The American Dietetic Association (ADA) pointed out (1997): "If vegetarian food is diversified and can meet the energy demand, then protein from plants alone can provide enough amino acids. The research thinks that for healthy people, there is no need to supplement protein while being vegetarian. The intake of amino acids from various sources in one day can ensure that there is enough nitrogen storage and utilization in the body. " Simply put, under the premise of rich and varied food, as long as you are full, you can get enough protein even if you don't eat meat, and it often exceeds the needs of your body. From 65438 to 0972, Dr. F. Stare of Harvard University conducted a comprehensive study on vegetarians. Targets include adult men and women, pregnant women and adolescents. The results show that all people consume more than twice the minimum necessary amount of protein every day. From this, we can draw a conclusion that eating a variety of vegetarian foods can easily ensure the human body's demand for protein.

Next, let's look at the nutritional value of vegetarian protein. Protein's main function is to form human tissues and synthesize various enzymes, hormones and antibodies. The basic elements that make up protein are amino acids, and there are about 20 kinds. Of these 20 kinds of amino acids, only 9 kinds can't be synthesized by human body and need to be ingested from food, which is called essential amino acid, and other amino acids can be synthesized by human body. In this way, whether protein in food completely contains these nine essential amino acids becomes the key to the problem, while whether other amino acids exist is not a big problem. Therefore, if protein in a certain food contains these nine essential amino acids, it is called "complete protein", otherwise it is called "incomplete protein". Meat protein and milk protein were once considered to have some advantages, mainly because they are completely protein. However, animal protein is not the only complete protein, so is soybean.

It is worth mentioning that the amino acids in protein of various foods are complementary to each other, so it is easy to get a complete protein when two or more vegetarians are paired. That is to say, amino acids lacking in one food protein may be "excessive" in another food protein. Therefore, the nutritional value of protein obtained by combining two kinds of foods is much higher than one of them (see the table below), such as cereals and beans. People all over the world seem to have realized this instinctively for a long time. For example, traditionally Chinese people eat rice, noodles and bean products, Indians eat rice and beans, and Central and South Americans eat corn and beans.