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Much Ado About Soy
By Carol Meerschaert, MBA, RD

Soy isn’t foreign to me. I drink my coffee with soymilk; soy chicken patties are my family’s time-crunch dinner of choice; and my friends and I often order edamame as an appetizer when dining out.

Not everyone, however, embraces soy. Since April is National Soyfoods Month, what better time to review what our clients may or may not know about soy and help them sort out the facts from fiction.

Just as science fiction takes a tiny bit of science to weave a story, Internet fiction often cites credible scientific articles, but weaves a tall tale by selectively choosing phrases from articles, ignoring expert consensus statements that disagree, and—borrowing an old phrase—using scientific literature like an intoxicated person uses a lamp post for support but not for illumination. Here, I’ll discuss the five most common misconceptions people have heard or read about soyfoods and present the facts dietitians can share with clients.

1. Soy and Hormones
Soyfoods contain isoflavones, compounds that bind to estrogen receptors in the body and can exhibit weak estrogenlike effects. Because hormones are misunderstood by many, the idea that soy’s phytoestrogen content may be harmful, especially to men and their maleness, keeps floating to the surface. Many websites cite animal studies, claiming that phytoestrogens alter hormone status, but it should be noted that “animal studies tend to be of little value in providing input about possible benefits or harm since the metabolism of isoflavones differs significantly between humans and rodents.”1 Ultimately, neither soyfoods nor isoflavones change the amount of testosterone in adult men or alter sperm viability.

2. Soymilk and Infants
Maybe clients have read an article about soy’s negative effects in infants. After all, formula-fed babies usually consume either cow’s milk- or soy-based formula as their major source of nutrition. The American Academy of Pediatrics’ position statement on this matter says, “Isolated soy protein-based formulas are safe and effective alternatives to provide appropriate nutrition for normal growth and development.”2

Breast is best, but it’s safe to suggest a soy-based formula if an infant can’t be breast fed, if parents don’t want to feed their baby a cow’s milk-based formula, or if the child is allergic to dairy proteins.

Families that eat soy products can add them to an older infant’s diet as appropriate. My children loved cubes of tofu as a finger food.

3. Breast Cancer Connection
A 2008 review of soy and breast cancer published in Nutrition Journal stated there’s little evidence demonstrating that soy will increase breast cancer risk in healthy people and cause harm in those already diagnosed with breast cancer.3 In 2006, the American Cancer Society concluded that breast cancer patients can safely consume up to three servings of traditional soyfoods per day.4

Can someone actually overconsume soy protein isolate? Maybe, but I doubt dietitians would suggest clients consume significant amounts of any protein isolate when they can suggest high-protein whole foods to obtain adequate vitamins and minerals.

4. Soy and Mineral Absorption
Soy has been blamed for causing poor mineral absorption. Soy contains phytate, which can decrease the absorption of minerals, including iron, but whole grains do the same.5 When recommending foods, RDs look at a food or food group’s contribution to health and nutrition, not just one aspect. Most people are more concerned about consuming protein sources with less saturated fat than iron absorption. However, those who are anemic are more concerned with mineral absorption, and dietitians should counsel these patients accordingly. Adult men may have greater concerns about getting too much iron than too little.

5. Soy and Thyroid Function    
Occasionally, clients hear concerns about soy’s negative impact on thyroid health. Some soyfoods contain goitrogens, substances that interfere with the production or utilization of the thyroid hormone thyroxine. Foods that contain goitrogens include cassava, millet, and cruciferous vegetables. Most of these goitrogens, however, are of no major clinical importance. Doerge and Sheehan concluded there’s little evidence indicating that soyfoods or isoflavones adversely affect thyroid function in healthy adults.6

A review of soy safety by Messina stated that soyfood consumption may lead to an increased intake of thyroid medication in patients with hypothyroidism because soy protein may interfere with its absorption, as do many herbs, drugs, and fiber supplements.1 However, thyroid medications are taken on an empty stomach, so absorption isn’t a concern.

So what’s the take home message? Like everything else, soy isn’t a miracle food, but it isn’t a villain, either. Everyone needs to eat a variety of foods in moderation. Soyfoods can provide taste, variety, and nutrients such as protein, fiber, calcium, B vitamins, and iron, depending on the form. As with most things in life, there are positive and negative aspects to foods, and the key to healthful eating is to balance the diet. Good thing there are nutrition professionals to assist the population in doing just that.

— Carol Meerschaert, MBA, RD, is a marketing professional and writer in Paoli, Pennsylvania.


1. Messina MJ. Soy and hormonal issues reviewed. Soy Connection website. http://www.soyconnection.com/newsletters/soy-connection/health-nutrition/article.php/Soy+and+Hormonal+Issues+Reviewed?id=314

2. American Academy of Pediatrics. Committee on Nutrition. Soy protein-based formulas: recommendations for use in infant feeding. Pediatrics. 1998;101(1 Pt 1):148-153.

3. Messina MJ, Wood CE. Soy isoflavones, estrogen therapy, and breast cancer risk: analysis and commentary. Nutr J. 2008;7:17.

4. Doyle C, Kushi LH, Byers T, et al. Nutrition and physical activity during and after cancer treatment: an American Cancer Society guide for informed choices. CA Cancer J Clin.2006;56(6):323-353.

5. Larsson M, Rossander-Hulthén L, Sandström B, Sandberg AS. Improved zinc and iron absorption from breakfast meals containing malted oats with reduced phytate content. Br J Nutr. 1996;76(5):677-688.

6. Doerge DR, Sheehan DM. Goitrogenic and estrogenic activity of soy isoflavones. Environ Health Perspect. 2002;110 Suppl 3:349-353.