UNLABELLED: Transgender and gender-diverse (TGD) adolescent populations are at a higher risk for obesity. The aim of this study was to explore possible reasons, such as differences in eating and exercise behaviors. This was a prospective cross-sectional study of TGD adolescent patients at the pediatric endocrinology outpatient clinic of the Vienna General Hospital from January to July 2022. Patients were included in the World Health Organization's Health Behaviour in School-Aged Children (HBSC) survey, which assesses for multiple measures including exercise, eating, and mental wellbeing. We recruited 32 patients via the outpatient clinic, and a further 55 adolescents self-identified as TGD through the survey. Responses from the cohort of 87 TGD adolescents were compared to the Austrian sample containing 10,110 participants. TGD adolescents reported significantly lower levels of physical activity than the national sample, both in instances of vigorous activity (p = 0.002) and any physical activity lasting >
60 min (p <
0.001) per week. Gender variance was here demonstrated to be a strong predictor for physical inactivity levels, even when correcting for low mental health scores. Regarding body image, TGD participants were also more likely to describe themselves as feeling "too fat" (p = 0.001). No statistically significant difference in eating behavior was found. CONCLUSION: The results of this study point towards the complexity of healthcare needs in the TGD adolescent population. The interconnectedness of mental health and exercise behavior is well described. However, qualitative work is needed to understand the specific relationship between gender expression, body image, eating and exercise behaviors, as well as social inclusion. WHAT IS KNOWN: • Transgender and gender-diverse (TGD) adolescents are at an increased risk for obesity. The causes for this are most likely complex, and remain poorly understood. • Survey studies in the United States and New Zealand have reported reduced levels of physical activity in the TGD population. However, data is scarce, particularly regarding adolescents. WHAT IS NEW: • This prospective, national survey study is the first to demonstrate reduced levels of self-reported physical activity in a cohort of central European TGD adolescents.