A 20-year study involving rhesus monkeys has provided the first strong evidence that caloric restriction slows the aging process in primates.
A diet that’s nutritionally adequate but provides 30 percent fewer calories than normal has been shown to extend life span and delay the onset of age-related diseases in other animals, including flies, worms, and rodents. But because studies on primates take much longer, the benefits had not yet been demonstrated to extend to them. Now researchers at the National Primate Research Center at the University of Wisconsin-Madison report that in rhesus monkeys, caloric restriction begun in adulthood reduces risk of the most common age-related conditions–diabetes, cancer, heart disease, and brain atrophy–by a third.
“With these results, we have become convinced that aging retardation is happening,” says Richard Weindruch, a professor of medicine at the University of Wisconsin-Madison, who began the study in 1989. The research involved 76 monkeys, half of them on the extreme diet. By now, the 33 surviving monkeys have reached old age. Thirty-seven percent of the monkeys on a normal diet have died of age-related diseases, compared with just 13 percent of the monkeys on the restricted diet. It’s still unknown whether caloric restriction extends the animals’ life span, but the results published today in the journal Science detail the benefits of the diet in preventing the most common such diseases.
The strongest evidence from the study concerns metabolic disorders. While five of the monkeys on a normal diet became diabetic and 11 were prediabetic (having blood glucose levels higher than normal), monkeys on the restricted diet were completely free of the disease. The incidence of both cardiovascular disease and tumors was reduced by 50 percent in the diet group. And magnetic resonance imaging showed that caloric restriction preserved gray-matter volume in the brain as the monkeys aged. In general, the dieting group appeared to be biologically younger: age-related diseases, if they developed, occurred later in life.
The work is significant because rhesus monkeys are more closely related to humans than other animals used so far in studies of caloric restriction. “Monkeys are so closely related to us; it’s a much easier jump that this is likely to work in humans,” says Ricki Colman, a lead researcher on the study. The Wisconsin researchers also took pains to make the study as applicable to humans as possible. “We treat each animal as an individual patient,” Colman says. The animals receive physical exams every six months, along with full dental care and medical interventions as needed. “We treat the diabetes with insulin, and when we identify tumors we remove them,” she explains.