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 percent of these gene changes.
"This is the first indication that these effects kick in pretty quickly," says Huber Warner from the National Institute on Aging near Washington, D.C..
No one yet knows if calorie restriction works in people as it does in mice, but 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, our bodies are less 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.
According to the passage, which of the following is NOT true?
A.Eating less than usual might make us live longer.
B.If we go on a diet when old, we may keep healthy.
C.Dieting might not be needed. ~
D.We have to begin dieting from childhood.
If we were asked exactly what we were doing a year ago,we should probably have to say that we could not remember. But if we had kept a book and had written in it an account of what we did each day, we should be able to give an answer to the question.
It is the same in history. Many things have been forgotten because we do not have any written account of them. Sometimes men did keep a record of the most important happenings in their country,but often it was destroyed by fire or in a war. Sometimes there was never any written record at all because the people of that time and place did not know how to write. For example, we know a good deal about the people who lived in China 4, 000 years ago, because they could write and leave written records for those who lived after them. But we know almost nothing about the people who lived even 200 years ago in central Africa because they had not learned to write.
Sometimes, of course, even if the people cannot write, they may know something of the past. They have heard about it from older people and often songs and dances and stories have been made about the most important happenings, and these have been sung and acted and told for many generations, for most people are proud to tell what their fathers did in the past. This we may call ?remembered history ” . Some of it has now been written down. It is not so exact or so valuable to us as written history is, because words are much more easily changed when used again and again in speech than when copied in writing. But if there are no written records, such spoken stories are often very helpful.
Which of the following is NOT suggested in the passage?
A.Written history is more reliable.
B.Written records play an important role in learning about history.
C.A written account of our daily activities helps to answer many questions.
D.Where there are no written records, there is no history.
Little is known about the central Africa 200 years ago because ______.A.there was nothing worth writing down at that time
B.people there ignored the importance of keeping a record
C.people there did not know how to write
D.the written records were perhaps destroyed by a fire
“ Remembered history” refers to ______.A.history based on a person’s imagination
B.stories of important happenings passed down from mouth to mouth
C.songs and dances about the most important events.
D.both B and C
“ Remembered history” is regarded as valuable only when ______.A.it is written down
B.No written account is available
C.it proves to be timely
D.People are interested in it
It is suggested that we could have learned more about our past if ancient people had ______.A.kept a written record of every past event
B.burnt their written records in wars
C.told exact stories of the most important happenings
D.made more songs and dances
请帮忙给出每个问题的正确答案和分析,谢谢!