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Adult women tend to slowly gain weight with age and many fret about the accumulation of fat on the hips, thighs and waist.

The usual response to tightening clothes is an occasional diet to shed unwanted pounds, and then the cycle begins anew.

But rarely do we ask what it would take to prevent weight gain in the first place.

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"Compared with the vast body of research on the treatment of overweight and obese individuals, little research exists on preventing weight gain," said I-Min Lee, an associate professor in the department of epidemiology at Harvard University in Boston.

More specifically, she said, the "amount of physical activity needed to prevent long-term weight gain is unclear."

So, Dr. Lee decided to study the question.

In new research published in today's edition of the Journal of the American Medical Association, she and her team provide an answer: 60 minutes of brisk physical activity a day will do the trick, as long as your food intake is reasonable.

The study involved 34,079 healthy U.S. women, average age 54, who were tracked from 1992 to 2007.

The women gained, on average, 2.6 kilograms (5.7 pounds) during the study period.

"This seemingly small amount of weight gain is sufficient to adversely affect health," Dr. Lee said.

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She also noted that "preventing weight gain is preferable to treating overweight and obesity because of the limited sustainability of weight loss."

Only 13 per cent of study participants maintained the same weight and same body-mass index during the study period. Their distinguishing characteristic was that they expended physical effort that totalled at least 21 metabolic equivalent (MET) hours per week - which translates into about 60 minutes of brisk physical activity daily.

(MET is a united used to estimate the amount of oxygen used by the body during physical activity; it allows researchers to compare the energy expenditure of people of different weight.)

The study also looked more closely at women who exercised, on average, 30 minutes daily and those who were essentially inactive. Surprisingly, there was no appreciable difference in how much weight the women in those two groups gained. Researchers noted, however, that women in the study all had "normal" diets, meaning they did not have excessive caloric intake.

Canada's physical activity guide suggests that adults should engage in 60 minutes a day of moderate-intensity activity such as brisk walking, and that children should be active for at least 90 minutes.

Fewer than one-third of Canadians meet those modest targets.

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About the Author
Public health reporter

André Picard is a health reporter and columnist at The Globe and Mail, where he has been a staff writer since 1987. He is also the author of three bestselling books.André has received much acclaim for his writing. More

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