This study evaluated changes in sex hormones after bariatric surgery in 34 obese men (age range: 14.6 to 19.8 years). The participants were followed for 5 years after surgery. Total testosterone, total estradiol, luteinizing hormone, follicle-stimulating hormone, sex hormone binding globulin, C-reactive protein, insulin, and glucose were measured at baseline, 6 months, and annually thereafter. Free testosterone, free estradiol and HOMA2-IR were calculated.

The participants of the study lost one-third of their body weight after bariatric surgery, with maximum weight loss achieved at 24 months for most participants. Free testosterone increased from 0.17 (95% CI: 0.13 to 0.20) at baseline to 0.34 (95% CI: 0.30 to 0.38) and 0.27 nmol/L (95% CI: 0.23 to 0.32) at 2 and 5 years (P  < 0.001 for both), respectively. Total testosterone increased from 6.7 (95% CI: 4.7 to 8.8) at baseline to 17.6 (95% CI: 15.3 to 19.9) and 13.8 (95% CI: 11.0 to 16.5) nmol/L at 2 and 5 years (P  < 0.001), respectively. Prior to surgery, 73% of the participants had subnormal free testosterone (<0.23 nmol/L). After 2 and 5 years, only 20 and 33%, respectively, had subnormal free testosterone concentrations. Weight regain was related to a fall in free testosterone concentrations.