Soy Protein Confers a Multitude of Benefits
Soybeans Contain Several Beneficial Compounds
Jan 8, 2009
Soybeans contain a variety of biologically active compounds: omega-3 fatty acids, isoflavones, lecithin, phytates, protease inhibitors, saponins, phytosterols, and others. Soybeans are also one of the few plant sources of “total protein.”
Soy protein contains all of the essential amino acids required by humans (including those that are only needed by infants). Furthermore—unlike most plant protein sources—soy protein contains sufficient quantities of each amino acid to meet biological requirements when consumed at the recommended level of protein intake. (Messina M, Messina V, Setchell K. The Simple Soybean And Your Health. Avery Publishing, 1994)
Because soy protein contains a higher level of sulfur-containing amino acids than other plant sources, soy is equivalent in many respects to animal protein. But the health benefits of soy extend beyond its nutritional value.
Health Benefits of Soy Protein
- Populations whose diets are high in soy protein and low in animal protein have lower risks of prostate and breast cancers. (Omoni A, Aluko R. Soybean foods and their benefits: potential mechanisms of action. Nutr Rev. 2005;63(8):272-283 and Qin L, et al. Soyfood intake in the prevention of breast cancer risk in women: a meta-analysis of observational epidemiological studies. J Nutr Sci Vitaminol (Tokyo). 2006:52(6)428-36)
- Several meta-analyses of randomized, controlled trials have shown that consumption of soy protein results in statistically significant reductions in total cholesterol, LDL, and triglyceride levels. In 1999, the U.S. Food and Drug Administration approved the health claim that “…a diet low in saturated fat and cholesterol that includes 25 grams of soy protein per day may reduce the risk of heart disease.” Such claims require a preponderance of evidence before the FDA is willing to extend its beneficence. (Henkel J. Soy. Health claims for soy protein, questions about other components. FDA Consum. 2000;34(3):13-20)
- Soy isoflavones bind weakly and preferentially to beta estrogen receptors, where they appear to act like selective modulators. Multiple studies have examined the clinical effects of this interaction; newer trials support claims of fewer menopausal hot flashes and lower bone fracture risk in women with high soy intake. (Khaodhiar L, et al. Daidzein-rich isoflavone aglycones are potentially effective in reducing hot flashes in menopausal women. Menopause. 2008;15(1)125-132 and Zhang X, et al. Prospective cohort study of soy food consumption and risk of bone fracture among postmenopausal women. Arch Intern Med. 2005;165(16):1890-1895)
Summary of Soy Protein's Benefits
- Improved lipid levels (although studies have not yet shown a reduction in cardiovascular risk)
- Potential reduction in frequency of hot flashes in menopausal women
- Decreased risk of bone fracture and apparent benefit in maintaining bone density in menopausal women
- Possible decrease in prostate and breast cancer risks (although study design [e.g., defining low-versus-high soy intake, defining endpoints as evidence of elevated tumor markers rather than development of cancer, etc.] has so far precluded collection of clearcut data)
- Current information supports neither a beneficial nor harmful effect of soy in women who already have breast cancer
It is worth noting that much of our current knowledge regarding soy’s mechanisms of action is derived from research using refined soy components. However, most epidemiologic studies are based upon data from subjects whose diets contain varying levels of whole soy protein.
It is premature to assume that supplementing with refined soy components will necessarily confer the same benefits as increasing dietary whole soy protein.
