Because the process during digestion causes food to become a new substance, digestion is a chemical change. A physical change occurs when a subject changes its shape, size or state.
Food is chemically digested by enzymes. Once food has been broken down, the nutrients are sent into the bloodstream where they find their way into the liver. The liver processes these nutrients and what is left works its way into the large intestine. There, it undergoes more of a chemical change as it is subjected to bacterial fermentation. It is in the large intestine that waste is produced and prepared for elimination from the body. Food provides the body with essential macronutrients that are extracted from it by the various chemical processes used during digestion.