Chemical digestion is the enzyme-and-acid breakdown of food into absorbable nutrients, and it happens in stages along the GI tract. It starts in the mouth, where saliva enzymes begin breaking starches into simpler sugars. In the stomach, acid and enzymes continue the process—especially on proteins—then the small intestine finishes most chemical digestion with pancreatic enzymes and bile that break down carbohydrates, fats, and proteins so nutrients can be absorbed.
