Even as Americans have been gaining weight, they have cut their average fat intake from 36 to 34 percent of their total diets in the past 15 years.  And indeed,  cutting fat  to control or lose weight makes sense. Fat has nine calories per gram. Protein and carbohydrates（碳水化合物） have just four. Moreover, the body uses fewer calories to metabolize fat than it does to metabolize other foods. Compared with protein and carbohydrates — which break down into amino acids and simple sugars, respectively, and can be used to strengthen and energize the body —— dietary fat is more easily converted to body fat. Therefore, it’s more likely to stay on buttocks, thighs and bellies. 
But cutting fat from your diet doesn’t necessarily mean your body won’t store fat. For example, between nonfat and regular cookies, there’s trivial difference in calories because manufacturers make up for the loss of fat by adding sugar. Low-fat crackers, soups and dressings can also be just as high in calories as richer versions. No matter where the calories come from, overeating will still cause weight again. The calories from fat just do it a little quicker. A Wisconsin computer programmer who decided with a diet coach to eat only 40 grams of fat a day learned the lesson firsthand. He wasn’t losing weight. Then he showed his food diary to his coach and revealed he’d been eating half a pound of jelly beans a day. “They don’t have any fat,” he explains. But they had enough sugar to keep him from shedding an ounce.  
Nonfat foods become add-on foods. When we add them to our diet, we actually increase the number of calories we eat per day and gain weight. That was borne out in a Pennsylvania State University study. For breakfast, Prof. Barbara Rolls gave two groups of women yogurt（酵母乳）that contained exactly the same amount of calories. One group’s yogurt label said “high fat”—the other, “low fat.” The “low fat” yogurt group ate significantly more calories later in the day than the other group. “People think they’ve saved fat and can indulge themselves later in the day with no adverse consequences,” says Richard Mattes, a nutrition researcher at Purdue University. “But when they do that, they don’t compensate very precisely, and they often end up overdoing it.”
What lessons did the computer programme learn ?

A．Overeating will cause weight gain

B．He can eat half a pound of jellybeans a day

C．He can’t didn’t eat any fat

D．His coach gave him a lecture

Prof. Barbara’s ecperiement proved that _______________.

A．two groups ate the same amount of calories

B．two groups ate the same wmount of yogurt

C．the “ low fat” yogurt group ate more calories later in the day than the other group

D．people increase the number of calories they eat per day and gain group

According to the author ,________has less calories.

A．fat

B．protein and carbohydrates

C．low-fat soups

D．sugar

What can you infer from the text ?

A．To keep from being overweight, people have to eat nofat food

B．The calories from fat just do it a little quicker than from protein and carbohydrates

C．People should avoid temptation

D．Americans realize that it is necessary to count calories before eating the food

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