Exploring the Soy Controversy: A Review of the Research

A Summary of “Soy Foods and Supplementation: A Review of Commonly Perceived Health Benefits and Risks” by Chris D’Adamo, PhD and Azize Sahin, MD

By Erin Peisach, RD, LDN

           

Soy, originally cultivated in Asia to preserve nitrogen in soil, is now a mainstream food and food product in the US market.  It is primarily available as soymilk, textured soy protein, soybean oil, infant soy-formula, soy protein powders, and faux animal products. US sales of soy foods increased from $1 billion in 1996 to $4.5 billion in 2009. The vast increase in the use and consumption of soy in the American diet warranted a thorough review of its safety and potential health benefits. As a dietitian, many of my patients ask me questions about soy and whether it may help or harm specific health conditions. The soy confusion stems from contradicting reports often seen in newspaper headlines, news articles, and health magazines over the past decade. One may say, “Soy Heals All” while the next may report, “Soy is Evil!” With such contrasting messages, digging deeper into current soy research will help elucidate the issue.

Chris D’Adamo, PhD, Assistant Professor at the University of Maryalnd School of Medicine in the Department of Family and Community Medicine and Director of Research in the Center for Integrative Medicine, and Azize Sahin, MD, University of Maryland School of Medicine Alumnus (’12), completed a comprehensive review of soy research to highlight its potential health benefits and risks. The article, recently published in the Alternative Therapies in Health and Medicine, focused on five perceived health benefits – relief of menopausal symptoms and prevention of heart disease, breast cancer, prostate cancer, and osteoporosis and five perceived health risks – increased risk of breast cancer, male hormonal and fertility problems, hypothyroidism, anti-nutrient content and harmful processing by-products. The authors reviewed and assessed the findings of scientific literature on soy through 2010. The findings revealed the following:

·         Perceived Health Benefits:

1.      Relief of Menopausal Hot Flashes: While women respond differently to soy consumption, some may benefit from the relief of menopausal symptoms.

2.      Protection Against Breast Cancer: The more soy foods consumed throughout one’s lifetime is inversely associated with the incidence of breast cancer

3.      revention of Prostate Cancer: There may be a reduction in prostate cancer risk in men who consume soy foods or soy supplements.

4.      Protection Against Coronary Heart Disease: Soy protein may be associated with a reduction in LDL cholesterol, with no impact on triglycerides, HDL and total cholesterol levels.

5.      Prevention of Osteoporosis: Soy does not appear to protect against osteoporosis.

·         Perceived Health Risks:

1.      Increased Risk of Breast Cancer:  There was no association found between soy phytoestrogen exposure and increased risk of breast cancer.

2.      Hormonal Imbalances in Men: There is no significant impact from soy consumption on male reproductive hormones, although more research is needed.

3.      Induction of Hypothyroidism: Soy supplements can unpredictably interfere with thyroid function and should be avoided in certain populations. 

4.      Adverse Outcomes from Antinutrients: Soy antinutrients include lectins, saponins, oxalates, enzyme inhibitors, phytates, and others.

§  Lectins- linked to food sensitivities, but almost entirely destroyed by heating

§  Saponins- may increase intestinal permeability which may contribute to autoimmune diseases; not removed by heating

§  Enzyme inhibitors- bind to enzymes which inhibit protein digestion and increases pancreatic function; maybe be the cause of pancreatic hyperplasia and adenomas; mostly destroyed by heating

§  Oxalates- may result in hyperoxaluria which may lead to kidney stones; binds calcium and other minerals reducing their absorption

§  Phytic acid- reduces bioavailability of vitamins A, B₁₂, D, and E and minerals calcium, zinc, magnesium, and iron creating the potential for multiple nutritional deficiencies; destroyed when soy is fermented

5.      Harm From Soy Processing By-Products:

§  Soy is processed with alkaline solutions that creates unnatural amino acids, possibly contributing to digestive problems

§  Use of hexane, a volatile hydrocarbon with known neurotoxic effects, is used in soy processing; there are no studies or FDA limits on hexane exposure from soy

In conclusion, there are specific health benefits and health risks associated with soy for certain people. The evidence does not suggest significant health risks from moderate soy intake in generally healthy populations. However, the presences of antinutrients and problematic processing techniques in soy should prompt people to use caution with consuming high levels of processed, non-fermented soy products. 

For more information about soy or nutrition in general, please feel free to call me at the University of Maryland Center for Integrative Health and Healing at 410-448-6361 or email me at CIMClinicInfo@som.umaryland.edu.  Also, consider attending the Center for Integrative Health & Healing Open House on June 20 & 21.  See www.compmed.umm.edu/open-house/ for details.