The Association Between Gut-Derived Metabolites, Body Composition, and Energy Expenditures in Adolescents: A Sex-Stratified Analysis of the COPSAC2000 Study

The gut microbiota has been implicated in regulating body composition, insulin resistance, and energy metabolism through microbial metabolites, including short-chain fatty acids (SCFAs) and amino acids. However, evidence in adolescents, particularly regarding sex-specific differences and lifestyle such as alcohol intake, remains limited. Characterizing sex-specific metabolic signatures in adolescence may improve early identification of metabolic risk. To address this gap, we investigated associations between fecal metabolites, body composition, insulin resistance, and energy expenditure in 158 adolescents aged 18 from the Copenhagen Prospective Studies on Asthma in Childhood (COPSAC2000). Quantitative fecal metabolomics was performed using proton nuclear magnetic resonance (1H-NMR) spectroscopy, profiling 32 metabolites. Associations with body composition, insulin resistance, and energy expenditure were evaluated using sex-stratified univariate and multivariate modelling with false discovery rate (FDR [≤] 0.05 and 0.2). Fecal acetate and ethanol were more associated with fat-free mass index (FFMI) and waist-to-height ratio (WHtR) than with body mass index (BMI) in females; in males, no associations remained after FDR. Lysine and leucine showed associations with BMI and insulin resistance in females. Acetate, butyrate, glucose, and methanol were associated with total energy expenditure (TEE) in females, whereas no association survived in males. Alcohol intake was positively associated with fecal ethanol, glucose, and methanol, and inversely with trimethylamine in females, while galactose showed a positive association in males. These findings demonstrate that gut microbiota-derived metabolites are related to body composition, insulin sensitivity, and energy balance in adolescents, particularly females, highlighting the utility of fecal metabolomics in exploring mechanisms underlying metabolic variation.