Few studies use longitudinal designs to assess patterns of body mass index (BMI) change from adolescence to adulthood or incorporate severe obesity as a unique subgroup.

To examine patterns of BMI trajectories from adolescence to adulthood and identify demographic characteristics associated with each BMI trajectory pattern.

Height, weight, and demographic characteristics were drawn from Waves I to V of the nationally representative school-based sample of the National Longitudinal Study of Adolescent to Adult Health (Add Health) conducted from 1994 to 2018 (data collection is ongoing).

Participants included 3,315 (55.5% female) subjects responding to in-home interviews across all five Waves of Add Health.

BMI at each wave modeled over time.

Latent class growth modeling and logistic regression analysis using population sample weights.

Five classes of weight patterns best fit the sample. Twenty-nine percent of the sample had an always healthy BMI (class 1) and 34.9% changed from healthy weight to overweight (class 2). Moving from healthy weight to obese comprised 21.8% of the sample (class 3). BMI patterns increasing from overweight to obese (class 4) and from obese to severely obese (class 5) comprised 7.6% and 7.1% of the sample, respectively. Weight change was similar for males and females with some racial or ethnic minority participants more likely to be severely obese in adulthood.

Results emphasize the importance of tracking weight longitudinally and point to a nationally representative trend of increasing BMI during the transition to adulthood. There was no substantive decreasing trend identified in the sample. Findings highlight the need for effective early and ongoing intervention and prevention strategies and can aid in identification of vulnerable youth who are at the highest risk for moving to problematic weight categories.