A Time to Fast

Over one hundred years ago researchers demonstrated that calorie restriction in rats increased lifespan, sometimes by as much as 50%. Since that time, the finding has been replicated and extended to primates. A few humans have taken up the diet but for most of us easy access to delicious food trumps willpower. A new paper in Science reviews the literature on calorie restriction and also offers some evidence that less restrictive regimes such as intermittent fasting may have similar effects.

First on calorie restriction. As noted, we have data on mice and primates showing increased lifespan and we also have data on humans showing the same physiological improvements as seen in other species:

In humans, short-term trials such as the multicenter CALERIE (Comprehensive Assessment of Long-Term Effects of Reducing Intake of Energy) study (2629), the observational studies of centenarians residing in Okinawa who have been exposed to CR for most of their lives (30), and observations of the members of the Calorie Restriction Society (CRONies) who self-impose CR (31) have shown the occurrence of many of the same physiological, metabolic, and molecular benefits typically associated with long-lived animals on CR. These studies support the observation that long-term CR preserves a more youthful functionality by improving several markers of health, including decreases in body weight, metabolic rate, and oxidative damage (14); lower incidence of cardiovascular disease (31) and cancer; and decreased activity of the insulin-Akt-FOXO signaling pathway (32, 33).

Although these findings clearly indicate that a reduction of caloric intake could be an effective intervention to improve health and prevent disease during aging in humans, there are several obstacles [including safety concerns and lack of data in older popualtions] and…The current “obesogenic” social environment makes it difficult for individuals to adhere to strict dietary regimens and lifestyle modifications for long periods of time. Thus, there is interest in alternative feeding regimens that may recapitulate at least some of the beneficial effects of CR by controlling feeding-fasting patterns with little or no reduction in caloric intake.

So what else works? Three regimes have shown promise. 1) Time Restricted Feeding (TRF), i.e. limiting eating time to a 4-12 period during the day and preferably earlier in the day, 2) Intermittent Fasting (IF)–say a 24-hour period of 1/4 calorie consumption once or twice a week and 3) a Fasting Mimicking Diet (FMD) in which calories are restricted to 30% of normal with a higher proportion coming from fat and doing this for five days periodically, i.e. once a month to once very couple of months. The diagram presents the main results and evidence.



Been there, done that... shed and kept off 50 pounds for 3 years now...and it is just not a big deal when you get used to it.

What's your body-mass index? When I ran a few years ago, before a foot injury (now I swim), I had the body-mass index of an Ethiopian/Eritrean man, according to a BBC online calculator.

Ethiopian and Eritrean Orthodox Christians fast to some degree on approximately 200 days a year.

I know, as a Greek Orthodox, living with my religious relatives. One auntie defied the doctors by living with thyroid cancer to a ripe old age, without any form of treatment. I think she finally died of heart disease. That Med diet? But she fasted like crazy, meat only on Sunday, unless it was a fast period, which as you say seemed to be most of the year. One time (since I tried to please her) I agreed not to even drink water for a 24 hour fast, and almost died of thirst but she managed fine. At her funeral a village of 200+ people not related to her came to see her buried; I doubt I'll have any unrelated people.

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Early in this century I was having a conversation with a colleague about this. He had friends who were on 800 calorie a day diets so they could live longer. I commented that they must not be able to do much physically. He said yes, they basically sit around all day.

I will take a shorter lifespan for the ability to walk around. On the other hand, my family is fairly long-lived, so I'm likely to live a long time barring accidents.

I'm also with cjared. I changed my diet to more protein and fat, less carbs six years ago. Lost 35 pounds and kept it off.

It's an interesting theory but will take 50 plus years to prove or disprove. More than likely it is like all of these whacko health nut theories and pure fantasy.

Anon, check out Dr. Jason Fung. This fasting not fantasy or nut theories

800 calories per day is way too few, and I believe below the threshold for malnutrition, or perhaps right at it. The caloric reduction range quoted in the graphic is 15% - 40% — if you're eating 2,000 calories per day, that means going down to 800 calories would represent the full 40% reduction, while 15% would leave you at 1,700 calories. But I imagine the 40% reduction would be for people who burn more energy to begin with, and who are starting from a higher maintenance level (where calories burned equals calories consumed).

I recently lost 20 pounds in 8 weeks by restricting my calories to 1,850 per day (down from probably 2,500). I hit my goal, then upped my intake to 2,100 per day, where I have held steady ever since. I feel better than I have in years, but I can't imagine continuing to restrict my calories - it wasn't hard to do after the first week or so (which was very hard), but I'm worried I would continue to shed weight and eventually lose both strength and energy.

So, you're dismissing extending your lifespan based on some anecdotes?

It seems like the idea that you can do less activity on a calorie restricted diet has pretty good intuition and science to back it up. If I wanted to regularly go out on the river to row, play a pick basketball game, do long-distance running or biking, or just keep up with my kids at the park, I don't think a calorie-restricted diet would allow for that just based on the first law of thermodynamics. If you don't put fuel in the engine, the car won't go.

Indeed. You can live longer but less intensely. The "living our life" index is constant, that is time times intensity = lived life is the same, people who live to 110 usually are ones who never did anything.

You should try a restricted calorie diet *after* having cut carbs, and particularly after having eliminated (or nearly eliminated) refined sugar. I'm probably 800-1100 ca/day (plus 40 hr weekend fasts) with plenty of energy. I moved a ton of gravel last weekend during my weekend no-food fast. The sugar causes all sorts of havoc in energy and cravings. I think there are several factors at play.

Check out Dr. Jason Fung your body cares / stores the fuel .
No need to count cals., just fast athletes improve with fasting.

Too late for some of us, haha! Should have posted this sooner, although I would have still eaten all the turkey and pie.

How is this different to "skipping meals" because hiking, a long bike ride, work, driving, plane travel, being sick, hangover? All these things end in calorie restriction.

We know it's about the food from the mice. They don't have pesky unobserved variables.

I can't think of a hiker or biker who doesn't make up those calories at some point. It's also different because what you are describing are occasional occurrences, whereas the authors are discussing permanently reduced calorie intake.

I have been doing the intermittent fasting ( eating only between 12 pm and 8pm) for 2 years now. I thought it would be harder but it’s not really hard. I think it’s the easiest of the 4 diet types above. I am really not hungry now before 11 am and I break it off now and then for social reasons.
I don’t know if it helps. I had good readings on everything on bio markers before I started anyway. They have improved marginally ( not especially conclusive). For example: I was slim, I am slightly slimmer ( 4 lbs). BP was average 115/82 , now 109/ 78. I avoid added sugar. I eat little red meat preferring fish or chicken or beans for protein. Chart says there’s no data to say if this diet increases lifespan. I feel good on the diet, but then I did before it too. I haven’t noticed a change in endurance( running/cycling). This diet may be more helpful for obese people forcing them to eat less. I followed the book “ The scientific approach to Intermittent fasting” by Michael Vanderschelden. More research is needed on this.

Note: What I do is called “ time restricted feeding” here not “ intermittent fasting”

All very odd. The data are pretty clear: for codgers the "overweight" and the "mildly obese" outlive the "normal". The skinny and the genuine fatties do worst.

Do the diet data here presented therefore imply an uncoupling between diet and BMI?

I suppose I'll know that this dieting suggestion is dangerous rubbish when it becomes official government policy.

Trying to find them, but I thought newer meta analyses undercut this "paradox" by pulling out the normal/underweight who were that way as a result of illness (cancer/chemo great for losing weight)

This. A large percentage of old people with what's typically regarded as a health BMI would be much heavier but for illness and studies that found longer life for chubbier seniors don't tend to control for this.

Not sure the data do say that (about "normal" weight folk) but taking this at face value it may be more of a case that calorie restriction decreases robusticity against diseases (infectious, others) that they've controlled out of their experimental mice populations.

well, " a reduction of caloric intake " is a very vague term -- meaningless in the context used above.

also, dietary studies & research are notoriously inaccurate and non-scientific. Extremely difficult to accurately track what people actually eat, even in small sample sizes and relatively short time periods... or causally connect it to various human outcomes.

Google diets, dietary advice, and dietary research -- you will be deluged with vast amounts of diverse and contradictory information.
Anyone pushing a general dietary approach to extend human life span is blowing highly speculative smoke.

CRONers do track what they eat and of course animal studies track everything

People with "heavy bones" are funnier and look younger. No wrinkles.

Of the Black Friday sales lured me into a sous vide machine, now shipping. Maybe I'll fast January?

I'm actually a big believer in periodic simple fasting, believer but not practitioner. But as I said maybe next year!

NAD+ boosting (e.g., nicotinamide riboside supplementation) may give the benefits of CR without the weakness and immune problems.

{Shhhh... commenters here don't like scientific methods when it comes to health.}

If actually interested in IF, caloric reduxtion, fasting etc: I recommend 3 resources. Marks's Daily Apple, Dr Rhond Patrick, Dr. Peter Attia. All have substantial web presences where you can inform yourself about the benefits. Here are just a few: increased NAD, autophagy of dieing cells, improved blood sugr levels.

As usual, many commenters seem to just have to post something 'critical' about a topic they know zero about.
Please inform yourself.

It makes intuitive sense that not eating 2000 or so calories every single day would be better for us.

We evolved in a much more feast or famine type setting. Some days maybe not eating anything at all, because there was nothing. Some days gorge.

The primate tests were not as clear cut as Alex suggest;
I am sure that there is an effect if you loose weight from being obese to less obese. Probably you will improve things like blood sugar and heart disease factors. But I doubt there is some mysterious factor that comes into play when you calorie restrict beyond these immediate effects. But who knows - ageing is definitely a deliberate mechanism rather than just your body gradually failing. It must be really needed by evolution to have such little variation among species.

'I am sure that there is an effect if you loose weight from being obese to less obese.'

Yep. And notice how many of the comments above talk about weight loss, and not calorie restriction per se - the idea of calorie restriction for lifespan extension as originally presented was not for those needing to lose weight, but those already at an 'optimal' weight - and who then lived on the edge of malnutrition with extremely carefully balanced diets to gain the lifespan extension benefits.

Showing that it's hard to reason from just common sense in nutrition, there may well be a "mysterious factor" - autophagy - see, e.g., Rhonda Patrick (mentioned above) who summarizes lots of research or Walter Luongo (USC) who has researched the health effects of a fasting mimicking diet. From what I've read there and elsewhere, it sounds like the stress of fasting may kill/recycle the weakest/mutated cells.

@JoeRini: "As usual, many commenters seem to just have to post something 'critical' about a topic they know zero about."

... spot on, Joe -- those commenters here who think they know it all ... are quite annoying to those of us that do ! ))))

Human body stands as an amazing complex system.

FWIW, I've had a ton of success decreasing body fat but maintaining muscle mass by using a combination of DH Kiefer's Carb Nite with intermittent fasting/fast mimicking diets.

Basically, if I'm not active. I eat a ton of whatever I want one night per week (or close to it depending on social calendar) over a 6-7 hour window. Rest of week, I eat ultralowcarb (<20g Carbs - fiber). In the ultralowcarb portion, will mix in a straight fast or one meal of 500 cal or less every other day if I want to lose fat.

I've kluged together the ideas of Jon Kiefer, Jason Fung, and Walter Luongo. Not sure what is right scientifically, but I know it's worked for me and my close friends in practice. It's a little screwy but I got a bit of that after having cancer/surgery/chemo. Science will likely prove it naive in 20+ years, but I do the best I can with current knowledge.

"but for most of us easy access to delicious food trumps willpower" implies that we all share the goal of a longer less pleasurable life. It's possible that some of us have chosen a shorter happier life deliberately.

This is what I was going to say. From what I've observed, being in your 80s is awful. It does not strike me as very desirable to go even further unless there's also some method of improving quality of old age.

Don't knock it if you haven't tried it.

Fasting and cr deprivation (for me and my wife at least) have the unintitive side effect of making the food we do eat vastly more satisfying. It turns out that having small treats after a fast can be an almost spiritually uplifting experience. I don't think that can be said about the second half of a daily serving of French fries.

We lived in Florida for a while and watching old people who seemed to be voluntarily relegated to trudging from one joyless restaurant meal to the next... No thanks, not for me.

And, when did it become ok to be overweight? Why is the new goal "not obese?"

No thanks, again. Mobility, exercise, minimal eating punctuated with joyous celebrations of food that tastes *loud*...that's living.

Other people have different sensations, pleasures, and priorities from you. Other people may find no enjoyment from so much movement, they may just find it painful. Other people may derive vastly more pleasure from the consumption of food, and in quantity, than you do. Other people may find fat bodies appealing. You don't get to decide what other people like or dislike or how they choose to live their lives.

Sorry if I sounded too globally prescriptive and seem to have touched a nerve. For the most part, everyone should do what they like.

The issue, in my mind, is that since the advent of the Pure Food and Drug act, the green revolution, and a few other things, we've been faced with conditions of plenty never seen before, and people are experiencing changes (obesity, obesity-related illness) at epidemic scale *seemingly, largely not seeing the extent to which it's a choice*. It might not be a choice for some...for some it certainly is.

If you *choose* some degree of fatness for aesthetic or other personal reasons, go for it.

I backed into being 40 lbs overweight through implicit choices I didn't understand I was making. Now that I'm back to my skinny high school weight (via low carb / cr / fasting)...I wouldn't want to do that again and I'd love to help anyone I could through (anecdotal) communication and example. Doesn't have to be right for anyone other than me.

Appetite is self-regulating. Best not to mess with it.

At least for me, it's not - when I fast (I do TRF - usually 8 hour window noon to 8 pm eating), I'm not that hungry - I often delay eating even further until 2pm or even 4pm because it's not hard,especially as you lose the habit of eating (so you get better at telling real hunger from habit, plus I think your body gets better at metabolizing fat when necessary). When I eat refined carbs, I get much hungrier than if I fast. If I ate a cookie in the morning, I could never make it that long. Frankly, I could never stop at the cookie - I would be really hungry right away.

Since my ancestors spent the last 70,000 years trying to assure an adequate food supply (and succeeding only in the last 200) and raising their life expectancy from 25 to the current 79, I'm going to eat what I can get, subject to taste, cost, and avoidance of obesity.

Started IF around November 2017, after hearing about and reading Jason Fung's blog/books, fasting 3 days a week. By May of this year managed to drop ~ 40 lbs from 210 at the start. I don't eat anything on the days that I fast. On days that I don't, I try to keep meals within a 6 to 8 hour window with no snacking outside of that window, but otherwise I make no restrictions on what or how much I eat. For me, fasting 2 days a week seems to do the trick of keeping my weight stable. At 3 days a week I will drop 1 to 2 lbs a week.

This is the first and only diet that has ever worked for me. I was on the verge of becoming diabetic and this has turned it around. I'm convinced it has saved my life .....

Time-Restricted Feeding is what I've been (unintentionally) doing for years, albeit not early in the day.

“molecular improvement” - how exactly is e.g. adenosine triphosphate improved by fasting?

Limiting my “eating” time to a window of 9 to 11 hours each day, over 6 days every week (I “feast” one day/week), helps me to stay slim. [I follow Dr. Mercola’s MMT lifetime nutritional plan—which includes this fasting strategy. From his book, “Fat for Fuel.”]

Anecdotally, my wife had a lot of success fasting while on chemotherapy. There's evidence this helps with both side effects (her nausea improved markedly) and perhaps efficacy.
There's a theory called "differential stress responses". When fasting, cancer cells keep growing and are thus a target for chemotherapy while normal cells enter a "protective mode". Cancer cells (almost by definition) don't have the growth checks normal cells do.
She writes on her experience and the somewhat limited evidence here:

Cut my carbs at the start of the year, and had some success losing weight, but found it difficult to enjoy life since my favorite foods are mostly carbo heavy. Went off the rails a bit and gained back some of the weight I lost. Also found it tough to improve my fitness while on restricted carbs.

Then found out about IF, and started 3 months ago. Still doing okay, and I'm not restricting my diet much, enjoying whatever I want to eat within the eating window (even went for a buffet two days ago). Lost some weight, but most importantly, cut some of the fat around my belly. My fitness also improved by quite a bit (can do handstands / my running intervals have improved to a point where I could do stuff I couldn't at 18 years old), so from my anecdotal experience, I think IF really works.

I wonder how much folks in these populations have increased their water intake to substitute for the times they're abstaining from eating.

Hey Bacon, if I'm in the population (cr / faster) I can say basically not at all. In fact, you tend to shed water weight during fasting. I was medicating for high bp before I came back to a low fat weight and bp goes down further during fasting. I don't drink more or retain water...

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