining fat tissue, I would wager that what most people mean by “weight loss” is “fat mass loss.” From the stuff I just linked, it looks like fasting burns fat, rather than just weight. But what about Conventional Wisdom which claims that fasting increases muscle wasting – maybe because your body will totally recognize the lethal nature of all that arterycloggingsaturated animal fat and choose to break down muscle instead? Is it true?

Let’s go to the research:

In one study, normal weight subjects ate just once a day without reducing overall caloric intake. Weight didn’t change, which isn’t really surprising, but body composition did change – and for the better. Body fat decreased and lean weight increased (in addition to a bunch of other beneficial changes) without an overall reduction in calories.

recent review of the relevant literature found that while fasting and caloric restriction are “equally as effective in decreasing body weight and fat mass,” fasting is “more effective for the retention of lean mass.”

Conventional Wisdom strikes out again.

In closing…

It appears that fasting “works” in several different ways:

1. It decreases caloric intake. In order to lose weight, you need a caloric deficit. That really isn’t in contention here, folks.

2. It increases fat oxidation while sparing lean mass. Since what we’re trying to do is lose fat (rather than just “weight”), the fact that fasting increases hormones that preferentially burn fat and decreases hormones that inhibit fat burning is extremely desirable.

3. It improves adherence. In most of the studies surveyed, participants found fasting to be an extremely tolerable way to diet, especially when compared to outright caloric restriction. Even AB, the fasting Scotsman, reported very little difficulty throughout his 382 day fast. If fasting is easier for you than trying to laboriously count calories, fasting is going to be the more effective weight – er, fat – loss method.

All in all, fasting is an effective way to lose body fat. It’s not the only way, and it isn’t “required” for Primal weight loss, but many in the community have found it to be very helpful and the literature backs them up. If you’re looking to jumpstart your fat loss, fasting may be just the ticket. To get some ideas, be sure to check out my post on various fasting methods.

In subsequent installments, I’ll highlight some of the other benefits of fasting. There are a ton, and new research is being released all the time, so I expect I’ll have a lot to discuss. Until then, I’d like to hear about your experiences with fasting for fat loss. Has it worked? Has it failed you? Let us know in the comment section!

Thanks for reading, everyone!

Here’s the entire series for easy reference:

Why Fast? Part One – Weight Loss

Why Fast? Part Two – Cancer

Why Fast? Part Three – Longevity

Why Fast? Part Four – Brain Health

Why Fast? Part Five – Exercise

Why Fast? Part Six – Choosing a Method

Why Fast? Part Seven – Q&A

Dear Mark: Women and Intermittent Fasting

You want comments? We got comments:

Imagine you’re George Clooney. Take a moment to admire your grooming and wit. Okay, now imagine someone walks up to you and asks, “What’s your name?” You say, “I’m George Clooney.” Or maybe you say, “I’m the Clooninator!” You don’t say “I’m George of George Clooney Sells Movies Blog” and you certainly don’t say, “I’m Clooney Weight Loss Plan”. So while spam is technically meat, it ain’t anywhere near Primal. Please nickname yourself something your friends would call you.

  1. Fasting works! AND jump starts a ZONE based lifetime diet and exercise program …
    Thanks Mark!

    Warren Carnell wrote on April 25th, 2012
  2. “It decreases caloric intake. In order to lose weight, you need a caloric deficit. That really isn’t in contention here, folks.”

    Zoe Harcombe’s piece “1lb does not equal 3,500 calories” is worth a read.

    Welthorpe wrote on April 25th, 2012
  3. All I know is that when I fast from 6pm to about noon the following day, and eat two very small meals consisting of 4 oz of organic protein and a handful of vegetables for lunch and dinner and eat a fruit as a snack 2x a day, the fat melted off of my belly, love handles, arms, thighs etc.. I lost no lean muscle. I was getting sculpted, and I’m 48. I have not tried a true fast where there’s no food at all for a period of days . . . i get too weak to work out.

    Laura wrote on April 25th, 2012
  4. you need a link to part 2 right at the end of this post, Mark. :-)

    Mtn Jim Fisher wrote on April 25th, 2012
  5. Im muslim n we fast thirty days every year. We eat before sunrise n fast till sunset, then eat again. Islam tells us to eat 1/3 for food, 1/3 rd for water, 1/3 rd for air. We also fast voluntary fasts throughout the year, i wont go into that here.

    It keeps your body really agile and not weighed down.

    Naureen wrote on April 25th, 2012
  6. I fasted for 10 days on what is called
    the Master Cleanse. You can find this particular fast on the Internet or the book is on Amazon. It basically consists of fresh lemon juice, maple syrup and a pinch of cayenne in 8 oz of water (to be drunk throughout the day – as much as you want). Honestly….I was NEVER hungry and completed the 10 days. I lost 16 lbs. of FAT and never gained it back. I have gone on to lose another 11 lbs on the Paleo plan. I fast for 16 hrs and eat within the 8 hr framework and feel great! Thanks Mark for all your insights and the studies to back what you say. Fasting lets your body clean house and breaks our obsession with food. No…we’re not going to die if we’re without food for a few days.

    Jeanette wrote on April 25th, 2012
  7. I want to try fasting, but I get a headache and light headed. Any suggestions.

    gayle wrote on April 25th, 2012
    • I would wager that you just might be magnesium deficient. Find a good absorbable magnesium, I use ionic magnesium by Eidon. Headaches can be caused by a magnesium defifincy. I had the annoying buggers and learned about magnesium deficincies when I began fasting. I began supplementing and not only did I have a marked reduction in headaches I use magnesium to stop an onset headache instead of tylenol.

      Mary Titus wrote on April 26th, 2012
  8. It’s good to see something like this that gives an alternative option to the ‘must have good breakfast’ school of thought. I always used to obey my actual hunger signals and very rarely had breakfast, sometimes going right through to early evening and never missing food…then I started following the ‘must have breakfast ‘ rule and started eating first thing even though I wasn’t hungry…funny thing is, I’m always starving by 11 am if I do this, whereas I don’t even feel hungry at this time if I don’t eat first thing.
    I would much rather be in tune with my body and give it what it appears to be asking me for, so I’m 100% behind the IF school of thought. It makes me feel more in control of my eating, as well.

    Penny wrote on April 26th, 2012
  9. I am reading in the book, Optimum Nutrition, that “Carbohydrates, not fat, are the premier fuel for performance. Also, carbohydrates can be stored as glycogen, while fat cannot…this is why endurance athletes eat rice or pasta…” Are carbohydrates necessary for sustained energy? Can the body convert protein and fats, through glucogenesis, into glycogen that can be stored in the muscle? Is this a huge misconception?

    Tielle wrote on April 26th, 2012
  10. Can a person with adrenal fatigue, low thyroid, and Hoshimotos fast? Specifically with veggie juices, supplements and raw adrenal and thyroid supplementation?

    Tiana Phillips wrote on April 26th, 2012
  11. I think that the idea of fasting is great and makes complete sense for an optimal or close to optimal human- that is, one not too metabolically deranged.

    Just personally speaking, I have tried fasting and while I feel GREAT not eating breakfast because I am generally not hungry until noon I then find that it always causes compulsive eating at night around 5pm where I am insatiable and eat past fullness. My understanding is that if you have any sort of adrenal issues then basically you are raising cortisol more by fasting which, for people like me who have too low morning cortisol, it stresses the adrenals out even more causing more long term damage. I am also still healing from an eating disorder (was never underweight however) so I believe my metabolism, at least for now, needs a larger window- I usually go 12/12 with three meals and no snacking.

    That said, I no longer have hypoglycemia since switching to vlc so if I do need to skip a meal due to external constraints I have no problem. I am looking forward to the day where I can really take advantage of IF.

    JASmith wrote on April 27th, 2012
  12. Just to get this straight – the Scot’s Man went 382 days with out eating anything???!!!
    Only taking vitamins and minerals?
    Did I read that right. Or was he IF’ing?

    John wrote on April 29th, 2012
  13. LMAO! Its good to know that some MD sitting in some fancy lab has FINALLY come around on fasting with the tests and stats!
    Fasting has been used for thousands of years by billions of people in traditional cultures around the world. So its the time tested built in system recovery tool-fast,smart and easy as Windows.

    sangos wrote on April 30th, 2012
  14. Just started IF – I find it very convenient and easy though – I am experiencing quite the mood swings – thoughts?

    Sara wrote on May 1st, 2012
  15. I am 60 hours in to my fast, didn’t intend for it to be this long but it is…and I am wondering when I should break it and with what? Eggs, avocado and bacon sounds good, pork tenderloin is in the running, chicken coconut curry with cauliflower could be the one….any thoughts on what is better? Avocado/eggs/bacon too heavy?

    Beth wrote on May 5th, 2012
  16. hey, does anybody know some quck and straightforward strategies of getting a six pack

    Charles m wrote on May 26th, 2012
  17. I have searched everywhere for a way to lose those extra pounds that seem to have appeared over the course of the last few years. I have tried every diet out there and nothing seemed to work. Then I discovered African Mango Supplements and Proactol and I finally started to see the weight drop. I highly recommend both these products. You can find them at

    Diane G wrote on May 31st, 2012
  18. I have grown to realise that eating natural food like steak, chicken, greens, and carbs such as sweet potato, because they are all natural. What ever you do, stay away from processed foods such as white flour, white bread, white sugar, processed meats or fast takeaway foods that you wouldn’t generally eat with a knife and fork like fried foods.
    Dont feel guilty about eating healthy, because you can still lose weight providing you eat in moderation and is a bonus if you are doing exercise on a regular basis with out over doing it. What ever you do to try and lose weight,Your pancrious makes insulin and tells your body to convert access foods such as white bread into fat, so stay away from those foods and you will be on the right track to losing weight and having a healthier body.

    William Bridges wrote on June 2nd, 2012
  19. Exactly what I need.. Great information tips…

    Joseph Wilson wrote on June 4th, 2012
  20. Hello! I recently starting IF, and I am very excited about it. I’m a 42 year old woman with about 50 lbs to lose. Over the past 8-9 yrs the weight has crept up… 4 or 5 lbs gained per year for several years sure do add up. Once upon a time, I was trim (not skinny), muscular and in great shape. Over the past few years, I tried losing weight several times but would fail miserably. I hate “mini” meals (what am I, a 5 year old?). I hate counting calories, weighing food (how depressing). I hate snacking on tasteless food all day. These are the reasons my weight loss attempts never worked. I can’t do these ridiculous things every day long term.

    So now I do IF and it’s awesome! I lost 10 lbs in about 4 weeks. On stupid diets I’ve tried, I’d be lucky to lose 3-4 lbs in an entire month which was discouraging. IF is encouraging! Finally something that works. I’ve also been walking, a lot which helps even more. IF is a life style that is good for me especially since I’m not much of a breakfast or dinner person.

    I do three 24-hr fasts per week on M-W-F. My fasting goes from around 6 p.m. (previous evening) to 6 p.m. on my fasting day(s). Sometimes I change the days around or do 2 fasts if I’m going away for a long weekend. I break the fast with a pretty big dinner (ie 800-1200 calories) with awesome food, often fish (big portion) or chicken, lots of veggies or a big salad. Dessert 2 hrs later, usually berries with cool whip light. On my Tuesday-Thursdays, I eat whenever I’m hungry (usually 2 snacks and a big healthy high protien low carb dinner). My favorite snack has become a whole avacado with a little lime and sea salt. On Saturdays and Sundays… party time! I have my cold light beers, burgers, sausages, pancakes, chips and dips etc. I create massive caloric deficit during the week that I can do this and still easily drop about 2 lbs per week. I still do not “pig out”… I stop eating when I’m full. I balance some healthy stuff in with my indulgence food. So I’ll likely have a salad with my burger or grilled veggies instead of potato salad. If I want potato salad and macaroni salad, I’ll go for grilled chicken or fish instead og a hotdog or burger. But basically I enjoy indulging a bit. On Monday… back to my fast and cleaner eating for the work week. Works like a charm!

    I walk 4-5 times per week, moderate pace for 3 miles (1 hr), burning 300-400 calories. I also have an active life style. I walk on fasting days too, near the end of my fast to maximize the fat burning. I have a lot of energy, none lost whatsoever. I start feeling REAL hunger after about 20 hrs and look forward to a healthy big dinner. Now I really appreciate food. Soon I will be doing cardio kick boxing 2 days per week. So I will walk two days and kick box 2 days. My exercise along with my fasting days create massive calorie deficit so the weight is coming off rather quickly, yay!

    And this life style still allows me to enjoy “naughty” foods and adult beverages. Imagine going all Summer with out some of these enjoyments? That would be complete misery!

    For those of you thinking about it, do it!!! You won’t regret it. I should also mention that on my fasting days I drink water all day, and a few cups of black coffee in the morning. On non-fasting days, I have light cream and sugar or splenda in my coffee which I prefer. I’m not thrilled about black coffee but I’ve gotten use to it and it’s not so bad 3 times per week. But on 24- hr fasts, I am strict about being certain I have absolutely no calories. If you like my routine, and you create something similar… you will shed some serious body fat.

    I am so looking foward to this journey :-)

    Melissa wrote on June 13th, 2012
    • Hi Melissa – glad you are finding IF to be an effective way of staying healthy.

      3 x 24 hour fasts per week sounds quite tough to me and I’ve never gone to that level myself – perhaps consider shortening one of those fasts if you do start feeling any weakness etc…

      Other than that, I like the ‘clean’ feeling I get following a fasted period and I also use cardio fasting to maximise the effect –

      Luke M-Davies wrote on June 14th, 2012
  21. Ooops, in my last post I said IF is pretty easy for me especially since I’m not a big breakfast or dinner person. But I meant to say “breakfast or lunch”. I am a big dinner person 😉 so every day I have dinner. That is one meal that is NEVER skipped. Good luck to everyone!

    Melissa wrote on June 13th, 2012
  22. I do my version of intermittent fasting. I eat no solid food before 3:00. I break my fast with a hearty primal meal that fills me up comfortably. Fasting improves my digestion and helps with constipation. I was not constipated before doing intermittent fasting but my regularity improved surprisingly. I fast for twenty hours and allow for a 4 hour window. Since I have grown comfortably with eating once daily, I may as well say that I eat one full meal a day. As for weightloss, I lost about 25 lbs. but regained it. I became peri-menopausal since I began intermittent fasting. I amped up my fsating and I am down 8 lbs. I like fasting. Food tastes better without having to overeat.I believe that we were built to eat fewer meals, that’s why ketosis exists. I also believe that eating frequently ( 3 meals with in-between snacks ) stresses and weakens the organs.I also believe that obesity and diabetes wouldn;t be at epidemic proportions if people would eat less often…

    mary titus wrote on June 14th, 2012

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