Energy expenditure and body composition in growth hormone deficient adults on exogenous growth hormone

Abstract

We assessed whether the obesity observed in growth hormone deficient adults is maintained by a reduction in energy expenditure. We studied the effects of exogenous growth hormone on energy expenditure and body composition. We performed an open study with growth hormone administered at 0.5 units per kilogram ideal body weight per week for 3 months. Seven growth hormone deficient adults were studied. Thirty-eight healthy volunteers had their resting metabolic rate measured, with seven of them proceeding to have their total energy expenditure assessed. Total energy expenditure was measured by the doubly labelled water method (D2O18), resting metabolic rate by ventilated hood indirect calorimetry, and fat free mass from the dilution volume of oxygen-18. Body composition and components of energy expenditure were assessed before, at 2 weeks and at the end of the 3-month treatment period on exogenous growth hormone. Growth hormone deficient adults did not have a low total energy expenditure compared to healthy controls (13.12 vs 12.75 MJ/24 h) with only one patient expending less than 10 MJ/24 h. None had a resting metabolic rate lower than the 95% confidence limits of normality. The amount of energy expended on physical activity and thermogenesis was significant (6.54 MJ/24 h) and was similar to healthy controls (6.47 MJ/24 h). Resting metabolic rate increased by 15.9% after 14 days on exogenous growth hormone and was elevated 12.1% after 3 months treatment but the ratio to fat-free mass remained unaltered. Total energy expenditure increased by 13.4% after 14 days therapy. Fat-free mass increased significantly after 3 months treatment by (mean) 4.5 kg with no change in fat mass and no loss in body weight. Obesity maintenance in growth hormone deficient adults is not a consequence of reduced total energy expenditure or a reduced exercise energy output. There was also no evidence for an energy sparing mechanism. Energy expenditure was increased by exogenous growth hormone but was not associated with a loss in fat mass or body weight suggesting the need for dietetic advice for those already obese at the outset of therapy.