Eating less fails to extend monkey lives

Who wants to live forever? Apparently, some humans do ? and many think eating less could help. But hungry monkeys who died at a normal age have cast doubt on the power of calorie restriction.

Laboratory animals on sparse diets enjoy impressive increases in lifespan, with calorie-controlled mice living up to 50 per cent longer than average. In 1987, a study began into the effects of calorie restriction on rhesus monkeys. The idea was to test if larger animals can reap the same benefits from eating less. If they can, it is possible humans can too.

"Now that the monkeys are reaching their maximal lifespan, we can start looking at the effects of calorie restriction on longevity," says Rafael de Cabo, who, along with his colleagues, inherited the long-running study at the National Institute of Aging (NIA) in Bethesda, Maryland.

The team's latest results show that monkeys eating 30 per cent less than control animals did not have longer lives. Dieting monkeys also died from age-related diseases just as often as controls.

The results not only conflict with findings from worms, flies, rats and mice, but also with those of a very similar study of rhesus monkeys at the University of Wisconsin-Madison, published in 2009.

Differing methodologies

Richard Weindruch, the lead author on the 2009 study, attributes the inconsistent results to differences in methodology. He says the higher-quality and slightly restricted diet of the NIA control monkeys meant they were already living longer than expected. By contrast, the monkeys in Weindruch's study were fed a refined diet high in fat and sucrose, more similar to a Western diet.

Janko Nikolich-Zugich at the University of Arizona in Tuscon, who was not involved in either study, is not surprised by the conflicting results. He noted that they are in keeping with previous tests, which show that the effects of calorie restriction vary with sex, genetics and environmental conditions.

Luigi Fontana at the Washington University School of Medicine in St Louis, Missouri, was not involved in either report. He believes both studies should have paid more attention to dietary composition.

"Fifteen per cent of the monkey diet came from protein ? that's too much," he says. "Our work suggests lowering protein, rather than calories, may be the key to increasing longevity ? so reducing protein intake could have led to better results."

De Campo agrees that dietary composition might play a role in lengthening life, but claims the benefits of calorie restriction are still strong. "Although we don't have the same lifespan findings as the Wisconsin group, what's really important is that we did show similar improvements in health," he says.

Journal reference: Nature, DOI: 10.1038/nature11432

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