Associations of childhood body composition trajectories and adolescent body dissatisfaction: Longitudinal evidence from the UK Millennium Cohort Study

PurposeBody dissatisfaction is common, particularly among those with higher BMIs. Issues with BMI as an adiposity measure may limit our understanding of body dissatisfaction determinants. We investigate the association of childhood trajectories of BMI, fat mass index (FMI), and fat-free mass index (FFMI) with body dissatisfaction at age 14, and sex differences in these associations. MethodsWe used latent class growth analysis to model trajectories of BMI (3-14 years), FMI and FFMI (7-14 years) in Millennium Cohort Study participants, and univariable and multivariable linear regression models to investigate their associations with body dissatisfaction. ResultsAmong 13,025 participants (49.2% female; 84.4% White), we found three BMI, FMI, and FFMI trajectories (low, moderate, high). Participants with moderate (adjusted mean difference [aMD] 0.32, 95% confidence interval [CI] 0.24, 0.39) and high (aMD 0.71, 95% CI 0.55, 0.86) BMI trajectories and those with moderate (aMD 0.33, 95% CI 0.25, 0.41) and high (aMD 0.73, 95% CI 0.57, 0.89) FMI trajectories had higher body dissatisfaction scores than those with low trajectories. For FFMI trajectories, boys with high (aMD 0.31, 95% CI 0.17, 0.31), but not moderate (aMD 0.07, 95% CI -0.03, 0.17) trajectories had greater body dissatisfaction. In girls, mean differences by FFMI trajectory were consistent with adiposity results. DiscussionOur findings suggest that both boys and girls are susceptible to weight-related body dissatisfaction. Higher FFMI is also associated with body dissatisfaction, but in girls, associations are present at lower levels compared with boys, potentially reflecting higher societal pressures on young girls.