Researchers study age-related weight gain

More than 30 percent of Americans are obese. Many try to lose the weight they've already gained, but they can get ahead of the game by avoiding weight gain as they age.

New research looked at the benefits of physical activity into middle age. Researchers studied a group of young adults ages 18 to 30 who were participating in a long-term study looking at coronary artery risk factors. Their physical activity levels were tracked at six different times over 20 years into middle age.

"Maintaining a high physical activity level makes a difference,” said Dr. Arlene Hankinson with the Feinberg School of Medicine at Northwestern University. “Nothing that we've seen prevents age-related weight gain entirely, but maintaining higher levels of physical activity over time were associated with gaining less weight as you transition from young adulthood to middle age."

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

It's not easy to maintain those levels over the long haul. Only 11 to 13 percent of those in the study achieved it. Researchers recommend people find activities they love to do and keep doing it.

By maintaining a high activity level over time, people don't have to keep increasing that level to continue seeing results, according to researchers.