The Digestive Track The BIG MAC is placed in the mouth. The bread is mainly starch, the special sauce is mainly fat, lettuce, pickles, and onions are niacin. The beef patties are protein,and cheeseis a form of calcium, fat, and protein. The piece of the BIG MAC is placed in the mouth and chewed, the starch is being digested by saliva. The starch becomes a kind of sugar which is used as a nourishment for the cells. Saliva changes food to a form that can be used by the body called enzymes. The burger is swallowed and passes into the esophagus. This is the muscular tube that contracts along its len