How many essential amino acids are not synthesized by the body?

The correct answer is nine because there are nine essential amino acids that the human body cannot synthesize. These amino acids must be obtained through diet, as they play crucial roles in protein synthesis, tissue repair, and various metabolic functions. The essential amino acids are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Understanding the importance of these essential amino acids highlights the need for a balanced diet that includes complete proteins, which contain all the essential amino acids necessary for optimal health.