A preliminary study in human suggests that reducing calories may well extend life, researchers report in this week's Journal of the American Medical Association.

"A lot of evidence already exists to suggest that calorie restriction increases maximum life span in several animal species. However, there hasn't been any proof of it being the case in humans," co-author Dr. Eric Ravussin, from Louisiana State University in Baton Rouge stated. "This is the first step toward looking at the beneficial effects of calorie restriction in humans."

Ravussin and his team enrolled 48 healthy overweight (but not obese) men and women in a 6-month trial looking at the effects of calorie reduction. Participants were assigned to one of four groups: a control group, which followed a normal diet; a calorie restriction group, which received 25 percent less calories than the daily requirement; a third group, which exercised and reduced calorie intakes (12.5 percent calorie restriction and 12.5 percent increase in energy expenditure); or a group that received a very low calorie diet, starting with 890 kcal a day and then increased to maintain a 15 percent weight loss.

After 6 months, while patients in the control group lost about 1 percent of their weight, both calorie restriction groups (with or without exercise) lost approximately 10 percent. Individuals on the very low-calorie diet lost nearly 14 percent of their weight.

The researchers also observed lower blood levels of insulin after fasting and a lower body temperature in all participants who undertook a restricted calorie regimen.

"Body temperature and blood insulin levels are markers of longevity like gray hair or wrinkles can be, " said Ravussin. "It has been shown both in animals and humans that those with lower body temperature tend to live longer, and so do those with lower fasting insulin levels."

Another important finding, according to Ravussin, was that less DNA damage seemed to occur in patients with lower calorie intakes.

"One of the many theories of aging is that there is more DNA damage happening, which is the destruction of genetic information -- smokers for example have more DNA damage," said Ravussin. "So this is a very important information, totally novel in humans, that calorie restriction can reduce DNA damage."

SOURCE: JAMA, April 5, 2006.