According to a joint American and Spanish study out on Tuesday, junk food, especially those with trans fat, can make healthy young men infertile by damaging their sperm.

Fertility doctors from Harvard University and the University of Murcia, southeastern Spain, analyzed sperm for hundreds of men between the ages of 18-22. They found those who ate more junk food had poorer quality sperm than those who ate a nutritious diet.

All the men used in the study were in optimum shape and had no problems that would affect their reproductive system, The Sun reported.

In a separate study conducted by Japan that used 215 men, also out on Tuesday, discovered that exercise can be good for a man's sperm. Those who took part in moderate exercise, such as brisk walking, can improve the swimming ability of sperm.

The lesson? If you want kids, exercise and eat healthy. If you don't--don't change a thing.

Via Fox News