Adherence to the Mediterranean Diet and Body Composition in Children and Adolescents with Obesity: A Cross-Sectional Study

Background/Objectives: Obesity in children and adolescents remains a major health challenge, while Mediterranean diet (MeDi) adherence among children and adolescents is often suboptimal. This study examined MeDi adherence and its association with anthropometric and body composition parameters in children and adolescents with obesity. Methods: This cross-sectional study included 132 participants aged 5–19 years with obesity and was conducted between February 2024 and September 2025 at the Department of Pediatrics, University Hospital Centre Split. MeDi adherence was assessed using the Mediterranean Diet Quality Index for children and adolescents (KIDMED), and body composition by multifrequency bioelectrical impedance analysis. Also, anthropometric measurements were recorded, and body mass index z-score adjusted for age and sex (BMI z-score) was calculated. Results: Based on the KIDMED score, 34.8% of participants showed optimal MeDi adherence, 49.2% moderate adherence, and 15.9% very low adherence. Significant inverse correlations were observed between KIDMED scores and body fat mass (kg) (ρ = −0.230, p = 0.008) and trunk fat mass (kg) (ρ = −0.234, p = 0.007), although these associations did not remain statistically significant after Benjamini–Hochberg correction (adjusted p = 0.06 for both). Multivariate linear regression analyses showed no statistically significant associations between KIDMED scores and the examined body fat parameters after adjustment for age and sex (all p > 0.05). Age was positively associated with body fat mass (kg), trunk fat mass (kg), and trunk fat (%) (all p < 0.001), whereas female sex was associated with higher body fat (%) (p < 0.001). Conclusions: Adherence to the MeDi was suboptimal in most children and adolescents with obesity. Our findings did not establish a statistically significant association between MeDi adherence and the examined body fat parameters after correction for multiple testing and adjustment for age and sex. Further prospective and intervention studies with a larger number of participants are needed to determine whether improving MeDi adherence can lead to favorable changes in body composition in this population.