The many faces of soy

Soyfoods have been popular for hundreds of years in Asian countries, but they hit the spotlight in the United States just over a decade ago when FDA approved a health claim relating soy protein to heart health. Since that time, new research has outlined the potential health benefits associated with the consumption of soybeans, soy proteins, soybean oil and soy isoflavones.

The whole bean

Soybeans are legumes that are high in fiber, potassium and folate, and contain all of the essential amino acids, making soy protein a complete protein. In addition, soybeans contain antioxidant isoflavones and the omega-3 fatty acid alpha-linolenic acid.

Numerous epidemiological studies have looked at the association between soyfood consumption and disease risk in Asian populations. Collectively, the research indicates soy intake is associated with a reduced risk of prostate cancer in men (American Journal of Clinical Nutrition, 2009; 89:1,155-1,163) and breast cancer in women (Journal of the National Cancer Institute, 2006; 98:459-471; British Journal of Cancer, 2008; 98:9-14). However, clinical studies havent supported the breast cancer benefits noted in epidemiological studies. A plausible explanation for this discrepancy, and one voiced by some of the leading experts in the field, is that to derive protection against breast cancer, soyfoods need to be consumed during childhood and/or adolescence. What is especially noteworthy about this hypothesis is that the evidence suggests that consuming just one serving per day can reduce risk later in life by as much as 50% (Journal of Nutrition, 2009;139:796S-802S).

In addition to the epidemiological data on cancer risk, clinical trials indicate that soy protein lowers low-density lipoprotein (LDL) cholesterol by 4% or 5% (Journal of Nutrition, 2009; 139:796S-802S). Since each 1% decrease in LDL lowers heart-disease risk by 1% to 2%, the effects of soy protein are significant. Furthermore, when soyfoods replace higher-saturated-fat protein sources in the diet, soyfoods will further reduce cholesterol," notes Mark Messina, Ph.D., president, Nutrition Matters, Inc., Port Townsend, WA. The overall effect is that soyfoods may reduce heart-disease risk by 10% or more. Plus, soyfoods may reduce heart disease risk unrelated to their effects on elevated cholesterol levels, which is just one risk factor for heart disease."

Soy protein particulars

Soy protein is a complete protein that boasts a high protein-digestibility corrected amino acid score (PDCAAS; a measure of the amino acids humans need combined with the digestibility of the protein). Research indicates that soy proteins satiating effect is similar to other proteins," says Michelle Braun, nutrition science specialist, Solae, St. Louis. And though soy protein is on par with other proteins in producing satiety and aiding in weight management, it offers a clinically proven and unique advantage of reducing the risk of heart disease by reducing LDL-cholesterol levels. Therefore, incorporating soy protein into weight-loss diets is an effective way to improve satiety, aid weight control, improve diet quality and reduce the risk of cardiovascular disease."

In addition to its effects on satiety, soy protein can be used for the maintenance, repair and recovery of muscle tissue in response to physical training. However, soy protein does not stimulate muscle protein synthesis to the extent that whey, milk proteins and egg do, presumably because soy has a lower leucine content (FASEB Journal, 2010; 24:97.5; American Journal of Clinical Nutrition, 2007; 85:1,031-1,040).

Focus on isoflavones

According to Messina, much of the recent interest in the role of soy in disease prevention and health promotion is because, among commonly consumed foods, the soybean is essentially the only nutritionally relevant source of isoflavones. Isoflavones have estrogen-like effects, although they are different from the hormone estrogen." These isoflavones are associated with many of the positive benefits of soy, including the decrease in breast and prostate cancer risk, as well as a decrease in hot flashes in post-menopausal women. Furthermore, the isoflavones in soyfoods have been shown to directly improve the health of arteries," he says. And finally, although still speculative, clinical studies suggest isoflavones may improve skin health."

Label and health claims

Title 21 of the Code of Federal Regulations (CFR), Part 101.82, outlines the FDA-approved health claim for soy protein and risk of coronary heart disease. Issued in 1999, this claim describes the relationship between diets that are low in saturated fat and cholesterol and also include soy protein, and risk of coronary heart disease: 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. A serving of [name of food] supplies __ grams of soy protein."

To qualify for this claim, the food must be:

Soyfoods are a healthy addition to the diet, adding nutrients and antioxidants. In addition, theres something unique about soy for decreasing breast and prostate cancer risk, and also lowering one or more risk factors for heart disease. Stay tuned for future research uncovering the health benefits of soybean oil enhanced with the heart-healthy omega-3 fatty acid stearidonic acid and any potential benefits of the soy peptide lunasin in the fight against cancer.

Marie Spano, M.S., R.D., CSCS, CSSD, is a nutrition communications expert and food industry consultant. Marie writes for popular press magazines and trade publications, has given cooking demos on NBC, ABC, FOX and CBS affiliates and helps companies formulate healthy products.

Photo: United Soybean Board