A meager（不足的）diet may give you health and longlife, but it's not much fun一and it might not even benecessary. We may be able to hang on to most of that youthful

（有青春活力的）vigor （精力）even if we don't start to diet until old age.

Stephen Spindler andhis colleagues from the University of California at Riversidehave found that some of an elderly mouse's liver genes can be made to behave asthey did

when the mouse wasyoung simply by limiting its food for four weeks. The genetic rejuvenation（恢复活力，返老还童） won't reverse other damagecaused by time for

the mouse,but couldhelp its liver metabolize（使进入新陈代谢过程）drugs or get rid of toxins.

Spindler's team fedthree mice a normal diet for their whole lives,and fed another three onhalf-rations.Three more mice were switched from the normal diet to half-feedfor a

month when they were34 months old一equivalentto about 70 human years.

The researcherschecked the activity of 11,000 genes from the mouse livers,and found that 46changed with age in the normally fed mice.The changes were associated with

things likeinflammation and free radical production一probably bad news for mouse health.In the mice that had dieted alltheir lives,27 of those 46 genes continued to behave

like young genes.Butthe most surprising finding was that the mice that only started dieting in oldage also benefited from 70 percent of these gene changes.

"This is thefirst indication that these effects kick in pretty quickly",says HuberWarner from the National Institute on Aging near Washington D.C.

No one yet knows ifcalorie restriction works in people as it does in mice,but Spindler ishopeful."There's attracting and tempting evidence out there that it willwork,"he says.

If it does work inpeople,there might be good reasons for rejuvenating the liver. As we getolder,our bodies are less efficient at metabolizing drugs,for example.A briefperiod

of time ofdieting,says Spindler,could be enough to make sure a. drug is effective.

But Spindler isn'tsure the trade-off is worth it."The mice get less disease,they livelonger,but they're hungry,"he says."Even seeing what a diet does,it'sstill hard to go to a

restaurant and say:Ican only eat half of that."

Spindler hopes wesoon won't need to diet at all. His company,Lifespan Genetics in

California, is looking for drugs that have the effectsof calorie restriction. What can beinferred about completely normally fed mice mentioned in the passage?

A.They will notexperience free radical production.

B.They willexperience more genetic rejuvenation in their lifetime.

C.They have more oldliver genes to behave like young genes.

D.They are morelikely to suffer from inflammation.