A complete protein contains all nine essential amino acids necessary for the body's function. These proteins are vital for processes such as muscle repair, immune function, and enzyme production. Complete proteins can be found in various sources, including animal products like meat, fish, eggs, and dairy. Additionally, some plant-based sources, such as quinoa, soy, and chia seeds, offer complete protein profiles. Including complete proteins in the diet ensures an adequate intake of all necessary amino acids to maintain health.