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Savvy Soy?

An analysis of soy protein and isoflavones

Katie McKillen




Recently, the increasing interest in healthy lifestyles has sparked people’s thoughts about the nutrition in the food they are eating. The leading causes of death relate back to healthy lifestyles. Therefore, people are searching for preventable was to reduce their risk for: heart disease, stroke, and various cancers. One of the causes associated with these diseases is an unhealthy diet. Diets high in fats in cholesterol currently fall under this category of unhealthy. Often sources of protein are major attributors to the high fat diets. A few years ago, the perfect product seemed to appear out of no where—SOY. But today some are beginning to question whether this so called ‘perfect’ food is really as healthy as people have made it seem. This website will examine the benefits of soy, more specifically the isoflavones found in this product.











Soy products come from the soybean, which is part of the legume family ( scientific name is Glycine max. They can be classified as a vegetable or an oilseed. It is approximately 38-45% protein and 20% oil. Soy products have been a staple in Asian cultures for centuries and have recently gained popularity in other parts of the world due to their possible health benefits. Soybeans are the United State’s leading agricultural export. They are often used to make imitation dairy products—soy milk, soy yogurt, and soy cream cheese. Soy can also be used to make oils, soap, cosmetics, resins, plastics, inks, crayons, solvents, clothing, and biodiesel (




Soy can be used as alternatives to a variety of dairy and meat products. People who are intolerant of lactose can eat imitation dairy products. Soy can also be a good source of protein for vegetarians. Along with providing alternative options of certain foods, soy protein and isoflavones are thought to have many health benefits. These isoflavones are thought to have potential benefits in the following areas: heart disease, bone health, menopausal symptoms, breast cancer, prostate cancer, lower cholesterol, increased bone density, and diabetic conditions.




The FDA approved a heart health claim in 1999 which states, “25 grams of soy protein a day as a part of a diet low in saturated fat and cholesterol may reduce the risk of heart disease.” The FDA stated in order to claim the health effects of soy and relationship between soy protein and Coronary Heart Disease the following must be included:



Lowering Cholesterol/Reducing Heart Disease


Many of the websites state that eating soy protein rather than animal protein can lower cholesterol ( USA Today connects this in a 1995 article in the New England Journal of Medicine which analyzes 38 clinical trials. Other news studies state that the soy protein and isoflavones lower LDL cholesterol and reduce blood clotting ( Some believe that they may inhibit certain effects of LDL creating less damage to the arteries (

Another website indicated that the U.S. government is currently studying that isoflavones may improve the health of the lining of blood vessels, thereby, reducing the risk for heart disease ( One news report stated that the protein and isoflavones found in soy provide antioxidants which not only reduce clogging of plaque but also protects the body from free radical damage and lowers the risk of atherosclerosis (


Reducing Cancers


The soluble fiber in soy products is claimed to help protect the body from many digestive related cancers ( Also, studies are currently being done to examine the relationship between the isoflavones and breast and prostate cancer. They have been shown to inhibit cancer cells in the prostate ( This is thought to be one reason why tumors grow slower in Japanese men where soy is one of their staple foods.


Reducing Menopausal Symptoms


Isoflavones are shown to provide significant relief to those suffering from hot flashes during menopause ( One news article explains that these isoflavones help to regulate estrogen levels when certain hormones are declining or fluctuating (


Improving Bone Health

Studies in Asia found a link between greater intake of isoflavones and stronger bones. They are still performing long-term studies, but they believe the data is promising thus far ( A study from the University of Illinois at Urbana-Champaign also found a relationship with high soy protein diets and favorable bone density (


Improving Diabetic Conditions


Some believe that the protein and fiber found in soy helps regulate glucose levels and kidney filtration, thereby, helping to control diabetic conditions along with kidney disease (


Harmful Sides of Soy


Soy is hardly a health food, and in the highly processed form used in most products, it's hardly natural either.”

~Debra Lynn Dadd
Author of Home Safe Home


Currently, some people disagree with all of the benefits of soy products. One website states that hundreds of studies show soy is linked health problems including:  malnutrition, digestive distress, thyroid dysfunction, cognitive decline, reproductive disorders, infertility, birth defect, immune system breakdown, heart disease, and cancer (


            Not a Complete Protein


Soy beans are just like all other legumes in that they are deficient in sulfur-containing amino acids ( Therefore, they are not complete proteins.


            Fails to Protect Against Heart Disease


While soy products may help to lower cholesterol, one website indicates that there is no evidence that this improves one’s risk of having heart disease (


            Isoflavones Have Harmful Side Effects


Isoflavones can prevent ovulation and actually stimulate cancer cell growth ( Also consuming soy products can result in lethargy, constipation, weight gain, and fatigue. Another website believes that soy products have high levels of aluminum which can be damaging to both the nervous system and the kidneys.


Improves Chances of Developing Cancer


One website indicates that the trypsin in soy interferes with digestion causing pancreatic orders ( Phytoestrogers also have the potential to cause breast cancer and thyroid cancer.


Scientific Literature Review


To evaluate the claims above about the benefits or harms to soy products, a review of professional and scientific journals will be provided. This overview is to provide a more critical perspective on the effects of soy protein and isoflavones.


Important questions in which to consider:


Setchell, Brown, and Lydeking-Olsen examine the effectiveness of soy and its isoflavones in respect to two different groups: those who are “equol-producers” from “nonequol producers” (2002). Equol is a nonsteroidal estrogen of the isoflavone class. Compared to all other isoflavones, it is superior in antioxidant activity. The failure to distinguish these groups which either produce or not could explain the variance in benefits reported. They explain that the large presence of soy foods is largely driven through the discovery that the soybeans and proteins are the riches source of isoflavones.  However, many studies have not taken into account that the effectiveness of soy may be dependent on the ability to produce equol. The main origins of equol in humans are soy protein and soy foods. Their review explains how about 30-50% of the adult population fails to excrete equol in urine after eating soy foods. Thereby, their study includes “nonequol producers” to be those who excrete less than 40 nmol where the “equol producers” excrete over 1000 nmol. After some 2 year long studies in which postmenopausal women were randomized to consume two 250mL glasses of soymilk each day either with or without isoflavones, the authors state that there is good rationale for expecting greater efficacy [in relation to stable bone density] in equol producers. However, the study concludes that the largely forgotten isoflavone—equol—may be the most important soy isoflavone in disease prevention and treatment.


Gardner, Newell, Cherin, Haskell (2001) examined the effects of soy protein on postmenopausal women. The randomized, double-blind study involved 12 weeks of dietary protein supplements—either milk protein, soy protein with trace amounts of isoflavones, and soy with 80 mg of isoflavones. The results of the study concluded that the soy protein supplements with isoflavones decreased LDL cholesterol concentration more than the soy protein supplement with trace amounts of the isoflavones. However, this study reported an unexpected lowering of LDL cholesterol in the milk group as well.

Bhathena and Velasquez (2002) review a variety of studies to indicate that evidence shows that diets rich in photoestrogens (isoflavones and lignans) can have beneficial aspects on diabetes and obesity. The review of the studies says that soy proteins may reduce insulin resistance by inhibiting insulin secretion or enhancing lipolysis in the liver. They show these isoflavones may be exerting beneficial effects due to the antioxidative actions. However, after reviewing the studies, Bhathena and Velasquez feel that there needs to be more long-term controlled trials on safety and effectiveness of soy.

American Heart AssociationFrank M. Sacks; Alice Lichtenstein; Linda Van Horn; William Harris; Penny Kris-Etherton; Mary Winston for the AHA Nutrition Committee (2006) focuses on the American Heart Association Science Advisory on soy proteins and isoflavones. It explains that in 22 randomized trials, the average effect of soy proteins on decreasing LDL cholesterol was only 3 percent. They show no significant effects on HDL cholesterol or blood pressure. They state that the efficacy and safety of the isoflavones for preventing or treating any types of cancer are currently not established. This states that earlier research indicating that soy proteins has more favorable effects than other types of proteins has yet to be confirmed. The review examines studies from the 1970s and 1980s by Sirtori and colleagues which indicates substantially reduced blood cholesterol was due to confounding variables as the the soy protein diets were also reduced in saturated fat and cholesterol and increased in polyunsaturated fat. This review also examines a variety of other studies to seek the possible benefits of soy:

Improving Cholesterol: 22 recent trials demonstrate no relation between isoflavones and cholesterol-lowering.

Lowering Blood Pressure: The majority of the studies indicate no relation between soy protein with isoflavones and blood pressure any more than regular milk.

Effects of Lipoprotein: Reviewing major studies shows that neither soy protein or soy isoflavones have positive effects on lipoprotein, an independent predictor of cardiovascular disease. 2 studies actually indicated an increase in lipoproteins in relation to soy protein, while 9 other studies demonstrated no change in the results, thereby demonstrating no evident benefits.

Menopause and Postmenopausal Effects: Neither soy protein or soy isoflavones have proved to improve symptoms of menopause. There are currently mixed results as to the effects of slowing bone loss in postmenopausal stages.

Benefits to Overall Health: While soy isoflavones supplements have no established safety, soy products—tofu, soy butter, soy nuts, soy burgers—should be beneficial due to their high content of fiber, vitamins, minerals, and polyunsaturated fats.


Conclusions and Recommendations


After reviewing a variety of web sites and literature, it appears that soy should not be hyped up as a miracle product nor looked upon as a dangerous product. There appears to be no confirmation that soy protein has important favorable effects. There also does not appear to be any confirmation that soy is causing any diseases or harm. However, many soy products seem to have beneficial cardiovascular and overall health because due to the healthy components. Soy products normally have high fiber, vitamins, minerals, polyunsaturated fats and low saturated fats. Since soy has increasingly become more popular in Western societies recently, it appears that there is still a lot of research and long-term studies, which need to be conducted in order to fully confirm any benefits directly from the soy proteins or isoflavones.


There appears to be no harm with consuming soy products past infancy. Currently, there seems to be no problems with using soy products as an alternative to dairy or meat products. Due to the lack of research, a certain extent of moderation is always a safe use.




Bhathena, S.J. & Velasquez, M.T (2002). Beneficial role of dietary phytoestrogens in obesity and diabetes. American Journal of Clinical Nutrition, Vol. 76, No. 6, 1191-1201, December 2002.


Daniel, K.T. The Whole Soy Story: The True Soy Story. 10 September 2006. <>


Falcon, M. (2001). Marilu Henner Rounds Up Soy Benefits. USA Today. 2 May 2001. <>


Gardner, C.D.,  Newell,  K.A., Cherin, R. & Haskell, W.L. (2001). The effect of soy protein with or without isoflavones relative to milk protein on plasma lipids in hypercholesterolemic postmenopausal women. American Journal of Clinical Nutrition, Vol. 73, No. 4, 728-735, April 2001.


Gilbert, M.N. Six Ways Soy Benefits Your Health. Holistic Health News. 15 September 2006.


“Living a Healthy Lifestyle.” Silk Soymilk. 15 September 2006.


“Myths & Truths About Soy Foods.” Soy Online Service. 10 September 2006.


Sacks, F.M., Lichtenstein, A., Horn, L.V., Harris, W., Kris-Etherton, P.,  & Winston, M. (2006). Soy Protein, Isoflavones, and Cardiovascular Health:A Summary of a Statement for Professionals From the American Heart Association Nutrition Committee.Arteriosclerosis, Thrombosis, and Vascular Biology. 2006;26:1689.


Setchell, K.D.R., Brown, N. M., Lydeking-Olsen, E. (2002). The Clinical Importanct of Metabolite Equol—A Clue to the Effectiveness of Soy and Its Isoflavones. Journal of Nutrition.


Tsang, G. (2006). “Benefits of Soy in Heart Disease: Cholesterol Lowering.” Health Castle. February 2006. <>



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