Soy

botanicallegume

What is it

Soy (Glycine max) is a leguminous oilseed in the Fabaceae family supplying high-quality protein (~36% by dry weight), polyunsaturated oil, and the isoflavone phytoestrogens genistein, daidzein, and glycitein. Supplements are sold as whole-bean protein isolates, fermented forms (natto, tempeh extracts), or standardized isoflavone concentrates.

Evidence for 4 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

LDL cholesterol reduction

Strong

25 g/day soy protein lowers LDL-C ~3-5%; supports FDA-authorized heart health claim.

Menopausal vasomotor symptoms

Good

Standardized isoflavone supplements (40-80 mg/day) modestly reduce hot flash frequency; effect is smaller than HRT but consistent across meta-analyses.

Bone mineral density (postmenopausal)

Good

Soy isoflavones, particularly genistein, attenuate lumbar spine BMD loss in postmenopausal women across multiple RCTs.

Breast cancer risk (epidemiologic)

Good

Asian-population cohort data link lifelong soy intake to ~30% lower breast cancer risk; supplemental isoflavones in established disease are considered safe.

Dosage

Whole-food intakes of 25 g/day soy protein qualify for the FDA heart-health claim; isoflavone supplements typically supply 40-80 mg/day of total isoflavones. Fermented natto extracts containing nattokinase are dosed at 2000-4000 FU/day.

Safety

Soy is one of the FDA top-9 allergens. Soy isoflavones bind estrogen receptors (preferentially ER-beta) and theoretically interact with tamoxifen and aromatase inhibitors, though clinical evidence is reassuring at dietary intakes. May suppress thyroid function in iodine-deficient individuals through TPO inhibition.

References

  • Wikidata: Soybean — Wikidata link
  • DSLD: Soy — NIH DSLD link

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Evidence-based·How we grade evidence

Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you’re pregnant, breastfeeding, on medications, or managing a chronic condition.