Essential amino acids are best described as which of the following?

Essential amino acids are best defined as those amino acids that are required for protein synthesis but cannot be synthesized by the body. This means that they must be obtained through dietary sources, as the body is unable to produce them internally. There are nine essential amino acids for humans, which include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

These amino acids play a crucial role in various bodily functions, including the building and repairing of tissues and the production of enzymes and hormones. The inability of the body to create these amino acids highlights the importance of a balanced diet that includes complete protein sources, which contain all essential amino acids. This distinguishes essential amino acids from non-essential amino acids, which the body can synthesize and therefore do not need to be obtained through diet.