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Life span

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Some readers may remember coverage of a concept called "caloric restriction" in science journals in the late 1980s. Caloric restriction - restricting the amount of food eaten - had been shown to increase life span almost proportionally in numerous species, from paramecia to mice. Studies were in progress or being started in a variety of other animals.

Yesterday, one of those studies - using rhesus monkeys as a subject, who are considerably more closely related to humans than mice - published their first set of statistically significant results. What they found was that caloric restriction, as compared to free feeding controls, resulted in:

- statistically significant reductions in "age related diseases" such as cancer, heart disease, and diabetes, including complete elimination of diabetes

- statistically significant reduction in mortality from age related diseases 20 years into the study, which had started with adult rhesus monkeys between 7 and 14 years old

- a reduction in total mortality - including causes not related to age, such as death from anesthesia and endometriosis - that is suggestive but not statistically significant at this point in the study.

This is of particular interest to me because I inadvertently practiced caloric restriction until age 35 or so. I'm also trying to get back into it now, as I didn't start having kids until 48 and I'd kind of like to see them have children.

If anyone gets Science magazine and doesn't mind lending the current issue to me so I can see the whole article, I'd appreciate it. In the meantime, there's a summary here:

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On July 13th, 2009 05:08 am (UTC), jaedian commented:
How do you inadvertantly practice that level of calorie restriction?
I am also interested in this, but my understanding of it was that it is very tricky to get all your nutrients on so little calories. Doable, but takes a lot of planning. It is basically a starvation response. Do you know what the comparable human level of calories is?

I saw something awhile back about someone living on such a diet.
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On July 13th, 2009 05:57 am (UTC), psychohist replied:
One thing to keep in mind is that the restriction is compared to "ad libitem" - free feeding - controls, for which one could imagine an environment like the software companies that offer free junk food. The numbers I've seen for human "free feeding" equivalents are typically in the range of 2000-2500 kcalories per day. In articles about people who practice caloric restriction, the numbers mentioned for the practitioners are typically in the range of 1600-1800 kcal per day. To me, that seems high for a "restricted" diet, but it's clearly below the modern American norms.

Note that the amount of life extension does seem to rise continuously with the amount of restriction within a fairly broad range, so some people practice "caloric restriction" of only 10% or so. Incidentally, the continuous variation makes me a bit skeptical of the "starvation response" mechanism that seems popular today, and I suspect the answer is more likely to be along the lines of "finite number of cell divisions".

As for inadvertently practicing it, I used to just not eat a lot. Possibly this habit was a result of being fed unappetizing food as a child because my parents couldn't afford better. Since I wasn't very interested in food, I didn't keep a lot around. For example, during one period I was eating one egg, one slice of bacon, and 6oz of orange juice for breakfast, a full fat hamburger with lettuce and tomato and nothing else for dinner, and snacking on two or three english muffins in between because that was all that I kept around the house. When I added it up, it was about 1200 kcal per day. I did have the standard caloric restriction symptoms - cold extremities, heat tolerance and cold sensitivity, and occasional greyouts from standing up too fast.

Of course when my doctor said I was the healthiest person he'd ever seen of my age - I think I was 36 - I took that as a green light to add lots of high trans fat chocolate to my diet, which caused my cholesterol to skyrocket at my next checkup. I think that was also when I pretty much fell off the de facto caloric restriction regimen.

With respect to getting all the recommended nutrients, I think that's tricky no matter how many calories one eats, and I think some of the recommendations - in particular calcium - may be questionable. Getting a normal level of nutrients - as opposed to carefully meeting every USDA recommendation - is in my experience achievable by cutting out the empty calories - for a broad definition of "empty" which includes such things as whole wheat bread that are generally viewed as "healthy", as well as generally recognized unhealthy things like soda. Elizabeth and I follow the paleolithic diet, which is fairly strict in that respect. If you really want to get all your RDAs, though, a prenatal vitamin goes a long way.
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