A pair of 27-year-old monkeys are part of a national study that failed to find a longevity benefit to calorie restrictions. The one on the left consumed 30 percent fewer calories than the monkey on the right.

National Institute on Aging

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SALT LAKE CITY Restricting calories may extend the life of rodents, but it doesn't seem to increase longevity for monkeys, according to surprise findings in a much-anticipated study published this week by the journal Nature. Monkeys do, however, get some health benefits from consuming fewer calories.

Many earlier studies suggested that restricting calories adds years to life in lab-bred rodents. The findings were so compelling, in fact, that many scientists and others have curbed their own caloric intake in anticipation of reaping extra years. Caloric restriction decreases calories by as much as 40 percent, but maintains the nutrients found in a standard diet.

Drug manufacturers have sought drugs that would "mimic the salutary effects of a skimpy diet without triggering severe hunger pangs," according to an article in the Wall Street Journal.

The new research, collected over 30 years (because that's the outer lifespan of monkeys), casts doubt on whether the benefits found for rodents would extend to people, since monkeys and humans are primates and more similar genetically.

"One thing that's becoming clear is that calorie restriction is not a Holy Grail for extending the lifespan of everything that walks on earth," Rafael de Cabo, an experimental gerontologist in the U.S. National Institute on Aging and lead study author, told WSJ.

To test the calorie restriction theory, the NIA scientists restricted by 30 percent the diets fed two sets of monkeys. The first group included monkeys ages 1 to 14, while the other group was made up of older monkeys, 16 to 23. They were compared to similar groups with more normal diets.

The male animals on calorie restriction had lower cholesterol; the females didn't. Cancer incidence appeared to fall with caloric restriction, but heart disease increased slightly. Age-related diseases, however, appeared a bit later in calorie-restricted animals.

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Calorie restriction doesn't add years of life, at least to monkeys