Don't tell him that you are not attracted to him anymore. You can't help what you are attracted to, but I feel that this will backfire. He will just be hurt and defensive, and possibly bitter. It could really poison your relationship.
I guarantee you that he knows that he has a problem, but I think men sometimes have an issue where they need to feel like THEY made the decision to improve themselves. If you complain to him, he'll just get defensive. It sounds silly, but I can be like this, and I am a man who has struggled with my weight for most of my life, so I think I understand the psychology well.
I think the trick would be to somehow get him to see how out of shape he is, but without him perceiving that it is YOU telling him this. I'm not sure how to do this. Maybe put up a full-length mirror in the house so he can see his figure. Maybe do something physical outdoors and invite him to do it with you so he can see how out of breath he gets. Maybe pay a group of school children to point and laugh at him and play a tuba when he walks by.
Just kidding on the last one