Typical first experience (assuming she's not a total ho) goes something like this....
Girl gives in, but holds back on the really fun(read nasty) stuff, to lure the guy in, in the hopes of even better things yet to come. Much like a good band leaves the audience wanting a little more, ensuring a good turnout next performance.
Meanwhile the guy pulls out all the stops, playing every trick in the book as well as a couple he made up along the way, in the hopes of convincing the girl he's the best lover she's ever met and can take her to the mountaintop every time they touch. This is obviously a shitty sales tactic because it sets up an unreasonable expectation that can't possibly be consistently met, but we do it anyway, geniuses that we are.
The fat girl, on the other hand, has to act more like the guy, pulling out all the stops, pulling every trick in her book, in the hopes the guy will enjoy it to the point he buys a ticket for a return performance.
This puts the fat girl in the position of always having to one-up her previous performance, which is a mindset guys are used to dealing with, and positive relations can then ensue, both in the mental realm as well as the physical. Plus she can already cook like a champ. If that ain't marriage material, I don't know what is.