One of the 3 main macronutrients, proteins are essential nutrients for the human body. Protein consumption has a strong correlation to muscle growth.

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function.

See Wikipedia Protein

Protein are one of the building blocks of body tissue, and can also serve as a fuel source. In nutrition, proteins are broken down in the stomach during digestion by enzymes known as proteases into smaller polypeptides to provide amino acids for the body, including the essential amino acids that cannot be biosynthesized by the body itself.