Washington: Cut those calories out - and look younger and live longer. That's what the latest research says.

While not much is known about how curbing calories affects aging, researchers working with mice found it decreases a thyroid hormone called triiodothyronine (T3) which, in turn, slows metabolism and tissue aging.

The new study, by scientists at Saint Louis University, found that even reducing 300 to 500 calories daily, had a similar biological effect on humans and, therefore, may slow the aging process.

"Over recent years, there has been a huge amount of debate about whether calorie restriction slows the aging process in humans," said Edward Weiss, co-author of the study.

"Our research provides evidence that calorie restriction does work in humans like it has been shown to work in animals. The next step is to determine if this, in fact, slows age-related tissue deterioration.

"The only way to be certain, though, is to do a long-term study."

In the study, Weiss, to determine if calorie reduction would lower T3 levels in humans, recruited volunteers to lose weight through exercise.

Volunteers were in good health and comprised sedentary, non-smoking, 50- to 60- year-old men and post-menopausal women with average or slightly above average body mass index (BMI) values.

Volunteers were randomly assigned to one of three groups -- a calorie-restriction group, an exercise group or a control group -- and followed for one year.

Volunteers in the calorie restriction group lost weight by reducing their daily calorie intake by 300 to 500 calories per day. Volunteers in the exercise group maintained their regular diet and exercised regularly.

Volunteers in both the calorie-restriction and exercise groups experienced similar changes of body fat mass. However, only volunteers in the calorie restriction group also experienced lower levels of the thyroid hormone.

Because it also slows metabolism, Weiss warned that calorie-restricted weight loss could make people more prone to weight gain over time.

On the other hand, people who lose weight through exercise are not as likely to gain weight back if they quit exercising. The key to maintaining a healthy weight, Weiss said, is keeping a consistent diet and exercising regularly.

The findings of the study have been published in the latest issue of the journal Rejuvenation Research. IANS