Associations Between Fat-Free Mass, Fat Mass, Basal Metabolic Rate, and Energy Intake in Lebanese Adolescents

Abstract

Background: Adolescence is a critical period of growth marked by substantial changes in body composition and energy requirements. Although energy intake is essential for supporting growth and development, the biological determinants regulating energy intake during adolescence remain incompletely understood. Emerging evidence suggests that fat-free mass, through its influence on basal metabolic rate, may play a central role in driving energy intake, challenging traditional fat-centric models of appetite regulation. However, data in adolescent populations, particularly from Middle Eastern contexts, are limited. Objectives: This study aimed to examine the associations between body composition, basal metabolic rate, and energy intake in Lebanese adolescents. Methods: This cross-sectional study included 150 Lebanese adolescents aged 15,18 years recruited as part of the Nutrition and Health in Arab Adolescents (NaHAR) project. Body composition was assessed using the deuterium dilution technique as the reference method, while basal metabolic rate was estimated by bioelectrical impedance analysis. Energy intake was assessed using a 24-hour dietary recall. Due to non-normal data distributions, results were summarized using medians and interquartile ranges. Associations were examined using Spearman correlation analyses, and mediation analysis was performed to assess the indirect role of basal metabolic rate in linking fat free mass and energy intake. Results: Energy intake was positively correlated with fat-free mass and basal metabolic rate, whereas adiposity-related measures, including fat mass index and percentage body fat, showed inverse or weak associations with energy intake. Mediation analysis demonstrated that basal metabolic rate significantly mediated the relationship between fat-free mass and energy intake, while fat mass did not exert a meaningful indirect effect. Sex-stratified analyses revealed similar patterns of association in males and females. Conclusion: These findings support a metabolic demand–driven model of energy intake regulation during adolescence, whereby fat-free mass influences energy intake primarily through its effect on basal metabolic rate. This study contributes novel evidence from a Middle Eastern adolescent population and underscores the importance of considering lean tissue mass, rather than adiposity alone, in understanding appetite regulation and energy balance during adolescence.