Scientists have long known a fairly reliable way to extend life span in rodents and other lab animals: Reduce the amount of calories they eat by 10 percent to 40 percent. 

This strategy, known as caloric restriction, has been shown to increase the life span of various organisms and reduce their rate of cancer and other age-related ailments.Whether it can do the same in people has been an open question.But an intriguing new study suggests that in young and middle-aged adults, chronically restricting calorie intake can have an impact on their health. 

In the new study, which was funded by the National Institutes of Health and published this month in the Lancet Diabetes & Endocrinology, researchers looked at a group of 143 healthy men and women who ranged in age from 21 to 50.They were instructed to practice caloric restriction for two years.They could eat the foods they wanted so long as they cut back on the total amount of food they ate, with the aim of cutting the calories they consumed by 25 percent. 

Many did not achieve that goal.On average, the dieters managed to slash about 12 percent of their total calories, or roughly 300 calories a day, the amount in a large bagel, a few chocolate chip cookies or a small Starbucks Mocha Frappuccino.But the group saw many of their cardiovascular and metabolic health markers improve,   even though they were already in the normal range. 

They lost weight and body fat Their cholesterol levels improved, their blood pressure fell slightly,and they had better blood sugar control and less inflammation.At the same time, a control group of 75 healthy people who did not practice caloric restriction saw no improvements in any of these markers. 

Some of the benefits in the calorie restricted group stemmed from the fact that they lost a large amount of weight, on average about 16 pounds over the two years of the study.But the extent to wluch their metabolic health got better was greater than would have been expected from weight loss alone, suggesting that caloric restriction might have some unique biological effects on disease path ways in the body, said William Kraus, the lead author of the studyand a professor of medicine and cardiology at Duke University. 

“We weren't surprised that there were changes,” he said.“But the magnitude was rather as-tounding.In a disease population, there aren't five drugs in combination that would cause this ag-gregate of an improvement.”

Calorie restriction may be a useful tool for better health and weight loss, but it's unclear whether the changes in the new study will ultimately translate into longevity and reductions in chronic disease, said Frank Hu, the chairman of the nutrition department at the Harvard T.H.Chan School of Public Health, who was not involved in the research.