WEDNESDAY July 2, 2008 (foodconsumer.org) -- A new study by researchers at Saint Louis University found some evidence to support the hypothesis that calorie restriction may be able to extend a person's lifespan.

Calorie restriction works well in some animals such as rats and mice to elongate their lifespan.   But it remains unknown how calorie restriction affects the aging process in rodents.

One theory is that calorie restriction slows aging by decreasing the level of a thyroid hormone called triiodothyronine (T3) in the body, which in turn slows metabolism and tissue aging.

“Over recent years, there has been a huge amount of debate about whether calorie restriction slows the aging process in humans,” said Edward Weiss, Ph.D., associate professor of nutrition and dietetics.

The current study published in the June 2008 issue of Rejuvenation Research was meant to see how calorie restriction would affect the same hormone in humans.

For the study, one group of volunteers followed a diet with its total energy cut by 300 to 500 calories ,one group followed a regular diet, but did exercise regularly and a control group did not cut calories nor did much of physical exercise.

The volunteers were sedentary, non-smoking men and post-menopausal women aged 50 to 60 with average or slightly above average body mass indexes.   They were free of cardiovascular disease, diabetes, lung disease, uncontrolled hypertension and evidence of malignancy when entering the study.

During the one-year follow-up, volunteers in both the calorie restriction and exercise groups experienced similar change in body fat mass. But the volunteers in the calories restriction group, not other two groups experienced lower levels of the thyroid hormone.

A long term study is needed to determine whether reducing T3 levels through calorie restriction slows the aging process, according to the researchers.   But the current study resulted in some evidence to suggest a possibility that T3 may be involved.

It is logically possible when intake of calories is low, human bodies would slow down their metabolism and other biochemical processes, and conserve the energy for more adverse condition the body may have to deal with in the future.   As a result, calorie restriction leads to slower aging process.