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Energy expenditure and body composition in growth hormone deficient adults on exogenous growth hormone
P K Chong1, R T Jung, C M Scrimgeour
1Department of Medicine, Ninewells Hospital and Medical School, Dundee, UK.
Objectives:
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.
Design:
We performed an open study with growth hormone administered at 0.5 units per kilogram ideal body weight per week for 3 months.
Patients:
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.
Measurements:
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.
Results:
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.
Conclusions:
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.