I told my wife, before we got married, that one of the reasons I wanted to marry her was her attractiveness. I told her that if she got fat, I would be gone. I have no intentions of introducing a fat wife to my friends and business people. Now keep in mind, I'm not talking heroin-chic runway-model thin here. But I expect her to take care of herself, and her looks.
So one day, a bit over a year after our son was born, I decided that I was dissatisfied with the pace at which she was loing the weight. She had asked me to bring her the cookies from the kitchen. I walked into the living room, sat beside her, she had a quizical look on her face and asked about the cookies. Well I asked, "Remember what I said before we got married?" She knew exactly what I was talking about.
Long story short: She got to the gym.
If your wife is as fat as it sounds, then she knows it. Its just up to you whether or not you'll tolerate it.