Enzymes create chemical reactions in the body. They actually speed up the rate of a chemical reaction to help support life. The enzymes in your body help to perform very important tasks. These include building muscle, destroying toxins, and breaking down food particles during digestion. To catalyze a reaction, an enzyme will grab on (bind) to one or more reactant molecules. These molecules are the enzyme's substrates. In some reactions, one substrate is broken down into multiple products. In others, two substrates come together to create one larger molecule or to swap pieces.