Gabrielle Viscardi, Songhee Back, Amna Ahmed, Shuting Yang, Sonia Blanco Mejia, Andreea Zurbau, Tauseef A Khan, Amanda Selk, Mark Messina, Cyril Wc Kendall, David Ja Jenkins, John L Sievenpiper, Laura Chiavaroli
Journal: Advances in nutrition (Bethesda, Md.) 2025;16(1):100327
PMID: 39433088
Despite dietary recommendations to increase plant-based food intake for both public and planetary health, concerns about the estrogenic effects of soy foods and their components, particularly soy isoflavones, remain a barrier to consumption. This study aimed to assess the effect of soy isoflavones on four measures of estrogenicity: endometrial thickness (ET), vaginal maturation index (VMI), follicle-stimulating hormone (FSH), and circulating oestradiol in postmenopausal women. A systematic review and meta-analysis of randomised controlled trials were conducted. It included forty trials (52 trial comparisons) involving 3285 postmenopausal women Results showed that soy isoflavone consumption had no significant effect on the four measures of estrogenicity. These findings remained consistent across sensitivity and subgroup analyses. The authors concluded that in postmenopausal women, soy isoflavones do not exert estrogenic effects, as indicated by ET, VMI, FSH, and estradiol levels.
Despite recommendations to increase plant food consumption for public and planetary health and the role that soy foods can play in plant-predominant diets, controversies around the effects of soy foods, especially soy isoflavones, are a barrier to their intake. Given their cardioprotective effects and ability to alleviate menopausal symptoms, addressing these concerns is particularly relevant to women. This systematic review and meta-analysis of randomized controlled trials aimed to determine the effect of soy isoflavones on measures of estrogenicity in postmenopausal women. MEDLINE, Embase, and Cochrane Library were searched through August 2024 for randomized trials ≥3-mo investigating soy isoflavones compared with non-isoflavone controls in postmenopausal women. Outcomes included endometrial thickness (ET), vaginal maturation index (VMI), follicle-stimulating hormone (FSH), and estradiol. Independent authors extracted data and assessed risk of bias. Grading of Recommendations, Assessment, Development and Evaluation was used to assess certainty of evidence. We included 40 trials (52 trial comparisons, n = 3285) assessing the effect of a median reported dose of 75 mg/d of soy isoflavones in substitution for non-isoflavone controls over a median of 24 wk. Soy isoflavones had no statistically significant effect on any measure of estrogenicity; ET [mean difference, -0.22 mm (95% confidence interval, -0.45, 0.01 mm), P = 0.059], VMI [2.31 (-2.14, 6.75), P = 0.310], FSH [-0.02 IU/L (-2.39, 2.35 IU/L), P = 0.987], and estradiol [1.61 pmol/L (-1.17, 4.38 pmol/L), P = 0.256]. The certainty of evidence was high to moderate for all outcomes. Current evidence suggests that soy isoflavones do not exhibit estrogenic effects compared with non-isoflavone controls on 4 measures of estrogenicity in postmenopausal women. This synthesis supports that soy isoflavones likely act as selective estrogen receptor modulators, differing clinically from the hormone estrogen. Addressing public health concerns may promote soy foods as high-quality plant protein sources with low environmental impact and cost, particularly benefiting postmenopausal women and aligning with sustainable dietary patterns and guidelines. This study was registered in PROSPERO as CRD42023439239.
Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.
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