Potential Health Benefits of Soy
Soy foods are best known as an excellent source of protein. Unlike other plant sources of protein, the protein found in soy is a “complete” protein (it contains all nine essential amino acids necessary for human growth and development), similar to the protein found in meats. Soy protein is alongside egg whites and the protein in milk among the easiest proteins for the body to digest and absorb. Unlike animal sources of protein, soy is low in total fat and saturated fat and has no cholesterol.
Soy is also a great source of dietary fiber and is rich in B vitamins and polyunsaturated fats, especially essential fatty acids such as omega-3 fats. Therefore, replacing even a small amount of meat protein intake with soy can help people to achieve a reduction in their intake of saturated fat and cholesterol and help them to cut down on calories.
Soy has been hailed for decades as a “miracle health food” that can help with a number of illnesses and their associated symptoms. However, there is a lot of contradictory evidence about the actual role of a soy diet in helping to prevent or reduce certain conditions. They include:
- Blood sugar. There is conflicting evidence on whether soy foods may help with blood sugar regulation and lower the risk for some complications of diabetes. There is also some evidence to the contrary.
- Cancer. Several studies suggest that a variety of compounds found in soy foods possess anti-cancer properties that may prevent the growth and spread of cancer tissue and tumors in some areas of the body. However, other studies show that soy consumption may actually increase the risk of some types of cancer by interfering with the hormone estrogen. Therefore, some doctors recommend that patients avoid soy products if they have certain forms of cancer, such as the breast, ovaries or uterus cancer, or a family history of estrogen-dependent breast tumors.
- Cholesterol. In the past decades, a number of studies have reported that soy protein intake may help reduce blood lipid levels (total cholesterol, LDL cholesterol and triglycerides). However, contrary to earlier advocacy of high-soy diets, some more recent studies have cast doubt on the cholesterol-reducing benefit of a diet high in soy proteins, stating that soy protein appears to have little or no effect on the risk factors associated with heart disease.
- Diarrhea in children. Soybeans are rich in fiber. Soluble fiber in soy can help to firm up a loose stool. Therefore, infants and young children who have diarrhea usually experience fewer bowel movements and a reduction in the incidence of diarrhea when consuming soy products. However, in some children and adults soy may lead to diarrhea, which is often due to soy intolerance.
- Digestion. Some beneficial bacteria that live in the intestines, called probiotics, can be also found in certain fermented and unpasteurized soy products. Probiotics have been shown to have positive effects on immunity, lowering the risk of atopic diseases and improving the symptoms of irritable bowel syndrome.
- High blood pressure. The evidence on the relationship between soy and the risk of heart disease remains cloudy. Recent studies suggest that the blood pressure lowering benefits of a high-soy diet may have been overstated (see “Cholesterol” above).
- Menopause. Many women consume soy products to relieve symptoms of menopause. Soy contains phytoestrogens that are similar in structure to the estrogen produced in the human body. Therefore, some researchers believe that increasing the intake of soy phytoestrogens may help reduce the severity of menopausal hot flashes.
- Osteoporosis. Scientific evidence of soy’s ability to prevent or reduce the risk of osteoporosis appears to be mixed as several recent studies have found little or no evidence of soy’s power in preventing osteoporosis. Potential benefits of soy on bone health are linked to calcium and isoflavones contained in soy, though not all soy products are good sources of calcium. However, fermented soy products, such as natto, are rich in vitamin K, which is essential to preventing osteoporosis.
In addition to the aforementioned potential benefits of soy foods, there are many different components in soybeans, such as essential fatty acids, lecithin, oligosaccharides, isoflavones, phytosterols and phytates, that are being studied individually for possible health effects.
Although a number of recent studies have raised doubts about several of the health benefits that have been previously associated with soy, soy products still offer substantial benefits. Because of their high content of polyunsaturated fats, fiber, vitamins, minerals and other nutrients as well as low levels of saturated fat and cholesterol, soy products can be used to replace meats as an alternative source of protein.
Where to Get More Information: University of Maryland Medical Center