What defines an incomplete protein?

An incomplete protein is defined by its deficiency in one or more essential amino acids. Essential amino acids are those that the human body cannot synthesize on its own and must be obtained from dietary sources. While complete proteins contain all the essential amino acids in adequate proportions—typically found in animal products—an incomplete protein lacks one or more of these crucial building blocks for protein synthesis.

This characteristic is particularly relevant for many plant-based proteins, which might miss one or two essential amino acids, making it essential for individuals relying on these sources to combine different foods to ensure they obtain all necessary amino acids in their diet. Thus, the definition highlights the limitations of certain protein sources in providing the full spectrum of amino acids necessary for optimal health and bodily function.