Obesity following hypothalamic damage is often severe and resistant to life style changes. It is postulated that differences in basal metabolic rate (BMR) and physical activity may contribute to hypothalamic obesity.

Objective: To investigate the role of energy expenditure, BMR and physical activity, in the aetiology of hypothalamic obesity.

Design: This was a cross-sectional study of three groups of children: those with hypothalamic obesity (HO), congenital hypopituitarism (CH) and simple obesity (SO).

Results: A total of 47 children (HO=18, CH=13, SO=16) had BMR measured, using indirect calorimetry (Deltatrac II). A lower BMR was seen in the HO group, which remained even after adjusting for lean mass. Physical activity, assessed using tri-axial accelerometry, demonstrated longer activity periods in the HO group, although the degree of activity was reduced. No significant differences were seen in calorie intake.

Conclusion: Energy expenditure, rather than energy intake has a greater role in the development of obesity following cranial tumour therapy. Reductions in BMR and physical activity, leading to a positive energy balance and weight gain despite an age-appropriate calorie intake, may contribute to hypothalamic obesity.