Young adults who maintained a high level of physical activity gained less weight in middle age, found researcher Arlene Hankinson, MD, an instructor of preventive medicine at Northwestern University Feinberg School of Medicine in Chicago.
''Activity has an effect, but it doesn't completely eliminate age-related weight gain," she tells WebMD.
But it does help, she finds, and the benefit appears greater for women, though she is not sure why.
Highly active women gained 13 pounds less over 20 years than women with low activity levels, while highly active men gained 6 pounds less than the men with low activity levels.
The study is published in the Journal of the American Medical Association.
While some who hope activity can wipe out age-related weight gain may see the results as discouraging, Hankinson disagrees. "I think it's extremely optimistic news," she says. "It's showing how beneficial activity is in reducing weight gain with age."
Physical Activity and Weight Gain: The Study
Hankinson evaluated 3,554 participants in the CARDIA study, an ongoing study that now has 20 years of follow up.
Participants were ages 18 to 30 at the start of the study. They answered questions about activity at follow-up exams done after two, five, seven, 10, 15, and 20 years.
Hankinson evaluated weight, body mass index (BMI), and waist circumference. She took into account such factors as age, alcohol use, and calorie intake.
She looked at the differences in activity levels in two ways: by comparing those in the top level of activity with those in the lowest level and by evaluating those who got 150 minutes or more of moderate to vigorous intensity activity a week. (The 150 minutes of moderate activity is recommended by the U.S. Department of Health and Human Services.)
When she compared the high activity group with the low? "Women who had low activity gained 33 pounds over the 20 years while women who had high activity gained 20 pounds over the 20 years," she says.
"Men who had low activity gained 28 pounds over the 20 years and men who had high activity gained 22 pounds over the 20 years."
Only 11% of the women and 12% of the men in the highest activity group at the study start kept it up over the 20 years. Over the 20 years, nearly 37% met the 150-minute a week goal.
When she looked at the 150-minute a week group, she found "women who didn't have 150 minutes of physical activity a week gained 32 pounds over 20 years; women who did gained 22 pounds. Men who didn't get 150 minutes gained 29 pounds; men who did gained 26 pounds."
Those in the high activity group also had smaller gains in waist circumference with age.
Physical activity included not just sports and other formal exercise but also occupational activity and home maintenance.
''Physical activity is something everyone can do in some form," Hankinson tells WebMD.
Move More, Gain Less: Second Opinion
The new study findings are scientifically sound and are important, says Tim Church, MD, PhD, director of preventive medicine research at the Pennington Biomedical Research Center in Baton Rouge, La. He reviewed the study findings for WebMD but was not involved in the research.
"It brings some more balance to the discussion [about the obesity epidemic],'' he says. Often, people zero in on food only, he says. "Here's more evidence that physical activity clearly has a role in preventing weight gain. The optimal way to control weight is both through diet and physical activity."
The link found by Hankinson between lesser weight gain among highly active people may be more encouraging than at first glance, he says. He points out that the study followed them only to ages 38 to 50. "I would expect to see bigger group differences [between low and high activity groups] as the groups continue to age," he says.
Minimizing weight gain is just one reason to stay active with age, he says. "You are going to be able to get around easier" if you stay active with age, he says.