填空题
Why Exercise Won"t Make You Thin
A. As I write this, tomorrow is Tuesday, which is a cardio day. I"ll spend five minutes warming up on the Versa Climber, a towering machine that requires you to move your arms and legs simultaneously. Then I"ll do 30 minutes on a stair mill. On Wednesday a personal trainer will work me like a farm animal for an hour, sometimes to the point that I am dizzy—an abuse for which I pay as much as I spend on groceries in a week. Thursday is "body wedge" class, which involves another exercise contraption, this one a large foam wedge from which I will push myself up in various hateful ways for an hour. Friday will bring a 5.5-mile run, the extra half- mile my grueling expiation of any gastronomical indulgences during the week.
B. I have exercised like this—obsessively, a bit grimly—for years, but recently I began to wonder: Why am I doing this? Except for a two-year period at the end of an unhappy relationship—a period when I self-medicated with lots of Italian desserts—I have never been overweight.
C. One of the most widely accepted, commonly repeated assumptions in our culture is that if you exercise, you will lose weight. But I exercise all the time, and since I ended that relationship and cut most of those desserts, my weight has returned to the same 163 lb. It has been most of my adult life. I still have gut fat that hangs over my belt when I sit. Why isn"t all the exercise wiping it out?
D. It"s a question many of us could ask. More than 45 million Americans now belong to a health club, up from 23 million in 1993. We spend some $19 billion a year on gym memberships. Of course, some people join and never go. Still, as one major study— the Minnesota Heart Survey—found, more of us at least say we exercise regularly. The survey ran from 1980, when only 47% of respondents said they engaged in regular exercise, to 2000, when the figure had grown to 57%.
E. And yet obesity figures have risen dramatically in the same period: a third of Americans are obese, and another third count as overweight by the Federal Government"s definition. Yes, it"s entirely possible that those of us who regularly go to the gym would weigh even more if we exercised less. But like many other people, I get hungry after I exercise, so I often eat more on the days I work out than on the days I don"t. Could exercise actually be keeping me from losing weight?
F. The conventional wisdom that exercise is essential for shedding pounds is actually fairly new. As recently as the 1960s, doctors routinely advised against rigorous exercise, particularly for older adults who could injure themselves.
G. Today doctors encourage even their oldest patients to exercise, which is sound advice for many reasons: people who regularly exercise are at significantly lower risk for all manner of diseases—those of the heart in particular. They less often develop cancer, diabetes and many other illnesses. But the past few years of obesity research show that the role of exercise in weight loss has been wildly overstated.
H. "In general, for weight loss, exercise is pretty useless." says Eric Ravussin, chair in diabetes and metabolism at Louisiana State University and a prominent exercise researcher. Many recent studies have found that exercise isn"t as important in helping people lose weight as you hear so regularly in gym advertisements or on shows like The Biggest Loser—or, for that matter, from magazines like this one.
I. The basic problem is that while it"s true that exercise burns calories and that you must burn calories to lose weight, exercise has another effect: it can stimulate hunger. That causes us to eat more, which in turn can negate the weight-loss benefits we just accrued. Exercise, in other words, isn"t necessarily helping us lose weight. It may even be making it harder. The compensation problem
J. Earlier this year, the peer-reviewed journal PLOS ONE—PLOS is the nonprofit Public Library of Science—published a remarkable study supervised by a colleague of Ravussin"s, Dr. Timothy Church, who holds the rather grand title of chair in health wisdom at LSU. Church"s team randomly assigned into four groups 464 overweight women who didn"t regularly exercise.
K. Women in three of the groups were asked to work out with a personal trainer for 72 min., 136 min., and 194 min. per week, respectively, for six months. Women in the fourth cluster, the control group, were told to maintain their usual physical activity routines. All the women were asked not to change their dietary habits and to fill out monthly medical symptom questionnaires.
L. The findings were surprising. On average, the women in all the groups, even the control group, lost weight, but the women who exercised—sweating it out with a trainer several days a week for six months—did not lose significantly more weight than the control subjects did. (The control group women may have lost weight because they were filling out those regular health forms, which may have prompted them to consume fewer doughnuts.) Some of the women in each of the four groups actually gained weight, some more than 10 lb. each.
M. What"s going on here? Church calls it compensation, but you and I might know it as the lip-licking anticipation of perfectly salted, golden-brown French fries after a hard trip to the gym. Whether because exercise made them hungry or because they wanted to reward themselves (or both), most of the women who exercised ate more than they did before they started the experiment. Or they compensated in another way, by moving around a lot less than usual after they got home.
N. The findings are important because the government and various medical organizations routinely prescribe more and more exercise for those who want to lose weight. In 2007 the American College of Sports Medicine and the American Heart Association issued new guidelines stating that "to lose weight... 60 to 90 minutes of physical activity may be necessary." That"s 60 to 90 minutes on most days of the week, a level that not only is unrealistic for those of us trying to keep or find a job but also could easily produce, on the basis of Church"s data, ravenous compensatory eating.
O. It"s true that after six months of working out, most of the exercisers in Church"s study were able to trim their waist lines slightly—by about an inch. Even so, they lost no more overall body fat than the control group did. Why not?