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  3. How exercise affects body weight is one of the more intriguing and vexing issues in physiology. Exercise burns calories.no one d

How exercise affects body weight is one of the more intriguing and vexing issues in physiology. Exercise burns calories.no one d

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问题     How exercise affects body weight is one of the more intriguing and vexing issues in physiology. Exercise burns calories.no one doubts that, and so it should, in theory, produce weight loss, a fact that has prompted countless people to undertake exercise programs to shed pounds. Without significantly changing their diets, few succeed. "Anecdotally, all of us have been cornered by people claiming to have spent hours each week walking, running, stair-stepping, etc. , and are displeased with the results on the scale or in the mirror, "wrote Barry Braun.an associate professor of kinesiology at the University of Massachusetts at Amherst.
    But a growing body of science suggests that exercise does have an important role in weight loss. That role, however, is different from what many people expect and probably wish. The newest science suggests that exercise alone will not make you thin, but it may determine whether you stay thin, if you can achieve that state. Until recently, the bodily mechanisms involved were mysterious. But scientists are slowly teasing out exercise’s impact on metabolism, appetite and body composition, though the consequences of exercise can vary. Women’s bodies, for instance, seem to react differently than men’s bodies to the metabolic effects of exercise. None of which is a reason to abandon exercise as a weight-loss tool. You just have to understand what exercise can and cannot do.
    "In general, exercise by itself is pretty useless for weight loss, "says Eric Ravussin.an expert on weight loss. It’s especially useless because people often end up consuming more calories when they exercise.The mathematics of weight loss is, in fact, quite simple, involving only subtraction. "Take in fewer calories than you burn.put yourself in negative energy balance, lose weight, "says Braun.who has been studying exercise and weight loss for years. The deficit in calorics can result from cutting back your food intake or from increasing your energy output the amount of exercise you complete or both. When researchers affiliated with the Pennington center had volunteers reduce their energy balance for a study by either cutting their caloric intakes by 25 percent or increasing their daily exercise by 12. 5 percent and cutting their calories by 12.5 percent, everyone involved lost weight.They all lost about the same amount of weight too about a pound a week. But in the exercising group, the dose of exercise required was nearly an hour a day of moderate-intensity activity. What the federal government currently recommends for weight loss is "a lot more than what many people would be able or willing to do, " Ravussin says.
    At the same time, as many people have found after starting a new exercise regimen, working out can have a significant effect on appetite. The mechanisms that control appetite and energy balance in the human body are elegantly calibrated. "The body aims for homeostasis, "Braun says. It likes to remain at whatever weight it’s used to. So even small changes in energy balance can produce rapid changes in certain hormones associated with appetite, particularly acylated ghrelin, which is known to increase the desire for food, as well as insulin and leptin, hormones that affect how the body burns fuel.
    The effects of exercise on the appetite and energy systems, however, are by no means consistent. In one study presented last year at the annual conference of the American College of Sports Medicine, when healthy young men ran for an hour and a half on a treadmill at a fairly high intensity, their blood concentrations of acylated ghrelin fell, and food held little appeal for the rest of that day. Exercise blunted their appetites. A study that Braun oversaw had a slightly different outcome. In it, 18 overweight men and women walked on treadmills in multiple sessions while either eating enough that day to replace the calories burned during exercise or not. Afterward, the men displayed little or no changes in their energy-regulating hormones or their appetites, much as in the other study. But the women uniformly had increased blood concentrations of acylated ghrelin and decreased concentrations of insulin after the sessions in which they had eaten less than they had burned. Their bodies were directing them to replace the lost calories. In physiological terms, the rcsults"arc consistent with the paradigm that mechanisms to maintain body fat are more effective in women, "Braun and his colleagues wrote. In practical terms, the results are scientific proof that life is unfair. Female bodies, inspired almost certainly"by a biological need to maintain energy stores for reproduction, "Braun says, fight hard to hold on to every ounce of fat. Exercise for many women increases the desire to eat.  
The best title for the passage is probably
选项 A、Exercise and Weight Loss.
B、Weighing the Evidence on Exercise.
C、Effect of Exercise on Men and Women.
D、Calories, Exercise and Weight Loss.
答案B
解析 主旨题。本文围绕运动对减肥的效果展开说明，开篇直接点明主题，指出锻炼者在锻炼后无法减肥的困惑。之后指出症结所在：锻炼本身无法减肥。通过科学家们得出的锻炼对人体新陈代谢、食欲以及身体成分等的结沦阐明锻炼对人体的影响。文中以一个实验为例，说明如何锻炼才能减肥。在末段，作者又通过一个具体实验，表明锻炼对食欲和能量系统的影响并不总是一致的，以男女测试组为例说明其不同。可见文章的主旨是围绕锻炼对影响人体体重的新陈代谢、食欲等的影响来进行说明的，文中给出一系列的实验数据和实验过程以说明主旨，选项[B]中的Weighing虽然不是“减肥”之意，但与weight loss和lose weight中的weight构成词汇复现，exercise是另一个主题词，而evidence将本文用事实数据说话的说明方式表达得很清楚，故[B]是合适的标题。
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