Soybeans are a rich source of isoflavones, which are classified as phytoestrogens. Despite numerous proposed benefits, isoflavones are often classified as endocrine disruptors, based primarily on animal studies. However, there are ample human data regarding the health effects of isoflavones. We conducted a technical review, systematically searching Medline, EMBASE, and the Cochrane Library (from inception through January 2021). We included clinical studies, observational studies, and systematic reviews and meta-analyses (SRMA) that examined the relationship between soy and/or isoflavone intake and endocrine-related endpoints. 417 reports (229 observational studies, 157 clinical studies and 32 SRMAs) met our eligibility criteria. The available evidence indicates that isoflavone intake does not adversely affect thyroid function. Adverse effects are also not seen on breast or endometrial tissue or estrogen levels in women, or testosterone or estrogen levels, or sperm or semen parameters in men. Although menstrual cycle length may be slightly increased, ovulation is not prevented. Limited insight could be gained about possible impacts of in utero isoflavone exposure, but the existing data are reassuring. Adverse effects of isoflavone intake were not identified in children, but limited research has been conducted. After extensive review, the evidence does not support classifying isoflavones as endocrine disruptors.
Bibliographical noteFunding Information:
Funds were provided by the Soy Nutrition Institute and the European Plant-based Food Association to MM and the Toronto 3D Knowledge Synthesis & Clinical Trials Foundation for work related to the development and writing of this paper.
Mark John Messina receives funding from the Soy Nutrition Institute as its Executive Director. Both Mindy Kurzer and John Sievenpiper are on the advisory board of the Soy Nutrition Institute. Ian Rowland is on the advisory board of the European Plant-based Foods Association. I have disclosed those interests fully to Taylor & Francis, and have in place an approved plan for managing any potential conflicts arising from these positions. Acknowledgements
© 2021 The Author(s). Published with license by Taylor & Francis Group, LLC.