禁食可以延长生殖寿命

Fasting Prolongs Reproductive Life Span

Scientific dogma has long asserted that females are born with their entire lifetime's supply of eggs, and once they're gone, they're gone.

However, this does not hold true — for nematode worms, at least, according to researchers at Fred Hutchinson Cancer Research Center.

During starvation, sexually mature adult worms stop ovulating and the germ-line component of their reproductive system — the sex cells, including mature and maturing eggs — dies off and leaves behind nothing but a few stem cells, according to the report that molecular physiologist Marc Van Gilst and colleagues published online Aug. 27 in Science.

However, once normal food conditions resume, the conserved stem cells can produce a new crop of sex cells, complete with youthful and fertile eggs.

This turning back of the reproductive clock all takes place in tiny C. elegans soil worms that are up to 15 times older than normally fed worms in their reproductive prime.

"For many, it has been assumed that cells and organs remain relatively stable during periods of starvation or caloric restriction," said Van Gilst, an assistant member of the Hutchinson Center's Basic Sciences Division. "The idea that an entire system would kill itself off during starvation and then regenerate upon food restoration was very surprising. The fact that extremely old worms could generate new eggs and produce healthy offspring long after their normally fed counterparts had reproduced and died was also unexpected."

The mechanism behind the preservation and extension of fertility long past the worms' normal reproductive prime, Van Gilst suspects, is a signaling receptor protein in the cell nucleus called NHR-49, which promotes a major metabolic response to dietary restriction and fasting.

Although it has been hypothesized that this protein may interface with calorie restriction to extend life span, its role in protecting and extending reproductive longevity in the face of starvation had not been known until now.

Van Gilst is quick to point out that, even if this mechanism is conserved in humans, it is still unknown what degree of caloric restriction would be required to affect human egg production.

"If such a process exists in humans, it likely evolved to help our ancestors preserve fertility during periods of famine or food shortage. We certainly don't have a prescription for famine. Consequently, our study should not be used to promote potentially dangerous interventions such as severe caloric restriction and starvation as a means to restore a woman's fertility," he said.