Tell him that the way he said what he told you hurt your feelings. It sounds to me (since you're saying you both love each other to bits and get along greatly) that he'd probably be really apologetic and confess to having tried to think about the best way to put it and that he didn't think he did a very good job of saying it either.
Guys don't know how to approach women about weight issues, we've had it banged into our heads since we were three that if we so much as mention the word weight in a conversation with a woman (even if she's 125 pounds) that she's going to freak out and yell at us for being horrible awful insensitive pigs.
Let him know that he can tell you things without being afraid of your reaction, and if he needs it, coach him on the wonders of TACT.
