Essential amino acids are needed for making protein, which the body requires for a variety of functions, states the National Institutes of Health's MedlinePlus. When the diet lacks an essential amino acid, such as lysine, it can lead to health issues, such as growth and developmental problems and decreased levels of energy, reports the University of Maryland Medical Center.
A diet that contains protein-rich foods provides these essential amino acids that become the building block of protein production in the body. Out of the 20 amino acids found in the body, nine are essential amino acids. This means that the body does not manufacture them, and they are available only through diet. The essential amino acids include lysine, valine, histidine, tryptophan, leucine and isoleucine, notes MedlinePlus.
Some functions of amino acids can include being sources of energy and helping in the digestion of food. Each essential amino acid has specific functions. For example, lysine is necessary for proper development and growth, the absorption of calcium and the building of connective tissues and muscles, notes the University of Maryland Medical Center. A lack of lysine can also lead to health issues, such as anemia.