How Protein Works in Your Body Understanding how your body uses protein can help you appreciate its importance even more. The journey starts the moment you eat. Digestion and Absorption When you eat protein-rich foods, your digestive system gets to work. In your stomach, hydrochloric acid and enzymes begin to break down the complex protein molecules into smaller chains called polypeptides. These chains then travel to your small intestine, where other enzymes break them down further into individual amino acids. These amino acids are the true building blocks. Once they are small enough, they are absorbed through the wall of your small intestine and enter your bloodstream. Building and Repairing Tissues From the bloodstream, your body transports these amino acids wherever they are needed. They become the raw materials for creating new proteins to build and repair everything from muscle fibers and skin cells to hormones and antibodies. Your body maintains an "amino acid pool" in the blood and tissues, which it can draw from as needed. This is why a consistent supply of dietary protein is so important—it keeps the pool topped up and ready for action.