Abstract Body (Do not enter title and authors here): Background: Adolescence has been identified as a critical time point when physiological adaptations deviate into pathological cardiometabolic disease processes. Large-scale prospective evidence on the direct impact of increasing fat mass from adolescence with alterations in cardiac structure among apparently healthy adolescents is limited. Adolescent dyslipidaemia and elevated blood pressure (BP) have been established as independent predictors of premature cardiac damage. However, understanding the mechanism through which fat mass alters cardiac indices will be crucial for public health intervention and preventive cardiology.

Purpose: To examine the longitudinal associations of total fat mass and trunk fat mass with progressive cardiac remodelling and examine the role of low-density lipoprotein cholesterol (LDL-c), systolic BP, and inflammation on the relationships.

Methods: From the Avon Longitudinal Study of Parents and Children (ALSPAC), UK birth cohort, 1803 adolescents aged 17 years who had repeated dual-energy Xray absorptiometry-measured fat mass at ages 17 and 24 years clinic visits were included. Echocardiography at 17 and 24 years assessed left ventricular mass indexed for height^2.7 (LVM). Repeated-measure longitudinal multivariate-adjusted analyses were conducted with generalized linear mixed-effect models with identity links. Structural equation model causal mediation analysis assessed the proportion of the association between fat mass and cardiac mass during ages 17 to 24 years mediated by LDL-c, systolic BP, or high-sensitivity C-reactive protein (hsCRP).

Results: Each unit increase of total fat mass from age 17–24 years (β = 0.12g/m^2.7 [95% CI, 0.09 – 0.15], p<0.001) and trunk fat mass (0.23g/m^2.7 [0.18 – 0.28], p<0.001) were independently associated with increased LVM over the 7-year growth period. Increased LDL-c, systolic BP, and hsCRP partly mediated (7.9%, 10.6%, and 7.4% mediation, respectively) the longitudinal associations between increased fat mass and increased cardiac mass during growth from adolescence to young adulthood (Figure 1).

Conclusions: Increased total and trunk fat mass in adolescence was associated with cardiac structural remodelling, partially explained by altered cardiometabolic and inflammatory indices. Trunk fat mass may have a two-fold worse deleterious effect on cardiac mass than total fat mass.