A dietary protein is considered "complete" when it ______.

Nonessential amino acids can be synthesized by the body, so their presence or absence in a food source has no bearing on whether that protein is classified as complete.

Being plant-based does not determine completeness - most plant proteins are considered incomplete because they are low in or missing one or more essential amino acids.

The nine essential amino acids - histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine - cannot be produced by the body and must come from food. A protein source that contains all nine in adequate amounts is classified as complete. Animal-based proteins are typically complete, as are some plant sources such as soy and quinoa.

Branched-chain amino acids (leucine, isoleucine, and valine) represent only three of the nine essential amino acids, and their presence alone does not satisfy the requirement for a complete protein.