It can be transformed into energy through each person's unique metabolism. The main reaction that occurs in the digestive system is called metabolism. Metabolism occurs everywhere, but primarily in the stomach where it breaks down substances into smaller molecular forms, which provide energy to the body (Encyclopedia Britannica Online School Edition, 2011). Our metabolism is a chemical reaction that occurs through a microcellular catalyst called an enzyme. Enzymes help chemically break down large nutrients, proteins, fats, and carbohydrates into smaller forms of amino acids, fatty acids, and simple sugars (Encyclopedia Britannica Online School Edition, 2011). Amino acids and fatty acids are mainly the sources from which we obtain our energy. The whole process begins when we eat and our metabolism breaks down the food. Amino acids and fatty acids are absorbed into the blood where, once attached to a cell, they are then able to speed up the chemical reactions that take place as the amino acids and fatty acids monitor the reactions in the cell, some energy is released. This energy can be stored in the body until it is needed (Encyclopedia Britannica Online School Edition, 2011). There are two forms of metabolism called anabolism and catabolism. Anabolism stores energy and maintains cells while catabolism consists of producing energy so that each cell has a specific amount of it