What is the sugar used for in bread making?

A small amount of sugar is necessary in bread, not for flavoring but to give the yeast something to eat and thus excrete carbon dioxide to leaven the dough. Two to three tablespoons of real sugar (not Aspartame, stevia, or Splenda) are enough for a loaf calling for three cups of flour and one packet (2 1/4 teaspoons) of active dry yeast.