New clues about calorie restriction

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Scientists have found new clues to how restricting the number of calories someone consumes may help increase longevity.

A number of studies found that severely restricting the caloric intake of rodents, fruit flies, worms and other animals makes them live longer. That has prompted some people to try to live on severely restricted diets. Although no one has shown that will actually work in people, a growing body of evidence suggests it might.

In the newest study, researchers at the Pennington Biomedical Research Center in Baton Rouge studied 36 people who were overweight but not obese. A third ate a diet fully meeting their energy needs. One-third ate 25 percent fewer calories, while the last third ate 12.5 percent fewer calories and increased their exercise to burn 12.5 percent more calories.

After six months, the researchers found that those who reduced their calories by 25 percent, either by diet alone or through diet and exercise, had a marked increase in the function of structures inside muscle cells known as mitochondria. Mitochondria produce energy for cells. They also experienced less DNA damage in muscle cells. In addition, there was increased activity by a gene known as SIRT1. The equivalent gene in yeast, worms and flies play a role in extending life span.

The researchers, who published their findings in the Public Library of Science's journal Medicine, cautioned that more research is needed to determine whether the effects are sustained for longer periods and translate into increased longevity.

-- Rob Stein