If having Barney isn't enough to motivate Dave to lose weight, than nothing will. I think the way Soaf encourages his bad eating habits makes me think she has a nice life insurance policy on him and is just waiting for him to drop dead, which will happen soon enough if he doesn't take his health seriously.
I still wonder what the hell she saw in Dave to date or marry him, even if he was a working actor at the time. He isn't funny, he doesn't come across as very intelligent, his looks are meh, and is talent is even more meh....and did she really look at his body and say to herself wow I can't wait to get naked with that!? I have never delved into how they met, but why was she attracted to him, because even back then he was heavy? Unless she liked having that bit of power over him, like see how wonderful I am to be with YOU sort of thing?