Explanation:

Our teeth break food down into small pieces when we chew. This is only a start to the process of digestion, as chewed pieces of food are still too large to be absorbed by the body. Food has to be broken down chemically into really small particles before it can be absorbed. Enzymes are the biological catalysts needed to make this happen quickly enough to be useful.

Enzymes
Enzymes are not living things. They are just special proteins that can break large molecules into small molecules. Different types of enzymes can break down different nutrients:

amylase and other carbohydrase enzymes break down starch into sugar
protease enzymes break down proteins into amino acids
lipase enzymes break down lipids (fats and oils) into fatty acids and glycerol.