Soy: Types, Sources and Dietary Guidelines
Soy is a term given to “health foods” made from yellowish brown beans of a legume Glycine max native to northeastern Asia. Today, most of the world’s soybeans are produced in the United States, Brazil and Argentina. China, the homeland of soybeans, is the fourth largest soybean producer in the world but with just 13% of the US volume. Soybeans are processed into a variety of products such as cheese, cereals, veggie burgers or milk.
Antinutrients in Soybeans
Like most other legumes, soybeans cannot be eaten raw. They require processing to make them edible. Some experts believe that the only effective method of eliminating all antinutrients present in soybeans is fermentation.
Raw and untreated soybeans contain certain toxins (antinutrients) and other potentially harmful substances. For example, lectins and saponins can damage the cells in the gastrointestinal tract. Protease inhibitors can block the enzymes needed for protein digestion, causing gastric distress and problems with protein absorption. Soybeans also contain hemagglutinin that can cause red blood cells to clot. Goitrogens are another potentially harmful substance found in soybeans. They can disrupt the production of thyroid hormones, eventually leading to the abnormal enlargement of the thyroid gland known as goiter. Furthermore, soybeans contain phytates, which can affect the absorption of vital minerals such as calcium, iron, magnesium and zinc in the intestinal tract.
Processing, such as fermentation and cooking at high temperatures, either eliminates or greatly reduces the number of potentially harmful substances present in the soy products. Other processes involve chemically treating soybeans.
Types of Soy Protein
There are four types of soy proteins used to make soy foods. They are available in powder, flake or pill form and include:
- Hydrolyzed soy protein. A chemical process called hydrolysis is used to break down the soy protein into amino acids. This protein also contains other substances such as monosodium glutamate (MSG), a popular taste enhancer in the food industry. Hydrolyzed soy protein is not regarded as the best source for soy protein or nutrients.
- Soy protein concentrates. This concentrate is made from defatted soybean flakes and it can be commonly found in frozen veggie burgers. Soy protein concentrate contains 70% of protein along with some fiber.
- Soy protein isolate. It is manufactured by extracting the soy protein from defatted soybean flakes and is most commonly used as an ingredient in soy protein bars and soy protein beverages. Soy protein isolate contains nearly 90% of soy protein and is the most highly refined source of soy protein.
- Textured soy protein. Also known as texturized vegetable protein is a by-product of extracting soybean oil. Textured soy protein is manufactured by processing defatted soy flour in an extrusion cooker. Methods may vary but hexane is often used to separate soy oil from soy protein. Trace amounts of hexane may be left in the textured soy protein after the extraction.
Good Sources of Soy
Soybeans are available in the pod (sold fresh or frozen), removed from the pod (fresh, dry, canned or frozen), or they are processed into a variety of foods. However, one of the main soy products is soybean oil. Soybean oil is used in many popular margarines, mayonnaise, salad dressings and vegetable shortenings as well as a feedstock for biodiesel. There is also a dark side to soybean oil as it has become a major contributing factor to growing rates of obesity in the US.
However, soy is best known as a fat-free and cholesterol free source of protein. In recent years, the food industry has created many different products to respond to the growing demand for soy-based “health” foods. Unfortunately, most of the new soy foods are non-fermented because many people do not like the flavour of fermented soy. Examples of soy products include:
- Egg replacers
- Miso soybean paste (fermented)
- Natto (fermented)
- Meat analogs (e.g., imitation bacon bits)
- Soy flour
- Soy grits
- Soy infant formula
- Soy milk
- Soy mayonnaise
- Soy nuts
- Soynut butter
- Soy oil and margarine
- Soy protein drinks
- Soy sauce (fermented but it can also be made using a chemical process)
- Soy supplements (soy isoflavones)
- Soy yogurt, cheese and sour cream
- Tempeh (fermented)
- Vegetable burgers or sausages
Dietary Guidelines for Soy
There are no dietary guidelines for an ideal intake of soy or isoflavones – soybean components that have been credited with numerous health benefits. However, according to the FDA, eating moderate amounts of soy, such as the 25 grams of soy protein per day, as part of a low-fat and low-cholesterol diet is considered absolutely safe and may help reduce the risk of coronary heart disease. Consumers should keep in mind that different soy products contain different amounts of proteins. Generally, soy protein isolate has the highest level of protein, followed by soy flour, whole soybeans and tofu.
There are many natural components in soy products that may benefit health. But, there are also some substances in soy that have generated controversy. However, the majority of the concern relates to the use of concentrated and isolated forms of these substances in dietary supplements, not as they appear in regular soy foods. Therefore, most dieticians agree it is better to consume soy foods rather than to use soy supplements. When it comes to different soy foods, many experts recommend choosing fermented soy products, such as miso paste, natto, fermented soy sauce or tempeh, which contain little, if any, antinutrients.
Potential Health Benefits and Risks of Soy
Soy is an excellent source of protein, fibre, beneficial phytochemicals, essential vitamins and minerals and is low in saturated fat and cholesterol. Many doctors recommend their patients to replace meat protein with soy protein to lose weight and prevent heart disease. For several decades, soy has been promoted as a miracle health food that can help control blood sugar, improve digestion, relieve symptoms of menopause, reduce the risk of heart disease, prevent osteoporosis and even help to fight cancer. However, in recent years, several studies have questioned some of the proposed health benefits of soy, some even suggesting the opposite – the negative impact of soy on human health. For more information on the pros and cons of soy foods as a dietary source of protein please refer the following articles: