The effect of obesity on male infertility has been well established. Up to 40% of men presenting to infertility clinics are overweight.
Obesity causes alterations in hormone profiles, sleep apnea, diabetes and increased scrotal temperatures, all of which negatively impact semen parameters.
Bariatric surgery leads to substantial weight loss and several positive effects, including an increase in life expectancy and improvement of medical comorbidities such as hypertension and diabetes. As such, it would make sense that sperm quality would improve for infertile men undergoing bariatric surgery.
But it does not. A study published in Reproductive Sciences (2012;19:1057-1062) followed 20 morbidly obese men, 10 of whom underwent weight reduction surgery.
While those who underwent surgery had increased sexual function as well as increased luteinizing hormone, follicle-stimulating hormone, and testosterone, their semen parameters went completely unchanged. New studies will need to look at birth rate as a primary endpoint.