A meager diet may give you health and long life, but it"s not much fun—and it might not even be necessary. We may be able to hang on to ¹ most of that youthful vigor even if we don"t start to diet until old age.

    Stephen Spindler and his colleagues from the UniversityofCaliforniaatRiversidehave found that some of an elderly mouse"s liver genes can be made to behave as they did when the mouse was young simply by limiting its food for four weeks. The genetic rejuvenation won"t reverse other damage caused by time for the mouse, but could help its liver metabolize drugs or get rid of toxins ².

    Spindler"s team fed three mice a normal diet for their whole lives, and fed another three on half-rations. Three more mice were switched from the normal diet to half-feed ³ for a month when they were 34 months old—equivalent to about 70 human years.

    The researchers checked the activity of 11,000 genes from the mouse livers, and found that 46 changed with age in the normally fed mice. The changes were associated with things like inflammation and free radical production ⁴—probably bad news for mouse health. In the mice that had dieted all their lives, 27 of those 46 genes continued to behave like young genes. But the most surprising finding was that the mice that only started dieting in old age also benefited from 70 per cent of these gene changes.

    “This is the first indication that thee effects kick in ⁵ pretty quickly,” says Huber Warner from the National Institute on Aging near Washington, D. C.

    No one yet knows if calorie works in people as it does in mice, bus Spindler is hopeful. “There"s attracting and tempting evidence out there that it will work,” he says.

    If it does work in people, there might be good reasons for rejuvenating the liver. As we get older, out bodies are les efficient at metabolizing drugs, for example. A brief period of time of dieting, says Spindler, could be enough to make sure a drug is effective.

    But Spindler isn"t sure the trade-off is worth it ⁶. “The mice get less disease, they live longer but they"re hungry,” he says. “Even seeing what a diet does, it"s still hard to go to a restaurant and say: "I can only eat half of that".”

    Spindler hopes we soon won"t need to diet at all. His company, Life Span Genetics inCalifornia, is looking for drugs that have the effects of calorie restriction.

词汇：

meager ["mi:gə] adj.不足的

youthful [ˈju:θfl] adj.有青春活力的

vigor ["vɪgə] n.精力，活力

metabolize [mə"tæbəlaɪz] vt.使(一种物质)进入新陈代谢过程

genetic [dʒəˈnetɪk] adj.基因的

rejuvenation [rɪˌdʒu:və"neɪʃn] n.恢复活力，返老还童

注释：

1.hang on to:继续保留。例如：You should hang on to that painting -it might be worth a lot ofmoney one day.你应该继续保留那幅画，或许有一天它会值很多钱。

2. The genetic rejuvenation won"t reverse other damage caused by time for the mouse,but couldhelp its liver metabolize drugs or get rid of toxins.老鼠的肝部基因恢复活力不会逆转老鼠在其他方面的老化，但却有助于肝脏代谢药物或除去毒素。other damage caused by time岁月造成的其他方面的破坏，即“其他方面的老化”。metabolize drugs:代谢药物，即“使药物参与新陈代谢以提高药效”。get rid of:摆脱，除去。

3.half-rations和half-feed：都是指“老鼠饲料正常定量(normal diet)的一半”。

4.free radical production:指“（有机体组织、器官等的）无限激增”。

5.kick in:意为“开始起作用”。例如：We"re still waiting for the air conditioning to kick in．我们还在等着空调开始起作用。

6.be worth it：意为“值得，有益”。例如：They are expensive,but they are worth it．那些东西很贵，但划得来。

What can be inferred about completely normally fed mice mentioned in the passage?

A:They will not experience free radical production B:They will experience more genetic rejuvenation in their lifetime C:.They have more old liver genes to behave like young genes D:They are more likely to suffer from inflammation.

By far the most common snake in Britain is the adder. In Scotland, in fact, there are no other snakes at all. The adder is also the only Britain snake with a poisonous bite. It can be found almost anywhere, but prefers sunny hillsides and rough open country, including high ground. In Ireland there are no snakes at all.
Most people regard snake bites as a fatal misfortune, but not all bites are serious, and very few are fatal: Sometimes attempts at emergency treatment turn out to be more dangerous than the bite itself, with amateurs heroically, but mistakenly, trying do-it-yourself surgery and other unnecessary measures.
All snakes have small teeth, so it follows that all snakes can bite, but only the bite of the adder presents any danger. British snakes are shy animals and are far more frightened of you than you could possibly be of them. The adder will attack only if it feels threatened, as can happen if you take it by surprise and step on it accidentally, or if you try to catch it or pick it up, which it dislike intensely. If it hears you coming, it will normally get out of the way as quickly as it can, but adders cannot move very rapidly and may attack before moving if you are very close.The effect of a bite varies considerably. It depends upon several things, one of which is the body-weight of the person bitten. The bigger the person, the less harmful the bite is likely to be, which is why children suffer far more seriously from snake bites than adults. A healthy person will also have better resistance against the poison.Very few people actually die from snake bites in Britain, and though these bites can make some people very ill, there are probably just as many cases of bites having little or no effect, as there are of serious illness.

A:normally friendly towards people B:unlikely to bite except in self-defence C:aggressive towards anyone in their territory D:not afraid of human beings

By far the most common snake in Britain is the adder(奎蛇). In Scotland, in fact, there are no other snakes at all. The adder is also the only British snake with a poisonous bite. It can be found almost anywhere, but prefers sunny hillsides and rough open country, including high ground. In Ireland there are no snakes at all. Most people regard snake bites as a fatal(致命的)misfortune, but not all bites are serious, and very few are fatal. Sometimes attempts at emergency treatment turn out to be more dangerous than the bite itself, with amateurs(外行人)heroically, but mistakenly, trying do-it-yourself surgery(手术)and other unnecessary measures. All snakes have small teeth, so that all snakes can bite, but only the bite of the adder presents any danger. British snakes are shy animals and far more frightened of you than you could possibly be of them. The adder will attack only if it feels threatened, as can happen if you take it by surprise and step on it accidentally, or if you try to catch it or pick it up, which it dislikes intensely. If it hears you coming, it will normally get out of the way as quickly as it can, but adders cannot move very rapidly and may attack before moving if you are very close. The effect of a bite varies considerably. It depends upon several things, one of which is the body-weight of the person bitten. The bigger the person, the less harmful the bite is likely to be, which is why children suffer far more seriously from snake bites than adults. A healthy person will also have better resistance against the poison. Very few people actually die from snake bites in Britain, and though these bites can make some people very ill, there are probably just as many cases of bites having little or no effect, as there are of serious illness.We are told that adders______.

A:normally friendly towards people B:unlikely to bite except in self-defense C:likely to attack people whenever they see them D:not afraid of human beings

By far the most common snake in Britain is the adder(奎蛇). In Scotland, in fact, there are no other snakes at all. The adder is also the only British snake with a poisonous bite. It can be found almost anywhere, but prefers sunny hillsides and rough open country, including high ground. In Ireland there are no snakes at all. Most people regard snake bites as a fatal(致命的)misfortune, but not all bites are serious, and very few are fatal. Sometimes attempts at emergency treatment turn out to be more dangerous than the bite itself, with amateurs(外行人)heroically, but mistakenly, trying do-it-yourself surgery(手术)and other unnecessary measures. All snakes have small teeth, so that all snakes can bite, but only the bite of the adder presents any danger. British snakes are shy animals and far more frightened of you than you could possibly be of them. The adder will attack only if it feels threatened, as can happen if you take it by surprise and step on it accidentally, or if you try to catch it or pick it up, which it dislikes intensely. If it hears you coming, it will normally get out of the way as quickly as it can, but adders cannot move very rapidly and may attack before moving if you are very close. The effect of a bite varies considerably. It depends upon several things, one of which is the body-weight of the person bitten. The bigger the person, the less harmful the bite is likely to be, which is why children suffer far more seriously from snake bites than adults. A healthy person will also have better resistance against the poison. Very few people actually die from snake bites in Britain, and though these bites can make some people very ill, there are probably just as many cases of bites having little or no effect, as there are of serious illness.We are told that adders______.

A:normally friendly towards people B:unlikely to bite except in self-defense C:likely to attack people whenever they see them D:not afraid of human beings

By far the most common snake in Britain is the adder(奎蛇). In Scotland, in fact, there are no other snakes at all. The adder is also the only British snake with a poisonous bite. It can be found almost anywhere, but prefers sunny hillsides and rough open country, including high ground. In Ireland there are no snakes at all. Most people regard snake bites as a fatal(致命的)misfortune, but not all bites are serious, and very few are fatal. Sometimes attempts at emergency treatment turn out to be more dangerous than the bite itself, with amateurs(外行人)heroically, but mistakenly, trying do-it-yourself surgery(手术)and other unnecessary measures. All snakes have small teeth, so that all snakes can bite, but only the bite of the adder presents any danger. British snakes are shy animals and far more frightened of you than you could possibly be of them. The adder will attack only if it feels threatened, as can happen if you take it by surprise and step on it accidentally, or if you try to catch it or pick it up, which it dislikes intensely. If it hears you coming, it will normally get out of the way as quickly as it can, but adders cannot move very rapidly and may attack before moving if you are very close. The effect of a bite varies considerably. It depends upon several things, one of which is the body-weight of the person bitten. The bigger the person, the less harmful the bite is likely to be, which is why children suffer far more seriously from snake bites than adults. A healthy person will also have better resistance against the poison. Very few people actually die from snake bites in Britain, and though these bites can make some people very ill, there are probably just as many cases of bites having little or no effect, as there are of serious illness.We are told that adders______.

A:normally friendly towards people B:unlikely to bite except in self-defense C:likely to attack people whenever they see them D:not afraid of human beings