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:
- In non-obese patients, alternate day fasting increased fat oxidation and weight loss.
- In obese patients, alternate day fasting was an effective way to lose weight; dietary adherence remained high throughout.
- In young overweight women, alternate day fasting was just as effective as caloric restriction at causing weight loss, and adherence to the former was easier than to the latter.
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.
A 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 Three – Longevity
Why Fast? Part Four – Brain Health
Why Fast? Part Five – Exercise
Why Fast? Part Six – Choosing a Method
Dear Mark: Women and Intermittent Fasting
Grab a copy of Primal Blueprint Quick & Easy Meals for over 100 Primal Recipes You Can Prepare in 30 Minutes or Less
Posted By: Mark Sisson
Fasting is definitely a superior way to lose fat.
It’s also VERY easy to incorporate into an active lifestyle when done ‘right’.
Nice post Mark.
Very inspiring stuff. I’m keen to try to help shift my baby weight. Commonsense (or maybe CW) makes me think I should wait to try IF till I finish breastfeeding?? My baby is only 10 weeks old and I’ll definately breastfeed him for at least 13months as I did my other 2 sons. Does anyone have experience with IF and milk supply? An aside: My supply is currently excellent due to primal fare! (With previous 2 babies I had very low supply on CW diet…was hard work!)
CW say you could breastfeed until the baby is 6 months old and then quit. I’ll say… listen to your body! Watch bitches!!!
Yes, I said bitches!! Female dogs naturally get to a point when they start biting their sons when they trying to breastfeed, because… well, I think they’re done with it. Do you feel you’re done with it? Probably not, since your baby is 10 months old! But the moment after the 6 months period (just to be sure) that you feel like “I’m done with this!” is probably the best moment to start to feed the baby the wonderful world of paleo foods. Just listen to your body (and hormones),you’ll know when the time is right!
Breastfeeding vs. food isn’t an all-or-nothing practice! The primal way to introduce foods would begin somewhere around the 6-9 month window, but food isn’t going to be a major source of nutrition until that baby is more than a year old. Human milk is more calorically dense and loaded with bioavailable nutrients than anything else.
More moms see their fat stores mobilized after several months of breastfeeding than right away — give your body time to do what it knows how to do!
Thanks for comments. I definately intend to introduce Primal fare around 6 months. Baby is only 10 weeks at the moment , not 10 months. Lets hope the baby fat will melt away by then
Never tried this but very intrigued by the science behind it. Obviously not the best option for me at the moment since I’m not looking to lose weight. But still a very interesting read!
My partner and I are debating the current health implications of IF when the soils that grow what we need to eat is deplete of nutrients. Is IF then, more harmful and would eating three squares daily and consistently but less volume, better for health?
Please comment…thanks
I’m intrigued by the idea of fasting, but in my experience (some very unhealthy attempts to lose weight in high school) sometimes after not eating enough, I would actually faint. I have low blood pressure so I’m prone to fainting often (about 5-6 times a year!) and usually I like to keep almonds in my bag and never really skip meals. So would IF be possible for someone like me?
I’ve been doing PB for just the past 2 weeks now. Lost 6 lbs and can feel my muscles start to build up. I’ve actually done IF (accidentally) twice now. Fasted for 19 hours one day, 16 hours another before having a really good primal meal! I had no hunger pangs, just kept drinking water, coffee, black tea. Amazing. I’m hypoglycemic also, so I wasn’t sure how well I’d do, but I feel great!
I love your timing, Mark! Just embarking on a 3 day fast/retreat starting NOW.
I got very lean last year doing intermittent fasting (18/6) and it is SO much easier than counting calories.
I run 8/16 right now, but break it with a pretty small lunch; 3 cups chopped vegetables with some olive oil/balsamic (1:1).
Have been meaning to try extending from 16 to 24. Only have to postpone the vegetables.
Hunger really hasn’t been an issue. Interested to see how I respond to fasted resistance training.
weight training while fasting enhances the production of growth hormone. Don’t ruin that with carbohydrates and don’t eat for an hour following weight training. You will produce healthier muscles and you will be able to maintain that muscle easily.
Great timing on this article for me. I’m having the hardest time getting rid of that last bit of belly fat. I think I’m going to use this as inspiration to do a fast. Thanks Mark!
I started playing around with Fasting aka The Warrior Diet at the same time I dove head first into Paleo- both made tough. I never worry about a missed meal and eat pretty damn good when I do
A healthy fast hurts no one. You can’t fast properly without a good healthy meal. A person with anorexia has no business trying to fast because they will do it incorrectly. A person who has a healthy psyche and understands how the body works can indeed fast and improve their health. Back in the day people did not have a corner grocery store, Mickie Dees, freezer or microwave. They ate in a manner that provided the nourishment needed to get them through several “foodless” days. They were not interested in making a fashion statement. They were interested in survival. Survival is a healthy stated to be in. It makes you understand what you need to eat, YET, in the days of “civilization” we can enjoy this ideal, survival. We can enjoy it more because we don’t have to hunt or gather. Everything is right at our fingertips and all we need is common sense. If you lack common sense then survival is out of reach.
I was a little nervous about starting an Intermittent Fast because I thought the hunger would really be a distraction and unbearably uncomfortable. But from what I read, I thought it deserved an honest try. I jumped in to see if I could go a few days. It’s been 2 weeks now and I am really enjoying it. IF is so black and white, so easily defined which is perfect for the way I am. It’s not a lot of rules in between to sort out. I fast 19 hours a day from 8:00 PM til 3:00 PM the next day. During my eating phase I have 2 meals. During the fast, I am more focused and calm, not obsessing over lunch or snacks like I used to. I don’t have brain fog and fatigue during the day. I used to want a 20 minute nap in the afternoon, but not anymore. I am very excited to see where IF takes me as I have about 50 pounds to lose.
I’m confused about the benefits of fasting vs. the myth of “eat less, move more.” Low-carb advocates say that our feedback systems will use various mechanisms to conserve energy when we eat less, e.g., increase our appetite, slow down metabolism. Then Mark presents evidence to the contrary. How can both arguments be right?
“Low-carb advocates say that our feedback systems will use various mechanisms to conserve energy when we eat less”… I’m talking out of my ass here, but I think that would happen ONLY if you don’t have any energy storaged for the fasted times… Like if you open your wallet and see you got like a 100 dollars of fat (in 1 dollar’s bills), would you go into slowing down your money expendage because you got no 10′s???
The whole idea of “Oh OK, I got lots of fat to burn, so now I’m fasting and I’m going to lose muscle instead” sounds so very wrong. Fat is there to support you when calories are low.
Okay, lets say everyone was a hanter-gatherer. You have no concept of medical research or nuthin’ but you do know that you can stand up under bad weather, famine, drought etc, if you kept your protein intake as high as possible. By keeping your fat intake high, you will also keep ketosis high. Ketosis exists to provide energy and maintainence to our cells during famine. Hydration is also maintained even on a reduced intake of fluids because, if there’s famine then no doubt, water will be very scarce. This is why we have no appetite or even feel less thirsty when in ketosis.Fat will be burned because of ketosis…It will be used as energy and whatever else the body needs for it function optimally.
I was never much of a dieter, but I was quite overweight. I decided enough was enough so started fasting 16-hours a day, with 8 hour eating windows. I also greatly up’d my Tea drinking and started eating a lot of the healthy super meat, Kangaroo Meat.
Fast forward 6 months, I’m down almost 50 pounds and have shown no signs of regaining weight.
Fasting is the dieting of the future.
For all of you who IF, do you still eat the same amount of calories in a day (assuming it’s less than a 24 hour fast)? Do you try to cram a ton of cals into your eating window, or just have normal sized meals?
I try to cram a ton of protein and fats in the eating window(three meals). I listen to my body. I stop if it doesn’t feel right. Eggs are harder to metabolize for me.
I do not restrict my caloric intake but I do not count calories…I make every meal, which is usually once a day, a meal of champions. Today I had leftover pork roast, collard greens, pumpkin walnut casserole and a sliced avocado.I used butter and coconut oil. I tell ya, it was delicious.I had one serving of everything. I did not overeat. But I did clear my plate so that I could make it through another fast…That’s exactly the way Grok would have done it.
Recipe for pumpkin walnut casserole, please! Sounds yummy.
O.K. The last time I seriously fasted was before Vatican II reported out. I’m convinced based on your writing that it can help me. I’ve been trying to stay Paleo/Primal but cheat a good deal. I’m going to try it because:
1. I think it will make me eat really great quality Paleo food on the non-fasting days.
2. It will save me time in the kitchen.
3. It will save me money.
4. I’m not overly active now, so it’s not like I have to cut back on my activity level.
5. It will help me lose the “last ten”.
I’ll be in touch!
i like to think i’m a bit of an old hand at fasting since i’ve been doing it for a month every year since i was a kid
it’s approximately a 12 hour window from dawn to dusk, pretty manageable once you get the hang of it. you do cut a lot of body fat when u’re fasting so it’s a good option for those who have hit a plateau and need to get just that little bit more off.
I was fasting once, for a week, but not in fat loss purpose. I was trying to cleanse myself.
). When I’m fasting the next time, I’ll make sure not to repeat the same mistake again. 
The experience was good, I enjoyed sauna once and really felt benefits from it. I was ‘eating’ vegetable soups 3x a day and was doing enema (if that’s how you use the word in a sentence;) in the morning. I can tell you thet this was my favourite part of fasting – emptying my colon. It sounds weird, maybe, but it’s true.
I am thinking on doing it again, the same way I did it before, I just have to gain some courage. I definately would say that it contributes to fat loss, if you go back to eating solid foods gradually (not like I did, on a picnic
The study on obese patients linked here actually had them consuming 25% of calories on fast days, so it wasn’t a simple eat-don’t eat. They would have been counting calories presumably.
Is anyone able to reassure me that I won’t kill my thyroid by doing this? When I had an eating disorder as a teen (yes, I know, not the same as just fasting…), I managed to induce hypothyroidism among other things. I’d like to know what the difference between the two situations would be in terms of hurting my poor thyroid…
May be you can help me on my question below?
@
Audrey
Healthy frequent short-term fasting includes & requires getting all your nutritional needs met when you do eat – macro- & micro-nutrients; it takes some knowledge and some planning to do it right. Once you know how to get your needs met when you do eat, it becomes much more flexible, if desired.
IFing will rip you up like Rambo…or Martin Berkhan.
I love intermittent fasting. However this is a very sensitive issue for people with (former) eating disorders.
I have a friend that used to be bulimic-anorectic. Now that she is overweight it is the general idea among friends, family and physicians just to let her eat anything and as much as she wants. This is way better than from the time when she was slowly dying because of not eating.
Is there anyone here with an idea on how I could take to her about healthier food and IF as ways of staying healthy without causing a psychic breakdown.
Balance is so hard for some people.
It’s really difficult because people have different levels of what will trigger them. I wouldn’t approach the subject of IF straight away, but start with healthy foods… and not for the purpose of losing weight, but for general health…
Everyone is different though, and had their own issues that lead to the eating disorder so it’s a tricky one.
Terriffic post. I think even informed Paleo people get confused sometimes about this issue. Firstly, there is so much paranoia and fear that dropping calories will reduce muscle – clearly that isn’t too much of a problem at all. Secondly, I think a common misunderstanding ermeges in low carb cricles re calories vs carbs, and there is sometimes an idea you can eat as much as you want if you lay off the carbs and still lose fat – not true. Gary Taubes gets misquoted on this level, and a UK writer Barry Groves to an extent also. To lose weight you will, as Mark points out, need a calorie deficit – but Mark does a brilliant job here of pulling it all together with supporting references and hormonal explanations that account for enhanced mental well-being and muscle sparing under conditions of calorie deficit. As always, much appreciated, thank you Mark.
I am a first year medical student and we just finished going over endocrine and gastrointestinal physiology, and for the most part, I have no argument with this article. It’s funny though, we learn all these mechanisms for dealing with different caloric sources and how the body reacts to fasting, and I feel like the students dont hear it. I have many vegetarian classmates, which is not a great lifestyle in America as it compromises mostly starches and carbs. There is an inherent disdain for fat, and even though it’s irrational and not founded in science, we don’t learn how to teach proper eating habits to patients. Fasting is a regular part of my diet, along with very low carbs and high fat intake from many sources, and I plan to teach it as an option for my patients. The body is not built to handle high carb loads. It is however built to intermittently fast. Primal eating habits have a home in modern medicine.
I’ve started eating Paleo this January, and now I’m at a point where I can fast ~16+ hours before I eat my next meal. Which means I eat dinner around 5PM and eat my next meal lunch next day.
I do however have to take medication in the morning, with Vitamin D3 and Cod Liver Oil. Does this influence the fasting negatively?
Oh, and coffee supports fasting, which I don’t drink, what about Green Tea, and Oolong tea, which I do drinnk ?
the comment that brain actually prefers to feed on macronutrients which are different than glucose and that glucose just stops that mechanism is really weird. is there scientific evidence related to this?i always had the conception that glucose was neccesary for our brain health :/ .though i do know that brain is constructed mainly by fatty acids like dha so it is kinda confusing.. anyone can help in this pls? this proves the stupidity of those that are empoyed in the research and development section..the more natural the better.it seems that our body is smarter than us ^^ we just get in its way.pissing it off
When you fast or eating only fats and protein your brain mostly use ketones as an energy source,(http://evolutionarypsychiatry.blogspot.com/2010/08/your-brain-on-ketones.html) but very little amount of sells in your body need glucase probably in the amount of 15 grams a day which body makes from proteins.
Glucose is necessary for brain and nervous system health. However, the liver is capable of synthesizing glucose from protein via gluconeogenesis. This makes up for any deficiencies the ketones may not be able to fulfill.
I honestly think that exercise is 1000 times better than fasting. So instead of preaching starvation lets preach exercise and good food.
You cannot starve by not eating for an extended period of time. Your body is not going to wait until there is absolutely nothing to eat to protect your muscles and cells. Ketosis happens long before the body is out of food so starvation is a little overstated and overused when it comes to fasting. The purpose of ketosis is to help you to survive to your next meal. Exercise,like fasting and the ketogenic diet, will induce ketosis.
Using exercise to loose fat is not working. I was 245lbs when I hired a personal trainer for a year, 3 times a week, plus I went 2 time just for cardio. I did everything they told me to, and I lost 5 lbs!!! during that time. I might have gained muscle, but at that point I wanted to loose the fat.
I’ve never been able to loose weight on any diet, but this time around with Paleo diet I’ve lost 21 lbs in two month, and I’ve never felt better. I don’t exercise yet, but I’m going to start doing some soon. Just a little bit though.
Mary,
Any link to holding off food until an hour post-workout? I’ve seen that mentioned other places, and wouldn’t mind reading about it further.
Thanks
I am questioning the following from the “A controlled trial of reduced meal frequency without caloric restriction in healthy, normal-weight, middle-aged adults” article:
“However, when consuming 1 meal/d, subjects had … significant increases in blood pressure and in total, LDL-, and HDL-cholesterol concentrations….”
Is blood pressure increase and a drop in good cholesterol reason for concern?