How much protein is in a soybean



Soybeans have been used as a source of protein since ancient times. First cultivated in China more than 2,000 years ago, they were brought to the United States early in the 19th century as animal fodder. Although soybeans are still most frequently used for animal fodder in this country, their versatility and nutritional value, as well as their low cost, are making them increasingly popular.

The dried soybean is a legume that has a higher proportion of protein (30 to 40 percent) than any other vegetable and also contains a generous supply of carbohydrates. Soybean crops yield many “calories per acre” and are an economic source of high protein to produce and to buy.

Soybeans lend themselves to many cooking techniques and, in fact, must always be cooked in order to be digested. Soybeans can also be roasted as a snack or sprouted for use in salads and sandwiches.

Soy protein may be ground into flour, which can be used in baking or for making pasta. Soy protein is also processed and textured to be used as a meat extender or as analogs – to be eaten in place of meat. Soy analogs, formed into shapes and flavored to resemble bacon, ham, fish, chicken, or beef, have limited appeal for most people, although they may satisfy the cravings of some who are forced to give up meat or help with a transition from a conventional to a vegetarian diet.

The most popular soy-protein product today is bean curd, also known by its Japanese name, “tofu.” Looking something like cheese, tofu is made by soaking, cooking, and curdling the soybeans to create a food that is mild in taste and easy to use in cooking.

It should be remembered, however, that no vegetable protein is as complete in essential amino acids as is animal protein – and even soy is no exception. It is low in the essential amino acid methionine, and must be supplemented with a food containing methionine. Modest amounts of eggs, cheese, milk, and other sources of animal protein supply this lack.

Protein emphasize the importance of a wide variety of foods in order to ensure an adequate supply of each of the essential amino acids.

The quality of a protein food is primarily determined by the amounts of essential amino acids it contains. Since most animal foods contain some amount of all the amino acids, it is the difference in the quantity of each essential amino acid that makes one food a “better” protein source than another. Most proteins of animal origin such as meat, milk, and eggs contain all of the essential amino acids. These proteins are able to maintain body cells and promote growth and are therefore considered complete, or high-quality, proteins.

Proteins from plant or vegetable sources are usually lacking sufficient amounts of one or more of the essential amino acids (except for soybeans, which are considered nearly the equal of animal protein); these are called incomplete, or partially incomplete, proteins. Each such lower quality protein food is lacking more of one particular essential amino acid than the others. Wheat, corn, and rice, for example, are most lacking in lysine, and beans in methionine. This deficient amino acid is known as the limiting one in that protein food.