There are **nine essential amino acids** considered necessary for human health. These amino acids cannot be synthesized by the body and, therefore, must be obtained through diet. The essential amino acids include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. They play vital roles in protein synthesis, tissue repair, and various metabolic functions. An adequate intake of these amino acids ensures optimal growth and maintenance of muscle mass, immune function, and overall health.