The human body uses amino acids to build proteins, which are used to control the processes that take place in cells.Proteins also accelerate chemical reactions in the body, making them necessary for survival. Although the body uses 20 amino acids, it only produces some of them on its own.he stomach contains cells that produce hydrochloric acid, a component of the gastric juice that helps humans digest food. This is one of the most important acids in the human body, as it helps break food into smaller pieces that are easy to digest.