Studies have long shown that reducing calorie intake slows the aging process in rats and mice. Considering the studies didn’t involve humans, this didn’t motivate us to start dieting.

Now, scientists have discovered health benefits that’ll encourage middle-aged people to cut out a few hundred calories.

Researchers at Saint Louis University studied healthy but sedentary, non-smoking, 50- to 60-year-old men and post-menopausal women.

For a year, the volunteers participated in one of three groups: a calorie-restriction group that cut their daily calorie intake by 300 to 500 calories per day, a group that stayed on their regular diet and exercised regularly or a group that maintained its normal routine.

While those in the calorie-restriction and exercise groups both lost body-fat mass, only those in the calorie-restriction group also had lower levels of the thyroid hormone.

A popular theory is that fewer daily calories decreases production of the thyroid hormone triiodothyronine (T3), which then slows metabolism and tissue aging.

"There is plenty of evidence the calorie restriction can reduce your risks for many common diseases including cancer, diabetes and heart disease," said Edward Weiss, Ph.D., associate professor of nutrition and dietetics at Saint Louis University’s Doisy College of Health Sciences. "And you may live to be substantially older."

—Based on the findings published in the June 2009 issue of Rejuvenation Research