>>97928155Basically this. If you want a chubby girl with a soft belly you go out looking for a delicate and thin girl, because once you're a couple she'll stop trying so hard and probably gain a bit of weight. Going straight for the chubby girl means she'll get fat, really fat, and potentially go straight for obesity. Wide hips do not feature in this theorem since they cannot be changed, so it's okay to have them as a preference.
This is without criticizing theoretical weight gain after giving birth and such, but even then I think the rule holds true.