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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.
We learn from the first two paragraphs that
选项 A、people are crazy about dieting in order to lose some weight.
B、experimental results show that dieting can prolong animals’ life.
C、in the study, two groups of people were asked to go on a diet.
D、few results have been worked out on the effects of calorie restriction.
答案B
解析 事实细节题。由题干提示定位至前两段。首段指出“限制卡路里摄入会延长老鼠、狗、鱼和猴子的寿命，推迟年龄相关性疾病的发病时间。”然后第二段首句指出有关限制卡路里摄入对人体是否有用的研究还是空白。紧接着第二句话锋一转：但是随着本月公布了第一个有关这一课题的系统性研究的初步结果，这一空白得以填补。可见限制饮食对延长人类寿命影响的试验研究已经得出结果，故[B]为答案。首段第三句指出成千上万的人长期忍受饥饿的目的是为了延长寿命，生活得更健康，并非为了“减肥”，故排除[A]；第二段提到该项研究包括一个控制组和一个卡路里限制组，第二组成员要求限制卡路里的摄人，故排除[C]；首段第二句中的“自20世纪30年代以来，越来越多的证据表明”说明有关卡路里限制摄人的研究结果很多，故排除[D]。
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