Soy and Health Facts
In comparison to many of today’s major food sources, soybeans are truly a nutritional superpower. They contain the highest amount of protein of any grain or legume, and substantial amounts of fat, carbohydrates, dietary fiber, vitamins, minerals and a virtual drugstore of phytochemicals useful for the prevention and treatment of many chronic diseases.
Soybeans vary widely in nutrient content based on the specific variety and growing conditions, but typically they contain 35-40 percent protein, 15-20 percent fat, 30 percent carbohydrates, 10 to 13 percent moisture, and around 5 percent minerals and ash.
Elements of the Bean
The protein in the soybean contains all of the essential amino acids necessary for humans, and can sustain health at all stages of development. Using the protein digestibility corrected amino acid score (PDCAAS) method, soy protein products generally receive scores of between 0.95 and 1.00, the highest value possible.
Soybeans, in comparison to other beans, grains and cereals, contain a high amount of fat. Fortunately, the fat found naturally in the soybean, and that which ends up in whole soybean-based foods (and most traditionally processed soyfoods such as tofu, soymilk, tempeh, full fat soy flour, and liquid soybean oil) can be categorized as a healthy fat.Approximately 50 percent of the fat in soybeans is linoleic acid, a polyunsaturated fat and an essential nutrient. In addition, soybean oil can contain as much as 8 percent alpha-linolenic acid, which is an Omega-3 fatty acid, the type of fat found in fish which is believed to be beneficial in lowering the risk of heart disease.
Carbohydrates and Fiber
Soluble and insoluble carbohydrates, including dietary fiber, make up about 30 percent of the soybean. The primary soluble carbohydrates in the soybean are the sugars stachyose, raffinose and sucrose. The amounts of these sugars vary according to both the variety of soybean and its growing conditions, but for the most part, together, they make up about 10 percent of the soybean. The oligosaccharides raffinose and stachyose are significant because they are not digested or used as nutrients directly by the human body, but instead are used as nutrients by the bifido bacteria in the lower intestine to sustain and promote their growth. These types of intestinal flora are considered important for human health, as it is believed that their presence can reduce the incidence of many diseases of the lower tract, including colon cancer.
Vitamins and Minerals
The major mineral components of soybeans are potassium, sodium, calcium, magnesium, sulfur and phosphorus. Mineral content can vary widely due to both the type of soil and growing conditions for the soybean. Although soybeans are not considered be very rich sources of any one particular vitamin, they do contribute to an overall nutritional well-being. The water-soluble vitamins in soybeans are thiamine, riboflavin, niacin, pantothenic acid, biotin, folic acid, inositol and choline. Fat-soluble vitamins present in the soybean are vitamins A and E. Vitamin A exists as provitamin beta carotene and is present in higher levels in the immature green vegetable soybean, than in the mature or dry soybean. Tocopherols are an important constituent of soy oil due both to the vitamin E supplied for human nutrition and the antioxidant properties of tocopherols that protect the oil.
Soy isoflavones are not only special because of the effect they are believed to have on health, but also, because for all practical purposes, no other food contains as significant an amount of these chemicals as does the soybean.The major isoflavones in soybeans are genistein, daidzein and glycitein. Of these, it is genistein which is believed to have the most potential to prevent or treat certain cancers. Isoflavones are also sometimes referred to as phytoestrogens, meaning plant estrogens, because they have a similar chemical make-up as does estrogen (although the estrogenic effect of isoflavones is approximately one thousand times weaker than the natural hormone).
The Soybean’s Effect on Health
In 1995 a meta-analysis of previous studies entitled "Health Benefits of Soy Protein" (written by Dr. James Anderson of the University of Kentucky) was published in the prestigious New England Journal of Medicine. Dr. Anderson’s study found that soy protein intake was associated with a 9.3 percent reduction in serum cholesterol, a 12.9 percent reduction in LDL cholesterol, and a 10.5 percent reduction in serum triglycerides. For HDL, the “good” cholesterol, concentrations increased by 2.4 percent. It is estimated that this serum cholesterol modification has the potential to reduce risk for coronary heart disease by 18 to 28 percent. Based on the findings from 34 out of the 38 studies reviewed, Dr. Anderson concluded that soy protein was clearly potent in decreasing LDL-cholesterol levels. But the positive effect of the soybean on heart health is not solely due to the protein and its related compounds; the fats that are found naturally in the soybean also can contribute to a reduction in cholesterol levels. It is understood now that oils that are high in unsaturated fatty acids, such as soybean oil, tend to decrease total serum cholesterol levels. Soybean oil contains about 50 percent linoleic acid, an essential polyunsaturated fat. In addition, soybean oil also contains about 8 percent linolenic acid, which is an omega-3 fatty acid, such as that found mainly in fish oils. This fatty acid has been the subject of numerous studies that link its consumption with a decreased incidence of heart disease and cancer. Soybeans are one of the few plant sources of omega-3 fatty acids.
Consumption of soyfoods may help to maintain and even rebuild bone density and strength, and act as an effective treatment for osteoporosis.Studies have shown that diets high in animal protein tend to cause more calcium to be leached from the bones and excreted in the urine and feces. On the other hand, protein from soybeans does not have this effect. Other studies have shown that the isoflavone genistein inhibited bone breakdown and may increase bone density as well.Much attention has been focused on the need to increase calcium intake to help prevent osteoporosis, and most people tend to focus on dairy products as the best source for calcium. But many soyfoods are naturally rich in calcium, and the calcium from soyfoods is absorbed as well as that which comes from milk. Among soyfoods, good sources of calcium are tofu (in particular, tofu which has been coagulated with calcium sulfate), calcium-fortified soymilk, whole soybeans, soy flour and tempeh.
Soybeans can produce at least twice as much protein per acre than any other major vegetable or grain crop, 5 to 10 times more protein per acre than land set aside for grazing animals to make milk, and up to 15 times more protein per acre than land set aside for meat production. Adding soy protein to breads, tortillas, corn meal, pasta, milk or any traditional food is a low cost and efficient way to ensure adequate nutrition for vulnerable populations. In this manner, not only do people receive enough high quality protein for the development and maintenance of their health, but they also get the added disease prevention benefits of soybean phytochemicals.
Since 1990, there have literally been thousands of studies conducted by researchers around the world hoping to identify which of these compounds may be the most valuable in the fight against cancer. And although it is not yet certain which one of these compounds is the most important, or if in fact some or all of them work together to a certain extent, many researchers believe that it is the isoflavones which are responsible for much of the anti-carcinogenic effect. Interestingly enough, soybeans are one of the few widely consumed foods that contain a significant amount of isoflavones.Because they look similar in structure, isoflavones tend to bind with the receptors normally used by estrogen to exert its effects on the body, some of which are cancer promoting. By binding to these receptors in place of the estrogen, the soybean’s phytoestrogens have in essence acted as anti-estrogens.These protective estrogen-related effects of isoflavones are not just beneficial to woman. It is possible that isoflavones may also exert a therapeutic effect for men with prostate cancer, as estrogen has been shown to be an effective therapy for treating that cancer.In experiments on human prostate cancer cells, genistein has been shown to inhibit cell proliferation. And in addition, genistein has been shown to inhibit angiogenesis, or new tumor vessel growth, thereby slowing the progression of existing cancer.
Still More to ComeResearch on soybeans and soyfoods continues to probe their role in the prevention and treatment of disease. For men, women and children, soybeans appear to be one of nature’s healthiest and highest quality food sources.
Content for the Soy & Health Facts page provided by Soyatech.
European Natural Soyfoods Association:
European Vegetable Protein Association Federation: www.euvepro.eu
French Soy Products Manufacturers Association (SOJAXA): www.sojaxa.com
Malnutrition Matters: www.malnutrition.org
Soy in Southern Africa: www.soyfood.co.za
Soyfoods Association of North America: www.soyfoods.org
Soyfoods Canada: www.soyfoodscanada.com
The Soyfoods Council: www.thesoyfoodscouncil.com
United Soybean Board: www.soybean.org
World Initiative for Soy in Human Health: www.wishh.org
World Soy Foundation: www.worldsoyfoundation.org