Weight-loss surgery may have a side benefit that most don't know about, with new research showing testosterone levels in male patients jump after the procedure is done.

Obesity can lead to lower testosterone levels, lower sexual satisfaction and reduced fertility in men, the study authors explained. A man's fertility declines an average of 10 percent for every 20 pounds he is overweight.

Most studies on the link between weight-loss surgery and fertility have focused on women. To learn more about the link with men, the researchers reviewed 28 studies that included more than 1,000 men.

The men had significant increases in testosterone levels and certain other hormones after weight-loss surgery, along with declines in female sex hormone levels. These changes led to significantly better erectile function.

However, there was little change in the men's sperm quality after surgery, according to the study, published recently in the journal Obesity Surgery.

"[Weight-loss] surgery appears to be effective in increasing male sex hormones and decreasing female sex hormones in obese male patients. However, our review also suggests that bariatric surgery has no benefits on sperm parameters," said study co-author Yung Lee, who's with McMaster University in Hamilton, Canada.

But the study did not prove that weight-loss surgery causes a man to become more virile.

"Long-term comparative studies or adequately powered randomized, controlled trials are warranted to further examine the impact of [weight-loss] surgery on male sex hormones and sperm quality," Lee said in a journal news release.