Because your body needs carbs.  Carbs are fuel.  I invite Gary Taubes and all his low carber buddies to go for a ride with me, or a run or a swim and see how you all do.  Your all going to get dropped like a bad habit while I munch on bananas - as many as I can possibly shove in without hurling.  Wait - look at all those Kenyan marathon runners.  They live on corn.  Look at how fat they are!