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  3. The Secret of Obesity A) Ask anyone why there is an obesity epidemic and they will tell you that it’s all down to eating too

The Secret of Obesity A) Ask anyone why there is an obesity epidemic and they will tell you that it’s all down to eating too

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问题                                                 The Secret of Obesity
    A) Ask anyone why there is an obesity epidemic and they will tell you that it’s all down to eating too much and burning too few calories. That explanation appeals to common sense and has dominated efforts to get to the root of the obesity epidemic and reverse it. Yet obesity researchers are increasingly dissatisfied with it. Many now believe that something else must have changed in our environment to precipitate (加速) such dramatic rises in obesity over the past 40 years. Nobody is saying that the "big two"—reduced physical activity and increased availability of food—are not important contributors to the epidemic, but they cannot explain it all. Earlier this year a review paper by 20 obesity experts set out the 7 most plausible alternative explanations for the epidemic.
    B) First, it’s not enough sleep. It is widely believed that sleep is for the brain, not the body. Could a shortage of shut-eye also be helping to make us fat? Several large-scale studies suggest there may be a link. People who sleep less than 7 hours a night tend to have a higher body mass index than people who sleep more, according to data gathered by the US National Health and Nutrition Examination Survey. Similarly, the US Nurses’ Health Study, which tracked 68,000 women for 16 years, found that those who slept an average of 5 hours a night gained more weight during the study period than women who slept 6 hours, who in turn gained more than those who slept 7.
    C) It’s well known that obesity impairs sleep, so perhaps people get fat first and sleep less afterwards. But the nurses’ study suggests that it can work in the other direction too: sleep loss may precipitate weight gain. Although getting figures is difficult, it appears that we really are sleeping less. In 1960 people in the US slept an average of 8.5 hours per night. A 2002 poll by the National Sleep Foundation suggests that the average has fallen to under 7 hours, and the decline is mirrored by the increase in obesity.
    D) Another factor is climate control. We humans, like all warm-blooded animals, can keep our core body temperatures pretty much constant regardless of what’s going on in the world around us. We do this by altering our metabolic (新陈代谢的) rate, shivering or sweating. Keeping warm and staying cool take energy unless we are in the "thermoneutral zone", which is increasingly where we choose to live and work.
    E) There is no denying that ambient temperatures (环境温度) have changed in the past few decades. Between 1970 and 2000, the average British home warmed from a chilly 13 ℃ to 18 ℃. In the US, the changes have been at the other end of the thermometer as the proportion of homes with air conditioning rose from 23％ to 47％ between 1978 and 1997. In the southern states—where obesity rates tend to be highest—the number of houses with air conditioning has shot up to 71％ from 37％ in 1978. Could air conditioning in summer and heating in winter really make a difference to our weight? Sadly, there is some evidence that it does—at least with regard to heating. Studies show that in comfortable temperatures we use less energy.
    F) Bad news: smokers really do tend to be thinner than the rest of us, and quitting really does pack on the pounds, though no one is sure why. It probably has something to do with the fact that nicotine is an appetite suppressant and appears to up your metabolic rate. Katherine Flegal and colleagues at the US National Center for Health Statistics in Hyattsville, Maryland, have calculated that people kicking the habit have been responsible for a small but significant portion of the US epidemic of fatness. From data collected around 1991 by the US National Health and Nutrition Examination Survey, they worked out that people who had quit in the previous decade were much more likely to be overweight than smokers and people who had never smoked. Among men, for example, nearly half of quitters were overweight compared with 37％ of non-smokers and only 28％ of smokers.
    G) However, sometimes, obesity is something that has nothing to do with outside factors. Your chances of becoming fat may be set, at least in part, before you were even born. Children of obese mothers are much more likely to become obese themselves later in life. Offspring of mice fed a high-fat diet during pregnancy are much more likely to become fat than the offspring of identical mice fed a normal diet. Intriguingly, the effect persists for two or three generations. Grandchildren of mice fed a high-fat diet grow up fat even if their own mother is fed normally—so your fate may have been sealed even before you were conceived.
    H) Besides, unfortunately, some groups of people just happen to be fatter than others. Surveys carried out by the US national center for health statistics found that adults aged 40 to 79 were around three times as likely to be obese as younger people. Non-white females also tend to fall at the fatter end of the spectrum: Mexican-American women are 30％ more likely than white women to be obsess, and black women have twice the risk.
    I) In the US, these groups account for an increasing percentage of the population. Between 1970 and 2000, the US population aged 35 to 44 grew by 43％; the proportion of Hispanic-Americans also grew, from under 5％ to 12.5％ of the population, while the proportion of African Americans increased from 11％ to 12.3％. These changes may account in part for the increased prevalence of obesity.
    J) Another thing that leads to the increase of obesity rate is mature mums. Mothers around the world are getting older. In the UK, the mean age for having a first child is 27.3, compared with 23.7 in 1970. Mean age at first birth in the US has also increased, rising from 21.4 in 1970 to 24.9 in 2000.
    K) This would be neither here nor there if it weren ’t for the observation that having an older mother seems to be an independent risk factor for obesity. Results from the US national heart, lung and blood institute’s study found that the odds of a child being obese increase 14％ for every five extra years of their mother’s age, though why this should be so is not entirely clear.
    L) Michael Symonds at the University of Nottingham, UK, found that first-born children have more fat than younger ones. As family size decreases, firstborns account for a greater share of the population. In 1964, British women gave birth to an average of 2.95 children; by 2005 that figure had fallen to 1.79. In the US, in 1976, 9.6％ of woman in their 40s had only one child; in 2004 it was 17.4％. This combination of older mothers and more single children could be contributing to the obesity epidemic.
    M) Another very interesting matter also makes its fair share of contribution to obesity. Just as people pair off according to looks, so they do for size. Lean people are more likely to marry lean and fat more likely to marry fat. On its own, like marrying like cannot account for any increase in obesity. But combined with others—particularly the fact that obesity is partly genetic, and that heavier people have more children—it amplifies the increase from other causes.
A comfortable ambient temperature might be a reason for the increase in obesity.
选项
答案E
解析 题干意为，舒适的环境温度可能是肥胖增长的一个原因。根据题干中的关键词ambient temperature定位到E段。该段倒数第一、二句中提到，有证据证明，夏天的空调和冬天的供暖确实能影响我们的体重，至少冬天的暖气是有影响的。而且有研究表明，在舒适的温度下，我们消耗的能量会更少，即在某种程度上增加了体重，由此可知，题干是对原文的同义转述，故选E。
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