GradedHealth

Do soy foods lower cholesterol and ease menopause symptoms?

Soy protein trims LDL cholesterol by a few points. For hot flashes, some trials show a small help and others find nothing.

Published October 2026

Short answer

Soy protein lowers LDL cholesterol by a small amount. For hot flashes, the evidence is mixed and limited. Evidence grade C (Limited). Meta-analyses of randomised trials; downgraded for inconsistent results and because LDL is a surrogate marker.

Key takeaways

  • Pooled trials show soy protein lowers LDL ('bad') cholesterol by about 5 mg/dL, roughly 3 to 4 per cent [1][2].
  • Isolated soy isoflavone supplements did not change the lipid profile in one meta-analysis, so soy protein looks like the active part [2][3].
  • For hot flashes, one meta-analysis found about 0.8 fewer a day, but the Cochrane review found no conclusive benefit [4][5].
  • A six-month trial of 270 women found no significant change in menopause symptoms from soy flour or daidzein [6].
  • A study of more than 300,000 Chinese women found moderate soy intake was not linked to breast cancer risk [7].

The short version

Soy protein lowers "bad" LDL cholesterol by a small amount, about 5 mg/dL in pooled trials [1][2]. For hot flashes and other menopause symptoms, the evidence is mixed and limited. Some reviews find a modest drop in hot flashes, but a Cochrane review found no conclusive benefit [4][5].

What the studies show

For cholesterol, a pooled analysis of 46 trials that the US Food and Drug Administration (FDA) reviewed for its soy heart-health claim found that soy protein, at a median of 25 g a day for about six weeks, lowered LDL by about 4.8 mg/dL [1]. A separate analysis of 35 trials found a similar drop, and a bigger one in people with high cholesterol [2]. A cumulative analysis of those same 46 trials found the LDL drop stayed statistically significant in every year after the FDA's 1999 claim [8].

For menopause, one analysis of 16 soy isoflavone trials, about 1,710 women, estimated that isoflavones cut hot flashes by about 25% once the placebo effect was removed. It also found the effect is slow, taking about 13 weeks to reach half its strength and at least 48 weeks to reach 80% of it [9]. A 2016 analysis of 62 trials of plant-based therapies linked soy isoflavones to about 0.8 fewer hot flashes a day [4]. In a trial of 90 women, hot flush frequency fell by about 44% to 49% on soy germ isoflavone doses, compared with about 28% on placebo [10].

Not every trial agrees. A six-month trial of 270 women given 40 g of soy flour a day or a soy compound called daidzein found no significant change in symptoms compared with placebo [6]. A Cochrane review of 43 trials with 4,364 women found no conclusive evidence that phytoestrogen foods or supplements reduce hot flushes or night sweats [5].

The nuances

Soy protein seems to matter more than isoflavone pills. Isolated soy protein lowered LDL more than isolated isoflavones in a meta-analysis of postmenopausal women [3]. Isoflavone supplements alone had no effect on the lipid profile in another meta-analysis [2].

The cholesterol effect is less certain after menopause. In a 2021 meta-analysis of 2,305 postmenopausal women, total cholesterol fell by about 4.6 mg/dL, but the LDL drop of about 1.9 mg/dL was not statistically significant [11].

Results vary a lot between trials. One 2015 analysis reported heterogeneity (a measure of how much the trials disagree) of 92 to 99% [2].

Many menopause trials were small and at high risk of bias, and placebo groups improved by between 1% and 59% [5][4]. Some products mix soy with other herbs such as black cohosh or hops, so their results do not show what soy alone does [12][13].

Mood is a mixed picture. A 2019 trial of 101 women found a soy drink had no effect on everyday mood [14]. A 2024 meta-analysis of five trials found a small drop in depression but no effect on overall menopause symptoms, and its authors warned that many included trials carried a high risk of conflict of interest [15].

Breast cancer: a study of more than 300,000 Chinese women found moderate soy intake was not linked to breast cancer risk [7]. In women already diagnosed, soy intake before diagnosis was linked to a small reduction in overall survival after menopause, but the evidence is limited [16].

Thyroid: in a 60-person trial of people with mild underactive thyroid, a high dose of 16 mg of soy phytoestrogens a day was followed by overt hypothyroidism in six people [17]. A small study of 12 women taking levothyroxine found a soy isoflavone supplement did not change how well the medicine was absorbed [18]. A review concluded that any such effect seems to have little clinical impact [19].

What this means for you

The LDL trials used a median of 25 g of soy protein a day [1]. Expect a small change: about 5 mg/dL in trials. Discuss your cholesterol plan with a doctor, who can weigh that against your overall risk.

For hot flashes, the best trial evidence suggests any effect is modest and takes months to appear [9]. If you have a thyroid condition, check with your doctor before taking soy isoflavone supplements [17]. Women with a history of breast cancer should also ask their doctor first, because the evidence in that group is limited [16]. If you are pregnant or breastfeeding, ask a doctor before taking soy supplements.

See the full soy topic page for doses, side effects and the caveats.

Go deeper

  • Soy — Soy protein lowers LDL cholesterol by a small amount, about 5 mg/dL in pooled trials, but the LDL effect was not statistically significant in one analysis of p…

References

  1. A Meta-Analysis of 46 Studies Identified by the FDA Demonstrates that Soy Protein Decreases Circulating LDL and Total Cholesterol Concentrations in Adults.. J Nutr, 2019.
  2. Soya products and serum lipids: a meta-analysis of randomised controlled trials.. Br J Nutr, 2015.
  3. The effects of isolated soy protein, isolated soy isoflavones and soy protein containing isoflavones on serum lipids in postmenopausal women: A systematic review and meta-analysis.. Crit Rev Food Sci Nutr, 2020.
  4. Use of Plant-Based Therapies and Menopausal Symptoms: A Systematic Review and Meta-analysis.. JAMA, 2016.
  5. Phytoestrogens for menopausal vasomotor symptoms.. Cochrane Database Syst Rev, 2013.
  6. Randomized controlled trial of whole soy and isoflavone daidzein on menopausal symptoms in equol-producing Chinese postmenopausal women.. Menopause, 2014.
  7. Soy intake and breast cancer risk: a prospective study of 300,000 Chinese women and a dose-response meta-analysis.. Eur J Epidemiol, 2020.
  8. Cumulative Meta-Analysis of the Soy Effect Over Time.. J Am Heart Assoc, 2019.
  9. Quantitative efficacy of soy isoflavones on menopausal hot flashes.. Br J Clin Pharmacol, 2015.
  10. Soy germ isoflavones improve menopausal symptoms but have no effect on blood lipids in early postmenopausal Chinese women: a randomized placebo-controlled trial.. Menopause, 2012.
  11. Effects of Soy Protein Containing of Isoflavones and Isoflavones Extract on Plasma Lipid Profile in Postmenopausal Women as a Potential Prevention Factor in Cardiovascular Diseases: Systematic Review and Meta-Analysis of Randomized Controlled Trials.. Nutrients, 2021.
  12. Assessing the combined effects of Black Cohosh, Soy Isoflavones, and SDG Lignans on menopausal symptoms: a randomized, double-blind, placebo-controlled clinical trial.. Eur J Nutr, 2025.
  13. Efficacy and Safety of a Standardized Soy and Hop Extract on Menopausal Symptoms: A 12-Week, Multicenter, Randomized, Double-Blind, Placebo-Controlled Clinical Trial.. J Altern Complement Med, 2021.
  14. The effect of a randomized 12-week soy drink intervention on everyday mood in postmenopausal women.. Menopause, 2019.
  15. The effect of soy isoflavones given to women in the climacteric period on menopausal symptoms and quality of life: Systematic review and meta-analysis of randomized controlled trials.. Explore (NY), 2024.
  16. Soy and isoflavones consumption and breast cancer survival and recurrence: a systematic review and meta-analysis.. Eur J Nutr, 2019.
  17. The effect of soy phytoestrogen supplementation on thyroid status and cardiovascular risk markers in patients with subclinical hypothyroidism: a randomized, double-blind, crossover study.. J Clin Endocrinol Metab, 2011.
  18. Evaluation of Levothyroxine Bioavailability after Oral Administration of a Fixed Combination of Soy Isoflavones in Post-menopausal Female Volunteers.. Drug Res (Stuttg), 2016.
  19. Interference or Noninterference Between Soy and Levothyroxine: That Is the Question. A Narrative Review of Literature.. Endocr Pract, 2023.