Rapid Suppression of Growth Hormone Concentration by Overeating: Potential Mediation by Hyperinsulinemia

Context: The very low GH concentration in obesity is commonly attributed to high body fat mass; however, the influence of overeating on GH secretion is not clear. Objective: The aim of the study was to examine the effects of 2 wk of overeating on changes in GH secretion. Setting: Subjects were admitted to the hospital and stayed within the Michigan Clinical Research Unit throughout the entire 2-wk overeating period. Participants: We studied seven healthy, nonobese men (body mass index, 24 +/- 1 kg/m(2); age, 25 +/- 1 yr). Intervention: Subjects ate standardized meals containing 70 kcal/kg fat free mass/d (similar to 4000 kcal/d) for 2 wk. Main Outcome Measures: Twenty-four-hour plasma concentrations of GH (every 20 min) and insulin (every 2 h) were measured before overeating (baseline), on d 3, and after 2 wk of overeating. Results: Compared with baseline, average 24-h plasma GH concentration declined nearly 80% by d 3 of overeating (1.30 +/- 0.18 vs. 0.36 +/- 0.09 ng/ml; P = 0.01). This marked suppression of GH secretion occurred in the absence of an increase in body weight (77.0 +/- 2.2 vs. 76.4 +/- 2.4 kg). At the same time, average 24-h insulin concentration doubled (16.6 +/- 2.1 vs. 31.7 +/- 5.8 mu U/ml; P = 0.009). After 2 wk, body weight significantly increased (79.0 +/- 2.1 kg; P < 0.001), and body fat increased by more than 10% (P = 0.002). However, this did not induce a further suppression in plasma GH concentration (0.33 +/- 0.08 ng/ml). Conclusion: Only a few days of overeating markedly suppressed GH secretion before any measurable weight gain and was accompanied by chronic hyperinsulinemia. Increased body weight and body fat by 2 wk of overeating did not further suppress GH secretion. (J Clin Endocrinol Metab 96: 824-830, 2011)