Proteins

Protein is another major macronutrient that, like carbohydrates, consists of small repeating units. But instead of sugars, proteins are made up of amino acids.

Proteins can be classified as either complete or incomplete. Complete proteins provide adequate amounts of all nine essential amino acids. Animal proteins, such as meat, fish, milk, and eggs, are good examples of complete proteins. Incomplete proteins do not contain adequate amounts of one or more of the essential amino acids. For example, if a protein does not provide enough of the essential amino acid leucine it would be considered incomplete. Leucine would be referred to as the limiting amino acid because there is not enough of it for the protein to be complete. Most plant foods are incomplete proteins, with a few exceptions, such as soy. The following link discusses limiting amino acids and protein complementation: https://nutrition.org/protein-complementation/

A useful resource for determining protein quality is the Digestible Indispensable Amino Acid Score (DIAAS) score. The DIAAS score is a good measurement of the completeness of a protein as this relates to the proportion of amino acids absorbed and used by the body.