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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.
The results of previous research on the effects of calorie restriction are unconvincing because
选项 A、the subjects of the research were either of overweight or slightly underweight.
B、calorie-restricted animals showed different physical signs in the research.
C、the decrease in body temperature may result from changes of outside temperature.
D、people cannot tell the benefits of losing weight from those of calorie restriction.
答案D
解析 事实细节题。由题干关键词定位至第三段。该段第二句明确指出以前研究项目的缺陷：其试验对象都是临床肥胖者，这就导致人们无法区分是减肥给健康带来了好处还是限制卡路里摄人给健康带来了好处，故[D]为答案。该句明确指出以前研究的对象是“临床肥胖者”，没有提到“偏瘦者”，故排除[A]；第四段提到了限制卡路里摄人的动物试验对象的表现：体温降低，血胰岛素水平降低，这里没有提到它们的表现差异，故排除[B]；文中没有提到体温降低的原因，故排除[C]。
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