If you have gone on a diet and reached your goal, chances are good that when you stop dieting you will regain all the weight you lost. After several weeks on a low-calorie diet — 900 calories or fewer — the body conserves energy by slowing the speed at which it burns calories. This slow-down explains in part why your weight loss may cease after a few weeks.
When you eventually return to eating a normal amount of food, your body may continue to burn calories at the slower rate,storing the remaining calories as fat.So if you are on a strict diet,your body may need fewer calories to maintain the same weight;losing weight becomes more difficult.
Doctors know that as you gain weight the fat cells in your body (most of us average 30 billion of them) become enlarged. But there is a limit to how big a fat cell can get, and very fat people develop additional fat cells — sometimes more than 100 billion. It now appears that you can add fat cells at any point during your life, although the number you have is influenced by a combination of your history of dieting and your genetic makeup.
Fat cells are different from other cells. They are made mostly of fat instead of protein, and apparently they never go away, even after dieting. Instead, they merely shrink. Dr. Jules Hirseh of Rockefeller University has examined the body tissue of very fat people who have lost weight, and found that it resembles that of starvation victims. Perhaps, he supposes, it is the billions of undersize, “hungry” cells that drive many formerly fat people off their diets.
New research suggests that your hungry cells aren’t the only signal senders that tempt you toward the refrigerator. Another criminal may be the hormone insulin（胰岛素）.Insulin turns sugar and fat into fuel for the body. In addition, some researchers believe that high levels of insulin are a factor in hunger and appetite and may drive you to overeat.
Exercise helps maintain your weight and seems to bring insulin levels down, says Dr. Donald S. Robertson, a medical director.“Any weight loss program must fail,”he said,“unless it incorporates（包括）a certain amount of exercise.”
1.When you stop dieting you will regain the weight you lost because ________.
A. the fat cells in your body have become enlarged
B. your appetite has become greater than before
C. your body can now consume only part of the calories you get from food
D. you have developed additional fat cells
详解：C)。细节题。根据第一段中的最后两句话“After several weeks on a low-calorie diet—900 calories or fewer — the body conserves energy by slowing the speed at which it bums calories. This slow-down explains in part why your weight loss may cease after a few weeks.”在减肥一段时期后，人体消耗卡路里的速度会放慢。第二段中说在恢复正常饮食后，人体消耗卡路里的速度仍会继续慢下去，而把所摄入的多余的卡路里以脂肪的形式储存起来。由此可知选项C)与所表达的意思相一致，即：当你停止节食后体重反弹是由于这时人体只能消耗掉摄入的卡路里的一部分。故选项C)为正确答案。
2.What tempts you toward the food is ________.
A. your hungry cells
B. your hunger and appetite
C. hormone insulin
D. both your hungry cells and hormone insulin
详解：D)。细节题。根据第四段中的最后一句话“it is the billions of undersize,‘hungry’cells that drive many formerly fat people off their diets.”与第五段的第一句话“New research suggests that your hungry cells aren’t the only signal senders that tempt you toward the refrigerator. Another criminal maybe the hormone insulin(胰岛素).”，我们可以知道是“hungry cells”和“hormone insulin”共同作用驱使着人们去饮食的。故正确答案为选项D)。
3.It can be inferred from the passage that ________.
A. dieting can in turn provide a good chance to regain all the weight lost
B. keeping a diet is not the best method of losing weight
C. it is advisable to maintain as low levels of insulin as you can
D. if you want to lose your weight, you should follow a strict diet
详解：B)。推理题。根据文章第一段的内容可知，节食后体重会反弹，可推知作者对节食减肥并不以为然。再根据下文详细的原因分析，可推出选项B)应为正确答案，即：节食并非是最好的减肥方法。选项A)的表述中误解了原文中的chances are good that= it is likely that(有可能)而非provide a good chance(提供了好的机会)。根据文章第五段可知“Insulin turns sugar and fat into fuel for the body”，故维持胰岛素在一定的水平上对身体是必要的，绝非选项C)中提及的“越低越好”。原文在第六段中曾指出“Any weight-loss program must fail,” he said,“ unless it incorporates(包括)a certain amount of exercise”，所以如果要减掉体重的话，减肥行动方案应包括控制饮食和适当的运动为宜，因此可排除选项D)。
4.According to the passage, it can be concluded that ________.
A. it has something to do with parents whether one is fat or not
B. there are many factors that contribute to overweight
C. the growth of fat cells depends to a great extent on one’s body weight
D. persistence and patience are what one needs to cope with overweight
详解：B)。结论题。根据全文可以看出，第一、二段说明卡路里的燃烧速度会影响一个人的体重;第三、四段介绍了“fat cells”，它也会影响一个人的体重;第四、五段告诉我们“hungry cells”和“hormone insulin”会驱使人们饮食，从而影响了一个人的体重。故综合整篇文章可以看出作者介绍了导致肥胖的几个因素，选项B)的表述与此吻合。文章主要说明的是节食未必减轻体重的原因，并未提及选项A)和选项D)中的内容。而由原文的第三段得知：单个脂肪细胞可以长到多大是有一个限定值的，故选项C)亦可排除。
5.The best title for the passage may be ________.
A. New Research Findings into Overweight
B. The Best Method of Losing Your Weight
C. Losing weight, A Sure Way to Keep Fit
D. Fat Cells and Gaining Weight