Protein digestion follows a very rigid process; the purpose is to break down the protein into smaller components, called amino acids, which are used to rebuild or replace damaged or dying proteins in the body after digestion is complete. There are nine essential amino acids, which are often referred to as building blocks. The physical act of protein digestion begins in the mouth, when the food containing the protein is chewed into smaller pieces. The chemical process of protein digestion begins when the food enters the stomach, and it is this part of the process that enables the protein to be broken down into molecules the body can use.
When food enters the mouth, it is broken down physically by the act of chewing. Some foods that contain a high amount of protein to be digested include meat, eggs, nuts, and dairy. The food mixes with saliva in the mouth, which aids its travel down the esophagus. Between the esophagus and the stomach is a valve called a sphincter, and when the food travels through that valve, the chemical process of protein digestion begins.
During the chemical process of protein digestion, hydrochloric acid, along with enzymes known as pepsins, mix with the protein molecules and break the bonds that hold the molecules together. Once these bonds are broken, through a process known as hydrolysis, the proteins are close to becoming the essential amino acids needed by the body. The process of protein digestion in the stomach can take up to four hours, but there are a variety of factors that may affect the amount of time it takes.
Once digestion in the stomach is complete, the nearly broken-down proteins move through the duodenum into the small intestine. At this point, the pancreas finishes the protein breakdown by releasing an enzyme called trypsin. Once this final breakdown is completed, the amino acids move through the wall in the small intestine into small capillaries. The digested protein, or amino acids, travels through the liver before entering the main bloodstream. The amino acids then travel throughout the entire body to the organs that most need to be replenished.
If the body has too much protein and it cannot all be digested and absorbed into the bloodstream, the remainder will continue through the large intestine and travel through the kidneys. At this point, it is converted into a waste product known as urea. It is then discharged from the body in the urine.