All around, I have a pretty great life and marriage. I work, she cooks and cleans. She wants sex more than me which means I control when and how it happens. I don't mince words which leads to the odd emotional outburst, like any woman would, but she admires me as alpha too much for that to do any damage. Basically, her life relies on me, and my life would be fairly similar without her. If she left, she'd be living with her parents and career-less. She's aware of this and it serves to maintain a stable dynamic.

Here's the thing: I mentioned she wants sex more than me. This is mostly because she is more attracted to me than I am to her. Far more. She is fat and super, super fucking self-conscious about it. I'm alpha and exactly the sort of body-type she is most attracted to. She wants to lose weight, and I want her to, but she has taken no initiative to get started. It's never bothered me until recently. I'm more and more disgusted, not by her physical form (I'm a bit of a chubby chaser) so much as by her hamster-ness and rationalization. She eats and sits on the couch, making no effort to become more physically active or eat better. Every "craving" she mentions makes me grimace, not at her body as much as her rationalizing, immature mind. She wants such and such, she expects to get it, and sit on the couch in an unflattering position while she eats it.

It's not in my nature to mince words. I refuse to walk on eggshells and I will not be made to wear kid gloves. This tendency has always served me well, but this is one of those big deals for females, especially the Wife. It would destroy her world if I fucked another woman. As I said, I'm basically all she has in her life. I'm pretty attracted to her, but I'd find her far, far sexier (and for that matter, I'd like her more) if she took the initiative to lose weight and get fitter. I care about her. I love her. Maybe that's naive, but it is what it is.

TL;DR: Wife is fat. I don't mind too much, but skinny is still better. Maybe I'm naive, but I love her. She's craaaazy insecure. How do I do this?

EDIT: Gentle-Mang mentioned that he wondered how this question would fare in /r/relationships. Curiosity got the better of me. FOR SCIENCE.