Interactions of Body Fat and Muscle Mass with Substrate Concentrations and Fasting Insulin Levels in Adults with Growth Hormone Deficiency

Abstract

1. Adults with growth hormone deficiency have an abnormal body composition. Alterations in body composition are closely related to substrate concentrations and insulin action. The lack of growth hormone has been associated with increased insulin sensitivity. 2. We investigated the correlations of body composition with fasting insulin levels and substrate concentrations in 24 adults with growth hormone deficiency over a wide range of adiposity (body mass index 18.8-42.3 kg/m2). 3. Lean body mass was measured by total body potassium, computer tomography of the thigh and urinary creatinine excretion. Muscle fibre distribution was evaluated from vastus lateralis biopsies. Fat mass was assessed by skinfold thickness measurements, computer tomography of the thigh, and waist and hip girth. 4. Fasting plasma insulin level increased with fat mass (r = 0.67, P = 0.0004) and with waist girth (r = 0.76, P = 0.0001). Fasting plasma insulin level increased with fasting plasma glucose level (r = 0.53, P = 0.01). Fasting plasma glucose level in turn was positively correlated with lean body mass (r = 0.49, P = 0.01) and with total thigh muscle area (r = 0.54, P = 0.01). There was no correlation between lean body mass and fat mass (r = 0.17, not significant) nor between muscle fibre types and fat mass or fat distribution. Fasting plasma insulin level showed no correlation with any measurement of lean body mass or muscle fibre type. 5. These data demonstrate that the presence of obesity is associated with hyperinsulinaemia as the result of insulin resistance in adults with growth hormone deficiency, which could contribute to the increased cardiovascular mortality in adults with growth hormone deficiency.