Women may be the luckier ones when it comes to keeping the middle-age weight off -- if they put in the work.
A new study from Northwestern University researchers found that although everyone gained weight as they got older, men and women who regularly exercised gained less weight over time than those who did not. Women, especially, gained less weight when they made exercise a habit.
"Stay active," said Dr. Arlene Hankinson, an instructor in the department of preventive medicine at Northwestern University Feinberg School of Medicine. "It's not just achieving a high level of activity. The difficult part is maintaining that level throughout your life."
More than 3,500 adults from four major cities took part in the 20-year study. Inactive women gained about 13 more pounds than those who were active. Sedentary men gained only about 6 more pounds than their exercising counterparts.
To measure results, researchers asked study participants questions on how often they undertook 13 different moderate to vigorous activities, including sports, jogging, housework and construction.
The highest activity levels were defined as 150 or more minutes per week of exercise.
The authors also noted that people who reported moderate or inconsistent activity levels generally had a similar outcome to those who reported low daily activity.
"It's important to understand that the type of activity is probably not as important as the moderate to vigorous intensity and how often someone is doing it," said Hankinson. "You don't have to look for a dramatically high intensity of activity as long you're able to maintain it."
Dr. Robert H. Eckel, professor of medicine, physiology and biophysics at the University of Colorado Denver Anschutz Medical Campus, said it was important to cite the difference between the effects of diet and exercise.
"Losing weight is diet (caloric intake), whereas prevention of weight gain is more physical activity," Eckel wrote in an e-mail. "I'm not sure what to make of the male-female difference, but [it] might have something to do with that group of women who are committed or obsessed with maintaining their shape and weight."
Inactivity: Socially Undesirable
But maybe that's not the answer, as other doctors said it could be due to self-reporting. Men may be less likely to accurately report their activity since the socially desirable response is to say, 'Yes, I'm active.'
, "The fact that [this] was observational and self-reported still leaves room for more studies to verify the findings," said Dr. Robert Kushner, professor of medicine at Northwestern University Feinberg School of Medicine. "It is interesting that all groups gained weight over time, an American phenomenon."
Obesity rates have soared throughout the United States and across the globe in recent years. According to the Centers of Disease Control and Prevention, more than 30 percent of American adults are obese.
And Hankinson said move from young adulthood to middle age is the riskiest time for weight gain, as metabolisms slow down and family and work obligations interfere with exercise.
"This study represents an evolution of how our culture has had activity engineered out of our lives," said Hankinson. "It's not that we should never take the elevators or escalators, but sometimes you're going to have to make the conscious choice to take the stairs."
"You have to look for the stairwell and know that being sedentary is not a reward at the end of the day," she said.
Many doctors say it's important to develop healthy eating and exercise habits when young, they'll be harder to break later in life.
"Overall," Eckel said, "[This is] an important study that supports what we thought we knew but really didn't."