Little is known about the effectiveness of behavioral strategies to prevent long-term weight gain in female adolescents and young adults. That’s why researchers set out to assess the connection between diet and physical activity in weight-control strategies (alone and together) and in subsequent weight gain.

Reporting in the January 2010 issue of The American Journal of Clinical Nutrition, researchers presented the findings of a prospective study of 4,456 females, aged 14–22, who were part of the ongoing Growing Up Today Study. Self-reported weight control behaviors from 2001 to 2005, including dietary changes and exercise, were used to predict the subjects’ weight change.

While none of the dietary approaches predicted less weight gain, females who exercised 5 or more days per week gained “significantly” less weight than did their peers. The most successful strategy for weight gain prevention among the females was limiting portion sizes, combined with frequent exercise.

“Our results suggest that physical activity is a necessary strategy for long-term weight control among adolescents and young adult females,” the study authors wrote. “Combining dietary weight-control approaches with physical activity is the most effective method for reducing weight gain.”