Will Losing Weight Improve Your Man's Fertility?

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If a woman's fertility is ruled by her biological clock, is a guy's fertility ruled by his bathroom scale? According to a new study from the University of Buffalo, obese teenage boys may already have up to 50 percent less testosterone than normal weight young men—a "grim message," say researchers, about the boys' risk of infertility in later life.

And this isn't the only study to show a connection between obesity and infertility. The same research team first reported in 2004 the presence of low testosterone levels—known as hypogonadism—in obese, type 2 diabetic adult males and confirmed it in 2010 in more than 2,000 obese men, both diabetic and non-diabetic.

"The implications of our findings are, frankly, horrendous..." says Paresh Dandona, MD, PhD, SUNY Distinguished Professor in the Department of Medicine, chief of the Division of Endocrinology, Diabetes and Metabolism in the UB medical school, and first author of this newest study.

Why does weight matter so much? Obesity seems to serve male fertility a double dose of trouble. First, obese males tend to produce an abundance of estradiol, an estrogen hormone made by certain fat cells. Excess estrogen may hamper the body's ability to produce adequate testosterone, which can then affect sperm production. Second, low testosterone increases men's tendency toward abdominal fat and reduced muscle, leading to insulin resistance which contributes to type 2 diabetes, another risk factor for infertility.

But there is a big however here, along with some encouraging news for heavy guys. They can reverse the situation, by—you guessed it—losing weight. "Testosterone levels do return to normal in obese adult males who [lose weight]," says Dandona.

Could this be the motivation your guy needs to lose that extra weight he's been carrying around? "No excuses, he's coming to the gym with me tonight," says Emily Fox of Whitehouse Station, New Jersey. "It takes two to tango. He knows it's a good idea to lose a few pounds, so better do it now before we start trying."