The nutritional value of protein depends on what protein is an important nutrient. Its existence is closely related to various activities of life, such as participating in the composition and metabolism of the body, participating in the composition and metabolism of genetic information, and providing heat for the body.

There are many kinds of protein, and protein from different food sources can be digested, absorbed and utilized by the human body to varying degrees. In other words, different kinds of protein have different nutritional values, and the main factors that determine the nutritional value of protein are the types and contents of essential amino acids in protein. Amino acid score is a common index to evaluate the types and contents of essential amino acids in protein.

What is the difference between protein nutrition of animals and plants? The reason why protein contains different amino acids is closely related to the source of protein.

Protein is mainly derived from animal food and plant food. The difference in amino acids between animal protein and plant protein means that their nutritional values are also different.

Animal protein mainly comes from the meat, eggs and milk of poultry, livestock and fish. Its protein is mainly composed of casein (78 ~ 85%), which can be well absorbed and utilized by adults. More importantly, protein, which has animal properties, has a complete range of essential amino acids and a reasonable proportion. It is easier to digest, absorb and utilize than ordinary plant proteins, and its nutritional value is relatively high. Generally speaking, protein, a meat (such as fish and beef) and protein, a dairy product, have an amino acid score of 0.9 ~ 1.0.

Plant protein mainly comes from rice flour and beans, but the nutritional value of rice flour and beans in protein is different. Protein from rice and flour lacks lysine (an essential amino acid), so its amino acid score is low, only 0.3 ~ 0.5, and this kind of protein will be absorbed and utilized by human body to a lesser extent. Of course, this deficiency can be improved by scientific methods. For example, adding lysine-rich beans to rice flour can significantly improve protein's amino acid score.

Among many plant proteins, bean protein (also known as soybean protein) has the highest nutritional value, and bean food does not contain cholesterol, which is a characteristic that animal food does not have. Protein, a soybean without any processing, has the disadvantage that the content of methionine (an essential amino acid) is relatively small. Therefore, the amino acid score of whole beans is about 0.6 ~ 0.7. Soybean protein is widely used because of its high content of protein and no cholesterol.

The quality of soybean protein processed by modern methods has changed greatly, and the fat content in soybean protein has been reduced (the fat content in the whole soybean is about 20%). Generally, the protein content of defatted soybean powder can reach 50%, and the protein content of soybean protein concentrate can be increased to about 70%, which can be used for infants with milk intolerance. After degreasing, water extraction, washing, drying and other modern technological processes, the protein content of soybean protein isolate can be as high as 90%, and the digestibility of processed soybean protein isolate has also been improved. Of course, these processes only increased the content of protein, but did not improve the amino acid pattern of protein. However, if methionine (also called amino acid fortification) which is relatively deficient in soybean itself or protein which is rich in methionine is properly added to soybean protein, the nutritional value of soybean protein will be significantly improved, and the amino acid score of protein will also be improved. If a proper amount of whey protein is added, the amino acid score of soy protein isolate can reach 1.0, and its nutritional value is consistent with the protein of eggs and milk, which is very close to the standard amino acid model and easy to be absorbed and utilized by human body.