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　　為了活著吃飯

　　節食可能使你健康長壽，但并不好玩――節食可能不是非做不可的事。即使上了年紀再節食，我們仍然有可能在很大程度上保持青春活力。

　　StephenSpindler和他在Riverside的加利福尼亞大學的同事們已經發現，一只高齡老鼠只要連續四周限制它進食，它的某些肝臟基因就會變得和衰老前一樣充滿活力，老鼠的肝基因恢復活力不會逆轉老鼠在其他方面的老化，但卻有助于肝臟代謝藥物或除去毒素。

　　Spindler的團隊正常飼養三只老鼠直到它們死，而另外三只老鼠只喂正常飼料定量的一半。另外三只老鼠在34個月大的時候――相當于人的70歲，從正常飼養轉到半量飼養一個月。

　　研究者檢查了這些老鼠肝臟的11000個基因的活動，發現正常飼養的老鼠隨著年齡的增長有46條肝臟基因發生變化。這種變化與炎癥和身體組織無限激增相關――這大概對老鼠的健康來說是個壞消息。在那些終生節食的老鼠中，這46條肝臟基因中的27條繼續像年輕的基因一樣活動，但最驚人的發現是那些上了年紀才開始節食的老鼠也能從70%的基因變化中受益。

　　華盛頓附近的國家老年協會的HuberWarner說：“這是這些影響迅速起作用的第一個跡象。”

　　還沒有知道熱量限制是否在人身上和在老鼠身上一樣起作用，但是Spindler懷有希望。他說：“有吸引人的證據表明它能起作用。”

　　如果它確實能在人身上起作用，那就有足夠的理由使肝臟煥發青春秋戰國。當我們變老時，我們的身體對藥物的新陳代謝就不那么高效。Spindler說短期的節食足以使藥物充分發揮藥效。

　　但是Spindler不能肯定節食是否值得。他說：“老鼠們病少了，活的更長，但是它們感到饑餓。即便明白節食的作用，仍舊很難在飯館里說我只吃一半。”

　　Spindler希望在不久的將來，我們不必節食，他的公司，加利福尼亞壽命遺傳學，正在尋找有熱量控制作用的藥物。

　　Eat to Live

　　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 most of that youthful vigor even if we don’t 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 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.

　　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 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―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 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. “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 in California, is looking for drugs that have the effects of calorie restriction.