A calorie-restricted diet can extend the lives of organisms from yeast to fruit flies to rodents, as well as improving their health and preventing disease. But just because cutting calories helps animals with short lifespans doesn’t mean that humans will reap similar benefits. So the 2009 discovery that calorie-restricted diets also increase the longevity of already-longer-lived rhesus monkeys was exciting news.
But don’t pull out a calorie calculator quite yet. The latest word on the subject, from a new paper in Nature, suggests that the 2009 study might not tell the whole story: this team found that caloric restriction doesn’t actually grant rhesus monkeys longer lives.
In this new 23-year-long study from the National Institute on Aging (NIA), rhesus monkeys, which have an average lifespan of 27 years in captivity, ate either a nutritious diet as control subjects or the same diet slashed by 30 percent. Some of the monkeys had their calorie intake restricted from a young age, while for others, the restricted diet only set in when they were 16 to 23 years old.
For the old-onset monkeys, a restricted diet improved health but did not increase longevity or influence cause of death. But among the young-onset monkeys, cutting calories significantly improved neither health nor longevity. (Although some of the young-onset rhesus monkeys are still alive, based on estimated probability statistics, there is less than a 0.1 percent chance that the calorie-restricted subjects will significantly outlive the controls.)
So why do these NIA results differ from the 2009 study, conducted by the Wisconsin National Primate Research Center (WNPRC)? For one thing, the makeup of the monkeys’ diets varied from one experiment to the other, and the monkeys themselves had different geographical origins and genetics. But perhaps a more significant detail was portion control. Even the control monkeys in the NIA study received carefully proportioned meals, albeit larger ones than the calorie-restricted monkeys. The WNPRC controls, on the other hand, set their own meal sizes on an all-you-can-eat basis, and generally outweighed their NIA counterparts.
Cutting calories, then, may make more of a difference in lifespan when you’re comparing extreme dieters to those who gorge to their hearts’ content.
Image courtesy of Nancy Collins / Wikimedia Commons