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Soy

What does the research say about Soy?

2 health outcomes synthesised

Research on soy has investigated its potential health effects across 2 outcomes, including menopausal symptoms and breast cancer recurrence. The strongest evidence, based on 3 studies, suggests soy isoflavones may reduce breast cancer recurrence, with effective doses around 25-50 mg of isoflavones per day (approximately 2-3 servings of traditional soy foods). Evidence for menopausal symptoms is weaker and less consistent, with a small effect observed at 60 mg/day of isoflavones in one study, primarily in perimenopausal and postmenopausal women.

Strongest evidence: The most consistent findings are for reduced breast cancer recurrence, where all 3 studies reported beneficial effects. Effect sizes were moderate to large, and the effective dose range was 25-50 mg isoflavones per day (2-3 servings of traditional soy foods). However, the evidence strength is rated low due to the small number of studies and reliance on observational data.

Mixed or weaker evidence: For reduced menopausal symptoms, the evidence is mixed. Of 3 studies, 2 found small-to-moderate benefits, while 1 neutral review found no clear benefit. The highest-quality evidence (a meta-analysis) showed a small but statistically significant effect (Hedges' g = -0.25), but the overall evidence strength is low, partly due to the small number of studies and preliminary nature of the conclusions.

Effective dose patterns: Across both outcomes, effective doses converge on a range of 25-60 mg isoflavones per day. For breast cancer recurrence, the range is 25-50 mg/day (2-3 servings of traditional soy foods). For menopausal symptoms, 60 mg/day was used in one study, though it was combined with Lactobacillus sporogenes, making it unclear if the effect is solely from soy.

Population insights: Research on menopausal symptoms focused on perimenopausal and postmenopausal women with symptoms. For breast cancer recurrence, the populations studied were women with breast cancer or breast cancer survivors, including postmenopausal and estrogen receptor-positive survivors.

Notable caveats: The evidence base for both outcomes is small (only 3 studies each), so conclusions are preliminary. For breast cancer recurrence, publication bias is a concern—null-result studies may be less likely to be published. For menopausal symptoms, the beneficial effect in one study was confounded by co-administration of a probiotic, and the single positive dose finding comes from a single RCT.

Frequently asked

  • What is Soy good for according to research?
    Research suggests soy may be beneficial for two health outcomes: reducing breast cancer recurrence and reducing menopausal symptoms. All 3 studies on breast cancer recurrence found beneficial effects, while 2 of 3 studies on menopausal symptoms reported benefits.
  • What dose of Soy is typically used in studies?
    Doses vary by outcome. For breast cancer recurrence, studies used 25-50 mg of isoflavones per day (about 2-3 servings of traditional soy foods). For menopausal symptoms, one study used 60 mg of isoflavones per day, though it was combined with a probiotic. The evidence for both doses is considered preliminary.
  • Who benefits most from Soy?
    Research on breast cancer recurrence focused on women with breast cancer and survivors, including postmenopausal and estrogen receptor-positive survivors. For menopausal symptoms, studies looked at perimenopausal and postmenopausal women with symptoms. Both are specific populations, and evidence may not apply to others.
  • Are there caveats or limitations in the research on Soy?
    Yes, the main limitation is the small number of studies (only 3 per outcome), making conclusions preliminary. For breast cancer recurrence, there is concern about publication bias, as null results may be less likely published. For menopausal symptoms, one positive study combined soy with a probiotic, making it unclear if soy alone is effective.
  • Does Soy help with reducing menopausal symptoms?
    Evidence is mixed. Two out of 3 studies found small-to-moderate benefits, including a meta-analysis showing a small but significant effect (Hedges' g = -0.25). However, one review found no clear benefit, and the overall evidence strength is low due to the small number of studies.
  • Does Soy help with reducing breast cancer recurrence?
    All 3 studies reported beneficial effects of soy intake on reducing breast cancer recurrence, with moderate to large effect sizes. The effective dose range was 25-50 mg isoflavones per day. However, the evidence strength is low, and most evidence comes from observational studies rather than randomized controlled trials.

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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