Across 15 randomized controlled trials enrolling 1,952 women aged 40–65, soy-based dietary interventions produced a moderate pooled effect on hot flash frequency and severity (SMD = −0.79; 95% CI −1.34 to −0.23), but failed to reach significance for broader vasomotor symptoms or psychological outcomes. GRADE certainty was rated very low throughout, driven by high heterogeneity (I² up to 86%), small trial sizes, and inconsistent protocols. Evidence for flaxseed was inconclusive; dietary patterns such as DASH and MIND showed narrative-only signals for mood and cognition.
Menopause affects roughly half the global population for a median of seven or more years, yet non-pharmacological dietary options remain poorly studied compared to hormone therapy. The isoflavone content of soy — acting as selective estrogen receptor modulators — has long been hypothesized to blunt vasomotor symptoms, and this review provides the clearest pooled signal yet, though the very low GRADE rating should temper enthusiasm. The high I² values suggest that soy food type, isoflavone dose, and gut microbiome composition (which governs equol production) vary enormously across trials, limiting actionable guidance. Practically, adding whole soy foods carries negligible risk and may offer modest symptomatic relief, making it a reasonable first dietary step for women seeking non-pharmacological options. This review is confirmatory and well-conducted, but ultimately highlights a research gap: the field urgently needs larger, longer, standardized trials before dietary prescriptions can be made with confidence.