A new study in mice has revealed that eating less can significantly increase lifespan instead of a regular exercise regime.

The team showed that hormonal changes that occur when mice eat significantly could extend the lifespan of rodents.

"We know that being lean rather than obese is protective from many diseases, but key rodent studies tell us that being lean from eating less, as opposed to exercising more, has greater benefit for living longer. This study was designed to understand better why that is," said Derek M. Huffman, the study's lead author.

However, Huffman did warn that the study applied only to rodents, which are different in some key ways from humans. Previous studies using mouse model had shown that exercising did prevent an early death from disease, but does not extend the maximal lifespan.

Together, these findings indicated that caloric restriction protects against disease better than exercise does, and has the added benefit of extending the life span of some rats.

Physiologists have been trying to unravel the reasons for this, and two major theories have emerged.

One theory is that exercise places stress on the body, which can result in damage to the tissues and DNA. Another theory is that caloric restriction leads to physiological changes, which benefit the body.

Huffman and colleagues designed a study to examine the roles of exercise and caloric restriction, singly and combined.

Both exercise and caloric restriction moderated the level of 8-hydroxyguanosine (8-OHdG), a marker of DNA damage. Among the animals that ate all they wanted, those that did not exercise had the highest levels of 8-OHdG and those that exercised had much lower levels.

The team concluded that DNA damage increases with age and is accelerated by obesity but could be slowed by caloric restriction and/or exercise.

The study suggested that caloric restriction created beneficial changes in the body's hormone levels which exercise does not. The researchers concluded that these metabolic changes play a role in extending life.

However, calorie restriction studies are difficult to carry out in people because participants often complain of feeling hungry, lethargic, and cold.

Huffman said that the benefits of exercise may be greater for humans than for mice because people are more prone to develop cardiovascular diseases, and exercise is particularly good at warding off those diseases.

"I wouldn't say this study has direct implications for people right now. But it shows what physiological changes caloric restriction and exercise produce. We can continue to build upon these findings until we can get a better understanding of how this works in people," said Huffman.

The study appears in the May issue of the American Journal of Physiology published by The American Physiological Society.