Effects of growth hormone administration on protein dynamics and substrate metabolism during 4 weeks of dietary restriction in obese women

OBJECTIVE Treatment of obesity with very low calorie diet (VLCD) is complicated by protein loss. We evaluated the effects of coadministration of GH on protein turnover, substrate metabolism, and body composition in VLCD treated obesity. DESIGN AND PATIENTS Fifteen obese women underwent 4 weeks of very low calorie diet (VLCD) in parallel with GH treatment (n = 7) or placebo (n = 8). MEASUREMENTS Protein metabolism and total glucose turnover were isotopically assayed. Plasma concentrations of amino acids were determined by an HPLC system. Estimated rates of lipid and glucose oxidation were obtained by indirect calorimetry. Fat free mass was determined by DEXA-scan. RESULTS Protein breakdown decreased in both groups (tyrosine flux mu mol/h): -12% +/- 3 (GH) vs. - 9% +/- 3 (placebo)). Phenylalanine degradation in relation to phenylalanine concentration decreased by 9% in the GH group, whereas an increase of 8% was observed in the placebo group (P = 0.1). Plasma concentrations of several amino acids were significantly decreased in the placebo group, while urea excretion decreased in the GH group. A decrease in FFM was found in placebo treated patients (2.14% +/- 1.9 (GH) vs. - 3.54% +/- 1.6 (placebo), P < 0.05). Rates of lipid oxidation tended to be increased by GH treatment (lipid oxidation (mg/minutes): 79.7 +/- 5.9 (GH) vs. 64.6 +/- 5.9 (placebo), P = 0.1). CONCLUSION During dietary restriction GH primarily seems to conserve protein by a reduced hepatic degradation of amino acids.