Sticking to a low-calorie diet over the long term slows the decline in heart function that normally occurs with aging, according to a study in the Journal of the American College of Cardiology.

“This paper is important because it is the first study in humans that strongly suggests that calorie restriction may delay primary aging,” Dr. Luigi Fontana said in a telephone interview with Reuters Health. Calorie restriction has previously been shown to slow aging and increase lifespan in small mammals.

Fontana, an assistant professor of medicine at Washington University in St. Louis, and colleagues assessed 25 healthy adults who had followed a severely calorie-restricted, nutritionally balanced diet for an average of 6.5 years, and 25 matched “control” subjects who ate a typical Western diet. The researchers looked specifically at diastolic function - how well the heart relaxed between beats.

The calorie-restricted diet provided about 1,670 calories per day, made up of approximately 23 percent protein, 49 percent complex carbohydrates, and 28 percent fat.

The Western diet delivered roughly 2,445 calories, made up of about 17 percent protein, 52 percent carbohydrates, and 31 percent fat.

The calorie-restricted diet included at least 100 percent of the recommended daily intake for all nutrients, and it was lower in salt than the Western diet.

According to Fontana, “people who followed a severe calorie-restricted diet but with optimal nutrition had a younger heart in terms of diastolic function, which is a well-accepted marker of primary aging because, independently of disease, as you get older your diastolic function gets worse and worse.”

Indictors of diastolic function were significantly better in the calorie-restricted participants than the Western diet group, the team reports, and blood pressures were significantly lower also.

The researchers plan to continue to follow the study subjects “to see if other markers of aging are delayed in these people and determine the implication for health and the aging process.”

The author of a related editorial, Dr. Gary Gerstenblith from Johns Hopkins Hospital in Baltimore, says that while it is not likely that many individuals would follow such a low-calorie diet, “the value of the study is that it points to possible mechanism explaining how aging occurs and, therefore, how it may be modified.”

He adds: “The authors, and the disciplined volunteers following the practice of caloric restriction, are to be congratulated for their important contributions to this effort.”

SOURCE: Journal of the American College of Cardiology, January 17, 2006.