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. IF works great for me and I don’t feel weary or worn down. What I do figure out (usually too late) is that I didn’t drink enough water and so I feel especially thirsty if I’ve gone an extended time without eating. I have a few days per week where I have a ridiculously long commute and am mostly sedentary (in meetings all day at the office) so IF is great on those days when I know my calorie burn is minimal.

    Brenda wrote on March 18th, 2012
  2. Has anyone experimented with 36 hour fasts? I’ve done 3 and found I have no problem with energy levels. But getting to sleep after 24 hours of fasting as proven to be difficult (for me at least).

    On benefit is that 24 fasts become the ‘easy’ option.

    Jack wrote on March 19th, 2012
    • My understanding from everything I’ve read is that a 16-18 hr. fast is optimal. The closer your body gets to 20 hrs. it switches from using stored body fat for fuel to breaking down protein for fuel, which is not ideal.

      Emma wrote on March 20th, 2012
      • I do know people who have gone several days without solid food. I also know that it takes somewhere around 3 days to digest a 6 oz piece of steak. That being the case, the body cannot begin to consume itself until dietary protein is digested and absorbed. I also know that the body needs just enough glucose that is equivalent to a teaspoon of sugar a day in order to survive. So the thought of your body consuming so much protein that you loose muscle mass is not anything to really worry about because you won’t go that long without food. But this should exemplify the importance and need for protein in the diet especially if one uses fasting as part of their diet.

        Mary Titus wrote on March 20th, 2012
        • Muscle loss issue aside, for the body to burn primarily stored body fat, the optimal time frame for that is the 16-18 hour fast, correct? I’m looking specifically at stored body fat loss.

          Emma wrote on March 22nd, 2012
  3. Wonderful and informative article! How long does an IF have to be for it to count as one? (is 20 hours the minimum, etc)

    Soji wrote on March 19th, 2012
    • Try 16 hours…

      Have your last meal in the evening by 7 or 8pm and eat your first meal the next day at noon.

      While you fast throughout the morning till noon drink water, herb tea etc.

      Karl Roberts wrote on March 19th, 2012
  4. I took a day trip twice for work to Indiana and New Jersey (flew to both states on different days though). Got up reeeeaaaalllll early and got home reeeaaaalllll late (around midnight). I didn’t eat all day (except when I got home – I ate ribs and eggs, ha!). I did not crash, still had energy, no dizziness, or anything really – not even heartburn! I had only been on PB for THREE DAYS! I didn’t realize how well fasting could help me until I woke the next day FULL of energy and excitement. It forced my body to burn. When we go camping this year I’m going to try it again – I think it will be epic if I do! Great post Mark!

    Judolizard wrote on March 19th, 2012
  5. This is so crazy about the year-long fast. It’s hard to wrap my brain around it.

    I used to IF regularly once a week, then I switched to The Warrior Diet eating absolutely nothing during the day and only allowing myself a 2-hr eating window at night.
    Nothing ever worked for me as far as weight-loss, and low and behold, the Warrior Diet didn’t do anything either.

    I still think IF is very beneficial outside of weight-loss and so I’m still practicing it once a week or so, but unfortunately, no one bill fits all.

    chocolatechip69 wrote on March 19th, 2012
  6. I’m experimenting a lot with IF. I’ve done cleanses and diets before but all have been shortlived and have not given me any long term positives, or not that I’ve picked up on.

    However. I’ve been experimenting with IF and have found it really helps. In general I like having breakfast and dinner. I don’t tend to have lunch or snack (unless it’s a high activity day). That means I get a “mini fast” between breakfast and dinner and then have a good period of time about 15 hours (I eat a very early dinner).

    I wrote a post about my experimenting with fasting on my blog earlier today. Have linked back to your,”The Myriad Benefits of Intermittent Fasting,” hope this is ok?

    Emily Jane wrote on March 19th, 2012
  7. Great to see more articles about fasting. I have been trying every different fasting protocol the past few months experimenting. I used LG Fasting to get from 30% bodyfat down to single digits in a few months. I love to be able to eat massive post workout meals of 1,500 calories. I was never a big breakfast eater and now all my friends want me to write them fasting protocols for the week after seeing the food I eat!! Amazing stuff!!

    Frank Sabia wrote on March 19th, 2012
  8. yayy. mark has quoted from my favourite book – siddhartha..
    awesome post!

    Aloka wrote on March 21st, 2012
  9. Considering this study how far fetched is this idea:

    Energy used by the body are in this order:
    Carbs, then fat, and then protein gets converted to energy once there is not enough fat. (Assuming I am correct?)

    So if a Guy/Girl wanting to build muscle and loose fat quickly, they want to fast, but also hit it hard at the gym, so they can fast by avoiding eating Carbs and Fat, but still eat protein in pure form (Lean meat, Lean fish (tuna) or only protein shakes with water).

    Am I right in saying that doing this will result in his/her body using body fat to fuel him while he fasts, but the protein will help build muscle mass and repair muscle after the workouts?

    Goran wrote on March 21st, 2012
  10. I have not tried IF and while I respect Sisson, of course, I feel like a speeding of the metabolism by eating more frequent, smaller meals throughout the day is a safer approach to weight loss. First thing that bothers me is the danger of producing tendencies towards anorexia. Many, if not most, teenage girls would read this article and the only thing they’d get from it is: “DO NOT EAT”

    Javier T wrote on March 22nd, 2012
    • We can’t stop people for using good information in a bad way.

      From what you’ve said, it suggests that you have not read into IF enough otherwise you would not have said what you said.

      I would suggest that you read through Mark’s current articles on fasting, and the comments as well. Sometimes you learn just as much from reading through the comments. Hope that helps. :)

      Emma wrote on March 22nd, 2012
  11. Javier,

    1 – the idea of eating more frequent meals to “speed metabolism” is a myth. the reason it feels “safe” to you is that you’ve heard it constantly over the past 15 years. this website is about opening your mind to the facts and reality… and that concept is simply not true.

    2 – Anorexia is a PSYCHOLOGICAL condition that a teenage girl can not acquire from a website. it is a mental illness where people look in the mirror and see a distorted image (one much “fatter” than they actually are). trying Intermittent Fasting will not cause anorexia if you are of sound mind beforehand. It just won’t.

    3 – After a year of low-carb and not being able to drop below 260 despite trying everything in the book, reading this one entry on IF has changed my life. Since this article was posted, I have implemented the IF fast every day. I have never felt better and I have lost 10 lbs in a week and a half. I simply only eat one meal a day (dinner). And trust me, if you saw what i ate and how much, you would not consider me anorexic! haha… last night had a HUGE bowl of chili. night before? 4 pieces of chicken with fried cauliflower.

    i have never felt better, mentally or physically, and the weight is coming off at a seriously rapid clip. Mind you, I am eating roughly the same calories as before… around 1200. But getting those calories in a 2-hour window and not consuming anything other than coffee the rest of the time has completely changed the game for me.

    i am living proof that this works. past 6 months at 1200 calories (hi fat, med prot, low carb) spread throughout the day resulted in NO weight loss. same 1200 calories at once, MASSIVE weight loss.

    i will come back here and give another update in a month or so, but i am shocked at how much impact this simple trick has had. i suggest everyone battling a weight loss plateau to try it.

    adam wrote on March 22nd, 2012
  12. I am coming up on Hour 18 of my weekly 24 hour fast. I usually break the fast with some coconut milk an hour before my first meal. My first meal is about a half pound of protein, and a salad with avocado and E.V.O.O. It seems to work pretty well for me.

    Justin wrote on March 22nd, 2012
  13. is there a limit of coffee one can take on this diet ? as i drink 4-6 cups while fasted as i feel it kills my hunger , i can’t take green tea on an epty stomach as i don’t know why but it makes my dizzy , does this happen to anyone else ?

    adrian wrote on March 26th, 2012
  14. I’m curious…is there an added benefit to IF during the day than over night. Seems silly but I would think it may be “cheating” if I account for the hours slept as part of, say my 16 hours, then going till lunch/dinner the next day for the initiation of my next 8 hours of feeding. I’m thinking maybe it’s a hormonal thing that would benefit me more to be “awake” during the IF to benefit most from it but I really don’t know and I really haven’t seen anything discussing that on here. Thanks in advance!

    ARP wrote on March 27th, 2012
    • Trust your body’s functions and cycles, which includes sleep. You do a lot of amazing fat burning and cell healing in sleep. You should search for and read some of the posts about sleeping on this site to really understand the importance that sleep has in healing and recovery of your body. Sleeping hours should most certainly be counted! (They call the first meal after waking break-fast for a reason) Your body is still going to get all the wonderful fasting benefits Mark laid out for us while sleeping. That includes fat burning and the cell recovering. Most of the IF’ers I know eat later in the day/evening with one big meal after their workout and another meal a couple hours before bed, with great results. This isn’t a rule thought, it’s just how most people I know do it. But at any rate it’s definitely not “waking” hours that you are counting, it’s all hours. In fact I’ll bet they will find out that it’s during sleep that most of the magic is done but I’m just speculating on this. Also there is the logistics of your question to consider. Let’s pretend you are going to count sleep as fasting hours…Therefore say you finish eating at 8pm and go to sleep at 10pm that’s 2 hours of fasting. Then let’s say you sleep until 6am. Well since you didn’t count the 8 hours of sleep as fasting, you need to go now until 8pm to have 16 “waking fasting hours”. That would be 8pm to 8pm – that’s called a 24 hour fast. If you want to do that OK but the dudes at leangains suggests that the hormonal benefits are best at the 16 hours range for day to day maintenance. Perhaps they are not right about this and 24 hour fasts are better for you, but even in a 24 hour fast you would certainly count the sleep hours within that time. Again it’s a possibility that 24 hour fast is better than 16 hour fast for you, but the guys at leangains seem to think 16 is best and they seem quite geeky about digging into the science-and they are pretty freaking ripped. Plus on a 24 fast you are eating once a day. Most people I know aren’t comfortable after shoveling down one 2000-2500 (or more) calories in one meal a day. So in closing, instead of counting sheep while you sleep, count hours that you are fasting.

      David Cole wrote on March 27th, 2012
    • Yes your hours sleeping count towards the fast. If they didn’t, you’d never be able to eat!

      I’ve been doing this for about 3 weeks now and feel great. I eat from noon until 7:30 pm. I eat around 2000 Calories and keep the carbs under 75 grams. My performance at the gym is also at an all time high.

      Matt wrote on March 27th, 2012
      • Thanks Matt (and David with your response up above). Yes, you’re both right…it definitely makes sense to count sleep since it otherwise would essentially be a 24 hour fast. I don’t think I’m ready for a 24 hour routine but I will definitely be trying the 16-8 routine a couple days a week.

        Oddly enough when I’m 100% primal I don’t even feel the need to have breakfast in the morning and am more than capable of not eating till noon the next day. Which I know is something Mark suggests is common and normal; you eat when you’re hungry not because conventional wisdom says to do so. I’ll try that out more often. Thanks again you two.

        ARP wrote on March 27th, 2012
  15. Hi! Has anyone tried Bulletproof coffee intermittent fasting? upgraded coffee is supposed to be of grea quality, and having the coffee with kerrygold butter and MCT oil in the morning s supposed to accelerate metabolism and the formation of ketones. Is there truth to this? Also, I would have thought consuming that much fat in the morning would break the fast and give my body energy to burn instead of using my own stored fat?
    I’ve been practicing IF for a few weeks now, I do just fine. I’m just wondering if the bulletproof method’s claims are true and will accelerate fat loss.
    Any thought?


    Jennifer Ugarte wrote on April 4th, 2012
  16. Awesome series of Posts Mark. Really digging this idea.

    Dan Pope wrote on April 5th, 2012
  17. In my numerous experiences with fasting, the first 8-12 hours are hardest. The hunger mechanism kicks in big time and tempts you to eat, but after that, it’s very easy. No hunger at all. Coffee definitely helps.

    Jason wrote on April 5th, 2012
  18. hello everybody!
    when I do IF ( mostly 16/8 style)sometimes I feel strong tingle in my skin specially in my face area and my breath feels like “hot” or something.. have anybody of you have similar experience? any idea where these symptoms may come?

    Sami wrote on April 6th, 2012
  19. I subscribe to MDA and Paleo Plan’s posts, but am I missing how long the IF goes on, or how often you do it? Is this the way everyone’s eating all the time or are you doing it weekly, monthly, as needed? My interest is mostly in fat loss, but also performance and energy. I CrossFit five days per week, and usually run on the other two days. I try hard to stick to a paleo/primal diet.

    Wendy wrote on April 17th, 2012

Leave a Reply

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

© 2016 Mark's Daily Apple

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