It might be important to look at nutrition, too. A lot of people who've experienced forced calorie restriction were malnourished. The kind of calorie restriction CRON advocates follow for instance involves eating less calories, but of more nutrient-dense foods to avoid starvation effects, as far as I understand it.
This was my response when David Brin made the religious argument: monastic or hermit diets are not famous for their variety or density, and one of the most common religious strictures is no meat - which immediately makes protein difficult to obtain. And yet, even with these impoverished diets, you still see frequent claims of very long lifespans (which are usually dismissed as implausible, but that's assuming the conclusion for the purposes of this CR discussion).
When I read about Buddhist monasteries in Japan, for example, the diets seem to be mainly rice and some vegetables. Few nuts, fruits, fish, or meat like you see throughout the CRON recipe book.
So I regard the religion argument as weak; much better to watch the preliminary results of the human study or any primate studies.
This was my response when David Brin made the religious argument: monastic or hermit diets are not famous for their variety or density, and one of the most common religious strictures is no meat - which immediately makes protein difficult to obtain.
Getting adequate complete protein on a vegetarian diet is not at all difficult, and in fact, usually does not even require attentiveness to one's food intake. Getting adequate protein on a strictly vegan diet generally does require attention to one's food intake, but is still entirely practical.
I'm sure it's doable. That doesn't mean it's done. As I pointed out, on the occasions that I've read of historical monastic diets, especially Buddhist ones, they did not strike me as paying any attention to protein.
Plus ¨servants, slaves, prisoners, or people who simply regularly don't have enough to eat¨ were/are all enduring stressful lifestyles, deprived of basic needs and enjoyment that surely lead to a shortened lifespan regardless of what they eat or did not eat -rendering any nutritional benefit (doubtful, due to the lack of control over one's diet patterns and contents) irrelevant in their cases-. One cannot consider a complex system like the human body without taking into account all major factors involved in its dynamics.
I think you accidentally a word in your title (should read "If calorie restriction works in humans, shouldn't we have observed it already?").
That said, you bring up a good point, and I would also like to see this question answered.
which would represent just a 10% improvement over life expectancy in Japan
Over the present-day life expectancy in Japan. My understanding is that the difference between life expectancy in Okinawa and the rest of Japan is a lot less dramatic now than it used to be.
Okinawa's expectancy shrank, basically, as they adopted more Westernized eating styles and the rest of Japan very slowly continued to improve.
EDIT: I added refs to a Wikipedia article or talk page on this a year ago or something, too lazy to look it up.
BTW, if I understand correctly, the main reason why the life expectancy at birth was over twice as short in pre-industrial civilizations as it in present-day developed world was the much larger childhood mortality, but the expected remaining lifespan for someone who has made it to (say) 40 hasn't increased by much more than a decade since palaeolithic times. If this is the case, and if the diet was actually the reason for the extraordinary longevity of pre-WW2 Okinawans, even though they had a similar life expectancy at birth as present-day developed countries they would have had a different mortality curve with more childhood mortality and less adult mortality. (Also, if those hypotheses are right and Okinawans had kept their traditional diet while adopting modern hygienic and healthcare standards, their life expectancy at birth would likely have exceeded 90 years.)
but the expected remaining lifespan for someone who has made it to (say) 40 hasn't increased by much more than a decade since palaeolithic times
I'm pretty sure that's too low - I remember consulting some table which put high medieval French adult life expectancy in the 50s, which would be 2 decades or so different rather than 1 decade.
Er... Yes. I've found this. So a 40-year-old in ancient Rome would have lived 23 more years in average, whereas the corresponding figure for the US in 2003 was 39.5 years.
Don't feel bad - you were at least informed enough not to give a ridiculous answer like '40 years'.
And often doesn't. Can you imagine what it'd be like to be a mouse, given our current knowledge of murine medicine? You'd have it damn posh.
Chronopause has a three-part article discussing the science of diet as a life extending tool.
Part 2 and 3 both touch lightly on the calorie restriction aspect of certain diets, and it doe seem to have benefits, but it looks like the majority of the actual applies-to-humans science primarily concerns composition of the whole diet, not simply calorie restriction.
The whole thing is definitely worth a read, since it provides a very good foundation for understanding the actual science behind the question :)
From Part 1:
However, life expectancy is not the same as mean, or average lifespan. Rather, life expectancy constitutes the expected number of years, on average, that a particular cohort of individuals in the population will survive if the rate of mortality remains constant (until the maximum lifespan is reached).[2] Life expectancy is thus the median number of years, at birth, that a population born in a particular year is expected to survive.
No, it isn't.
Example taken and adapted from Wikipedia: in a stationary population where 51% of people die at the age of 5 and 49% dies at the age of 70, the life expectancy at birth (defined in the sentence immediately before the [2]) is 36 years 10 months, whereas the median lifespan is 5 years. Life expectancy is the “same as mean, or average lifespan” in stationary populations no matter how skewed the distribution of death ages is -- the reason why it isn't in real populations is that mortality rates change with time.
I think there's a phenomenon that would confound measuring such effects in a population wide epidemiological study: chronic illness (especially cancer) often causes loss of hunger, and automatic calorie restriction.
In general, I think the "lipostasis system" which regulates hunger in humans makes long term calorie restriction in healthy individuals very difficult, and very rare.
Probably a good strategy to overcome this obstacle would be to hack the lipostasis system to defend a lower body fat setpoint, with techniques such as a very low food reward diet (links: (http://boingboing.net/2012/03/09/seduced-by-food-obesity-and-t.html) (http://sethroberts.net/)).
Well, overeating is known to reduce the life expectancy in humans and other animals, and most animals tend to overeat when food is in abundance, so one logically hopes that reducing the calorific intake should give you a little extra time before you kick the bucket. Too bad it does not seem to work out this way.
This is referring to a significantly more specific claim than merely avoiding overeating - significantly restricting caloric intake below 'normal' levels.
(Upvoted to cancel a downvote on a post indicative of simply not knowing. Why would you downvote such a post without bothering to say something about it?)
My thinking was that if one assumes that there is a function: calories -> life expectancy, all else being equal, then the normal intake may or may not correspond to a local maximum. If it does not, then mild starving ought to increase life expectancy a bit. Of course, it tells us nothing about the global behavior, including significant restriction.
Oh, and I'm not sure what you meant about upvoting/downvoting. Not that it matters.
There are certainly anecdotes of Taoist monks with insanely long lifespans. And Moses lived to 120. What even counts as evidence here?
Under the Bayesian definition, the Taoist anecdotes would be pretty weak evidence, and the Biblical accounts of Moses barely evidence at all. Under a scientific defintion, on the other hand, neither of those is evidence at all. I think that the point of this post was "can anyone find any scientific, or at least non-weak Bayesian, evidence that calorie restriction improves lifespan?"
I thought the point of the post was that there isn't any scientific evidence, and the author was scouring for anecdotes, generally involving monks. I was asking what makes one monk-anecdote better than another - in general, what counts as evidence.
Irony is surprisingly hard to detect over the internet. I too have interpreted your original comment wrong.
I'm confused. Did you think that my comment was ironic before, or do you think so now?
I was asking a straightforward question, I thought.
I was thinking that this
There are certainly anecdotes of Taoist monks with insanely long lifespans. And Moses lived to 120. What even counts as evidence here?
is ironic. Especially because "Moses lived to 120" is most probably false if taken literally.
Although there are no long-term scientific studies of calorie restriction in humans, there are religious groups, cults, and ascetics who voluntarily practice calorie restriction or intermittent fasting. Presumably there have been tens or hundreds of thousands of people who have practiced calorie restriction throughout most of their adult lives. There were/are probably also groups that involuntarily practice calorie restriction - servants, slaves, prisoners, or people who simply regularly don't have enough to eat.
If calorie restriction has a dramatic effect on life expectancy in humans, shouldn't we expect to observe extended life expectancy in at least some groups? Or would each of these groups likely have some mitigating circumstances that would shorten their lifespans, such as lack of medicine?
With an hour on Google, I found some references to Okinawa, to monks on Mount Athos, and to similar groups. In no case was there a reasonable claim of life expectancy over 90 (which would represent just a 10% improvement over life expectancy in Japan).
This paper reviews the evidence on calorie restriction in humans and other animals, including discussion of religious fasting, but there's no evidence there of fasting extending lifespan.
I found a few other sources where people asked this question (or made this point as an attack on CR), but I haven't yet found any good answers on the subject, and didn't find any discussion on LessWrong yet.