Life extension is a relevant topic here, and I was wondering if people are aware of the apparently life-extending effects of calorie restriction (CR) and intermittent fasting (IF). To the extent of my knowledge, this is the best method using currently realized technology that has shown repeated and significant life-extension benefits.

Studies show that reducing calories by 20% to 40% from ad libitum feeding (but maintaining the supply of required protein and micro-nutrients) gives improvements in markers related to aging, and extends life span in rodents and other organisms.

Other rodent studies have also shown similar results in subjects which were kept on various intermittent fasting schedules. Rats that were fed only on alternating days gained up to 25% lifespan (see Table 2).

The benefits of IF are seen even if the total calorie intake is the same as in ad libitum subjects.

There are ongoing full-lifespan studies in rhesus macaques to test the effects in primates, but none of these studies have completed. This abstract of the interim results appears promising, though.

Studies of CR and IF on humans have shown effects consistent with reduced mortality, including:
- Improved triglyceride profiles (a marker for heart disease)
- Increased insulin sensitivity
- Reduced cell proliferation (a marker for cancer)

Generally, these diet modifications appear to not just extend life span, but improve the quality of life too. In aged subjects they improve things like: muscle mass, cognition, energy, appearance, and activity level.

Have people heard about this or tried it? If you are trying to maximize your chance of surviving to the point that technology can lengthen lifespan indefinitely, it seems like something worth exploring.

I tried an IF schedule for about 6 months during 2010. I followed a schedule of 3 x ~thirty hour fasts every 7 days and found it somewhat tolerable. I exercise regularly and found that exercising on the non-fasting days was not a problem. I'm thinking of starting up such a schedule again.


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...improve the quality of life.

...found it somewhat tolerable.

Maybe you meant something like "improve physical health and functioning".

Which isn't the same thing as quality of life.

When you're old it's a big component of your quality of life. I think this is a classic pain now vs. pain later tradeoff.

Maybe I didn't use the best choice of words. Food did taste pretty amazing on the feast days, though.


Upvoted! IF makes food taste better.

most people can see huge gains in health just with cutting out the majority of their processed sugar intake and upping their activity level. no need to resort to stronger methods until you've exhausted the low hanging fruit.

I think you're right for most cases, but it does depend on your utility function. If you have a strong sweet tooth & love bread, but don't have a need to fill your stomach regularly, then this might be a less difficult alteration than cutting out most processed sugar.


Agreed. But it would probably also be good to address one's addictions to sugar and gluten eventually. I've seen enough people with strong sweet teeth who loved bread do it; it is more achievable / less painful than most people seem to imagine.

overestimating the risks/costs of any habit change is almost universal.

"Sudden adult onset Calorie Restriction shortens the lifespans of mice. Though the lifespan enhancing effects of calorie restriction have been known since the 1930s, it was also known that if adult mice were suddenly put on a calorie restricted diet, their lifespans were actually shortened. Dr. Walford found in the 1980s, however, that if mice were slowly transitioned from an ad lib to a calorie restricted diet, then their lifespans increased. The time for this transition recommended by Dr. Walford is a minimum of 6 to 9 months, but preferably 1 to 2 years. [p. 78, BY120YD]"

from the CR society

A couple months ago, I fasted for a day (<800 calories) to assess the personal viability of IF. I haven't given much consideration to a long term trial recently, but I did just realize that it served as a way to extend the perceived length of the day :) It also inspired me to spend some time cooking, which is something I've avoided in the past due to inconvenience. If I try it again, I would skip Saturday dinner, fast during Sunday, and then cook a nice, late dinner Sunday night, and consciously utilize these side effects.

I too have (accidentally) consumed less than 800 calories in a day (got caught up in something and lost track of time). I felt noticeably worse.

Does anyone know if/how much people can get used to such a diet? For people that fasted regularly (more than one day), is it always like that, or do you sort of get used to it? Being distracted by being hungry is a pretty big downside for me since I spend a lot of time programming, and distractions make me considerably less productive.

The feeling of hunger never disappeared, but it got easier to accept.

Some days that were really busy at work flew by without a problem at all. It was easier for me when I was engaged in a task that demanded most of my concentration.


One day is not enough time to adapt to a major dietary modification. I'd suggest giving any change at least a week or two, but preferably a month, before deciding if you can tolerate it or not.

And try out CR and IF independently, don't jump into both at the same time.

ETA: If you go more than a week on IF and you still feel terrible, you (like most people, sadly) have larger metabolic issues to resolve first. So switching to a Weston A. Price traditional/paleo-ish or Perfect Health Diet setup, getting your health up a few levels, and then trying IF after that.

Anecdotally, I found it fairly easy when younger to do an IF diet. The first few times fasting for a day, the waves of craving/hunger could be fairly bad, and fasting for a second or third day was pushing it much too far, but overall it wasn't so bad. And it was fun eating double on the non-fasting days.

I fast once a month (sometimes more), generally the first sunday of the month. One does get used to doing that.

I have also fasted for a week at a time, being one small meal each day. It isn't so bad especially if one is used to fasting for a day time period previously.

CR inhibits mTOR (mTOR1, I think), and, likely through mTOR, increases the production of mitochondria. Increasing the number of mitochondria in a cell, all else being equal, reduces the voltage across each individual mitochondrial membrane, and thus reduces the amount of reactive oxygen species predicted, and thus the rate of mitochondrial DNA damage. Mitochondrial DNA damage reduces ATP production, reducing the ability of the cell to do its work, and also to produce protein for its own upkeep; and may also lead to apoptosis.

This is a brief summary, but there's lots of evidence IMHO that either mitochondrial proliferation, or else the general downregulation of anabolism, is responsible for the effects of CR.

I note that that first theory doesn't even get mentioned on:

Obligatory C. R. Society link:

Best site on IF:

I have gone on and off this diet for the last few months and found it better to do intermittently. In other words, if you are in a constant IF mode, your body will adapt and gains will stop, but if you do it irregularly and just when you feel like it, then it works great. Main point of the philosophy is not being afraid to skip a lot of meals. Never eat when you are not hungry just because it's a certain time a day and you HAVE to eat. Also, skipping breakfast will not make you unhealthy.

I'm on this and refeeds are essential, check out martin's posts on eating whole cheesecakes. I refeed binge on carbs once every couple weeks. The only thing that happens is that I hold more (~2lbs) water for a day or so (carbs suck up quite a bit of water). I haven't seen any negative effects at all.

Here's another interim report on the longitudinal effects of CR on rhesus monkeys, this one a bit more recent (2009) than the one linked in the OP. From the abstract:

We report findings of a 20-year longitudinal adult-onset CR study in rhesus monkeys aimed at filling this critical gap in aging research. In a population of rhesus macaques maintained at the Wisconsin National Primate Research Center, moderate CR lowered the incidence of aging-related deaths. At the time point reported 50% of control fed animals survived compared with 80% survival of CR animals. Further, CR delayed the onset of age-associated pathologies. Specifically, CR reduced the incidence of diabetes, cancer, cardiovascular disease, and brain atrophy. These data demonstrate that CR slows aging in a primate species.

In aged subjects they improve things like: ... activity level.

Could you expand on this? I'm curious, because it doesn't match my personal experience; I find that if I eat less or skip meals, my activity level is reduced, to such a degree that I wouldn't do calorie restriction or intermittent fasting even if it did increase lifespan by a significant amount. Biochemistries vary, of course, and I'm not exactly biotypical, but it seems intuitively that consuming more calories ought to correlate with activity, since they're a resource that calories consume.

Some articles said that the CR subjects exhibited more restlessness, or "foraging" type behavior. This hypothesis wasn't tested as far as I know, though.

Based on my experience, I didn't feel less active or lethargic, just hungry. I think my body conserved its calories by reducing resting metabolic rate: Decreases in pulse, blood pressure, body temperature, body mass. My desire to exercise did not diminish, and neither did my capacity for aerobic exercises like running and swimming.

I believe this is a long-term trend, relative to controls. "Aged" CR subjects exhibit more activity than non-CR subjects the same age.

It is also widely believed there are short-term effects. Maybe the subject gets into a mildly stressed state where they are motivated towards taking action which might result in food being consumed. Maybe they spend less of their time incapacitated while digesting food. Whatever the explanation, these are not just long-term effects, I am pretty sure.


It seems quite reasonable to apply this to life. If the mental abilities are not weakened, there's no significant downside to me (besides the hunger). 20% life extension seems to be worth it for me, especially taking into account nshepperds calculation on AI takeoff. The time where the AI will probably take off is also the time I will probably die, so why not lenghten my life? Hunger now, enjoy life later.

What has always fascinated me about fasting, particularly water fasting, is the issue of cravings versus hunger. Skipping a meal or two usually produces cravings. Cravings could signal a need but more likely mean an addiction (and I'm using that definition loosely here. think coffee, salt, wheat).

My understanding is that 24 hours is the minimum for the detection of unhealthy cravings and that 3-7 days is the average time needed to overcome them. The idea that skipping meals (some even consider skipping snack-time IF) will produce beneficial effects I can only guess is the result of giving the body an unlikely time to rest.

I exercise regularly and found that exercising on the non-fasting days was not a problem.

Did you mean that fasting days?

No, I meant that exercising on feast days was no problem.

I did not try to exercise on fasting days more than a couple of times. It wasn't terrible, but I don't know if it's healthy.

This is encouraging. I think I could live with ADF, while I imagine I'd be miserable on CR. I am especially happy that the effect seems not to be an artifact of weight loss, as that's the most obvious confounding factor.


Interesting and I will look into this.

OTOH, from the Varrady and Hellerstein review article you linked: "it is important to note that the control animals in both the CR and ADF studies are likely to have been obese, because they were fed ad libitum."

So at the very least, IF you are obese, AND you think you could get to a normal weight by ADF, THEN you should go for it.

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