Scientists are edging closer to proving in primates what's been demonstrated dozens of times in rodents since the 1930s: Sharply reducing caloric intake can slow the process of aging to a crawl. At a Society of Toxicology meeting last week in Reston, Virginia, three groups presented data showing that rhesus monkeys fed severely calorie-restricted diets show fewer signs of diseases associated with advancing age, including diabetes, heart disease, and cancer, than their comfortably full--and in some cases comparably lean--counterparts.
The three groups kept the animals on tight rations, but well above starvation levels. At the University of Wisconsin, Madison, and the National Institute on Aging, the test animals were given 30% fewer calories than the controls (while enhancing their diets with a vitamin and mineral supplement), while a team at the University of Maryland, Baltimore, tailored the monkeys' food intakes to prevent them from putting on more pounds than they carried in young adulthood. In all three studies, the monkeys on low-calorie diets fared better than controls, exhibiting everything from lower blood lipids to less arthritis to fewer cancer cases. The monkeys also seemed unfazed by hunger.
Why caloric restriction has such dramatic effects remains under debate. One possibility, advanced by the Wisconsin team, is that restricting food consumption reduces the production of tissue-damaging oxygen free radicals that are a byproduct of food metabolism. This oxidative damage leads to muscle atrophy, producing the frailty common in old age.
The studies haven't gone on nearly long enough to determine whether caloric restriction in monkeys will result in the kind of increases in life-span seen in near-starving rodents, which live up to 40% longer than controls fed normal diets. And even if monkeys do live longer on low-calorie diets, it doesn't necessarily follow that humans would experience similar benefits--or that they would be enthusiastic about going hungry. But researchers hope that these animals might provide clues to why calorie restriction is beneficial--information that could point to strategies and medications for delaying aging in humans. The primate data are "very tantalizing preliminary results," says Mark Lane, who heads the NIA group. "But [I'm] not at the point where I'm willing to stand up and wave the flag and say it works."