Big Mam is clearly competing in beauty against Hancock and Shirahoshi.
No, I'm serious. What if she's actually incredibly beautiful, but her DF, if she has one, is the more she eats, the stronger she gets. And when she finally battle against people, she loses pounds after pounds till she's finally skinny again. I'd laugh so hard if Sanji rejects here, presuming Big Mam will fall in love with her, and then chapters later she's all beautiful and stuff, but just now hates Sanji for rejecting him.
Called it.