This article is written by Dr. Mark Messina, Soy Nutrition Institute executive director. 

It’s not unusual to come across blog posts and articles that are packed with misinformation about soyfoods. It’s a little surprising, though, to see such articles being highlighted by the leading U.S. authority on nutrition.

Writing for the Popsugar website recently, contributor Rosy Pahwa set out to settle “The Great Soy Debate.” In the process, she and those she quoted ended up reinforcing misinformation about soy and health. To make matters worse, the Academy of Nutrition and Dietetics shared the article with members through their weekly Nutrition and Dietetics SmartBrief.

The article suggested that soyfoods raise blood estrogen levels and lower semen quality (they don’t) and that fermented soy is the only good option for those who want to consume soy (it isn’t). It suggested that soy might raise cancer risk when substantial observational data suggest that soy could actually protect against some cancers.^1,2 It promoted scaremongering messages about genetic modification and suggested that processed soy is “frankensoy.”

In building her case against soy, the author cherry-picked a few news items and outlier studies and sometimes misstated the findings. She ignored results from well-conducted meta-analyses and the bulk of the scientific evidence. For example, she referenced a “news” type article from 2006 in Endocrine Reviews primarily about soy infant formula to make the case that soy raises estrogen levels.³ But the article didn’t mention estrogen levels. Better resources are a meta-analysis⁴ and narrative review,⁵ which show neither soy nor isoflavones raise estrogen levels in men or women.

In suggesting that soy raises breast cancer risk, she linked to a 2014 study that didn’t actually look at cancer as an outcome.⁶ Furthermore, this study actually found there were no adverse effects of soy isoflavones on two markers of breast cancer risk, cell proliferation and apoptosis. The growing body of evidence to suggest that soyfoods may be protective in women being treated for breast cancer wasn’t even mentioned.⁷

To make the case that soy lowers testosterone levels, she linked to a letter (co-authored by me, in fact) to the editor of Cancer Epidemiology Biomarkers and Prevention which argued that soy doesn’t raise testosterone levels.⁸ She also ignored the substantial body of research (more than 30 clinical studies) that show neither soy nor isoflavones affect testosterone.⁹ The article warned readers away from processed soyfoods. But if it’s the soy isoflavones she’s worried about, this makes no sense since “processed” soyfoods are generally lower in isoflavones (on a mg/g protein basis) than traditional choices like tofu, soymilk, miso and tempeh.^10,11

Finally, a dietitian suggested that genetically modified soy raises risk for digestive problems and allergy. She was quoting anti-GMO activist Jeffrey Smith who misrepresented the actual findings, or in some cases, appeared to ignore them altogether. For example, his stance about the digestibility of GMO soy is based on a study in mice that didn’t even look directly at digestibility.¹² Based on the research that has examined this issue, digestibility of isolated soy protein from genetically modified soybeans is approximately 100%.¹³ The study that Smith cites to demonstrate allergenicity of GMO soybeans doesn’t show them to be more allergenic than wild, unmodified soybeans.¹⁴ Although it would be good to see more research in this area conducted, several studies have found no difference in allergenicity between genetically modified and non-genetically modified soybeans,^15,16 nor is there evidence, as was suggested, that genetically modified soy kills off intestinal bacteria.¹⁷

While the evidence in support of the safety of soy is substantial, so is the amount of misinformation about soy that is shared daily on the internet. Most likely, the Academy of Nutrition and Dietetics flagged this particular article for promotion because it quotes several dietitians. That’s not reason enough to share an article with health professionals or the public when it is so fraught with misinformation.

References

1. Xie Q, Chen ML, Qin Y, et al. Isoflavone consumption and risk of breast cancer: a dose-response meta-analysis of observational studies. Asia Pacific J Clinical Nutr. 2013;22(1):118-27.
2. Applegate CC, Rowles JL, Ranard KM, et al. Soy consumption and the risk of prostate cancer: An updated systematic review and meta-analysis. Nutrients. 2018;10(1).
3. Barrett JR. The science of soy: what do we really know? Environ Health Perspect. 2006;114(6):A352-8.
4. Hooper L, Ryder JJ, Kurzer MS, et al. Effects of soy protein and isoflavones on circulating hormone concentrations in pre- and post-menopausal women: a systematic review and meta-analysis. Hum Reprod Update. 2009;15(4):423-40.
5. Messina M. Soybean isoflavone exposure does not have feminizing effects on men: a critical examination of the clinical evidence. Fertil Steril. 2010;93(7):2095-104.
6. Shike M, Doane AS, Russo L, et al. The effects of soy supplementation on gene expression in breast cancer: a randomized placebo-controlled study. J Natl Cancer Inst. 2014;106(9).
7. Chi F, Wu R, Zeng YC, et al. Post-diagnosis soy food intake and breast cancer survival: A meta-analysis of cohort studies. Asian Pacific J Cancer Prev. 2013;14(4):2407-12.
8. Messina M, Hamilton-Reeves J, Kurzer M, et al. Effect of soy protein on testosterone levels. Cancer Epidemiol Biomarkers Prev. 2007;16(12):2795.
9. Hamilton-Reeves JM, Vazquez G, Duval SJ, et al. Clinical studies show no effects of soy protein or isoflavones on reproductive hormones in men: results of a meta-analysis. Fertil Steril. 2010;94(3):997-1007.
10. Murphy PA, Barua K, Hauck CC. Solvent extraction selection in the determination of isoflavones in soy foods. Journal Chromatography B, Analytical Technologies Biomedical Life Sciences. 2002;777(1-2):129-38.
11. Murphy PA, Song T, Buseman G, et al. Isoflavones in retail and institutional soy foods. J Agric Food Chem. 1999;47(7):2697-704.
12. Malatesta M, Biggiogera M, Manuali E, et al. Fine structural analyses of pancreatic acinar cell nuclei from mice fed on genetically modified soybean. Eur J Histochem. 2003;47(4):385-8.
13. Hughes GJ, Ryan DJ, Mukherjea R, et al. Protein digestibility-corrected amino acid scores (PDCAAS) for soy protein isolates and concentrate: Criteria for evaluation. J Agric Food Chem. 2011;59(23):12707-12.
14. Yum HY, Lee SY, Lee KE, et al. Genetically modified and wild soybeans: an immunologic comparison. Allergy Asthma Proc. 2005;26(3):210-6.
15. Hoff M, Son DY, Gubesch M, et al. Serum testing of genetically modified soybeans with special emphasis on potential allergenicity of the heterologous protein CP4 EPSPS. Mol Nutr Food Res. 2007;51(8):946-55.
16. Lu M, Jin Y, Ballmer-Weber B, et al. A comparative study of human IgE binding to proteins of a genetically modified (GM) soybean and six non-GM soybeans grown in multiple locations. Food Chem Toxicol. 2018;112216-23.
17. Nielsen LN, Roager HM, Casas ME, et al. Glyphosate has limited short-term effects on commensal bacterial community composition in the gut environment due to sufficient aromatic amino acid levels. Environ Pollut. 2018;233364-76.