综合类考试：阅读理解Eat to Live
A meager diet may give you health and long life， but its not much fun—and it might not even be necessary. We may be able to hang on to1 most of that youthful vigor even if we dont start to diet until old age.
Stephen Spindler and his colleagues from the University of California at Riverside have found that some of an elderly mouses 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 wont reverse other damage caused by time for the mouse， but could help its liver metabolize drugs or get rid of toxins2.
Spindlers 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-feed3 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 production4—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 in5 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. “Theres 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 isnt sure the trade-off is worth it6. “The mice get less disease， they live longer but theyre hungry，” he says. “Even seeing what a diet does， its still hard to go to a restaurant and say： I can only eat half of that.”
Spindler hopes we soon wont need to diet at all. His company， Life Span Genetics in California， is looking for drugs that have the effects of calorie restriction.
词汇：
meager [mi：ɡ？(r)] adj. 不足的
youthful [ju：θful] adj. 有青春活力的
vigor [v？ɡ？(r)] n. 精力，活力
metabolize [m？tæb？laiz] vt. 使(一种物质)进入新陈代谢过程
genetic [d？？net？k] adj. 基因的
rejuvenation [ri？d？u：v？nei∫？n] n. 恢复活力，返老还童
liver [liv？] n. 肝脏
toxin [t？ksin] n. 毒素
ration [ræ∫？n] n. 定量
calorie [kæl？ri] n. 卡 (热量的单位)
inflammation [？infl？mei∫？n] n. 炎症，发炎
trade-off n. 交换，交易
rejuvenate [rid？u：vineit] vt. 使恢复活力
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 of money 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 could help 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，但却有助于肝脏带血药物或除去毒素。 other damager 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”。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。