Research
Hormonal
Soy isoflavones can induce goitrogenic effects in individuals with pre-existing hypothyroidism or iodine deficiency, potentially advancing subclinical hypothyroidism to overt hypothyroidism.
If you have hypothyroidism, consult your doctor before consuming large amounts of soy isoflavones, as they may worsen thyroid function in some cases, especially if iodine intake is adequate.
ModerateQualifiesMEDIUM confidence
A randomized, double-blind, and cross-over trial carried out in 60 patients with subclinical hypothyroidism and an adequate iodine intake reported an advance to overt hypothyroidism in 10% of cases (6 females) after administering soy protein with isoflavones for 8 weeks [118].
Why this rating
Based on specific RCTs showing effects in hypothyroid/iodine-deficient groups, but not in euthyroid populations.
Source
Effects of Dietary Phytoestrogens on Hormones throughout a Human Lifespan: A Review
Inés Domínguez‐López et al. · Nutrients · 2020
DOI 10.3390/nu12082456
narrative_reviewCited 182×
Read the paper DOI resolved against Crossref · corpus check 2026-06-10
More from this paper
- Dietary phytoestrogens (specifically soy isoflavones) do not significantly alter circulating testosterone, free testosterone, or estradiol levels in healthy adult men, refuting concerns that soy intake causes feminization or hypogonadism.Good
- Soy isoflavone supplementation improves insulin sensitivity and reduces fasting insulin levels in postmenopausal women, particularly those with metabolic syndrome or hyperinsulinemia.Good
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