Final answer:
The essential amino acid that is in the smallest supply in the diet and thus determines the extent to which the remaining essential amino acids can be utilized is known as the limiting amino acid.
Step-by-step explanation:
The essential amino acid that is in the smallest supply in the diet is called the limiting amino acid. This term is used to describe an amino acid that is available in the least amount relative to the body's needs. The nine essential amino acids, which include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine, cannot be synthesized by the body and must be obtained from dietary sources.
Getting an adequate amount of each essential amino acid is crucial for protein synthesis, as the lack of the limiting amino acid can hinder the body's ability to build proteins.