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Evidence-Based Supplement Research
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Soy

What does the research say about Soy?

2 health outcomes synthesised

Research on Soy has examined 2 health outcomes. The strongest evidence is for reduced breast cancer recurrence, with 3 studies showing beneficial effects at doses of 25-100 mg isoflavones daily (approximately 2-3 servings of traditional soy foods). Evidence for menopausal symptoms is more limited, with mixed results from 3 studies.

Strongest Evidence

Moderate evidence indicates that soy intake (as isoflavones from whole foods) may reduce breast cancer recurrence. All 3 studies reported beneficial effects, with moderate to large effect sizes. The most-studied dose range is 25-100 mg isoflavones daily (2-3 servings of traditional soy foods).

Mixed or Weaker Evidence

Low evidence exists for menopausal symptoms. Of 3 studies, 2 reported benefit (one small, one moderate) and 1 found no effect. A meta-analysis of 7 studies (533 participants) showed a small but statistically significant benefit (Hedges' g = -0.25). One RCT used 60 mg soy isoflavones daily for 12 months.

Effective Dose Patterns

Both outcomes involve isoflavone intake from whole soy foods. For breast cancer recurrence, the range is 25-100 mg daily; for menopausal symptoms, one study used 60 mg daily. Doses were not consistently reported across all studies.

Population Insights

Breast cancer recurrence studies focused on women with breast cancer or survivors. Menopausal symptom studies involved perimenopausal and postmenopausal women.

Notable Caveats

The evidence base is small (only 3 studies per outcome), and conclusions should be considered preliminary. A publication bias favoring positive results is possible for breast cancer research. Doses and forms were not consistently reported, limiting generalizability.

Frequently asked

  • What is Soy good for according to research?
    Research suggests that soy, particularly isoflavones from whole soy foods, may help reduce breast cancer recurrence in women with a history of breast cancer (3 studies, moderate evidence). There is weaker evidence that it may modestly reduce menopausal symptoms (2 of 3 studies, low evidence).
  • What dose of Soy is typically used in studies?
    For breast cancer recurrence, doses of 25-100 mg isoflavones daily (approximately 2-3 servings of traditional soy foods) were used. For menopausal symptoms, one study used 60 mg soy isoflavones daily for 12 months, though doses were not consistently reported across all studies.
  • Who benefits most from Soy?
    Studies on breast cancer recurrence focused on women with breast cancer or survivors. For menopausal symptoms, participants were perimenopausal and postmenopausal women. These populations appear to be the most studied.
  • Are there caveats or limitations in the research on Soy?
    Yes. The evidence base is small (only 3 studies per outcome), and conclusions are preliminary. There is a risk of publication bias toward positive results, and doses and forms of soy were not always consistently reported, which limits generalizability.
  • Does Soy help with menopausal symptoms?
    Evidence is low and mixed. Two of three studies reported a beneficial effect (one small, one moderate), while one found no effect. A meta-analysis of 7 studies showed a small statistically significant benefit, but its clinical significance may be modest. More research is needed.

Most-studied combinations with Soy

most supplement research is combination research
Also studied with:Soy Protein (3), natto (2), Red Clover (3)

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