There are two main factors to compare the quality of protein: the amino acid composition (including content and type) and the digestibility of the protein.
⑴ Amino acid composition
Amino acid content, protein energy/total energy ratio: The energy provided by different food proteins is different. Generally speaking, animal protein has a higher protein/energy ratio than plant protein.
Types of amino acids: Amino acids are the basic building blocks of protein. There are 20 types in total. Among them, 9 are the “essential amino acids” that the human body cannot synthesize and must obtain from food. The content of the most ideal protein essential amino acids is close to that of the human body. Conducive to human protein synthesis.
Animal protein: It is a complete protein, which can provide all 9 essential amino acids.
Plant protein: usually lacks one or several essential amino acids, especially lysine, the sulfur-containing amino acids methionine and cysteine, and threonine. But soy protein is a “complete protein”.
⑵ Restricted amino acids
Whether protein can be used by the body does not depend on the most abundant amino acid, but often depends on the least amino acid. This is the “barrel effect” of amino acids. How much water the barrel can hold depends on the shortest piece of wood, and the “restricted amino acid”, the essential amino acid with the least content, refers to the short board in protein. For example, the restricted amino acid of rice is lysine, and corn lacks tryptophan.
⑶ Digestibility of protein
Digestibility refers to the ability of the amino acids in protein to be absorbed and utilized by the body.
Highest digestibility: animal protein, low-gluten flour, peanuts and soybeans (94-99% digestibility).
Low digestibility: other legumes (72-84%)
The good news is that cooking and processing can make the protein in food better absorbed. Therefore, plant-based protein requires more processing and cooking steps to become well absorbed.