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  3. Dieting, according to an old joke, may not actually make you live longer, but it sure feels that way. Nevertheless, evidence has

Dieting, according to an old joke, may not actually make you live longer, but it sure feels that way. Nevertheless, evidence has

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问题     Dieting, according to an old joke, may not actually make you live longer, but it sure feels that way. Nevertheless, evidence has been accumulating since the 1930s that calorie restriction—reducing an animal’s energy intake below its energy expenditure—extends lifespan and delays the start of age-related diseases in rats, dogs, fish and monkeys. Such results have inspired thousands of people to put up with constant hunger in the hope of living longer, healthier lives. They have also led to a search for drugs that mimic the effects of calorie restriction without the pain of going on an actual diet.
    Amid the trend, it is easy to forget that no one has until now shown that calorie restriction works in humans. That omission, however, changed this month, with the publication of the initial results of the first systematic investigation into the matter. This study took 48 men and women and assigned them randomly to either a control group or a calorie-restriction regime. Those in the second group were required to cut their calorie intake for six months to 75% of that needed to maintain their weight.
    The study is a landmark in the history of the field, because its subjects were either of normal weight or only slightly overweight. Previous projects have used individuals who were clinically fat, thus confusing the unquestionable benefits to health of reducing fatness with the possible advantages of calorie restriction to the otherwise healthy.
    At a molecular level, it suggests these advantages are real. Those on restricted diets showed drops in body temperature and blood-insulin levels—both phenomena that have been seen in long-lived, calorie-restricted animals. They also suffered less damage to their DNA.
    Eric Ravussin, of Louisiana State University, says that such results provide support for the theory that calorie restriction produces a metabolic adaptation over and above that which would be expected from weight loss alone. Nevertheless, such metabolic adaptation could be the reason why calorie restriction is associated with longer lifespan in other animals—and that is certainly the hope of those who, for the past 15 years, have been searching for ways of triggering that metabolic adaptation by means other than semi-starvation.
    The search for a drug that will delay old age is itself as old as the hills—as is the wishful thinking of the suckers who finance such efforts. Those who hope to find it by mimicking the effect of calorie restriction are not, however, complete snake-oil salesmen, for there is known to be a family of enzymes, which act both as sensors of nutrient availability and as regulators of metabolic rate. These might provide the necessary biochemical link between starving and living longer.
People might take enzymes as a substitute for calorie restriction in that
选项 A、they establish a chemical link between starving and living long.
B、they can provide people with enough nutrition.
C、they work in a similar way that calorie restriction does.
D、they are favored by people who finance the drug research.
答案C
解析 推理判断题。由题干关键词enzymes，substitute和calorie restriction定位至最后一段。该段第二句提到了酶，指出酶不仅能够感受营养成分吸收的情况，还能调节新陈代谢。根据前面的“限制卡路里摄入会调整新陈代谢”，可知酶与卡路里限制的工作原理相同，故[C]为答案。末句指出“这些酶可能提供了饥饿和长寿之间的必要的生物化学联系”，并非“建立了化学联系”，故排除[A]；同样，文中提到酶能够感受营养成分的吸收情况，并非提供足够的营养成分，故排除[B]；末段首句提到“付出财力的人”，但并没有特别表明或暗示他们对研究酶情有独钟，故排除[D]。
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