Eat More, Weigh Less, Live Longer Clever genetic detective work may have found out the reason why a near-starvation diet prolongs the life of many animals. Ronald Kahn at Harvard Medical School in Boston, US, and his colleagues have been able to extend the lifespan of mice by 18 per cent by blocking the rodents increase of fat in specific cells. This suggests that thinnessand not necessarily dietpromotes long life in calorie restricted animals. Its very cool work, says aging researcher Cynthia Kenyon of the University of California, San Francisco. These mice eat all they want, lose weight and live longer. Its like heaven. Calorie restriction dramatically extends the lifespan of organisms as different as worms and rodents. Whether this works in humans is still unknown partly because few people are willing to submit to such a strict diet: But many researchers hope they will be able to trigger the same effect with a drug once they understand how less food leads to a longer life. One theory is that eating less reduces the increase of harmful things that can damage cells. But Kahns team wondered whether the animals simply benefit by becoming thin. To find out, they used biology tricks to disrupt the insulin receptor gene in lab micebut only in their fat cells. Since insulin is needed to help fat cells store fat, these animals were protected against becoming fat, explains Kahn. This slight genetic change in a single tissue had dramatic effects. By three months of age, Kahns modified mice had up to 70 per cent less body fat than normal control mice, despite the fact that they ate 55 per cent more food per gram of body weight. In addition, their lifespan increased. The average control mouse lived 753 days, while the thin rodents averaged a lifespan of 887 days. After three years, all the control mice had died, but one-quarter of the modified rodents were still alive. That they get these effects by just manipulating the fat cells is controversial, says Leonard Guarente of the Massachusetts Institute of Technology, who studies calorie restriction and aging. But Guarente says Kahn has yet to prove that the same effect is responsible for increased lifespan in calorie-restricted animals. It might be the same effect or there might be two routes to long life, he points out, and that would be very interesting. A offering them less food. B giving them a balanced diet. C disrupting the specific genes in their fat cells. D preventing them growing larger. 42 According to the passage, we do not know whether humans will benefit from taking in fewer calories partly because A humans, worms and rodents are different. B most people are not willing to be put on a strict diet. C the effect is not known. D genetic changes in tissues can not be performed on humans. 43 What does the last sentence in the third paragraph imply? A People like to lose weight, but they do not like to eat less. B People want to go to heaven, but they do not want to die. C Mice will go to heaven if they lose weight. D Mice enjoy losing weight. 44 The average modified mouse lived A 3 years. B 753 days. C More than 3 years. D 887 days. A It remains to be studied. B It has already been discovered. C Eating more leads to long life. D Eating less leads to long life. 答案： 41. C 42. B 43. A 44. D 45. A 41. C 根据第二段的第一句话以及第六段的第一句话可知答案为C。 42. B 答案可从第四段的最后一句话中找出。 43. A 文中说这些老鼠随便想吃什么就吃什么，还能减肥，活的更长，就像在天堂一样。这是带着幽默意味的一句话，暗含的意思是人们对这样的老鼠有点嫉妒，人们也想减肥，也不想节食，但是人却不能像这些老鼠一样。 44. D 从倒数第三段第一句话可得到答案。 45. A Guarente 说的话用了两个might, 说明还只是一种不确定的猜测，还需进一步研究。