Editors' ChoiceAging

You Can Have That Dessert—Sometimes

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Science Translational Medicine  12 Sep 2012:
Vol. 4, Issue 151, pp. 151ec166
DOI: 10.1126/scitranslmed.3004903

Earlier this year, the U.S. National Institutes of Health released an ominous report on obesity. The study suggested that without efforts to thwart the rise in obesity rates, the life expectancy for average Americans could fall by up to 5 years. Scientists speculate—and disagree—about the upper limit of human life in terms of years, and numerous studies in a variety of model systems have implied that calorie restriction can lengthen life. Now, the surprising results of a new long-term study show that caloric restriction did not enhance longevity in rhesus monkeys.

Starting in 1987, 40 young monkeys were randomized to caloric restriction (CR) of ~25%, and 46 served as controls. Food portioning was also regulated in the control group, which prevented obesity. In a second cohort, CR was started later in life, at the age of 16 to 23 years. In the late-onset group, monkeys undergoing caloric restriction were not starved because their feeding behavior was largely unchanged after CR was initiated, but they weighed less, and their metabolic health was improved (for example, lower fasting cholesterol and glucose blood levels in old age diet onset) relative to controls. However, CR did not result in an increase in mean or maximum life span in either cohort. Furthermore, there were no differences in causes of death between the two diets. However, autopsy studies reported a lower incidence of cancer in monkeys with early-onset CR.

The data from this prospective trial in primates were eagerly awaited. Some studies in mice and rats had shown a benefit of CR, whereas some did not. There was one other trial in monkeys at the Wisconsin National Primate Research Center that reported an improved survival after CR. The design of the two studies differed in several aspects, perhaps most importantly in the unrestricted access to food in the control group in the Wisconsin study, which resulted in higher body weights in the non-CR monkeys. Thus, the jury is still out on whether very skinny, well-nourished people have a prolonged life span. It is clear, however, that obesity is a potent risk factor for a number of lethal diseases; so it is important not to misinterpret these mixed messages when perusing a dessert menu.

J. A. Mattison et al., Impact of caloric restriction on health and survival in rhesus monkeys from the NIA study. Nature, published online 29 August 2012 (10.1038/nature11432). [PubMed]

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