Monkeys that eat less than normal live longer and are healthier than other monkeys, meaning the same is likely true for humans, according to a new study by scientists at UW-Madison and the National Institute on Aging.
The institutions teamed up to look at why their previous, separate studies yielded contradictory results. Monkeys put on restricted diets in Madison saw benefits in survival and warding off disease, but similar monkeys at the federal institute in Baltimore, Maryland, did not.
The discrepancy raised questions about whether caloric restriction, found to increase lifespan in yeast, worms, flies and mice, could do the same in primates, including people.
Now, after combining data and comparing notes, the two groups of scientists found that the UW-Madison conclusions hold true overall, they reported Tuesday in the journal Nature Communications.
“Reducing calorie intake improves health and survival,” said Rozalyn Anderson, a UW-Madison associate professor of medicine involved in the study. “What you eat and how much you eat will affect how you age.”
The cooperative analysis led to a new proposition, however. The level of caloric restriction necessary to extend life and improve health, initially thought to be 30 percent below a normal diet, might be considerably less. Researchers hope additional studies can pinpoint the amount.
“Is it 10 percent? It is 15?” Anderson said. “Maybe a little bit of food intake reduction is good enough.”
That premise stemmed from differences in how the studies at UW-Madison and the aging institute have been conducted. The institutions run the only long-term studies of caloric restriction in rhesus monkeys, considered good models of human biology.
The university’s study, started in 1989, involved 76 monkeys. The aging institute’s study, which began in 1987, enrolled 121 monkeys. Many of the monkeys have died naturally over the years, but the studies continue.
Both groups of scientists fed half of their monkeys less than normal. But in Madison, the food has been higher in fat and sugar, and monkeys on regular diets have been more free-fed. The university’s study didn’t initiate caloric restriction until monkeys were adults, but the aging institute started some monkeys on special diets when they were young.
At the aging institute, monkeys on regular diets didn’t eat much more than those whose caloric restriction started as adults. The body weight of monkeys on regular diets and special diets didn’t vary much.
That made it seem like eating fewer calories didn’t help the monkeys. But when both groups of monkeys at the aging institute were compared with those at the university, where food intake and weight among the groups differed more, it became clear that eating less prolongs life and improves health.
Another finding from the new analysis is that caloric restriction in monkeys is beneficial in adulthood but not when started at a young age, which is different from what had been found in mice.
Rhesus monkeys generally live 26 years, but those on the restricted diets live about 28 years, which translates to a gain of about six years for humans, Anderson said.
Rates of cancer, diabetes, heart disease and other conditions are more than twice as high among monkeys on regular diets than those on restricted diets, she said.
Among the 10 monkeys from the UW-Madison that are still alive, eight have been on restricted diets, with the oldest one nearly 36 years old, said Ricki Colman, a senior scientist at the Wisconsin National Primate Research Center, involved in the study. In the aging institute study, the oldest monkey is 43.
A caloric restriction study in people, based at Washington University in St. Louis, found that eating less than normal appeared to lower the risk of cardiovascular disease and make people more sensitive to insulin.
But the study, in which people aimed to cut daily calorie intake by 25 percent over two years but achieved only a 12 percent reduction, did not find metabolic benefits identified in animal studies, according a report published in 2015 in the Journal of Gerontology: Medical Sciences.
The goal of the UW-Madison study is to better understand how the aging process increases the risk for disease, with the potential to identify new targets to prevent disease, Anderson said.
“When we can figure out what (caloric restriction) is doing, that will inform what is creating disease vulnerability in aging,” she said.
‘What you eat and how much you eat will affect how you age.’ Rozalyn Anderson,
associate professor of medicine