Sugar has a somewhat complicated molecular structure, one that packs a lot of calories of energy that the human digestive system can extract, and it tastes good, too. Splenda is a popular sugar substitute. It differs from sugar at only three points in it molecular structure. Where sugar has a hydroxyl molecule (an OH), Splenda has a chlorine molecule (Cl). It makes only a slight difference in taste. However, the enzymes in the human digestive system can't latch on to Splenda molecules and extract the calories from the molecule. That's why Splenda is a popular sugar substitute. ~ Page 64