The practice of restricting calories has often been wrapped in controversy — and now a new set of findings reveal that it helps monkeys live healthier, longer lives.

A long-running monkey trial concluded that calorie restriction made them live around three years longer than usual, translating to about nine years in humans.

While a calorie-restricted diet may not be the right fit for everyone, better understanding the mechanisms behind its potential benefits may lead to anti-aging solutions in the future, according to Julie Mattison of the National Institute on Aging.

“The goal is to improve human health,” said Mattison in a New Scientist report.

Conflicting Results

Previous research has demonstrated how calorie restriction extends lab organisms’ lifespan, from mice to worms. Many individuals have tried keeping their daily count from 1,500 to 1,800 kilocalories, whereas the usual recommendations are 2,500 kcal for men and 2,000 for women.

Two trials on the controversial matter had stood out. The studies on nearly 200 macaques, which usually live up to 26 years in captivity, were established in the late 1980s and yielded seemingly conflicting results.

The group from University of Wisconsin-Madison reported in 2009 that the monkeys on a restricted intake were living longer than the control group and having significant reductions in cancer, heart disease, and insulin resistance, while the NIA team found in 2012 the same trend toward better health but no difference in the animals’ survival rates.

“These conflicting outcomes had cast a shadow of doubt on the translatability of the caloric-restriction paradigm as a means to understand aging and what creates age-related disease vulnerability,” said study author and UW-Madison associate professor of medicine Rozalyn Anderson.

The Benefits Stand Out

The two teams recently compared their conflicting results and previous analyses, and now the positive findings emerged stronger. The NIA research, for one, faced several issues: some control monkeys eating fewer-than-expected calories, and some creatures started their calorie restriction as youngsters, therefore facing reduced lifespan.

In the NIA trial, too, it is worth noting that four of the monkeys that started the diet during adulthood exceeded age 40 and broke longevity records in their species.

A previous study, this time conducted in humans, showed that non-obese individuals have better mood and overall health with 25 percent calorie restriction.

Studying 218 human subjects, a Pennington Biomedical Research Center team found that the calorie-restricted group shed 15.2 percent of body weight at the end of the first year. After two years, the researchers compared results with their baseline data and saw that the same group had an average weight loss of 16.7 pounds, while the control group lost only less than a pound.

The calorie-restricted group also showed better mood and sleep, sexual drive, and overall health.

Focusing On Potential Human Benefits

The new findings may not yet be the final word on whether the diet indeed makes one live longer.

Luigi Fontana from Italy’s University of Brescia pointed to the calorie-restricted monkeys’ lower rates of cancer and heart disease — the major causes of death in humans — as the one actually lending support to the idea that the benefits also apply to people.

Brian Delaney, who chairs the Calorie Restriction Society and practicing calorie restriction for over two decades now, said the dietary restriction already comes easy for him. For others, however, it could mean very precise planning of meals, and it may not necessarily be all that helpful.

“I’m not at all certain that people who are a healthy body weight should restrict to some emaciation level. Life might seem longer, but it wouldn’t necessarily be longer,” explained aging expert Steve Austad from the University of Alabama.

Researchers of the report, discussing their findings in the journal Nature Communications, delved on the seeming promise of the diet on slowing aging.

“[I]t puts emphasis now on the idea of aging itself being a druggable target,” Anderson added.