A new study that found that a lower-calorie diet slowed the aging process in monkeys could be the best proof yet that restricted diets might do the same for humans.
The big question in aging research is, 'Will caloric restriction in species closely related to humans slow aging?'" said Richard Weindruch, senior author of a paper appearing in the July 10 issue of Science. "This is the first clear demonstration that, in a primate species, we're inducing a slowdown of the aging process -- showing increased survival, resistance to disease, less brain atrophy and less muscle loss.
"This predicts humans would respond similarly," added Weindruch, professor of medicine at the University of Wisconsin-Madison and an investigator at the Veterans Hospital in Madison.
Another expert noted that, despite some highly publicized studies in certain species, the link between restricted eating and longer lifespan has been far from proven.
"The idea that dietary restriction extends lifespan in all species is not true. Many strains of rats and mice do not respond. In some strains, it's actually deleterious," explained Felipe Sierra, director of the biology of aging program at the U.S. National Institute on Aging (NIA), which supported the new study. "The fact that it didn't work in some mice but it does seem to work in monkeys is surprising and it gives us hope."
But there's a larger question: how to change humans' increasingly lax eating habits. "This [finding] doesn't give me hope that humans are going to go into dietary restriction," Sierra said.
Another expert agreed. "I think this is wonderful and it has promising benefits but the problem is not that we don't know this stuff, the problem is doing it, is getting people to eat less," added Marianne Grant, a registered dietitian at Texas A&M Health Science Center Coastal Bend Health Education Center in Corpus Christi.
As Sierra sees it, the ultimate value of this and other research like it will be to unveil the physiological mechanisms behind a slowdown in the aging process, and then come up with ways to mimic those processes with drugs or other interventions.
Previous research had shown that calorie restriction can increase survival and stave off many diseases in yeast, worms, flies and, as Sierra pointed out, in some strains of mice.
The new, two-decade-long study ultimately involved 76 rhesus monkeys, all of whom started the study as adults (aged 7 to 14 years). Thirty-three monkeys are still alive, 13 of whom are allowed to eat as they like. The other 20 are allowed a diet with 30 percent fewer calories.
Eighty percent of the original monkeys eating fewer calories are still alive, versus half of those in the control group, the researchers reported.
Among the benefits enjoyed by the lower-calorie group: fewer cancers, less cardiovascular disease, better preserved brain health (especially in regions of the brain involved in motor control and memory) and no diabetes whatsoever, despite this being a common problem in monkeys.
Weindruch said his group is continuing to study the monkeys, a process that could go on for 15 years. Meanwhile, they are collecting a new group of monkeys to more closely study mechanistic processes.
The NIA currently supports a study looking into calorie restriction in humans although, Sierra pointed out, such a study is difficult to conduct.
"Studies in humans can be done but they're not going to address longevity and it's a self-selected group," he said. "Monkeys are the closest we can get."
The findings come a day after U.S. researchers reported in Nature that rapamycin, a drug typically given to transplant patients, significantly extended the lifespans of mice.