A key recommendation in the recently released 2010 Dietary Guidelines is for Americans to consume less than 10 percent of their calories from saturated fat. To reach this target, the government recommends that we consume more plant proteins including beans and peas, soy products and unsalted nuts and seeds.
With the recent government push to consume soyfoods plus April marked as National Soyfoods Month, now is a great time to learn more about this versatile legume. In this article, the health benefits of consuming soy are reviewed.
In our companion article, The Top 10 Soyfoods, a review of the most popular soy-containing foods is provided along with information on their nutritional profile. Also covered is where to find these foods in the supermarket or health food store and most importantly, how to use soyfoods in a wide variety of conventional recipes.
What are Soybeans?
Soybeans like other beans, peas, lentils, clover and peanuts belong to a family of plants called legumes. The fruit of legumes is a characteristic seed pod that opens up along a seam and splits into two pieces. Inside the pod, the seeds attach to one side of the case.
Legumes share a symbiotic relationship with nitrogen fixing bacteria located in their roots. This unique situation makes legumes valuable not only for crop rotation (planted in nitrogen poor soil) but for their higher protein content than non-legume crops. Soybeans are considered a complete protein because they provide all nine essential amino acids.
Immature soybeans (80% maturity) which are green when harvested are sold as edamame. Mature soybeans which usually yellow but also tan or black in color are processed into a wide variety of soy products.
Soybeans are broadly classified as vegetable or oil types. Due to their mild nutty flavor, better texture, larger size and higher protein content and lower oil content, vegetable soybeans are used in a wide variety of soyfoods. The oil types are extracted and made into soybean oil which is sold as liquid or more often partially-hydrogenated and used as an ingredient in myriad of processed foods.
Health Benefits of Soy
Soybeans are associated with a number of health benefits including heart health, breast cancer protection, relief of menopausal symptoms and bone support.
Heart Health. Soy may protect heart health by helping lower cholesterol and inhibiting platelet aggregation.
Unlike animal based proteins – eggs, dairy, meat and poultry - soy protein contains virtually no saturated fat or cholesterol. The fat that soybean contains is mostly polyunsaturated (Omega-6 fats). When soyfoods are used to replace animal protein sources, LDL or “bad” cholesterol levels are lowered. A study published in the Journal of Nutrition showed that soy protein lowers heart disease risk by increasing the size of LDL particles. Small, dense particles of LDL are considered the most dangerous form of cholesterol. Large particles of LDL is considered much less risky.
Soybeans also provide a good amount of fiber. Fiber binds to cholesterol and fats in food, helping to lower cholesterol levels through elimination. Phytonutrients in soy also promote the production of prostacyclin, a potent natural inhibitor of platelet aggregation and a blood vessel dilator.
As a result of numerous studies demonstrating that consumption of soy protein significantly decreased LDL cholesterol and triglyceride levels, the FDA granted the following heart healthy claim for soy: “25 grams of soy protein a day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease.”
Breast Cancer Protection. Soybeans contain plant chemicals called isoflavones including genistein and daidzen. These so-called phytoestrogens have a weaker estrogenic effect in the body than human estrogens but may play a role in breast cancer protection by binding to human estrogen sites.
In Asian populations, the incidence of breast cancer is lower and the consumption of soy is much higher than in Western populations (the average Japanese person eats 50-80 grams of soy per day in a variety of forms; the average American eats just 5 grams mostly in the form of partially-hydrogenated oil). However, research on the relationship between soy consumption and breast cancer has been mixed.
While women who have been diagnosed with breast cancer can probably eat soyfoods, it is not recommended that they consume soy-containing supplements. It is not clear whether isoflavone-containing supplements promote breast cancer cell growth in humans.
Relief of Menopausal Symptoms. More than 50 clinical trials have examined the impact of soy isoflavones on providing symptomatic relief of menopausal symptoms like hot flashes. While the results have been mixed, some women found relief by just moderate consumption of soy isoflavones – the amount found in 2-4 servings of soyfoods like soymilk, tofu or edamame.
Bone Support. In addition to providing relief from hot flashes, studies have shown that consuming isoflavone-containing soy foods significantly inhibits bone loss and stimulates bone formation in menopausal women. Although the phytoestrogens in soy have much weaker effects than estradiol (an estrogen), these plant compounds may function like estrogen to maintain bone mass.
A Cautionary Note
While soy and soyfoods offer a number of health benefits, eating soyfoods poses a problem for some individuals.
Soy is one of eight most common allergens that account for 90 percent of all documented food allergies. The others include milk, eggs, peanuts, treat nuts (almonds, cashews, walnuts), fish (bass, cod, flounder), shellfish (crab, lobster, shrimp) and wheat. If you’re serving soyfoods for guests be sure to determine ahead of time if anyone is allergic to soy.
Soybeans also contain a high level of phytic acid a substance made by plants but unable to be processed by humans as we lack the enzyme phytase. Phytic acid is found within the hulls of nuts, seeds and grains. As a chelating agent, phytic acid has been associated with reduced mineral absorption especially zinc, iron, calcium and magnesium. However, according to the Soy Foods Association, recent research indicates that over the long term, daily soy consumption has a negligible impact on overall mineral balance. Additionally, cooking soy containing foods reduces the phytic acid to some degree.