Winter 2001 Issue — Soy Nutrition beyond protein and isoflavins

Marian Verbruggen, Ph.D.

SoyLife Nederland BV

< Back

The interest in soy for its health benefits has risen dramatically the last few years. It is well known that soy protein lowers cholesterol levels,1 which is why FDA approved a dietary health claim for soy foods in October 1999. Accidentally, soy isoflavones show real promise in the prevention and treatment of heart disease, osteoporosis, certain cancers and menopausal symptoms. But there is more to the soy story than protein and isoflavones alone. Leading researchers are starting to understand the complex ways that other soy nutrients work with protein and isoflavones in synergy to benefit health. This is referred to as the "soy matrix", needed to receive the true benefits of soy.

Major Soy Nutrients and their contribution to health

The role of dietary fatty acids in Cardiovascular Disease (CVD) is well established. A diet high in saturated fats negatively affects cholesterol levels while unsaturated fats have been shown to improve plasma lipid profiles. Soybean oil consists mainly of unsaturated fatty acids including linolenic acid from the omega-3 (n-3) family. Omega-3 fatty acids have demonstrated beneficial effects on triglycerides levels. In soybean oil, the typical ratio of n-6/n-3 fatty acids is 7.5. interestingly enough, the oil soy germ is even more unsaturated, with an improved n-6/n-3 ratio of 3.

Fiber and oligosaccharides that are present in soy play a role in both cardiovascular and gut health. Fiber helps lower cholesterol levels by binding intestinal bile acids, which causes their excretion in the feces.2 Further, oligosaccharides have been shown to lower blood pressure.3

In the gut, many fibers show a high capacity to bind water, resulting in a decal bulking effect. This is beneficial for the health of the colon. What's more, although soy fiber and oligosaccharides are relatively indigestible, they can stimulate gut microflora in a positive way. This can lead to an overall improvement of absorption and metabolism of many nutrients, including soy isoflavones.4

Other Key Players

Vitamin E is associated with the prevention of CVD and cancer. The oxidation of LDL ("bad") cholesterol promotes plaque build-up in arteries, which contributes to heart attacks. As an antioxidant, Vitamin E protects LDL cholesterol from oxidation thereby decreasing the risk of heart disease.5 In addition; antioxidants like vitamin E can help inhibit the damaging effects of free radicals which contribute to the development of cancer. Aside from its role in reducing free radicals, vitamin E can further protect against the development of cancer by enhancing immune function.

Saponins, which are largely concentrated in the soy germ, play a role in reducing cholesterol. Similar to fiber, saponins bind bile acids, causing their excretion. They are gaining more attention in research, as they have recently been shown to have antioxidant and potential anti-carcinogenic properties in in vitro experiments6.

Phytosterols are another soy component that can assist in reducing plasma cholesterol levels, especially LDL cholesterol.

Folic Acid nutritional status, also known as folate, is associated with a decreased risk of various forms of vascular disease, certain cancers and the occurrence of a neural tube defect in an infant should pregnancy occur. The soy germ has been found to be a good source of natural folate.7

Lecithin, a major component of cell membranes is a well-known antioxidant and emulsifier. Soy lecithin has been shown to lower plasma total cholesterol and non HDL-C in monkeys and hamsters,8 indicating potential for human cholesterol control. Immune modulator effects have also been described by increased phagocytosis upon bacterial and fungal infections.9

Phytate in soy has antioxidant effects and (like several other soy components) has been shown to reduce cholesterol levels.9 Yet it is a known chelating agent as well, often suspected of reducing the bioavailability of certain nutrients. However, the in vivo effect of phytate is hard to estimate since our diets contain other compounds, which may reduce the bioavailability of nutrients as well. For example, fiber is a well-known chelating agent, though its beneficial effects on gut function are considered more important. The same holds true for phytate.

Phytic acid is increasingly being investigated for its anti-carcinogenic activities. Both preventive and therapeutic effects have been found for a selection of cancers, such as colon and mammary cancer, by anti-proliferative and differentiation promoting mechanisms.10

Conclusion

In conclusion, soy is more than just an excellent source of protein and isoflavones. All of the constituents, as discussed above, play their own important roles in modifying risk factors for various diseases and attribute to general health.

Further scientific information about soybean components in the "soy matrix" will be presented this fall during the 4th International Symposium on the Role of Soy in Preventing and Treating Chronic Disease. The symposium will be held at the Hyatt Islandia in San Diego, CA from November 4-7, 2001.

< Back