Men are you overweight? Don’t worry about sperm production
In news that makes me quite happy, a new study indicates that overweight men don’t inherently have a problem with sperm production. Of course you may have other problems, but this issue won’t be one of them.
I know that Malky has some legitimate problems with this study and I’m sure that she’ll bring them up in the comments, but for now I’m going to have some more ice cream. 
UPDATE: Digging into some older news items I found this opposing viewpoint.
Podcast
My thoughts on the 2 articles: probably if your just a little overweight BMI of 28 or less then it wouldn’t affect fertility in men, more than 28 BMI it might. Jury still out on the issue.