What is the “superiority” of high-quality protein?

Author: Cui Yihui, registered dietitian, master of medicine

Reviewer: Wang Junbo, Associate Professor and Doctoral Supervisor, Peking University Health Science Center

Before listing the selection criteria for high-quality protein, let’s briefly introduce the basic unit of protein - amino acids. If the basic unit of society is a family and the basic unit of the human body is a cell, then the basic unit of protein is amino acids.

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As we all know, the protein we eat is not used by the body in its original form. For example, the chicken breast you eat will not directly turn into your pectoral muscles; the pig heart you eat cannot make up for the broken heart after a breakup.

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So how is the protein in food used by the human body?

Simply put, food protein is broken down into amino acids in the gastrointestinal tract. These amino acids, as raw materials, are accurately delivered to tissue cells throughout the body through the blood, a "delivery system". They can only play their important role after being reassembled and synthesized into proteins in the human body on the "production line" there. There is a vivid metaphor - protein is a chain of beads of various colors, and each bead is an amino acid. After the "protein bead chain" in the food enters the human body, the beads (i.e. amino acids) are first disassembled in the digestion workshop, and then transported to different manufacturing workshops (i.e. cells) to be strung into new chains (i.e. proteins) of different sizes and arrangement orders according to the needs of the human body. Beads of different colors or shapes represent different types of amino acids. How many kinds of amino acids make up the protein in the human body? The answer is 20. Although the number does not sound like a lot, if these 20 amino acids are used in different arrangements and combinations, the types of "protein bead chains" produced will be very many.

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Protein-containing foods must meet the following two criteria to be selected as high-quality proteins.

Standard 1: The types of essential amino acids should be complete

As mentioned above, a total of 20 amino acids are needed to synthesize human proteins, and they can form up to 100,000 different proteins through different arrangements and combinations. Among these 20 amino acids, 8 cannot be synthesized by cells in the human body and must be "imported", that is, they must be supplied through external food. We call them essential amino acids. If a protein wants to be on the list of "high-quality proteins", it must have all 8 essential amino acids at the same time. It cannot be "listed" if it lacks any of the essential amino acids. Using the above conditions as the selection criteria, milk, eggs, meat, fish and beans can all be on the list.

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Standard 2: The composition ratio of essential amino acids should be reasonable

Proteins from different food sources have different nutritional values ​​even if they contain all eight essential amino acids. To be considered high-quality protein, it is not enough to have a complete range of types, but its composition ratio must also be reasonable. A reasonable composition ratio of essential amino acids means that the composition ratio of the essential amino acids in these foods should be as close as possible to the composition ratio of the essential amino acids in the human body. The closer the composition ratio of the two, the easier it is for the protein to be absorbed and utilized by the human body, and the food can be selected as a high-quality protein.

According to this standard, animal proteins such as eggs, milk, meat, fish and beans can still be on the list. It is not difficult to find from the above that animal foods are more likely to become high-quality proteins. This is not surprising. After all, from an evolutionary perspective, humans and animals are closer. So, a new question arises, how should vegetarians supplement protein? Is there no way for vegetarians to obtain high-quality protein?

Vegetarians who eat "grass" in the eyes of "carnivores" can also become outstanding artists, painters, mathematicians and athletes. Because vegetarians can also obtain high-quality protein, their body functions are not inferior to those of meat eaters. A conclusion of the National Food and Nutrition Association of the United States pointed out that "vegetarianism can fully provide the human body's needs for protein and all essential amino acids, and may even improve human health."

Have you discovered a problem at this point? Isn't it said that most plant proteins lack one or more essential amino acids? Then how do vegetarians get high-quality protein? The answer is simple, that is, through the principle of "complementarity of protein and amino acids". For example, the rice we often eat lacks lysine but is rich in methionine, while beans are just the opposite, rich in lysine and lacking in methionine. Therefore, as long as we develop a good habit of adding a handful of beans when steaming rice or making rice porridge, it just complements the lack of essential amino acids between these two foods. Many traditional Chinese foods, such as tofu buns and eight-treasure rice, are foods that complement amino acids.

As a vegetarian, it is not difficult to consume high-quality protein as long as you always keep in mind the complementary effect between protein amino acids in your three meals a day.