Jul 14 2009

Calorie Restriction for Life Extension – in Primates

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I have been following the research in this area – using calorie restriction to extend the life span by slowing the aging process. This has been demonstrated for decades now in several species: mice, yeast, and roundworms. The big question has always been – does this research apply to humans. There are those who are banking on the answer being yes, but the data is just not in.

Previous research suggests we may not be able to extrapolate this research to humans. One of the correlates of life extension in mice with calorie restriction is reduced levels of the hormone IGF-1.  However, humans on a restricted calorie diet did not have reduced levels of IGF-1. We do not yet understand enough about the effects of calorie restriction and their relationship to life extension to know exactly what this means.

Therefore the question of whether or not calorie restriction will work in humans remains open. But new research shows, for the first time, that calorie restriction extends life expectancy in primates.  The journal Science reports:

Studying aging in monkeys takes patience. Mice and rats only live for a couple of years, while these monkeys can live to 40, and the average life span is 27 years. Now that the surviving monkeys have reached their mid- to late 20s, the Wisconsin group could glean how calorie restriction was affecting their life span. Sixty-three percent of the calorie-restricted animals are still alive compared to only 45% of their free-feeding counterparts. For age-related deaths caused by illnesses such as cardiovascular disease and cancer, the voracious eaters died at three times the rate of restricted monkeys: 14 versus five monkeys, respectively. Another seven control and nine lean monkeys died from causes not related to aging such as complications from anesthesia or injuries. Leaner diets also reduced muscle and brain gray matter deterioration, two conditions associated with aging.

There are three groups studying calorie restriction in primates – this is the first group to publish their results.  This group of rhesus monkeys will continue to be followed to years, and so we will still get more data from them, plus we will be able to compare to the two other groups. If all three groups show statistically significant life extension, that will be fairly solid evidence for an effect.

This is very significant to the question of whether or not this calorie restriction effect applies to humans. It is a much shorter trip from monkeys to humans than it is from yeast or even mice to humans. This is precisely why for certain questions we still need to do research on primates.

Even still, monkey research will not be definitive. We will still need to study the effect in humans, which of course is very difficult. It takes decades to see an effect, and it is tedious to follow many individuals in sufficient detail over that period of time. So far research has focused on studying biological markers (like the IGF-1 study) not net effects. While this type of research is very useful and often predictive, it is never definitive. Eventually we will need studies looking at the net effects of calories restriction in large numbers of humans over decades.

The monkey research is a significant boon to those claiming calorie restriction extends life, but it does not end the debate.

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