The human body requires nine essential amino acids for proper functioning. These amino acids cannot be synthesized by the body, necessitating their intake through diet. They include lysine, threonine, valine, leucine, isoleucine, methionine, phenylalanine, tryptophan, and histidine. Essential amino acids play critical roles in protein synthesis, tissue repair, and hormone production, making them vital for overall health and well-being.