By Amy Norton

NEW YORK, Nov 21 (Reuters Health) - Cutting calories has been shown to extend the life span of mammals, and now it seems a strict diet can even buy extra time for an already long-lived mutant mouse.

Scientists say their success in extending the lives of the unusually aged rodents was a surprise--one that gives more weight to the idea that counting calories can help people lead longer lives.

Reporting in the November 22nd issue of Nature, Illinois researchers describe their experiments with Ames dwarf mice, a type of mouse that lives 50% longer than their normal brethren thanks to the "longevity" gene they carry.

These mutant mice are similar in some respects to normal mice whose life spans have been extended by calorie restriction, according to Andrzej Bartke and his colleagues at Southern Illinois University in Carbondale.

To see whether calorie restriction could confer still-longer lives to the mutants, the scientists divided 2-month-old Ames dwarf mice into two groups: one allowed to feast at will, and one on a strict diet. They did the same with normal mice.

The investigators found that the dieting dwarf mice lived the longest of the four groups, while normal mice allowed to eat as they pleased had the shortest lives.

Bartke told Reuters Health that before this experiment, the possibility of extending the mutant mice's lives seemed "exceedingly unlikely."

"In fact," he said, "we did not expect it. This certainly adds to the evidence that calorie restriction has a very impressive ability to prolong life."

As for humans, Bartke said the steep calorie cuts used in lab mice would not be healthy or acceptable to most people.

However, he noted, such research echoes the general health advice people are used to hearing. "Avoid overeating," he said, "and maintain a reasonable balance between energy intake and exercise."

Experts suspect that the benefit of calorie restriction on life span has evolutionary roots. In times of food shortage, the body's metabolism adjusts to aid survival. And certain hormonal regulators of metabolism have been shown to help determine the life spans of flies, worms and yeast.

There is "an emerging concept that limited availability of food can lead to physiological adaptations that favor survival," Bartke said. "This could be viewed as 'waiting until food is more plentiful.'"

SOURCE: Nature 2001;414:412.

http://www.reutershealth.com/archiv...121elin002.html