Researchers just added more weight to the idea that a low-calorie diet extends lifespan.

A 2009 image of rhesus monkeys in a landmark study of the benefits of caloric restriction. The then 27-year-old monkey on the left was given a diet with fewer calories while the then 29-year-old monkey on the right was allowed to eat as much as it liked.
Credit: Jeff Miller/University of Wisconsin-Madison

As it so often happens, competing teams would have much better results if they worked together instead of trying to surpass each other. This time, a team from the University of Wisconsin-Madison and one from the National Institute on Aging (NIA) have worked together for the first time, leading them to settle a long-standing controversy.

In 2009, the UW-Madison study team found that a low-calorie diet caused significant health improvements, including reductions in cancer, cardiovascular disease, and insulin resistance. Monkeys that ate less than their peers were healthier and lived longer. But then, in 2012, the NIA team reported no significant improvement in survival, but did find a trend toward improved health.

“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,” says UW-Madison Associate Professor of Medicine Rozalyn Anderson one of the report’s corresponding authors.

But when they stopped contradicting each other and worked together, they not only realized what the low-calorie diet was doing, but why they were seeing such different results.

The first difference was that the two teams restricted the diets of the monkeys starting at different ages. Analysis has shown that eating less is beneficial in adult and older primates but is not beneficial for younger animals. This is a bit counterintuitive, especially when we consider that in rodents it’s exactly the opposite. Secondly, in the old-onset group of monkeys at NIA, the control monkeys ate less than the Wisconsin control group. Even small differences could lead to broadly different results. Thirdly, the two teams had completely different monkey diets. At the end of the day, it’s not just about the calories but also about the types of foods the monkeys were eating. The NIA monkeys ate organic food while most animals from the Wisconsin National Primate Research Center ate processed foods rich in sugar.

When all these things are controlled for, the improvements in health were clearly visible. Researchers also made another observation: male and female monkeys are affected by calories in different ways. For males, the calorie intensity of the meals was much more important than for females.

At this point, it’s not clear exactly how this translates to humans, but with this type of study, results likely translate as well. In other words, there’s a good chance that reducing the number of calories in your diet could lead you to live a longer and healthier life. This is a landmark finding which could serve as inspiration to countless people all around the planet.

Journal Reference: Julie A. Mattison, Ricki J. Colman, T. Mark Beasley, David B. Allison, Joseph W. Kemnitz, George S. Roth, Donald K. Ingram, Richard Weindruch, Rafael de Cabo, Rozalyn M. Anderson. Caloric restriction improves health and survival of rhesus monkeys. Nature Communications, 2017; 8: 14063 DOI: 10.1038/ncomms14063