Enzymes are sometimes referred to as organic catalysts because they are substances in the body that speed up chemical reactions.
An important characteristic of catalysts is that they are very specific, meaning that particular enzymes work on specific substrates.
The food we eat contain different nutrients, e.g. proteins, carbohydrates,and fats.
Each of these represent a different substrate to an enzyme and therefore different enzymes are needed to breakdown each nutrient into smaller molecules that can be absorbed into the blood stream for use by the body.
For example: lipases break down fats into fatty acids and glycerol; proteases break down proteins to amino acids; and amylases break down carbohydrates to glucose.