[maryz]

makes them more sensitive to sweetness, meaning that they may use less sugar than someone who doesn’t have this polymorphism

I think you have to distinguish between sensitivity to sweetness and liking sweetness. Personally, I dislike whole wheat bread because it tastes too sweet to me -- well, not nearly sweet enough for dessert, but sweet enough to ruin anything that's not supposed to be dessert! So I think I'm pretty sensitive to sweet. OTOH, when I do want something sweet, it ain't gonna be whole wheat bread. ;-)

[SuzyQue]

I agree with that! And, for me, it should include chocolate.