Eating less is the best-tested and surest way to a younger body and an increased life span. But it’s a hard discipline to maintain, and many of us would welcome an easier alternative. Perhaps we can realize some of the benefits applying a more temporary exercise of willpower, with intermittent fasting. It’s counter-intuitive, but seems to be true, that health and longevity are better served by clumping up our food consumption (feast and famine) than by spreading food consumption evenly through the day and through the week. The topic is controversial, and the evidence is not just unclear, it’s contradictory. The bottom line is that it is worth trying. Some people who drift away from diets involving consistent discipline find that they can comply on an intermittent schedule. Experiment with different schedules, because individual response varies widely.
The link between restricted diet and longer life goes back at least to Benjamin Franklin: “To lengthen thy life, lessen thy meals,” said Poor Richard. Formal experiments on mice established the benefits of calorie restriction in the 1930s. But calorie restriction remained a backwater of research, unknown to most biologists, let alone the public. Beginning in 1946, intermittent fasting was introduced as an alternative lab regimen that required less measuring and monitoring. These early experiments suggested great promise for cancer prevention and life extension by restricting access to food on various schedules. This was exploratory work, and the experimenters were not keeping proper controls, or varying just one factor at a time, so it’s hard for us now to fit those results into the base of later experiments.
In the 1980s, caloric restriction was already well-established as a robust way to extend life span, and alternate-day feeding and fasting was re-discovered. In the best outcome, rats lived 83% longer when fed every other day. Looking back from today, we would want to ask: how much of that benefit came from lower consumption overall, and how much from the schedule and periods of fasting? Did they eat much less overall? Or did they gorge themselves on the in-between days and make up for lost time? Though no records were kept of the animals’ food consumption, the results seemed to be too good to be due to reduced calories alone. The schedule seemed to be at least a contributing factor in the success of the diet.
Some species are adapted to graze continuously, while others have a much greater capacity to store food and digest it slowly. Even within the same species, different varieties may react very differently to alternate-day diets. A study by Goodrick (1990) highlighted the different responses of two strains of mice. Both were put on the same every-other-day regimen. Both maintained their body weights, with no significant differences from control animals fed ad libitum. But one strain enjoyed consistent life extension, and the other suffered a slight decrease in life span from EOD feeding.
Experience with people
People have a hard time adapting to no food at all every other day, so the four regimens that have been suggested for humans are
- Concentrating food intake in a portion of each waking day, or eating one meal a day, or fasting every day for 12-16 hours
- Fasting or eating lightly on alternate days
- Fasting one day a week
- Longer fasts of several days, less frequently.
Long-term human studies of EOD fasting and longevity are not available. (People don’t like to live in cages, or eat the same thing as other subjects for years on end.) So instead we look for hints in the short-term metabolic response to intermittent fasting. The metabolic connection of diet to aging is mediated through the insulin metabolism, so it is logical to ask what are the effects on insulin levels, insulin sensitivity, and blood glucose. EOD fasting shows benefits comparable to CR for some but not all of these. Higher levels of HDL (“good cholesterol”) have been reported for humans and animals, and there is good support for lowering of cancer risk in animal studies, but no data yet for humans. In the most pessimistic study, combining calories of 3 meals into one big meal in the evening had a negative effect on the insulin metabolism.
Protecting the Aging Brain
An intriguing benefit of the EOD regimen seems to be an increase in BDNF (brain-derived neurotropic factor). This is a hormone that promotes new nerve growth in the brain, and presumably is related to the ability to learn. BDNF levels decline with age. There is good evidence that some of the benefits of EOD fasting and of CR generally are not direct effects on the metabolism, but are mediated through the nervous system. Maybe you have to feel hungry to receive the health benefits. The BDNF connection supports that idea.
Weight loss – a good indicator
For some people, losing weight is an end in itself, and a primary goal. But even if your focus is on other benefits (life extension or long-term health), weight loss is a good sign that the diet is working for you. If you are not losing weight, there still might be benefits from intermittent fasting, but it is harder to know.
For most people, trying to eat less via willpower is counterproductive. A large majority of people who stay on a diet using discipline find that they regain more weight than they lost after their resolve runs out. Such statistics, of course, always apply to other people, and each of us knows we can do better. And some of us are right.
Experiment with a chosen fasting schedule. Stick with it at least a month to give yourself time to adapt, and to average over varying life circumstances. The right diet for you is the one you can live with. When you find a schedule that is right for you, you will enjoy lightness and alertness; you won’t feel deprived or resentful; there will be satisfaction in caring for yourself well, and sensing it.
Krista Varady of Univ of Illinois has a research program helping people with every-other-day diets with 7 years of experience. Varady reports good success using a schedule of alternate day dieting, in which subjects eat one meal on the in-between days, a normal lunch of 400-600 calories depending on body size. On the eating days, she says subjects average 10% more than their usual diet, but do not pig out regularly, once they get used to the routine. Some subjects drop out of the program, but for >80% compliance is good. She says many people are able to stick with this EOD schedule long-term, to lose weight quickly and keep it off.
In summary, intermittent fasting is likely to work, but not for everyone. Only personal experimentation can tell you if you’re able to accommodate to fasting, if it can fit into the demands of your life, if you tend to overeat before and after.
Personal note: I’ve found I can live with a complete fast one day a week (usually on Thursday). I also try to extend my overnight fast at least 12 hours. I don’t think I eat less overall, because I actually gained a couple of pounds when I started doing this in 1997. But weekly fasting offers a kind of sabbath that feels right to me, makes me a little less focused, less verbal, less patient but more introspective.
I usually eat only dinner every day, never breakfast, seldom lunch; a BMI of 23 for the past 10 years!!!
If you haven’t already, you might want to check out Dave Asprey’s blog Bulletproofexec.com. He’s does intermittent fasting with a twist – he drinks coffee in the morning with butter and MCT oil in it – he calls it “Bulletproof Coffee”. He claims that because the butter and MCT oil do not elicit an insulin response, you remain in a fasted state – or, state of ketosis. Anyway, I’ve tried it, it works but because I prefer iced coffee, I use a couple tablespoons of whole raw cream and MCT oil – I also eat the butter on the side.
Also, this is one of the best posts on intermittent fasting for the lay person I’ve ever read.
Nice to see others trying the Every Other Day (EOD) fasting. I started this regimen almost two years ago and have had no problems with it. My aim was to loose weight. I had been at 220 lbs for more than 10 years and was determined to get down to the 170-180 range. I was in that range in about six months and have maintained it now for more than a year.
I was very skinny in college, 145-150, but started to put on weight after joining the Air Force and getting married. At 5′ 11″, I didn’t look particularly obese at 220 but was clearly overeating and experiencing high blood pressure and other health issues. As I turn 70, I was also concerned with life extension.
I begin fasting in the morning after a night’s sleep and do not eat again until the next morning. I take a double dose of vitamins each day along with blood pressure and cholesterol lowering drugs. I do have a half banana to help me swallow my pills. But the rest of the day I have nothing but non-nutritive fluids, most often decaf coffee mixed with ginger tea (which I prepare from ginger root). I sweeten it with Splenda. I do not experience any great hunger during the day, nor do I detect any lowering of my energy level. I play several hours of tennis twice or three times a week on fast days and non-fast days.
I do the fasting primarily to keep my weight under control and love the ease with which I can police my non-eating days — having nothing is so much easier than counting calories or limiting portions. If I see some food that looks particularly appealing on a fast day, I will save a portion for my next eating day. I don’t have any restrictions on my eating days but find I get full on lesser amounts of food than before. I suspect that my total calorie intake is less than half of what I was taking in before EOD fasting. I like candy and ice cream and make pretty good cookies. I like vegetables, salads and fruit but also eat plenty of potatoes, meat and bread.
I’m not particularly rigid with my schedule. If social engagements lead to eating several days in a row, I might fast for two days to get back on schedule but I don’t have a problem going out with friends and having coffee or diet soda while they eat. Turning down home cooked meals is more of a problem and that’s where flexibility wins out.
If you’ve never gone a whole day without eating, you might imagine it would be very difficult. I tried it and found it was easy for me and worked really well. Whether it will give me lots of good benefits in the long range remains to be seen.
PLEASE switch to stevia!!
Splenda has been PROVED to be toxic; stevia is not!!!
Stevia is awesome! I thought I could never live without sugar and boy was I wrong. Put it in hot tea in the morning and in bottled water throughout the day. By the way, it helps me consume 80-100 ozs of water/day. Try it. No bitter aftertaste. But get the real thing. I bought mine online. The stuff in most grocery stores marked, “Contains Stevia” also has refined sweeteners in it too.
Interesting blog. In surprised I haven’t come across it before. Thanks for writing it.
I just wanted to add to the comments here. My wife and I have been fasting in various configurations for just over two years.
Initially we fasted 48 hrs/week.
After six months we doubled that to two 48 hr fasts per week.
After another six months we switched to a single 72 hour fast per week (in my case mainly because it was more socially convenient).
Just recently having read Valter Longo espousing four-day fasts, I’ve done a couple of them.
When fasting we have zero food, and black tea/coffee, water and the occasional diet coke.
Neither of us has lost weight, nor were we trying to do so. I’ve found it increasingly easy to do the fasting. I rarely feel hungry.
The reason I’m posting this is to ask if you know of anyone who’d be interested in using us for long-term fasting research. I’ve written to various authors of research papers, but no-one has responded positively to my offer. We’re based in the UK, near London.
Keep up the good work.
Thanks for your story, Simon. I’m fascinated by how different people are in what dietary models work for them. If you notice health consequences from fasting, I’d be eager to hear. As for putting stories together to make an academic study: I think it’s tricky to make sense of stories from small numbers of people, each of whom adopts a different regimen. The person who has done the most with this is Luigi Fontana at Washington University, St Louis, MO. He might be interested to hear from you.
I’ve heard that since rodents have a much faster metabolic rate 24 hour fast for them may not necessarily be equivalent to 24 hour fast for humans.
That said, very strong Calorie Restriction is said might affect bone integrity. If it is true that very high calorie restriction affects bone integrity that may affect the maximum lifespan benefits of CR, which may be higher if bone integrity can be preserved.
It is conceivable that despite antiaging benefits allowing up to 83% lifespan increase, fasting too at least in rodents may impair bone integrity as it is effectively 100% CR on some days. If that hypothetical side effect was true it could limit the lifespan increase of fasting, which one might hypothesize might be higher if the side effect could be appropriately dealt with.