Too many fatty foods are dangerous not only to men's waistlines, but also to their sperm production.

In research presented at a meeting of the European Society of Human Reproduction and Embryology, scientists found that obese men have more bad-quality sperm than men of normal weight.

"There is a very long list of health hazards from being overweight," said Ghiyath Shayeb, the study's lead researcher at the University of Aberdeen. "Now we can add poor semen quality to the list."

But experts aren't sure if that necessarily means obese men face major difficulties having children.

"If you have a man who isn't fantastically fertile with a normal partner who is fertile, her fertility will compensate," said Dr William Ledger, a professor of obstetrics and gynecology at Britain's University of Sheffield.

But if both partners are heavy, Ledger said that could be a problem, since obesity is known to decrease women's fertility.

Shayeb and colleagues analyzed the sperm samples of more than 5,000 men in Scotland, and divided the men into groups according to their Body Mass Index. Men who had an optimal BMI (20 to 25) had higher levels of normal functioning sperm than those who were overweight or obese.

Fat men had a 60 percent higher chance of having a low volume of semen, according to Shayeb's research. They also had a 40 percent higher chance of having sperm abnormalities.