['To test the hypothesis that individuals who are active but who decrease physical activity (PA) over time have a higher risk of becoming obese in young adulthood, when compared to individuals who are consistently active throughout childhood and adolescence.', 'Iowa Bone Development Study cohort members (242 males and 251 females) participated in accelerometry assessments, dual-energy X-ray absorptiometry scans, and dietary questionnaire surveys at ages 5, 8, 11, 13, 15, 17, and 19 years. Group-based trajectory analyses identified distinct trajectory patterns of moderate- to vigorous-intensity PA (MVPA), percentage of body fat, and energy intake. A multivariable logistic regression model was fit to estimate the odds of "becoming obese" based on the MVPA trajectories, adjusted for mother\'s education, somatic maturation, and energy intake.', 'Among males, 74.7% had a "normal" body fat pattern, 14.6% had a "becoming obese" pattern, and 10.7% had a "consistently obese" pattern, while among females, the percentages were 58.6%, 28.6%, and 12.8%, respectively. Participants who were active (≥45 min MVPA) as children but decreased MVPA with age were more likely to become obese, compared to consistently active participants (adjusted OR\u2009=\u20092.77; 95% CI\u2009=\u20091.16, 6.58).'] Does active lifestyle in childhood and adolescence prevent obesity development in young adulthood?