Effect of Roux-en-Y gastric bypass on testosterone and prostate-specific antigen.

Background: Obese men have lower serum levels of testosterone, dehydroepiandrosterone (DHEA) and prostate-specific antigen (PSA), but an increased risk of dying from prostate cancer. The aim of this study was to examine the effect of surgically induced weight loss on serum testosterone, DHEA and PSA levels in obese men.

Methods: Consecutive men undergoing Roux-en-Y gastric bypass (RYGB) participated in a prospective, longitudinal study. Main outcomes were changes were body mass index (BMI), percentage excess weight loss, serum levels of testosterone, DHEA and PSA, PSA mass and plasma volume, measured before operation and 3, 6 and 12 months later.

Results: In 64 patients, mean BMI fell from 48.2 kg/m(2) before operation to 39.2, 35.6 and 32.4 kg/m(2) at 3, 6 and 12 months after RYGB. Testosterone levels rose significantly from 259 ng/dl to 386, 452 and 520 ng/dl respectively. Serum PSA levels increased significantly from 0.51 ng/ml to 0.67 ng/ml at 12 months. There were no significant changes in DHEA or PSA mass.

Conclusion: RYGB normalizes the serum testosterone level. PSA levels increase with weight loss and may be inversely correlated with changes in plasma volume, indicating that PSA levels may be artificially low in obese men owing to haemodilution.