Effects of gastric bypass on the GH/IGF-I axis in severe obesity – and a comparison with GH deficiency

Abstract

Overfeeding suppresses GH secretion and makes evaluation of a suspected GH deficiency (GHD) difficult. In normal weight subjects, gender is known to influence GH concentrations, which is most apparent in the ambulatory, morning-fasted state. In this study, we examined the GH/IGF-I axis in obese men and women and the effect of surgically induced weight loss. Sixty-three subjects (body mass index (BMI) 45 +/- 6 kg/m2; 54 women, 9 men) were studied prior to, and 6 and 12 months following Roux-en-Y gastric bypass (RYGBP) surgery. Fifty-four patients with classic GHD (BMI 27 +/- 6 kg/m2; 35 men, 19 women) were included for comparison. Hormones were analysed in fasting morning serum samples. RYGBP resulted in a decreased BMI to 35 +/- kg/m2 at 6 months and 32 +/- 6 kg/m2 at 12 months. GH and IGF-I increased at 6 months in the women and at 12 months in both sexes by > or = 300 and 11% respectively. Prior to RYGBP, GH concentrations were low in the obese men and similar to those of GHD men (mean 0.09 mU/l). Obese women had tenfold higher values than obese men and sevenfold higher than GHD women. IGF-I levels were in the low reference range in the obese and below -2 S.D. for age in 13%. Surgically induced weight loss partially restores GH secretion. Despite a marked suppression of GH values, a gender influence is maintained in severe obesity. In obese women, single morning GH and IGF-I values seem sufficient to exclude a suspicion of classic GHD.