VOA标准英语2010年-An Hour Workout A Day Helps Keep Extra（在线收听）

Here is sobering news. The World Health Organization says more than one billion adults are fat, and at least 400 million people are obese. As old fashioned as it sounds, doctors say the best way to lose weight is to eat less and exercise more. But for women who are middle aged or older, experts say one hour of daily exercise per day is necessary just to maintain weight. The heavier a woman is, the harder she will have to work - at cutting calories.

Life's just not fair. Biologically speaking, women carry more body fat than men.  They require fewer calories than men.  For most men and women, fitting in an hour of moderately intense exercise in an already hectic day is difficult, if not impossible.

But for many women, most hours are already filled with a full-time job and raising a family. 

At the end of the day, at least in the U.S., there is little incentive to prepare a real dinner when fast food is so available - and so much more fattening.  But some women working out at a Boston gym say they would be willing to wedge that hourly workout into their day.

"I would be willing to do it if it was going to maintain my weight and keep my health," Jane Davern said.

"All right, I would do it," Jean Holmes states. "I would exercise to maintain my body weight, yes."

The U.S. Centers for Disease Control says the percentage of overweight Americans increased 60 percent between 1991 and 2000.

The World Health Organization says more than one billion adults in other nations are in the same shape.

While there is advice aplenty on how to lose pounds or kilograms, a new study focuses on middle aged and older women who maintain normal body weight, or BMI (Body Mass Index)  and do not diet.

"We found that physical activity was effective in controlling weight only among women who started off with a normal BMI," I-Min Lee states. She and colleagues at Brigham and Women's Hospital in Boston studied data from 34,000 women, whose average age was 54. 

During a 13-year period, the women were separated into three groups. The first group exercised daily for 60 minutes.
The second exercised 30 minutes a day, and the third group worked out less than half an hour daily.

"These two lesser activity groups of women were significantly more likely to gain weight," she said. "Compared to the most active group of women."

During the study, the average weight of the participants went up by six pounds, or 2.7 kilograms. 

So, what can overweight women do?  Surprisingly, I-Min Lee and her colleagues found more exercise did not help.

"Once a woman became overweight or obese, there was no relation between physical activity and weight change among these women," Lee said. But I-Min Lee says heavier women should keep on exercising. 

"While our study shows that this might not be sufficient to maintain normal weight, it clearly is sufficient to reduce the risk of developing many chronic diseases, including heart disease, certain types of cancer, type two diabetes," Lee explained.

The researchers say while exercise helps prevent disease, the only way that heavier women can lose weight is to simply cut calories.

The study was published in the Journal of the American Medical Association.