Restrict calories, increase life span? Not so easy

The anti-aging effects of calorie restriction were first identified in the 1930s by Cornell University researchers who showed that lab rats fed a diet that provided all their needed nutrients, but only 30% of their usual caloric intake, lived 30% longer than rodents on the usual lab-rat diet. The underfed rats not only lived longer, they looked and acted younger too.

The life-extending effects of low-calorie diets have since been replicated in mice, yeast, worms and fruit flies. And last Friday, researchers reported in the journal Science that adult rhesus monkeys fed a diet for as many as 20 years that consisted of 30% fewer calories than normal lived longer than a control group fed a regular diet.

During the study period, the calorie-restricted animals were more likely to develop age-related diseases and conditions such as arthritis, diabetes, heart disease, cancer, brain atrophy and muscle loss. And by study's end, only 13% of the animals in the calorie-restricted group had died of causes related to age compared with 37% of the controls.

Scientists are currently studying such a diet's effects on people -- a tougher proposition because human diets are hard to control, especially for long periods.

A preliminary study of 48 adults showed that overweight people who reduced their caloric intake by 25% for six months significantly lowered their fasting insulin levels and their core body temperatures -- both key trends seen in animals who lived longer as a result of eating less. The research was conducted by scientists at Louisiana State University in Baton Rouge and published in 2006 in the Journal of the American Medical Assn.

Calorie restriction may seem promising, but it has potential downsides, including constant hunger, sensitivity to cold, weakened immune function and sour mood, says Susan Roberts, professor of nutrition and psychiatry at Tufts University, where she is leading a study on calorie restriction diets.

Roberts says many of her subjects appear to be improving in health on their calorie-restricted regimens, but it's too early to draw any hard conclusions on the diet's benefits. "When I see them after two years, they look great," Roberts says of her subjects. "But would I be writing a book about longevity? Not yet."

health@latimes.com