Body composition differences between males and females emerge during adolescence and continue throughout adulthood; however, whether sex moderates body composition changes after a lifestyle intervention is unknown. The objective of this study was to explore sex as a moderator of changes in body composition in response to an intensive lifestyle intervention.


136 Latino youth with obesity (BMI% 98.2±1.28) aged 14-16 years old were randomized to either a 12-wk lifestyle intervention (27 male/40 female) or control (35 male/34 female) group. The intervention included nutrition education (1 hr/wk) and moderate-to-vigorous physical activity (3 hrs/wk). Age- and sex- adjusted BMI percentiles were calculated, waist circumference was measured at the umbilicus, total fat mass was measured using bioelectrical impedance, and fat free mass was calculated as the difference between weight and total fat mass.


We observed significant reductions in BMI (-0.7 kg/m2, p<0.001), BMI% (-0.4%, p<0.001), waist circumference (-2.1 cm, p<0.001), and fat percent (-2.8%, p<0.001) in intervention youth compared to control youth. Sex did not moderate changes in BMI [F(1,118)=0.002, p=0.9], BMI% [F(1,118)=0.068, p=0.8], or waist circumference [F(1,118)=0.5, p=0.5]. Sex significantly moderated changes in body fat percent [F(1, 118)=4.9, p=0.03], fat mass [F(1, 118)=4.3, p=0.04], and fat free mass [F(1, 118)=4.0, p<0.05]. Compared to sex-specific changes in the control group, males in the intervention significantly reduced fat percent (-4.1 ±0.8 vs.-1.1±0.7%) and fat mass (-4.9±1.0 vs. -1.3±0.9 kg), and gained significantly more fat free mass (3.7±0.9 vs. 0.2±0.8 kg) compared to females in the intervention (all p<0.05).


The lifestyle intervention led to a differential response between males and females for fat percent, fat mass, and fat free mass. These findings suggest that sex-specific interventions may better serve the adolescent population leading to a more pronounced impact on health outcomes.