Obese men who undergo gastric bypass surgery will not only lose weight; their sex lives are likely to improve, too, new research shows.

“We wanted to know if obesity was biologically associated with an unsatisfying sex life, and if so, could it be reversible,” Dr. Ahmad Hammoud of the University of Utah in Salt Lake City, who led the study, said in a press release accompanying the new report. “Our results show that the answer to both questions may be yes.”

While obesity in men has been linked to low testosterone levels, high levels of estrogen, impaired fertility, and worse sexual quality of life, Hammoud and his colleagues note in the Journal of Clinical Endocrinology and Metabolism, there is little information on what happens to these men’s sex hormones and sexual function if they lose weight.

To investigate, Hammoud and his team looked at 22 men who had undergone gastric bypass surgery and 42 obese men who didn’t have the operation. At the study’s outset, participants weighed 330 pounds, on average, while the average BMI for the group was 46.2, what is considered to be .

The heavier the men were, the lower their testosterone, and the more likely they were to report dissatisfaction with their sex lives-especially avoiding sexual encounters and having difficulty performing sexually.

Two years later, the men who’d had weight loss surgery had dropped an average of nearly 17 points from their BMI. Their estrogen levels had fallen significantly, while their testosterone levels had gone up. And all showed improvements on each of the four measures of sexual quality of life the researchers looked at: they were less likely to avoid sexual encounters, have difficulty with sexual performance, have little sexual desire, or report not enjoying sex.

There were no significant changes in measures of sexual quality of life or hormone levels in the group of men who didn’t have the surgery.

Because other both biological and psychological factors involved in obesity can affect both sexual health and hormone levels, Hammoud and his team conclude, more research is needed to determine whether there is a causal relationship between hormone changes and sexual quality of life.

SOURCE: Journal of Clinical Endocrinology and Metabolism, April 2009.