六级冲刺练习阅读（113）

　　Eat more, Play more Weigh Less

　　In the United States, 20 to 40 percent of the adult population has a weight problem. To many people, the cause seems obvious; we eat too much. But scientific evidence does little to support this idea. Going back to the America of 1910, we find that people were leaner than today, yet they consumed more food. In those days people worked harder physically, walked more, used machines much less, didnt watch television.

　　Several modern studies, moreover ? have shown that fatter people do not eat more on average than thinner people. In fact, some investigations, such as a 1979 study of 3454 London office workers, reveal that, on balance, fat people eat less than slimmer people.

　　Studies show that slim people are more active than fat people. Measurement of calorie intake in slim, active populations compared with moderately overweight, inactive groups routinely shows striking differences. A study by my research group at Stanford University School of Medicine found that among slim, tennis-playing women average daily calorie intake was 2417, while among sedentary , moderately overweight women of the same age it was 1490. Here were slim women remaining slim on 62 percent more calories than overweight women. The critical difference; physical activity.

　　In another Stanford study, 48 sedentary men ages 30 to 55 started on a one-year jogging program. We observed these changes after the training period:

　　The more the men ran, the greater their loss of body fat.

　　The more they ran, the greater their increase in food intake.

　　Thus, those who ran the most ate the most, yet lost the greatest amount of body fat!

　　I believe that this illustrates the evolution of moderately overweight people to relatively slim individuals via a progressive program of regular exercise. The crucial ingredient is regular, enjoyable activity.

　　Use of energy by the body falls into two categories. The first is energy used for essential bodily functions digestion, heart beat, breathing and is known as the basal metabolic rate, or BMR. In an average-sized adult, BMR requires about 1400 calories per day.

　　The second category is energy used for physical activity standing, walking and all other movements. Together with the BMR, it makes up total calorie use, which should be balanced by food intake for weight to remain stable.

　　An inactive person might add only 300 calories a day to his BMR, for an average total of 1700. But a marathon runner might add 2300, for a total of 3700. For endurance athletes in training, 4000- to 5000-calorie intakes are not uncommon.

　　We can see from such figures that the sedentary person has a BMR-dominated total calorie expenditure, so that anything he does to increase his BMR will help burn fat, whereas anything he does to decrease his BMR will compound his overweight problem.

　　For years now, we have known that dieting especially severe dieting decreases BMR. This is the bodys defense mechanism to conserve energy when food supply is reduced. Unfortunately, it tends to undermine the diets effects by enabling the body to get by on fewer calories. For this reason, I believe that severe dieting should be used sparingly, and all dieting should be seen as a temporary measure.

　　A fascinating concept that has emerged in recent years has been the apparent effect of vigorous exercise in temporarily increasing BMR. A jogger returning from a five-mile run may have a higher BMR. While this effect probably lasts only a few hours, the jogger who runs every day should maintain an increased BMR.

　　We can see, then, that the sedentary, overweight person who diets severely without exercise decreases his BMR; does not increase calorie expenditure; has an initially rapid rate of weight loss that soon becomes disappointingly slow; and does not enjoy the experience.

　　On the other hand, the sedentary, overweight person who diets moderately and adopts a slowly progressive exercise program tends to increase his BMR; increases calorie expenditure; has a moderate rate of weight loss that does not slow down after a few weeks; and often enjoys the experience.

　　In addition to facilitating weight loss and continued weight control, regular exercise has many other features to recommend it. While weight loss by dieting alone results in some loss of muscle as well as fat, weight loss by exercise and moderate dieting leads to an increased proportion of muscle mass. The regular exerciser has good heart function too. He is physically fit and can perform better

　　than the unfit dieter when it comes to hiking, furniture moving, even making love.

　　Regular exercise helps to raise blood levels of high-density lipoprotein , the good cholesterol that may work to prevent coronary heart disease, while it reduces levels of low-density lipoprotein , the bad cholesterol. Since the results of a ten-year study on 3806 middle-aged men were announced in January 1984 by the National Heart, Lung, and Blood Institute, we can say that lowering LDL levels will definitely reduce the number of heart attacks and save lives.

　　Exercise also slow mineral loss from bones, and improves ones mental outlook. A study of 17,000 Harvard alumni from 1962 to 1978 provided the first substantial evidence that physical activity maintained through adulthood leads to longer life.