These classifications resulted from early studies on human nutrition, which showed that specific amino acids were required for growth or nitrogen balance even when there is an adequate amount of alternative amino acids. In nutrition, amino acids are classified as either essential or non-essential.
These amino acids must be supplied from an exogenous diet because the human body lacks the metabolic pathways required to synthesize these amino acids.
Essential amino acids, also known as indispensable amino acids, are amino acids that humans and other vertebrates cannot synthesize from metabolic intermediates.