Monkey caloric restriction study shows big benefit; contradicts earlier study

The study of 76 rhesus monkeys, reported Monday in Nature Communications, was performed at the Wisconsin National Primate Research Center in Madison. When they were 7 to 14 years of age, the monkeys began eating a diet reduced in calories by 30 percent. The comparison monkeys, which ate as much as they wanted, had an increased risk of disease 2.9 times that of the calorie-restricted group, and a threefold increased risk of death.

“We think our study is important because it means the biology we have seen in lower organisms is germane to primates,” says Richard Weindruch, a professor of medicine at the School of Medicine and Public Health, and one of the founders of the UW study. “We continue to believe that mechanisms that combat aging in caloric restriction will offer a lead into drugs or other treatments to slow the onset of disease and death.”

Restricting the intake of calories while continuing to supply essential nutrients extends the lifespan of flies, yeast and rodents by as much as 40 percent. Scientists have long wanted to understand the mechanisms for caloric restriction. “We study caloric restriction because it has such a robust effect on aging and the incidence and timing of age related disease,” says corresponding author Rozalyn Anderson, an assistant professor of geriatrics. “Already, people are studying drugs that affect the mechanisms that are active in caloric restriction. There is enormous private-sector interest in some of these drugs.”

Still, the effects of caloric restriction on primates have been debated. An influential 2012 report on 120 monkeys being studied at the National Institute of Aging (NIA) reported no differences in survival for caloric restriction animals and a trend toward improved health that did not reach statistical significance.

The discrepancy may be a result of how the feeding was implemented in control animals in the NIA study, say the Wisconsin researchers. Ricki Colman, a senior scientist at the Wisconsin Primate Center, who presently co-leads the project, suggests that NIA’s control monkeys were actually calorie-restricted. “In Wisconsin, we started with adults. We knew how much food they wanted to eat, and we based our experimental diet on a 30 percent reduction in calories from that point.” In contrast, the NIA monkeys were fed according to a standardized food intake chart designed by the National Academy of Science.

Through their own experience in monkey research, and by reference to an online database recording the weight of thousands of research monkeys, the Wisconsin researchers concluded that the NIA controls were actually on caloric restriction as well, says Colman. “At all the time points that have