A digestive enzyme is an enzyme in the digestive system which aids the biochemical breakdown of food into absorbable units. Each macronutrient has its specialists: salivary and pancreatic amylases attack starch; pepsin in the stomach and trypsin in the intestine dismantle proteins; lipases split fats into fatty acids and glycerol; and the brush-border enzymes — lactase, sucrase, maltase — finish the job at the intestinal wall. They work in sequence down the tract, each tuned to its local pH, which is why the system fails gracefully: without lactase, milk sugar ferments; without pancreatic lipase, fat passes through. Enzyme supplements replace what disease removes — pancreatic extracts for cystic fibrosis and chronic pancreatitis, lactase tablets for the intolerant. Digestion is enzyme chemistry from first bite to absorption, and these are its catalysts.