Consuming fewer calories may slow down the effects of aging in both the heart and body.

Primary aging refers to the maximal length of a person's life. Secondary aging refers to any disease, such as heart disease or cancer that can prevent a person from reaching their maximum life span. By reducing or eliminating factors that interfere with secondary aging, a person should be able to better reach their projected lifespan. By slowing primary aging, a person can effectively increase the length of their projected lifespan.

Previous research has suggested that calorie restriction helps make the heart more elastic, allowing it to relax more between beats. This effect appears to allow older hearts to beat more like young hearts.

As part of the new study, researchers from the Washington University School of Medicine in St. Louis examined 28 people who had participated in a calorie restricted diet for an average of six years. These participants' daily diet consisted of an average of only 1,800 calories per day, though their diets did include 100 percent of the recommended daily amounts of protein and micronutrients.

A second group of 28 people was composed of sedentary individuals who maintained a typical Western diet that included about 2,700 calories per day. A third group of 28 participants ate a Western diet, but also engaged in endurance training.

The researchers found that only those participants who practiced calorie restriction experienced a reduction in concentrations of a thyroid hormone called triiodothyronine (T3). T3 has previously been shown to help control the energy balance and cellular metabolism in the body.

Individuals who practiced calorie restriction also experienced a reduction in an inflammatory molecule called tumor necrosis factor alpha (TNF). The researchers believe, based on earlier animal studies, that this combination of lowered T3 levels and reduced inflammation may slow down the aging process by reducing the body's metabolic rate. It may also help reduce any oxidative damage being done to cells and tissues.

The effects of calorie restriction on primary aging had previously been hinted at in animal studies, which showed that calorie restriction can extend the life of rats more than exercise.

"Sedentary rats who ate a standard diet had the shortest average life-spans. Those who exercised by running on a wheel lived longer, but animals on calorie restriction lived even longer," explained John O. Holloszy, M.D., professor of medicine at Washington University School of Medicine, in a 1997 report that appeared in the Journal of Applied Physiology.