Soy isoflavones and safety

What 2 graded rows on soy isoflavones agree on for safety, and where they differ. Counted side by side, never averaged.

Consensus finder Rows from the Soy isoflavones page, reviewed Oct 21, 2026 How it decides

What the rows agree on

Each block and row is one graded row from the Soy isoflavones page, with its PubMed record.

Your question

Menopause4 Bone2 Safety2

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Soy isoflavones and safety

2 rows · 3,661 people

Split. 1 row found no difference and 1 found a worse outcome.

No difference or worse

Improved

Each block is one evidence row, sized by how many people it enrolled, with its grade inside. Red: a worse outcome.

Grade C× 1
No effect× 1

Rows: 2
Trials: 41
People: 3,661; Pooled reviews may count some twice

Where they differ

From the rows

Trial sizeStudy designHow longWhen published

The best-graded row, grade C, is a randomized trial of 376 people (2004) and found a worse outcome. 1 row is graded No effect, our grade for adequately powered trials that found no effect.

The row that found no difference was larger: 3,285 people, against 376 people for the row that found a worse outcome.

The row that found no difference is a pooled review of several trials; the row that found a worse outcome is a single study.

The row that found a worse outcome ran longer (5 years) than the row that found no difference (6 months).

The row that found no difference is newer (2025) than the row that found a worse outcome (2004).

The rows

1 no difference · 1 worse

No effectEndometrial thickness and estrogen-related measures (safety) · No difference
Meta-analysis, 40 studies · n 3,285 · 2025 · Postmenopausal women in 40 RCTs of 3 months or longer
Median 75 mg/day · Median 24 weeks
No significant change vs non-isoflavone controls in endometrial thickness (−0.22 mm, 95% CI −0.45 to 0.01), vaginal maturation index, FSH or estradiol; certainty of evidence high to moderate.
Row on the Soy isoflavones page · PubMed 39433088 (opens PubMed)
Grade CEndometrial hyperplasia (safety) · Worse
RCT · n 376 · 2004 · Healthy postmenopausal women with an intact uterus (Italy)
150 mg/day · 5 years
Endometrial hyperplasia occurred in 3.37% on isoflavones vs 0% on placebo; no cancers were found.
Row on the Soy isoflavones page · PubMed 15237003 (opens PubMed)

Read onRead the full evidenceThe full evidence chapter on its page, with every outcome and its sources.