单选题 As a volunteer, John Apollos is losing weight—the old-fashioned way—by eating less. Apollos has lowered his daily caloric intake 25% over the past eight months. The fat, not surprisingly, has melted away. But that"s not the real reason Apollos and the other participants in the program are eating only three-quarters of what they used to. The researchers are trying to determine whether restricting food intake can slow the ageing process and extend our life span. "I feel better and lighter and healthier," says Apollos. "But if it could help you live longer, that would be pretty amazing."
The idea is counterintuitive: If we eat to live, how can starving ourselves add years to our lives? Yet decades of calorie-restriction studies involving organisms ranging from microscopic yeast to rats have shown just that. Last July a long-term study led by researchers at the University of Wisconsin, found that calorie restriction seemed to extend the lives of humanlike rhesus monkeys (恒河猴) as well. The hungry primates fell victim to diabetes, heart and brain disease and cancer much less frequently than their well-fed counterparts did.
Scientists have suspected that calorie restriction could extend the life span of animals since at least 1935, when researchers at Cornell University noticed that severely food-restricted lab rats lived twice as long as normal ones and were healthier. Other investigators began exploring the idea and learned that the secret is not merely a matter of body weight.
One theory is that a state of slight hunger acts as a mild but constant stressor that makes an organism stronger and more resistant to the ills of ageing. Taking in fewer calories also slows metabolism (新陈代谢), and some data indicate that humans with a slower metabolism live longer. But even if these theories are correct, simply defining the mechanism is not the same as identifying the molecular pathways behind it. If researchers could determine those pathways, they might be able to pharmacologically mimic (模仿) the effect of calorie restriction. That could be the ultimate benefit of the CALORIE study. "Calorie restriction is pretty much the only thing out there that we know will not just prevent disease but also extend maximal life span," says Dr. Marc Hellerstein, a nutritionist at the University of California.