Objective: We evaluated the influence of two types of calorie restriction, total fast or very low calorie diet, on GH responsiveness to GHRH in severely obese patients.
Design: Twenty patients with massive obesity underwent one of two types of calorie restriction, total fast (10 patients) or very low calorie diet (10 patients).
Measurements: Fasting GH, IGF-I, glucose, insulin and GH secretion after GHRH (100 ug i.v.) were assessed in all patients before and after diet therapy.
Results: Both types of diet produced similar weight reduction (total fast, 5.6 +/- 1.6 kg/m2 vs very low calorie diet, 5.6 +/- 1.5 kg/m2 mean +/- SD). A significant increase in the integrated GH secretion was observed after weight loss with very low calorie diet (17 +/- 9 vs 27 +/- 12 mU/l min; P < 0.05). However, no change was found in GH response after weight loss with total fast (13 +/- 5 vs 15 +/- 7 mU/l min). Glucose, insulin and IGF-I levels showed a significant decrease with weight reduction which was similar for both groups.
Conclusion: These findings suggest that the type of dietary manipulation during calorie restriction in obese patients may influence the changes in GH response to GHRH after weight loss.