Nutritional Monitoring During Gender-Affirming Hormone Therapy: Body Composition and Metabolic Implications

Background/Objectives: Gender-affirming hormone therapy (GAHT) is associated with clinically relevant changes in body composition, energy metabolism, and functional capacity in transgender and gender-diverse individuals. The nutritional implications of these adaptations remain insufficiently characterized, and current assessment models, largely derived from cisgender populations, may not fully capture hormone-related body composition and metabolic changes. This narrative review aims to synthesize the metabolic and body composition effects of GAHT, evaluate methodological limitations in assessing nutritional status, and propose an integrated framework for clinical nutritional management. Methods: A narrative literature review was conducted through searches of PubMed/MEDLINE, Scopus, and Web of Science, complemented by screening of relevant guidelines and reference lists. Priority was given to longitudinal studies, mechanistic studies, systematic reviews, meta-analyses, and clinical guidance addressing GAHT-related changes in body composition, metabolism, nutritional status, and functional outcomes. Results: Available evidence suggests that GAHT is associated with sex steroid-related, tissue-specific changes in body composition and metabolism. In transgender men, testosterone is generally associated with increases in lean body mass (LBM), reductions in fat mass, and potential increases in visceral adiposity, alongside possible increases in energy expenditure and altered cardiometabolic profiles. In transgender women, estrogen therapy, combined with androgen suppression, is generally associated with reductions in LBM and redistribution of subcutaneous fat, with heterogeneous metabolic and functional responses. Across both groups, changes in body composition are not consistently reflected by the Body Mass Index or functional outcomes, suggesting a possible dissociation between structural and functional adaptation. Common assessment tools show limitations, including reliance on cisgender-derived reference standards and inability to capture dynamic hormonal transitions. Conclusions: Current evidence supports the need for a longitudinal and individualized interpretation of nutritional and body composition changes during GAHT. A shift toward longitudinal, multimodal nutritional assessment, integrating body composition, functional measures, biochemical markers, dietary intake, and clinical context, may improve clinical monitoring and reduce misclassification.