It seems plausible that increased aromatase activity in obese men, as a result of a larger fat mass, is responsible for decreased levels of testosterone. Therefore aromatase inhibition increases testosterone levels, which may affect hepatic and cardiac function.

In this intervention study two groups of hypogonadal obese men are compared. Group A is treated with Letrozole 2.5 mg (aromatase inhibitor) once every two days during four months; a group with normal testosterone and low oestrogen concentrations. Group B is treated with placebo once every two days during four months; this group will retain low testosterone - and high oestrogenic concentrations.

The primary objective of the study is to evaluate effects of changed sex steroids in obese men on hepatic and cardiac function.

Inclusion Criteria:

• Obese male subjects
• Planned for gastric bypass (BMI > 30 kg/m²)
• low testosterone levels
• age between 20 and 65

Exclusion Criteria:

• Primary hypogonadism or secondary hypogonadism due to genetic causes (Kallman syndrome etc.), tumours, infiltrative diseases, infections, pituitary apoplexy, trauma, critical illness, chronic systemic illness or intentional.
• Treatment with corticoids, opiates (on a daily basis), androgen- or estrogen analogs or CYP2A6 substrates (Dexmedetomidine, Ifosfamide, Methoxsalen, Miconazole, Tranylcypromine).
• Impaired renal function defined as serum-creatine > 1.5 mg/dL
• Clinically significant active cardiovascular disease including history of myocardial infarction within the past 6 months and/or heart failure (NYHA class III or IV) at the discretion of the investigator
• Cancer or any clinically significant disease or disorder, which in the investigator's opinion could interfere with the results of the trial
• Palpable prostate nodule or induration, Prostate-specific antigen (PSA) > 3 ng/mL, prostatism, untreated sleep apnea syndrome, erythrocytosis (hematocrit > 50%) or hyperviscosity. (cfr. Endocrine Society Clinical Practice Guideline by Bhasin S et al.)
• Known or suspected abuse of alcohol or narcotics