Functional Foods · Legume foods
Soy Foods
Glycine max · also called Soy, soya, soybeans
Soy foods are made from the seeds of the soybean plant. They give plant protein, fibre and iron. Soy protein in place of other protein lowers LDL cholesterol a little in trials, and soy foods went with less heart disease in large observational studies, which cannot prove cause. The main cautions are soy allergy, MAOI antidepressants, thyroid medicine questions and soy in pregnancy above food amounts.
General information, not medical advice. Last substantive update · Not medically reviewed. A named clinician has not signed off on this page. How this page is made
About Soy Foods
Soy foods are foods made from soybeans, a legume. They are a source of plant protein, fibre and iron. They are foods, not proven remedies: the cholesterol findings come from studies of soy protein, and the heart disease findings are observational.
What soy foods are
Soy foods come from the seeds of the soybean plant, Glycine max, in the legume family (GBIF). NCCIH names tofu, miso, tempeh, edamame and soy milk as common soy foods, and says soy is also sold as supplements containing soy protein or isoflavones, plant compounds similar in structure to the hormone estrogen.
Tofu, edamame, soy milk, tempeh, miso, natto and soy sauce each have their own page here. This page covers soy foods in general, using whole cooked soybeans for the nutrition figures.
What is in cooked soybeans
USDA data for soybeans, cooked and boiled without salt, per 100 g: 172 kcal, 18.21 g protein, 8.97 g fat (1.297 g saturated), 8.36 g carbohydrate, 6.0 g fibre, 102 mg calcium, 5.14 mg iron, 86 mg magnesium, 245 mg phosphorus, 515 mg potassium and 1 mg sodium.
One cup (172 g) has about 296 kcal, 31.3 g protein, 10.3 g fibre, 8.8 mg iron and 886 mg potassium. Raw dry soybeans are far more concentrated per 100 g (446 kcal, 36.49 g protein) because cooked beans hold water. These are nutrient facts; how much of the iron and other minerals the body takes up was not studied in the sources read.
What the research shows
The firmest findings are about soy protein, not whole soy foods. Across 43 trials, soy protein in place of other protein (mostly dairy) lowered LDL by about 4.76 mg/dL and total cholesterol by 6.41 mg/dL. An older analysis found falls of 4.2% to 5.5% depending on trial design. These are protein swaps, and the changes are small.
Heart disease findings are observational. A 2017 pooled analysis found soy intake went with 16% less cardiovascular disease and 17% less coronary heart disease, mainly in case-control studies and Asian populations, and no link for isoflavones alone. A 2024 pooled analysis of cohorts linked higher isoflavone intake with less coronary heart disease. In about 210,700 US adults, tofu once a week or more went with 18% lower risk, while soy milk was not significantly linked. These studies can show a link, not cause.
Isoflavones have mostly been tested as preparations. They gave a small, mixed benefit for menopause symptoms and no significant effect on hot flushes. In 40 trials in postmenopausal women they did not significantly change womb lining, vaginal cells, FSH or estradiol. Breast cancer links are observational.
The US label claim
US rules allow a labelled health claim linking diets low in saturated fat and cholesterol that include soy protein with a lower risk of coronary heart disease. The rule limits the wording and does not allow a stated amount of risk reduction. It is a labelling rule for certain foods, not a personal target, and we did not check how it is enforced today.
Food versus supplements
The cholesterol results are for soy protein products. The heart disease results are for soy foods and isoflavones eaten in the diet. The menopause, hormone and breast cancer results are mostly for isoflavone preparations or pooled foods and isoflavones. NCCIH says soy supplements have not been shown to lower breast cancer risk and that effects may differ between soy products. Soy protein powders and isoflavone supplements are different products from whole soy foods.
At a glance
Traditional uses history, not proof
- Eaten as a staple food in many cuisines, in forms such as tofu, tempeh, miso, edamame and soy milk
- Long use as food is not proof that it treats any condition
Studied for research
- Protein, fibre, iron and minerals, high certainty for the nutrient content of cooked soybeans
- Cholesterol, moderate certainty for soy protein swapped for other protein (not whole beans alone)
- Heart disease, low certainty (observational)
- Menopause symptoms, mixed (isoflavone preparations, not foods)
- Hormone and estrogen-like measures, moderate certainty of no clear estrogen-like effect (isoflavone studies)
- Breast cancer risk and survival, low certainty (observational)
- Bone, blood pressure and type 2 diabetes, insufficient evidence here (agency statements only)
Main compounds
- Soy protein
- Dietary fibre
- Iron, magnesium, phosphorus, potassium and manganese
- Isoflavones (genistein, daidzein, glycitein)
Common forms
- Whole mature soybeans, boiled without salt (USDA values read)
- Raw dry soybeans (USDA values read)
- Tofu, edamame, soy milk, tempeh, miso, natto and soy sauce are different foods with their own pages
- Soy protein powders and isoflavone supplements are different products and are not covered
Research links: 2019 review: soy protein and LDL cholesterol (43 trials) · 2020 study: isoflavones, tofu and coronary heart disease · 2023 review: soy and levothyroxine · Research Library · Genes & Biomarkers Library
What it is and its history
- Accepted scientific name
- Glycine max (L.) Merr.
- Naming authority
- (L.) Merr. (GBIF accepted; the plant whose seeds make soy foods)
- Common names
- Soy (English); Soybean (English); Soya (English); Soja (Spanish)
- Family or group
- Fabaceae (the legume or pea family), as given by GBIF.
- Classification
- Plantae > Tracheophyta > Magnoliopsida > Fabales > Fabaceae > Glycine > Glycine max
- Native range
- Not verified from a source read. NCCIH says soybeans have long been cultivated in Asia and are now also produced elsewhere, including the United States.
- Habitat
- Not verified from a source read.
- What it looks like
- Roots: Not verified.; Stems: Not verified.; Leaves: Not verified.; Flowers: Not verified.; Fruit: Soy foods come from the mature seeds (and, for edamame, young green seeds). USDA gives a household portion of 1 cup (172 g) for cooked, boiled soybeans.
- Cultivation
- Not verified from a source read beyond the NCCIH statement above.
- Harvest and processing
- Not verified from a source read. NCCIH lists tofu, miso, tempeh, edamame and soy milk as common soy foods.
- Look-alikes and adulterants
- Name: Tofu, edamame, soy milk, tempeh, miso, natto and soy sauce; Note: Soy foods with their own pages; they differ in nutrients, tyramine and processing.; Name: Soy protein and isoflavone supplements; Note: Supplements used in many trials; NCCIH says effects may vary by type of soy product.
Photographs
What is inside, and how it may work
What it contains and how those compounds act in cells and animals. Laboratory and animal mechanisms are not proven effects in people.
Main compounds
| Compound | Family | Where it is concentrated | Activity studied | Level of evidence |
|---|---|---|---|---|
| Soy protein | protein | Seed USDA per 100 g: 18.21 g cooked, boiled; 36.49 g raw dry seeds | In pooled trials, soy protein in place of other protein lowered LDL cholesterol a little; it is also the source of the soy allergen. 24 23 2 | Human data |
| Dietary fibre | fibre | Seed USDA per 100 g: 6.0 g cooked; 9.3 g raw dry seeds | A nutrient fact; no fibre-specific trial was read. 24 23 | Human data |
| Iron | mineral | Seed USDA per 100 g: 5.14 mg cooked; 15.7 mg raw dry seeds | Absorption from soybeans was not studied in the sources read. 24 23 | Human data |
| Genistein PubChem 5280961 | isoflavone | Seed Not read. | NCCIH describes isoflavones as compounds similar in structure to estrogen. 22 20 | Human data |
| Daidzein PubChem 5281708 | isoflavone | Seed Not read. | A soybean isoflavone; identity checked in PubChem only. 22 | Lab |
| Glycitein PubChem 5317750 | isoflavone | Seed Not read. | A soybean isoflavone; identity checked in PubChem only. 22 | Lab |
| Tyramine | amine | Some fermented or stored soy products Not read for soy foods. | NCCIH reports dangerously high blood pressure with high-tyramine soy products and MAOIs; a 2018 review says modern foods contain much less tyramine. 20 5 | Human data |
Mechanisms, receptors and pathways
| Target or pathway | Gene or receptor | What was found | Level |
|---|---|---|---|
| Estrogen receptors and isoflavones | Not specified in the sources read | NCCIH describes isoflavones as similar in structure to estrogen. The 2025 authors suggest, from trial results showing no estrogen-like effect on four measures, that isoflavones likely act as selective estrogen receptor modulators. This is their interpretation, not a tested mechanism. 20 13 | Human data |
| LDL cholesterol lowering by soy protein | Not specified in the sources read | No mechanism was read. The trials show a small fall in LDL when soy protein replaces other protein; NCCIH says isoflavones may not have the same effect. 2 20 | Human data |
| Thyroid hormone absorption | Not specified in the sources read | A 2006 review says soy foods may reduce absorption of thyroid hormone tablets and describes a theoretical concern from lab and animal data when iodine intake is low; this is not a proven mechanism in people. 9 | Human data |
Absorption, metabolism and elimination
- Absorption
- Not found for soy nutrients or isoflavones in the sources read.
- Distribution
- Not found.
- Metabolism
- Not found.
- Elimination
- Not found.
- Bioavailability
- Not established for soy iron, calcium or isoflavones in the sources read.
Isolated compounds versus whole extracts
The heart disease results are for soy foods and isoflavones eaten in the diet. The cholesterol results are for soy protein products compared with other protein, mostly dairy. The menopause, hormone and breast cancer results are mostly for isoflavone preparations or pooled foods and isoflavones. Soy protein powders and isoflavone supplements are different products from whole soy foods, and NCCIH says effects may differ between soy products.
Nutritional composition
Nutrition from USDA FoodData Central (SR Legacy, April 2018 release; values read 2026-10-26 from the repo's saved copy of the data because the public API key is rate-limited). Soybeans, mature, cooked, boiled, without salt (FDC 174271), per 100 g: 172 kcal, 18.21 g protein, 8.97 g fat (1.297 g saturated), 8.36 g carbohydrate (3.0 g sugars), 6.0 g fibre, 102 mg calcium, 5.14 mg iron, 86 mg magnesium, 245 mg phosphorus, 515 mg potassium, 1 mg sodium, 1.15 mg zinc, 0.824 mg manganese, 0.407 mg copper, 54 micrograms folate (DFE), 19.2 micrograms vitamin K and no cholesterol. One cup (172 g, the 100 g values multiplied by 1.72): about 296 kcal, 31.3 g protein, 15.4 g fat, 14.4 g carbohydrate, 10.3 g fibre, 175 mg calcium, 8.8 mg iron, 148 mg magnesium, 421 mg phosphorus, 886 mg potassium, 1.4 mg manganese and 93 micrograms folate. Raw dry seeds (FDC 174270), per 100 g: 446 kcal, 36.49 g protein, 19.94 g fat, 30.16 g carbohydrate, 9.3 g fibre, 277 mg calcium, 15.7 mg iron and 280 mg magnesium; raw is higher per 100 g because cooked beans hold water. Tofu, soy milk, tempeh, miso, natto and soy sauce differ and have their own pages.
1 high certainty2 moderate certainty1 mixed findings3 low certainty1 not enough evidence
What was looked at
The 8 benefits and uses checked for Soy Foods, each with how strong the evidence is. Tap one to open it.
- Protein, fibre, iron and minerals (nutrient content of cooked soybeans)High certainty
- Cholesterol (soy protein in place of other protein)Moderate certainty
- Heart disease and stroke (observational)Low certainty
- Menopause symptoms (isoflavone preparations)Mixed findings
- Hormone and estrogen-like effects (women)Moderate certainty
- Breast cancer risk (observational)Low certainty
- Breast cancer survival and recurrence (observational)Low certainty
- Bone health, blood pressure and type 2 diabetes (agency statements only)Not enough evidence
Lab markers tracked in the studies
LDL cholesterolTotal cholesterolHDL cholesterol and triglyceridesCoronary heart disease (heart attack and coronary death)Estradiol (an estrogen hormone)FSH and LH (pituitary hormones)Endometrial thickness (womb lining)Hot flushes and sweatingOverall survival after breast cancer diagnosis
What is Soy Foods good for?
The main studied uses and how strong the human evidence is for each. Most results are for soy protein or isoflavones in general, not for one soy food on its own.
Benefits, one by one
Each card is a research question, not a promise. Tap a goal to filter. Open a card to see the studies, doses and limits.
Protein, fibre, iron and minerals (nutrient content of cooked soybeans)
High certaintyCooked, boiled soybeans without salt have 18.21 g of protein, 6.0 g of fibre and 5.14 mg of iron per 100 g (USDA). One cup (172 g) has about 296 kcal, 31.3 g of protein, 10.3 g of fibre and 8.8 mg of iron. This describes the whole bean, not tofu, soy milk or other soy foods, which differ.
2 studiesWhole mature soybeans, boiled without salt (USDA item 174271), and ra…
Studies, doses and limits
What the trials found
Nutrient values come from the USDA FoodData Central database (SR Legacy). No human trial was read for this item. How much of the iron, calcium and other minerals the body takes up from soybeans was not studied in the sources read.
Results
Soybeans are a source of plant protein, fibre, iron, magnesium, phosphorus, potassium and manganese on paper.
Effect sizes as reported
Per 100 g cooked: 172 kcal; protein 18.21 g; fat 8.97 g (1.297 g saturated); carbohydrate 8.36 g; fibre 6.0 g; iron 5.14 mg; calcium 102 mg; magnesium 86 mg. Per 100 g raw dry seeds: 446 kcal; protein 36.49 g; fibre 9.3 g; iron 15.7 mg.
Why this rating
High for the nutrient content (a reference database). Nothing here is a health effect, and absorption was not shown.
Form and dose studied
Whole mature soybeans, boiled without salt (USDA item 174271), and raw dry seeds (174270). Processed soy foods differ.
Limits
One USDA entry for one preparation. Values vary with variety and cooking. Does not cover tofu, soy milk, tempeh, miso, natto or soy sauce, which have their own pages.
Why researchers looked
Soybeans are a protein-rich legume and a staple food in many countries.
Traditional use
Soy foods are eaten in many cuisines. Long use as food is not proof that they treat any condition.
Proposed mechanism Nutrient database
Not applicable. This is a nutrient fact, not a treatment effect.
A proposed mechanism does not show that the effect happens in people.
Soy is a major food allergen. See the Safety tab.
Cholesterol (soy protein in place of other protein)
Moderate certaintyIn trials, soy protein in place of other protein lowered LDL ("bad") cholesterol by about 4.76 mg/dL, roughly 3 to 4%. The trials used soy protein products, often compared with dairy protein, so this is a small effect of a protein swap, not a result for whole soybeans on their own.
4 studiesSoy protein as isolated protein, soy foods, soy milk or mixtures, mos…
Studies, doses and limits
What the trials found
A 2019 pooled analysis of 43 trials (41 with LDL data) found soy protein lowered LDL by 4.76 mg/dL and total cholesterol by 6.41 mg/dL compared with non-soy protein. An older 2011 analysis of 43 trials found LDL falls of 5.5% in the higher-quality parallel trials and 4.2% in crossover trials, with higher HDL and lower triglycerides in the parallel trials.
Results
A small, fairly consistent fall in LDL when soy protein replaces other protein. About 75% of trials showed a fall, but only a minority were individually significant.
Effect sizes as reported
2019: LDL -4.76 mg/dL (95% CI -6.71 to -2.80); total cholesterol -6.41 mg/dL (-9.30 to -3.52). 2011: LDL -0.23 mmol/L (5.5%) in parallel and -0.16 mmol/L (4.2%) in crossover trials; HDL +3.2%; triglycerides -10.7% (parallel only).
Why this rating
Moderate: two pooled analyses of randomised trials agree on a small fall. Held back by short trials, moderate to high differences between trials (I2 55%), mostly soy protein products rather than whole beans, and industry links (see Evidence tab). Our grading; the 2019 abstract gives no GRADE rating.
Form and dose studied
Soy protein as isolated protein, soy foods, soy milk or mixtures, mostly compared with dairy protein. Trial amounts are not advice.
Who was studied
Adults, baseline LDL 110 to 201 mg/dL in the 2019 analysis.
Limits
Short trials (median 6 weeks). It describes replacing other protein, not adding soy to an unchanged diet. Whole soybeans were not tested alone.
Why researchers looked
Soy protein has been tested against other proteins for blood cholesterol for many years.
Traditional use
Soy foods are eaten in many cuisines. Long use as food is not proof that they treat any condition.
Proposed mechanism Authoritative guidance
Not shown for whole soy foods. NCCIH says soy protein in place of other proteins may lower cholesterol to a small extent and that isoflavones may not have the same effect.
A proposed mechanism does not show that the effect happens in people.
See the Safety tab for soy allergy and medicine cautions.
Heart disease and stroke (observational)
Low certaintyIn large groups of people followed over time, those who ate more soy foods or soy isoflavones had somewhat less heart disease. In a 2017 pooled analysis, soy intake went with 17% lower coronary heart disease and 16% lower cardiovascular disease, mainly in case-control studies and in Asian populations. In three US cohorts, tofu once a week went with 18% lower coronary heart disease. These are links, not proof.
3 studiesSoy foods as eaten (tofu, soy milk and others) and estimated isoflavo…
Studies, doses and limits
What the trials found
A 2017 pooled analysis (10 cohort and 7 case-control studies, 17,269 events) linked soy intake with lower cardiovascular disease (relative risk 0.84), stroke (0.82) and coronary heart disease (0.83); isoflavones alone were not linked. A 2024 pooled analysis of cohorts linked higher isoflavone intake with lower coronary heart disease (0.92; 0.89 in Western populations). A US analysis of three cohorts (about 210,700 people) linked tofu weekly with lower coronary heart disease (HR 0.82), while soy milk was not significantly linked.
Results
Consistent small links in observational studies; nothing from trials with heart attacks or strokes as the outcome.
Effect sizes as reported
Soy and CVD SRR 0.84 (0.75 to 0.94); stroke 0.82 (0.68 to 0.99); CHD 0.83 (0.72 to 0.95). Isoflavones and CHD RR 0.92 (0.85 to 0.99). US cohorts: tofu HR 0.82 (0.70 to 0.95); isoflavones HR 0.87 (0.81 to 0.94).
Why this rating
Low: observational studies cannot show cause, differences between studies are large (I2 71% in 2017), the 2017 link is mainly in case-control studies and Asian populations, and the 2017 analysis found no link for isoflavones alone while later analyses did.
Form and dose studied
Soy foods as eaten (tofu, soy milk and others) and estimated isoflavone intake from food questionnaires.
Who was studied
Adults in Asian, Western and US cohorts.
Limits
Food questionnaires; other lifestyle differences; no trial of soy foods on heart attacks or strokes was read.
Why researchers looked
Soy foods are eaten daily in some countries with lower heart disease rates, so researchers compared eating patterns with heart outcomes.
Traditional use
Soy foods are eaten in many cuisines. Long use as food is not proof that they treat any condition.
Proposed mechanism Not established
Not established. Differences in other foods and lifestyle may explain part of the link.
A proposed mechanism does not show that the effect happens in people.
See the Safety tab.
Menopause symptoms (isoflavone preparations)
Mixed findingsA 2025 pooled analysis found a small overall improvement in menopause symptoms with soy isoflavone preparations, but no significant effect on hot flushes or sweating. NCCIH calls the hot flash effect small and inconsistent. The studies used isoflavone preparations, not whole soy foods.
2 studiesIsoflavone preparations, not whole soy foods.
Studies, doses and limits
What the trials found
The 2025 analysis (12 studies; 7 with 533 participants for overall symptoms) found a small overall benefit (Hedges' g -0.25) and benefits on headache, psychosocial symptoms, palpitation and depression scores, but no significant effect on hot flushes, sweating, insomnia, vasomotor symptoms, fatigue or physical symptoms. The authors urged caution because of small samples.
Results
Small, mixed effects; hot flushes, the usual target, did not improve significantly.
Effect sizes as reported
Overall Hedges' g -0.25 (95% CI -0.42 to -0.08); depression -0.72 (-1.17 to -0.28); hot flushes not significant.
Why this rating
Mixed: some symptom scores improved, hot flushes did not, samples were small and results are not fully consistent (NCCIH).
Form and dose studied
Isoflavone preparations, not whole soy foods.
Who was studied
Perimenopausal women.
Limits
Small studies, many scales, preparations rather than foods.
Why researchers looked
Isoflavones in soy are similar in structure to estrogen, so researchers asked whether they ease menopause symptoms.
Traditional use
Soy foods are eaten in many cuisines. Long use as food is not proof that they treat any condition.
Proposed mechanism Authoritative guidance
Not established. NCCIH describes isoflavones as similar in structure to estrogen.
A proposed mechanism does not show that the effect happens in people.
See the Safety tab.
Hormone and estrogen-like effects (women)
Moderate certaintyIn 40 trials in postmenopausal women, isoflavones had no significant effect on womb lining, vaginal cells, FSH or estradiol. In premenopausal women an older analysis found lower FSH and LH and a menstrual cycle about one day longer, with no change in estradiol; the authors said the clinical meaning was undetermined.
3 studiesSoy isoflavone preparations, soy protein and soy foods pooled.
Studies, doses and limits
What the trials found
A 2025 pooled analysis of 40 randomised trials (3,285 postmenopausal women, median 75 mg isoflavones a day for 24 weeks) found no significant effect on endometrial thickness, vaginal maturation index, FSH or estradiol; the authors rate the certainty high to moderate. A 2009 analysis of 47 trials found no change in estradiol, estrone or SHBG in premenopausal women, lower FSH and LH, and a cycle about 1 day longer; in postmenopausal women there was a small non-significant estradiol rise of about 14% (p = 0.07).
Results
No clear estrogen-like effect on the measures tested in postmenopausal women; small hormone shifts in premenopausal women of unknown clinical meaning.
Effect sizes as reported
2025: endometrial thickness -0.22 mm (-0.45 to 0.01); FSH -0.02 IU/L (-2.39 to 2.35); estradiol +1.61 pmol/L (-1.17 to 4.38). 2009: cycle +1.05 days (0.13 to 1.97).
Why this rating
Moderate: the 2025 authors rate the certainty high to moderate for postmenopausal women; the premenopausal data are older and of unclear meaning. The 2025 analysis was funded in part by a soy industry body and has an author from a soy industry-linked institute (see Evidence tab). Our grading.
Form and dose studied
Soy isoflavone preparations, soy protein and soy foods pooled.
Who was studied
Postmenopausal women (2025); pre- and postmenopausal women (2009).
Limits
Four measures; not about men, children or breast tissue; mostly preparations rather than foods.
Why researchers looked
Isoflavones look like estrogen in structure, so people ask whether soy acts like the hormone.
Traditional use
Soy foods are eaten in many cuisines. Long use as food is not proof that they treat any condition.
Proposed mechanism Authors interpretation
The 2025 authors suggest, from the absence of effect on four measures, that isoflavones likely act as selective estrogen receptor modulators. This is their interpretation, not a tested mechanism.
A proposed mechanism does not show that the effect happens in people.
See the Safety tab on hormone-sensitive conditions.
Breast cancer risk (observational)
Low certaintyIn prospective studies, women who ate more soy isoflavones had less breast cancer. NCCIH says this is seen in Asian and Asian-American women, that Western intakes may be too low to see it, and that soy supplements have not been shown to reduce risk. These are links, not proof.
2 studiesDietary isoflavones and soy intake from food questionnaires; suppleme…
Studies, doses and limits
What the trials found
A 2022 pooled analysis of prospective studies found an inverse link between isoflavone intake and breast cancer in pre- and postmenopausal women; the abstract gives no numbers or study count. NCCIH says observational studies in Asian and Asian-American women link higher soy intake with lower risk.
Results
A consistent inverse link in observational studies; no trial was read.
Effect sizes as reported
No numbers in the abstract read.
Why this rating
Low: observational, abstract without numbers, and the authors' wording that isoflavones "can reduce" risk goes beyond what such studies can show.
Form and dose studied
Dietary isoflavones and soy intake from food questionnaires; supplements are not shown to reduce risk (NCCIH).
Who was studied
Pre- and postmenopausal women, mainly in Asian populations.
Limits
Observational; confounding; NCCIH says Western intakes may be too low to see the link.
Why researchers looked
Breast cancer rates differ between countries with high and low soy intake, and isoflavones act on estrogen receptors.
Traditional use
Soy foods are eaten in many cuisines. Long use as food is not proof that they treat any condition.
Proposed mechanism Hypothesis
Not established. The 2022 authors describe isoflavones as imitating estrogen by binding estrogen receptors; no tested mechanism is given.
A proposed mechanism does not show that the effect happens in people.
Ask your care team if you have had breast cancer.
Breast cancer survival and recurrence (observational)
Low certaintyIn women diagnosed with breast cancer, soy intake before diagnosis went with slightly better overall survival (HR 0.84). After diagnosis there was no significant link with overall or breast-cancer-specific survival. Isoflavone intake before and after diagnosis was linked with less recurrence. The authors call the evidence limited.
1 studiesSoy foods and isoflavones from food questionnaires.
Studies, doses and limits
What the trials found
A 2019 pooled analysis of 12 articles (37,275 women with breast cancer): pre-diagnosis soy and isoflavone intake, overall survival HR 0.84 (0.71 to 0.98), breast-cancer-specific survival HR 0.89 (0.74 to 1.07, not significant); post-diagnosis, overall survival HR 0.80 (0.62 to 1.04) and specific survival HR 0.83 (0.64 to 1.07), neither significant.
Results
A small possible benefit for pre-diagnosis intake; no clear effect after diagnosis; not a basis for personal decisions.
Effect sizes as reported
Pre-diagnosis overall survival HR 0.84; post-diagnosis HR 0.80 (not significant).
Why this rating
Low: observational studies; the authors say the evidence is limited; the post-diagnosis results are not significant.
Form and dose studied
Soy foods and isoflavones from food questionnaires.
Who was studied
Women with breast cancer.
Limits
Observational; cannot guide an individual.
Why researchers looked
Women with breast cancer ask whether soy foods are safe and whether they affect outcomes.
Traditional use
Soy foods are eaten in many cuisines. Long use as food is not proof that they treat any condition.
Proposed mechanism Not established
Not established.
A proposed mechanism does not show that the effect happens in people.
Ask your cancer care team how soy fits your care.
Bone health, blood pressure and type 2 diabetes (agency statements only)
Not enough evidenceNCCIH says soy isoflavones probably help bone density after menopause, may modestly lower blood pressure, and that high-soy diets may go with lower type 2 diabetes risk. We did not read the studies behind these statements, so the evidence here is rated insufficient.
1 studiesIsoflavones (bone, blood pressure) and soy-rich diets (diabetes), per…
Studies, doses and limits
What the trials found
NCCIH's fact sheet (last updated April 2025) makes these statements. It also says it is uncertain whether soy improves blood sugar control in people who already have type 2 diabetes, and that results on thinking and memory conflict. The studies behind each statement were not read here.
Results
Not assessed.
Effect sizes as reported
No numbers read.
Why this rating
Only a secondary agency summary was read; no study was checked.
Form and dose studied
Isoflavones (bone, blood pressure) and soy-rich diets (diabetes), per NCCIH.
Who was studied
Postmenopausal women (bone).
Limits
Secondary source only.
Why researchers looked
NCCIH lists these among the possible effects of soy.
Traditional use
Soy foods are eaten in many cuisines. Long use as food is not proof that they treat any condition.
Proposed mechanism Not established
Not described in the source read.
A proposed mechanism does not show that the effect happens in people.
None specific.
Connections to the rest of health
How Soy Foods connects to the rest of our health knowledge graph. Every link says what kind of connection it is. A safety link (for example to the liver) is a warning, not a benefit. A study that merely mentions a topic never creates a benefit link.
Explore every connection: goals, body systems, organs, symptoms, genes
A. Wellness goals
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Preventive Wellness | High certainty | Protein, fibre, iron and minerals (nutrient content of cooked soybeans): Cooked, boiled soybeans without salt have 18.21 g of protein, 6.0 g of fibre and 5.14 mg of iron per 100 g (USDA). One cup (172 g) has about 296 kcal, 31.3 g of protein, 10.3 g of fibre and 8.8 mg of iron. This describes the whole bean, not tofu, soy milk or other soy foods, which differ. | 24 23 | |
| Cholesterol Balance | Demonstrated clinical effect | Moderate certainty | Cholesterol (soy protein in place of other protein): In trials, soy protein in place of other protein lowered LDL ("bad") cholesterol by about 4.76 mg/dL, roughly 3 to 4%. The trials used soy protein products, often compared with dairy protein, so this is a small effect of a protein swap, not a result for whole soybeans on their own. | 2 1 20 16 |
| Heart Health | Demonstrated clinical effect | Moderate certainty | Cholesterol (soy protein in place of other protein): In trials, soy protein in place of other protein lowered LDL ("bad") cholesterol by about 4.76 mg/dL, roughly 3 to 4%. The trials used soy protein products, often compared with dairy protein, so this is a small effect of a protein swap, not a result for whole soybeans on their own. | 2 1 20 16 |
| Heart Health | Low certainty | Heart disease and stroke (observational): In large groups of people followed over time, those who ate more soy foods or soy isoflavones had somewhat less heart disease. In a 2017 pooled analysis, soy intake went with 17% lower coronary heart disease and 16% lower cardiovascular disease, mainly in case-control studies and in Asian populations. In three US cohorts, tofu once a week went with 18% lower coronary heart disease. These are links, not proof. | 15 10 8 | |
| Menopause Support | Mixed findings | Menopause symptoms (isoflavone preparations): A 2025 pooled analysis found a small overall improvement in menopause symptoms with soy isoflavone preparations, but no significant effect on hot flushes or sweating. NCCIH calls the hot flash effect small and inconsistent. The studies used isoflavone preparations, not whole soy foods. | 7 20 | |
| Womens Wellness | Mixed findings | Menopause symptoms (isoflavone preparations): A 2025 pooled analysis found a small overall improvement in menopause symptoms with soy isoflavone preparations, but no significant effect on hot flushes or sweating. NCCIH calls the hot flash effect small and inconsistent. The studies used isoflavone preparations, not whole soy foods. | 7 20 | |
| Womens Wellness | Moderate certainty | Hormone and estrogen-like effects (women): In 40 trials in postmenopausal women, isoflavones had no significant effect on womb lining, vaginal cells, FSH or estradiol. In premenopausal women an older analysis found lower FSH and LH and a menstrual cycle about one day longer, with no change in estradiol; the authors said the clinical meaning was undetermined. | 13 6 20 | |
| Menopause Support | Moderate certainty | Hormone and estrogen-like effects (women): In 40 trials in postmenopausal women, isoflavones had no significant effect on womb lining, vaginal cells, FSH or estradiol. In premenopausal women an older analysis found lower FSH and LH and a menstrual cycle about one day longer, with no change in estradiol; the authors said the clinical meaning was undetermined. | 13 6 20 | |
| Womens Wellness | Low certainty | Breast cancer risk (observational): In prospective studies, women who ate more soy isoflavones had less breast cancer. NCCIH says this is seen in Asian and Asian-American women, that Western intakes may be too low to see it, and that soy supplements have not been shown to reduce risk. These are links, not proof. Breast cancer survival and recurrence (observational): In women diagnosed with breast cancer, soy intake before diagnosis went with slightly better overall survival (HR 0.84). After diagnosis there was no significant link with overall or breast-cancer-specific survival. Isoflavone intake before and after diagnosis was linked with less recurrence. The authors call the evidence limited. | 3 20 11 | |
| Preventive Wellness | Low certainty | Breast cancer risk (observational): In prospective studies, women who ate more soy isoflavones had less breast cancer. NCCIH says this is seen in Asian and Asian-American women, that Western intakes may be too low to see it, and that soy supplements have not been shown to reduce risk. These are links, not proof. | 3 20 | |
| Bone Health | Not enough evidence | Bone health, blood pressure and type 2 diabetes (agency statements only): NCCIH says soy isoflavones probably help bone density after menopause, may modestly lower blood pressure, and that high-soy diets may go with lower type 2 diabetes risk. We did not read the studies behind these statements, so the evidence here is rated insufficient. | 20 | |
| Heart Health | Not enough evidence | Bone health, blood pressure and type 2 diabetes (agency statements only): NCCIH says soy isoflavones probably help bone density after menopause, may modestly lower blood pressure, and that high-soy diets may go with lower type 2 diabetes risk. We did not read the studies behind these statements, so the evidence here is rated insufficient. | 20 | |
| Blood Sugar Balance | Not enough evidence | Bone health, blood pressure and type 2 diabetes (agency statements only): NCCIH says soy isoflavones probably help bone density after menopause, may modestly lower blood pressure, and that high-soy diets may go with lower type 2 diabetes risk. We did not read the studies behind these statements, so the evidence here is rated insufficient. | 20 |
B. Body systems
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Digestive System | Biological association | High certainty | Studied for: Protein, fibre, iron and minerals (nutrient content of cooked soybeans) | 24 23 |
| Musculoskeletal System | Biological association | High certainty | Studied for: Protein, fibre, iron and minerals (nutrient content of cooked soybeans) Studied for: Bone health, blood pressure and type 2 diabetes (agency statements only) | 24 23 20 |
| Cardiovascular System | Biological association | Moderate certainty | Studied for: Cholesterol (soy protein in place of other protein) Studied for: Heart disease and stroke (observational) | 2 1 20 16 15 10 8 |
| Reproductive System | Biological association | Mixed findings | Studied for: Menopause symptoms (isoflavone preparations) Studied for: Hormone and estrogen-like effects (women) | 7 20 13 6 3 11 |
| Endocrine System | Biological association | Mixed findings | Studied for: Menopause symptoms (isoflavone preparations) Studied for: Hormone and estrogen-like effects (women) | 7 20 13 6 |
C. Body parts and organs
E. Health conditions
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Food allergy | Adverse effect or risk | Documented risk | Soybeans are a major food allergen; challenge-verified soy allergy was about 0.3% in a European review. Soybeans are a major food allergen; about 0.3% of people in Europe had challenge-verified soy allergy. Preparation or compound: Soy protein |
17 12 |
| High cholesterol | Preliminary | Soy protein in place of other protein lowers LDL a little in pooled trials; not a treatment. Preparation or compound: Soy protein |
2 1 |
I. Biomarkers
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| LDL cholesterol | Biological association | Moderate certainty | Measured in trials: lowered. A lab change is not the same as a health benefit. | 2 1 |
| Total cholesterol | Biological association | Moderate certainty | Measured in trials: lowered. A lab change is not the same as a health benefit. | 2 |
| HDL cholesterol and triglycerides | Biological association | Low certainty | Measured in trials: HDL higher, triglycerides lower (parallel-design trials only). A lab change is not the same as a health benefit. | 1 |
| Coronary heart disease (heart attack and coronary death) | Biological association | Low certainty | Measured in trials: lower risk in observational studies. A lab change is not the same as a health benefit. | 8 15 10 |
| Estradiol (an estrogen hormone) | Biological association | Moderate certainty | Measured in trials: no significant change. A lab change is not the same as a health benefit. | 13 6 |
| FSH and LH (pituitary hormones) | Biological association | Low certainty | Measured in trials: FSH: no change after menopause; lower FSH and LH before menopause. A lab change is not the same as a health benefit. | 13 6 |
| Endometrial thickness (womb lining) | Biological association | Moderate certainty | Measured in trials: no significant change. A lab change is not the same as a health benefit. | 13 |
| Hot flushes and sweating | Biological association | Mixed findings | Measured in trials: no significant change. A lab change is not the same as a health benefit. | 7 20 |
| Overall survival after breast cancer diagnosis | Biological association | Low certainty | Measured in trials: pre-diagnosis intake: slightly better; post-diagnosis: no significant link. A lab change is not the same as a health benefit. | 11 |
K. Biological pathways
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Protein | Preliminary mechanism | Human | Cooked soybeans are a plant protein food by USDA data. | 24 |
| Isoflavones | Preliminary mechanism | Human | Compounds similar in structure to estrogen; studied for menopause symptoms, hormones, bone and breast cancer. | 20 22 |
| LDL cholesterol | Preliminary mechanism | Human | A small fall when soy protein replaces other protein in trials. | 2 1 |
L. Active compounds
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Soy protein | Biological association | Human | In pooled trials, soy protein in place of other protein lowered LDL cholesterol a little; it is also the source of the soy allergen. Preparation or compound: Seed |
24 23 2 |
| Dietary fibre | Biological association | Human | A nutrient fact; no fibre-specific trial was read. Preparation or compound: Seed |
24 23 |
| Iron | Biological association | Human | Absorption from soybeans was not studied in the sources read. Preparation or compound: Seed |
24 23 |
| Genistein | Biological association | Human | NCCIH describes isoflavones as compounds similar in structure to estrogen. Preparation or compound: Seed |
22 20 |
| Daidzein | Biological association | Lab | A soybean isoflavone; identity checked in PubChem only. Preparation or compound: Seed |
22 |
| Glycitein | Biological association | Lab | A soybean isoflavone; identity checked in PubChem only. Preparation or compound: Seed |
22 |
| Tyramine | Biological association | Human | NCCIH reports dangerously high blood pressure with high-tyramine soy products and MAOIs; a 2018 review says modern foods contain much less tyramine. Preparation or compound: Some fermented or stored soy products |
20 5 |
Each connection is stored with the ingredient, the connected record, the kind of connection, the evidence status, the supporting studies, the preparation or compound involved, and a review date (last reviewed October 26, 2026).
Evidence at a glance: what changed in 2 lab markers
Tap a number to show only those markers. Counts are markers, not people.
The evidence
The research centre for Soy Foods. Every record here was checked against PubMed or the publisher's page; we never list a study we have not verified.
Evidence by outcome
Bars show how many studies we found for each outcome, not how well it works. People are added up across trials only (reviews are not added, to avoid double counting).
How we rate evidence
High certainty
Several well-run trials or reviews agree; further research is unlikely to change the picture much.
Moderate certainty
Good trials point the same way, but some doubt remains.
Low certainty
Small, short or inconsistent trials. The finding could change with better research.
Very low certainty
Very little or very weak human data. Treat as a possibility only.
Mixed findings
Trials or reviews disagree with each other.
Not enough evidence
Not enough human research to say either way.
Evidence against
Good research found no benefit, or found harm.
We take the reviewers' own risk-of-bias and GRADE statements where they exist, and otherwise judge from study size, design, consistency, directness and whether a product matches what is sold. Many publications do not make evidence high. Method note: We rebuilt this page from our earlier soy summary, re-checked nutrition against saved USDA FoodData Central data, read the health agency pages (NCCIH, FDA, MedlinePlus, NIDDK) and the US food label rule, and re-read PubMed abstracts for the reviews and cohort studies cited. Only abstracts were read for studies, plus the funding statements of two analyses. Items we could not verify are flagged in the research gaps.
Study library: every study we checked 24
| Study | Design | People | Product, dose, length | Result |
|---|---|---|---|---|
| Anderson 2011 Soy protein effects on serum lipoproteins: a quality assessment and meta-analysis of randomized, controlled studies. J Am Coll Nutr · PMID 21730216 · DOI |
Systematic review meta analysis |
43 randomised trials (20 parallel-design, 23 crossover), searched 1996 to 2008 | Soy protein compared with non-soy protein Soy protein as used in the trials Median about 30 g of soy protein a day (trial description, not advice) 4 to 18 weeks · vs Non-soy protein |
Soy protein lowered LDL by 0.23 mmol/L (5.5%) in the higher-quality parallel trials and by 0.16 mmol/L (4.2%) in crossover trials. In parallel trials HDL was 3.2% higher and fasting triglycerides 10.7% lower than with the comparison diet. LDL -0.23 mmol/L (parallel) and -0.16 mmol/L (crossover); HDL +3.2% and triglycerides -10.7% (parallel only) (LDL parallel -0.28 to -0.18; crossover -0.22 to -0.11 mmol/L) Methods, limits and fundingOutcomes: Serum lipoproteins (LDL, HDL, triglycerides) Limitations: An older analysis (trials to 2008). Crossover trials were of lower quality and showed smaller effects. The abstract recommends 1 to 2 servings a day; that is the authors' advice and not repeated here. Funding and conflicts: The abstract does not state funding or conflicts; they were not read in full text. Read: abstract |
| Blanco Mejia 2019 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 · PMID 31006811 · DOI |
Systematic review meta analysis |
Adults in 43 randomised controlled trials (41 with LDL data); baseline LDL 110 to 201 mg/dL | Soy protein (isolated protein, soy foods, soy milk or mixtures) compared with non-soy protein Soy protein as used in the trials Median 25 g of soy protein a day (description of the trials, not advice) Median 6 weeks · vs Non-soy protein; per the full text, mostly dairy protein (72%) |
Soy protein lowered LDL cholesterol by 4.76 mg/dL and total cholesterol by 6.41 mg/dL compared with non-soy protein. About 75% of trials showed an LDL fall, though only a minority were individually significant. The authors call it a reduction of roughly 3 to 4%. No dose-response effect or publication bias was seen. LDL -4.76 mg/dL; total cholesterol -6.41 mg/dL (LDL -6.71 to -2.80; total cholesterol -9.30 to -3.52 mg/dL) Methods, limits and fundingOutcomes: LDL and total cholesterol Limitations: Short trials (median 6 weeks). Moderate to high differences between trials (I2 55% for LDL, 74% for total cholesterol). It describes a swap of protein sources, not an extra food. Many trials used soy protein products rather than whole soy foods. Funding and conflicts: Funded by the Canadian Institutes of Health Research (full text). One author is at the Soy Nutrition Institute, a soy industry-linked body. Of the 43 trials, 12 (27.9%) were funded by industry alone and 16 (37.2%) by industry together with an agency (full text). Registration: clinicaltrials.gov NCT03468127 Read: abstract |
| Boutas 2022 Soy Isoflavones and Breast Cancer Risk: A Meta-analysis. In Vivo · PMID 35241506 · DOI |
Systematic review meta analysis |
Prospective studies of pre- and postmenopausal women (study count and numbers not given in the abstract) | Dietary soy isoflavones Dietary intake · vs Lower intake |
Prospective studies showed an inverse link between the amount of isoflavones eaten and breast cancer in pre- and postmenopausal women. The authors conclude isoflavone intake can reduce risk; observational data cannot show that. Inverse association; no numbers in the abstract (Not given in the abstract) Methods, limits and fundingOutcomes: Breast cancer occurrence Limitations: Observational. The abstract gives no numbers or study counts, and the authors' causal wording goes beyond what observational data can show. Funding and conflicts: The authors declare no conflicts of interest (PubMed record). Read: abstract |
| Gatta 2023 Interference or Noninterference Between Soy and Levothyroxine: That Is the Question. A Narrative Review of Literature. Endocr Pract · PMID 37633413 · DOI |
Narrative review |
Case reports, case series and original studies on soy and levothyroxine (L-T4) absorption, to November 2022 | Soy products and soy isoflavones with levothyroxine Soy products and isoflavones |
Few data, mainly case reports, suggested soy might interfere with levothyroxine tablet absorption. The only prospective randomised crossover study found no difference when levothyroxine and soy isoflavones were taken together. Data on liquid levothyroxine were too thin for conclusions, though one double-blind placebo-controlled trial showed no impaired absorption. The authors conclude any interference seems to have little clinical impact. No pooled number (Not applicable) Methods, limits and fundingOutcomes: Levothyroxine absorption Limitations: A narrative review, not a systematic one. Case reports can show a possible problem but not how common it is. Funding and conflicts: The authors report nothing to disclose (PubMed record). Read: abstract |
| Gillman 2018 A reassessment of the safety profile of monoamine oxidase inhibitors: elucidating tired old tyramine myths. J Neural Transm (Vienna) · PMID 30255284 · DOI |
Narrative review |
Review of over 150 recent papers on the tyramine content of modern foods and the blood pressure response to tyramine in people on MAOIs | Tyramine in foods, including fish and soy sauces among many others Foods and condiments |
The author reports that few modern foods have problematically high tyramine, owing to starter cultures and hygiene rules, and that the risk of harm from the blood pressure response has been overstated. Fish and soy sauces were among the foods reviewed. People differ in sensitivity, so a doctor's judgement is still needed. The abstract gives no soy-food-specific numbers. No pooled number (Not applicable) Methods, limits and fundingOutcomes: Tyramine content of modern foods; blood pressure response Limitations: A single-author narrative review; the abstract does not name tofu or whole soy foods. Not a study of soy foods. Funding and conflicts: Funding is not stated in the abstract. Read: abstract |
| Hooper 2009 Effects of soy protein and isoflavones on circulating hormone concentrations in pre- and post-menopausal women: a systematic review and meta-analysis. Hum Reprod Update · PMID 19299447 · DOI |
Systematic review meta analysis |
47 randomised or residential crossover trials of 4 weeks or more (11 in premenopausal, 35 in postmenopausal and 1 in perimenopausal women), searched to December 2007 | Soy foods, soy protein or isoflavones Soy foods, soy protein or isoflavones Trial detail not given in the abstract 4 weeks or more · vs Control groups |
In premenopausal women soy or isoflavones did not change estradiol, estrone or SHBG but lowered FSH and LH by about 20% (standardised) and lengthened the menstrual cycle by about one day. In postmenopausal women there were no significant effects, with a small non-significant rise in estradiol of about 14% (p = 0.07). The authors say the clinical meaning of these modest changes is undetermined. Menstrual cycle +1.05 days; FSH and LH about -20% (SMD); postmenopausal estradiol about +14% (not significant) (Cycle length 0.13 to 1.97 days) Methods, limits and fundingOutcomes: Circulating estradiol, estrone, SHBG, FSH, LH, progesterone and thyroid hormones Limitations: An older analysis (trials to 2007). The abstract gives no result for thyroid hormones. Pools foods, protein and isoflavones together. Funding and conflicts: The abstract does not state funding (not read in full text). Read: abstract |
| Luan 2025 Effects of soy isoflavones on menopausal symptoms in perimenopausal women: a systematic review and meta-analysis. PeerJ · PMID 40718787 · DOI |
Systematic review meta analysis |
12 studies in the meta-analysis of perimenopausal women (7 studies, 533 participants for overall symptoms), searched October 2024 | Soy isoflavone preparations Isoflavone preparations, not whole soy foods · vs Control groups |
Isoflavones gave a small overall improvement in menopausal symptoms and in headache, psychosocial symptoms, palpitation and depression scores. They had no significant effect on hot flushes, sweating, insomnia, vasomotor symptoms, fatigue, paresthesia or physical symptoms. The authors urged caution because of small samples. Overall symptoms Hedges' g -0.25; headache -0.38; psychosocial -0.29; palpitation -0.42; depression -0.72 (Overall -0.42 to -0.08; hot flushes not significant) Methods, limits and fundingOutcomes: Menopausal symptoms (overall and by symptom) Limitations: Small studies; many symptom scales; isoflavone preparations rather than whole soy foods. Funding and conflicts: No competing interests declared by the authors (PubMed record). Read: abstract |
| Ma 2020 Isoflavone Intake and the Risk of Coronary Heart Disease in US Men and Women: Results From 3 Prospective Cohort Studies. Circulation · PMID 32200662 · DOI |
Prospective cohort study |
210700 74,241 women (Nurses' Health Study), 94,233 women (Nurses' Health Study II) and 42,226 men (Health Professionals Follow-Up Study), free of heart disease and cancer at the start; 8,359 coronary heart disease cases over 4.8 million person-years |
Isoflavone intake, tofu and soy milk eaten as food (food frequency questionnaires) Foods as eaten Follow-up to 2012 or 2013, depending on the cohort · vs Lowest intake (tofu: less than once a month) |
Highest isoflavone intake went with moderately lower coronary heart disease risk. Tofu once a week or more went with lower risk than less than once a month. Soy milk was not significantly linked. In women the tofu link was stronger in younger women before menopause and postmenopausal women not on hormone therapy. Isoflavones HR 0.87; tofu HR 0.82; soy milk HR 0.87 (Isoflavones 0.81 to 0.94; tofu 0.70 to 0.95; soy milk 0.69 to 1.10 (not significant)) Methods, limits and fundingOutcomes: Coronary heart disease (non-fatal heart attack and coronary death) Limitations: Observational and based on food questionnaires, so other lifestyle differences may explain part of the link. Mostly US health professionals. It cannot show cause. Funding and conflicts: Support from the US National Institutes of Health (PubMed record); the authors report no conflicts of interest. Read: abstract |
| Messina 2006 Effects of soy protein and soybean isoflavones on thyroid function in healthy adults and hypothyroid patients: a review of the relevant literature. Thyroid · PMID 16571087 · DOI |
Narrative review |
14 trials of soy foods or isoflavones and thyroid function in presumably healthy adults, plus hypothyroid patients | Soy protein and soy isoflavones, soy foods Soy foods and isoflavones |
With one exception, trials in healthy adults found no effects or only very modest changes. The authors found little evidence that soy foods or isoflavones harm thyroid function in people with healthy thyroids and enough iodine. Some evidence suggests soy foods may increase the thyroid hormone dose needed by hypothyroid patients by reducing absorption, but hypothyroid adults need not avoid soy foods. They advise making sure iodine intake is adequate. No pooled number (Not applicable) Methods, limits and fundingOutcomes: Thyroid function; thyroid hormone absorption Limitations: A 2006 narrative review. Thyroid function was not the main outcome in any of the 14 trials. The older evidence may have been overtaken by newer studies. Funding and conflicts: Funding is not stated in the abstract (not read in full text). Read: abstract |
| Naghshi 2024 Soy isoflavone intake and risk of cardiovascular disease in adults: A systematic review and dose-response meta-analysis of prospective cohort studies. Crit Rev Food Sci Nutr · PMID 36705465 · DOI |
Systematic review meta analysis |
13 publications in the review and 12 in the meta-analysis of prospective cohort studies in adults, searched to September 2021 | Dietary soy isoflavones (from foods, as estimated in cohort studies) Dietary intake · vs Lowest intake |
Higher soy isoflavone intake was linked to lower coronary heart disease (all populations) and, in Western populations, to lower overall cardiovascular disease and coronary heart disease. Coronary heart disease RR 0.92 (all populations); overall CVD 0.91 and CHD 0.89 (Western populations) (CHD 0.85 to 0.99; CVD 0.84 to 0.98; CHD (Western) 0.83 to 0.96) Methods, limits and fundingOutcomes: Cardiovascular disease and coronary heart disease Limitations: Observational. The abstract does not say how much of the isoflavone intake came from soy foods versus supplements; intake is estimated from food questionnaires. It cannot show cause. Funding and conflicts: Funding is not stated in the abstract. Read: abstract |
| Qiu 2019 Soy and isoflavones consumption and breast cancer survival and recurrence: a systematic review and meta-analysis. Eur J Nutr · PMID 30382332 · DOI |
Systematic review meta analysis |
37275 12 articles in 37,275 women with breast cancer (overall survival 5,770 cases; breast-cancer-specific survival 2,386; recurrence 1,500) |
Soy foods and isoflavone intake (from food questionnaires) Dietary intake · vs Lowest intake |
Soy and isoflavone intake before diagnosis went with slightly better overall survival, more clearly in postmenopausal women. After diagnosis there was no significant link with overall or breast-cancer-specific survival. Isoflavone intake before and after diagnosis was linked with lower recurrence. The authors call the evidence limited. Pre-diagnosis overall survival HR 0.84; breast-cancer-specific survival HR 0.89 (not significant); post-diagnosis overall survival HR 0.80 and specific survival HR 0.83 (not significant) (Pre-diagnosis OS 0.71 to 0.98; BCSS 0.74 to 1.07; post-diagnosis OS 0.62 to 1.04; BCSS 0.64 to 1.07) Methods, limits and fundingOutcomes: Overall survival, breast-cancer-specific survival and recurrence Limitations: Observational. Food questionnaires. It cannot show cause and cannot guide an individual. Funding and conflicts: Funding is not stated in the abstract. Read: abstract |
| Spolidoro 2023 Prevalence estimates of eight big food allergies in Europe: Updated systematic review and meta-analysis. Allergy · PMID 37405695 · DOI |
Systematic review meta analysis |
93 studies from Europe, all ages, published 2000 to 2021 | Prevalence of food allergy to eight big allergens, including soy |
For soy, self-reported lifetime allergy was 0.5% and food-challenge-verified allergy was 0.3% across all ages in Europe. Most studies were at moderate risk of bias. Soy: self-reported 0.5%; challenge-verified 0.3% (Self-reported 0.3 to 0.7%; challenge-verified 0.1 to 0.4%) Methods, limits and fundingOutcomes: Self-reported and food-challenge-verified food allergy Limitations: European data; rates differ by region and age. Soy in general, not any one soy food. Funding and conflicts: Not stated in the abstract (not read in full text). Registration: PROSPERO CRD42021266657 Read: abstract |
| Viscardi 2025 Effect of Soy Isoflavones on Measures of Estrogenicity: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Adv Nutr · PMID 39433088 · DOI |
Systematic review meta analysis |
3285 Postmenopausal women in 40 randomised trials (52 comparisons) |
Soy isoflavones compared with non-isoflavone controls Isoflavone preparations and soy foods Median 75 mg of isoflavones a day (trial description, not advice) Median 24 weeks (at least 3 months) · vs Non-isoflavone controls |
Isoflavones had no statistically significant effect on any of the four measures of estrogen-like action. The authors rate the certainty of evidence as high to moderate and conclude isoflavones do not show estrogenic effects on these measures. Endometrial thickness -0.22 mm; vaginal maturation index +2.31; FSH -0.02 IU/L; estradiol +1.61 pmol/L (none significant) (Endometrial thickness -0.45 to 0.01 mm; VMI -2.14 to 6.75; FSH -2.39 to 2.35 IU/L; estradiol -1.17 to 4.38 pmol/L) Methods, limits and fundingOutcomes: Endometrial thickness, vaginal maturation index, FSH and estradiol Limitations: Four measures only, in postmenopausal women. Not a study of men, premenopausal women or breast tissue. Mostly preparations, not foods. Funding and conflicts: Supported by the United Soybean Board (a US soy industry check-off program) and the Canadian Institutes of Health Research (full text). One author works at Soy Nutrition Institute Global, which is partly funded by the United Soybean Board. The paper says the sponsors had no role in the design, analysis or writing. Registration: PROSPERO CRD42023439239 Read: abstract |
| Wiesner 2021 Levothyroxine Interactions with Food and Dietary Supplements-A Systematic Review. Pharmaceuticals (Basel) · PMID 33801406 · DOI |
Systematic review |
121 studies identified; 63 included after full-text evaluation, on levothyroxine and food or supplements | Food and supplements taken with levothyroxine, including soy products Various |
The review found limited evidence that coffee, soy products, fibre, calcium or iron supplements and enteral nutrition all decreased levothyroxine absorption. It suggests keeping a proper interval between levothyroxine and these items, especially coffee and calcium or iron supplements. No pooled number (Not applicable) Methods, limits and fundingOutcomes: Levothyroxine absorption Limitations: Soy is one of many items and the evidence is described as limited. The abstract does not separate soy results. Funding and conflicts: The authors declare no conflict of interest (PubMed record). Read: abstract |
| Yan 2017 Association between consumption of soy and risk of cardiovascular disease: A meta-analysis of observational studies. Eur J Prev Cardiol · PMID 28067550 · DOI |
Systematic review meta analysis |
10 prospective cohort and 7 case-control studies; 17,269 cardiovascular events (6,265 stroke, 10,806 coronary heart disease) | Soy foods (tofu, soy milk and others) eaten as food Soy foods as eaten · vs Lower intake |
Higher soy intake was linked to less cardiovascular disease, stroke and coronary heart disease. The link was mainly seen in case-control studies and in Asian populations. For tofu, the link with cardiovascular disease was borderline. Soy isoflavones alone were not linked to these outcomes. Soy and cardiovascular disease SRR 0.84; tofu and cardiovascular disease 0.80; stroke 0.82; coronary heart disease 0.83 (Soy 0.75 to 0.94; tofu 0.64 to 1.00; stroke 0.68 to 0.99; coronary heart disease 0.72 to 0.95) Methods, limits and fundingOutcomes: Cardiovascular disease, stroke and coronary heart disease Limitations: Observational, with large differences between studies (I2 71%). Case-control studies are weaker than cohorts. It cannot show cause. Funding and conflicts: Funding is not stated in the abstract. Read: abstract |
| s-ecfr-101-82 US eCFR: 21 CFR 101.82, Health claims: Soy protein and risk of coronary heart disease · Source |
Regulation n/a |
Methods, limits and fundingRead: full-text | ||
| s-fda-allergens US FDA: Food Allergies (the "Big 9") · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text | ||
| s-gbif-glycine-max GBIF Backbone: Glycine max (L.) Merr. (usageKey 5359660) · Source |
Reference database n/a |
Methods, limits and fundingRead: full-text | ||
| s-medlineplus-foodallergy MedlinePlus: Food allergy · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text | ||
| s-nccih-soy NCCIH (US National Institutes of Health): Soy: Usefulness and Safety · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text | ||
| s-niddk-gas NIDDK: Gas in the Digestive Tract, Eating, Diet and Nutrition · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text | ||
| s-pubchem-isoflavones PubChem: genistein (CID 5280961), daidzein (CID 5281708), glycitein (CID 5317750) · Source |
Reference database n/a |
Methods, limits and fundingRead: full-text | ||
| s-usda-fdc-174270 USDA FoodData Central: Soybeans, mature seeds, raw (FDC 174270, SR Legacy, April 2018) · Source |
Reference database n/a |
Methods, limits and fundingRead: full-text | ||
| s-usda-fdc-174271 USDA FoodData Central: Soybeans, mature cooked, boiled, without salt (FDC 174271, SR Legacy, April 2018) · Source |
Reference database n/a |
Methods, limits and fundingRead: full-text |
What we do not know yet
- No trial of whole soybeans or any one soy food was read for cholesterol, menopause symptoms or hormones; most results are for soy protein or isoflavones.
- The heart disease and breast cancer results are observational and cannot show cause.
- How much of the iron and minerals in soybeans the body absorbs was not shown in people in the sources read.
- The NCCIH statements on bone, blood pressure and type 2 diabetes were not checked against the studies they cite.
- Soy-peanut allergy overlap, raw soybeans, infants and soy formula, kidney disease, gout, FODMAP, contamination and specific medicines such as tamoxifen and warfarin were not researched.
- Only US regulators were read; no European or other agency statement was checked.
How new research is added
New studies are found by a saved PubMed search and placed in a review queue before the page changes.
Lab markers
What changed in blood or saliva tests during trials. A changed number is not the same as feeling or being healthier, and we give no "normal ranges".
Hormonal 1
Estradiol (an estrogen hormone)
No significant change in trials
The main estrogen hormone in the blood.
Moderate certaintyResults and what it means
Why it was measured
To see whether soy isoflavones act like estrogen in the body.
Statistical vs. clinical meaning
No clear estrogen-like effect on this measure.
Safety implication
Reassuring on this measure; not a trial of whole soy foods.
| Study | Result | People | Product |
|---|---|---|---|
| 13 | Estradiol +1.61 pmol/L (95% CI -1.17 to 4.38), not significant | 3,285 postmenopausal women in 40 trials | Soy isoflavones, median 75 mg a day, median 24 weeks |
| 6 | Premenopausal: no change in estradiol or estrone. Postmenopausal: about +14%, not significant (p = 0.07) | 47 trials | Soy foods, soy protein or isoflavones, 4 weeks or more |
Metabolic 2
LDL cholesterol
Lowered in trials
The "bad" cholesterol carried in the blood. Higher levels are linked to more heart disease.
Moderate certaintyResults and what it means
Why it was measured
It is the usual blood marker used in diet trials for heart risk.
Statistical vs. clinical meaning
A small average fall, from a protein swap, in short trials; whole soybeans were not tested alone.
Safety implication
None specific.
| Study | Result | People | Product |
|---|---|---|---|
| 2 | LDL -4.76 mg/dL (95% CI -6.71 to -2.80) with soy protein versus non-soy protein | Adults in 41 trials with LDL data (baseline 110 to 201 mg/dL) | Soy protein, median 25 g a day, median 6 weeks |
| 1 | LDL -0.23 mmol/L (5.5%) in parallel trials; -0.16 mmol/L (4.2%) in crossover trials | 43 randomised trials | Soy protein, 4 to 18 weeks |
Total cholesterol
Lowered in trials
All the cholesterol carried in the blood, including LDL and HDL.
Moderate certaintyResults and what it means
Why it was measured
A common routine blood test reported in diet trials.
Statistical vs. clinical meaning
A small fall, mostly reflecting LDL.
Safety implication
None specific.
| Study | Result | People | Product |
|---|---|---|---|
| 2 | Total cholesterol -6.41 mg/dL (95% CI -9.30 to -3.52) | Adults in 43 trials | Soy protein, median 25 g a day, median 6 weeks |
Other 6
HDL cholesterol and triglycerides
HDL higher, triglycerides lower (parallel-design trials only) in trials
HDL is the "good" cholesterol; triglycerides are a blood fat linked to heart risk.
Low certaintyResults and what it means
Why it was measured
Reported alongside LDL in the older analysis.
Statistical vs. clinical meaning
Seen only in the parallel trials of an older analysis (2011); not reproduced in the 2019 analysis abstract, which reported LDL and total cholesterol only.
Safety implication
None specific.
| Study | Result | People | Product |
|---|---|---|---|
| 1 | HDL +3.2% and fasting triglycerides -10.7% in parallel trials | 20 parallel-design trials | Soy protein, 4 to 18 weeks |
Coronary heart disease (heart attack and coronary death)
Lower risk in observational studies in trials
Disease of the heart's own blood vessels, leading to heart attacks.
Low certaintyResults and what it means
Why it was measured
It is the clinical outcome that cholesterol markers stand in for.
Statistical vs. clinical meaning
Links, not proof; no trial of soy foods on heart attacks was read.
Safety implication
None specific.
| Study | Result | People | Product |
|---|---|---|---|
| 8 | Tofu once a week or more versus less than once a month: HR 0.82 (0.70 to 0.95). Isoflavones, top versus bottom fifth: HR 0.87 (0.81 to 0.94). Soy milk HR 0.87 (0.69 to 1.10), not significant | About 210,700 US adults, 8,359 CHD cases | Foods as eaten, from food questionnaires |
| 15 | Soy intake and CHD: SRR 0.83 (0.72 to 0.95) | 10 cohort and 7 case-control studies | Soy foods as eaten |
| 10 | Isoflavone intake and CHD: RR 0.92 (0.85 to 0.99) | 12 prospective cohort studies | Dietary isoflavones |
FSH and LH (pituitary hormones)
FSH: no change after menopause; lower FSH and LH before menopause in trials
Hormones from the brain that signal the ovaries; FSH rises after menopause.
Low certaintyResults and what it means
Why it was measured
Another check for estrogen-like effects.
Statistical vs. clinical meaning
Premenopausal changes are modest and of unknown clinical meaning, per the authors.
Safety implication
Not known.
Endometrial thickness (womb lining)
No significant change in trials
How thick the lining of the womb is on scan; estrogen thickens it.
Moderate certaintyResults and what it means
Why it was measured
A safety check for estrogen-like effects.
Statistical vs. clinical meaning
No thickening seen; the interval only just crosses zero, toward a thinner lining.
Safety implication
Reassuring on this measure for isoflavones; not a trial of whole soy foods.
| Study | Result | People | Product |
|---|---|---|---|
| 13 | Endometrial thickness -0.22 mm (95% CI -0.45 to 0.01), not significant (p = 0.059) | Postmenopausal women | Soy isoflavones, median 24 weeks |
Hot flushes and sweating
No significant change in trials
Sudden feelings of heat and sweating common around menopause.
Mixed findingsResults and what it means
Why it was measured
A main complaint that people hope soy will ease.
Statistical vs. clinical meaning
Other symptom scores improved a little; hot flushes did not. NCCIH calls the effect small and inconsistent.
Safety implication
None specific.
| Study | Result | People | Product |
|---|---|---|---|
| 7 | No significant effect on hot flushes or excessive sweating | Perimenopausal women in 12 studies | Soy isoflavone preparations |
Overall survival after breast cancer diagnosis
Pre-diagnosis intake: slightly better; post-diagnosis: no significant link in trials
Whether a woman with breast cancer is still alive over follow-up.
Low certaintyResults and what it means
Why it was measured
The main outcome in studies of diet and breast cancer.
Statistical vs. clinical meaning
Observational; cannot guide an individual.
Safety implication
Ask your cancer care team.
| Study | Result | People | Product |
|---|---|---|---|
| 11 | Pre-diagnosis HR 0.84 (0.71 to 0.98); post-diagnosis HR 0.80 (0.62 to 1.04), not significant | 37,275 women with breast cancer, 12 articles | Soy foods and isoflavones, from food questionnaires |
Safety
What studies and official sources say about side effects, medicines and who should check first. Each point shows what kind of evidence it comes from.
Main points to know 5
- Soy is a major food allergen. The US FDA lists soybeans among the nine major food allergens, and MedlinePlus lists soy among common food allergies, mostly in children. A 2023 European review put challenge-verified soy allergy at about 0.3% of people. In the US, soy must be named on the label of packaged foods and supplements (NCCIH). If you have a soy allergy, soy foods are not safe for you. For trouble breathing or swelling of the face, lips or throat, call 911 or your local emergency number. Authoritative guidance 17 19 12 20
- MAOI antidepressants and tyramine. NCCIH reports that soy products high in tyramine, such as tofu and soy sauce, have been linked with dangerously high blood pressure in people taking MAOIs. A 2018 review says modern foods contain far less tyramine than in the past and that the risk has been overstated, but that people differ. It reviewed soy sauces among many foods and gave no soy-food-specific numbers in its abstract. If you take an MAOI, ask your prescriber or pharmacist about soy foods. Authoritative guidance 20 5
- Thyroid medicine (levothyroxine). A 2023 review found mainly case reports of soy affecting levothyroxine tablet absorption and one randomised crossover study with no difference, and judged any effect to have little clinical impact. A 2021 systematic review found limited evidence of lower absorption with soy products. A 2006 review says hypothyroid adults need not avoid soy foods and should make sure their iodine intake is adequate. Ask your prescriber about timing. Case reports and review 4 14 9
- Pregnancy and breastfeeding. NCCIH says soy in pregnancy may be unsafe in amounts greater than those commonly found in foods, and that little is known about larger amounts while breastfeeding. It does not single out ordinary soy foods. Ask your midwife, doctor or dietitian about your own diet. Authoritative guidance 20
- Supplements are not the same as food. NCCIH says soy protein supplements have been used safely in research for up to 16 weeks and concentrated isoflavone extracts for up to 6 months. Those are supplements and trial periods, not a safe-amount statement for foods. Effects may differ between types of soy product. Ask a doctor or pharmacist before using protein powders or isoflavone supplements. Authoritative guidance 20
Side effects 2
| Effect | How often | Severity and recovery | Evidence |
|---|---|---|---|
| Allergic reactions to soy, from mild itching and hives to anaphylaxis Prevalence data are for soy in general, not for any one soy food. | Europe, all ages: self-reported lifetime soy allergy 0.5% (95% CI 0.3 to 0.7); food-challenge-verified soy allergy 0.3% (0.1 to 0.4) | can be severe (anaphylaxis) Not described for soy in the sources read. | Observational 12 17 19 |
| Bloating, constipation, diarrhea and nausea NCCIH's list is for soy products and supplements in general; NIDDK names legumes (beans, peas, lentils) and does not name soy in the part read. | No frequency given by NCCIH. NIDDK lists legumes among foods that can cause gas. | mild Not described. | Authoritative guidance 20 21 |
Liver
No liver injury from eating soy foods was found in the sources read. A liver-safety source (such as LiverTox) was not searched.
How often. No frequency was found.
Monitoring. No agency monitoring advice was found.
This is a safety connection. It is not evidence that Soy Foods supports liver health.
Medicines and supplements 3
| With | Why it matters | Importance | Evidence | What to do |
|---|---|---|---|---|
| MAOI antidepressants (monoamine oxidase inhibitors) prescription | Tyramine in some soy products (NCCIH names tofu and soy sauce) can raise blood pressure when an MAOI is blocking its breakdown. | NCCIH reports dangerously high blood pressure with high-tyramine soy products and MAOIs. A 2018 review says the tyramine risk in modern foods has been overstated, though people differ. Whole cooked soybeans were not named in the sources read. | Reported interaction and review Low certainty 20 5 | Ask your prescriber or pharmacist before eating soy foods on an MAOI, and tell them which soy foods you eat and how fresh they are. |
| Levothyroxine (thyroid hormone tablets) prescription | Soy products may reduce absorption of levothyroxine tablets; this rests mainly on case reports. | A 2023 review found mainly case reports and one randomised crossover study with no difference, and judged any effect to have little clinical impact. A 2021 review found limited evidence of lower absorption. A 2006 review says soy foods may raise the thyroid hormone dose needed, but hypothyroid adults need not avoid soy. | Case reports and review Very low certainty 4 14 9 | Do not change your medicine yourself. Ask your prescriber whether timing matters for you. |
| Other medicines general | Not researched for soy foods beyond the two entries above. | NCCIH advises talking with your health care provider before using soy or other herbal products if you take any medicine. Tamoxifen, warfarin and other specific medicines were not researched here. | Authoritative guidance Not enough evidence 20 | Tell your pharmacist about regular soy foods, soy protein powder or isoflavone supplements. |
Who should check first 5
| Situation | Advice | Evidence |
|---|---|---|
| Known or suspected soy allergy | Avoid soy foods and read labels. Ask an allergist about your own case. For trouble breathing or swelling of the face, lips or throat, call 911 or your local emergency number. | Authoritative guidance 17 19 |
| Taking an MAOI antidepressant | Ask your prescriber or pharmacist about soy foods before eating them. | Authoritative guidance 20 |
| Pregnancy or breastfeeding | Ordinary soy foods are not singled out as unsafe by the source read. NCCIH says soy in amounts greater than those found in foods may be unsafe in pregnancy. Ask your midwife, doctor or dietitian about your own diet. | Authoritative guidance 20 |
| Breast cancer or another hormone-sensitive condition | Ask your cancer care team how soy foods fit your care. The studies read are observational and none is a trial of soy foods. | Observational 11 3 20 |
| Taking thyroid hormone, or having an underactive thyroid | A 2006 review says hypothyroid adults need not avoid soy foods but should make sure iodine intake is adequate. Ask your prescriber about timing. | Review 9 4 |
Overdose, product quality and regulators
Summary. No toxicity from soy foods eaten as ordinary food was found in the sources read. The safety points are allergy, the MAOI question and the thyroid medicine question.
Animal. Not reviewed.
High dose or long term signals. NCCIH says soy protein supplements have been used safely in research for up to 16 weeks and extracts with concentrated isoflavones for up to 6 months. These are supplements, not foods. NCCIH says soy in pregnancy may be unsafe in amounts greater than those commonly found in foods.
Overdose response. Not found.
Genotoxicity. Not researched.
Toxic or hazardous parts. Not researched. Raw soybeans, anti-nutrients and cooking were not researched for this page.
Contamination (heavy metals, pesticides, mould), genetic modification, raw or undercooked soybeans and spoilage were not researched for this page.
| Body | Action | Date |
|---|---|---|
| US FDA (United States) | Food Allergies: soybeans are one of nine major food allergens identified by law in the US. source | 2026-03-11 |
| US FDA (21 CFR 101.82) (United States) | Permitted health claim about diets low in saturated fat and cholesterol that include soy protein and the risk of coronary heart disease. The rule limits the wording and does not allow a stated degree of risk reduction. It is a labelling rule, not a personal target. source | 2026-10-01 |
| NCCIH (US National Institutes of Health) (United States) | Soy: Usefulness and Safety. Some people are allergic; high-tyramine soy products and MAOIs have been reported to cause dangerously high blood pressure; soy above food amounts may be unsafe in pregnancy; little is known about larger amounts while breastfeeding. source | 2025-04 |
| MedlinePlus (US National Library of Medicine) (United States) | Food allergy: soy is among common food allergies, mostly in children; call 911 or the local emergency number for serious or whole-body reactions after eating any food. source | 2024-10-29 |
When to get medical help
- Trouble breathing, wheezing, hoarse voice, swelling of the lips, face, tongue or throat, widespread hives, dizziness, fainting or repeated vomiting after eating a soy food (possible anaphylaxis): use epinephrine if prescribed, then call 911 or your local emergency number
- Signs of dangerously high blood pressure after eating soy foods while taking an MAOI: seek urgent medical help
Stop using the product and contact a clinician or emergency service. In the US, Poison Control is 1-800-222-1222.
General information only, not medical advice. Ask a clinician or pharmacist before use, especially with medicines, in pregnancy or with a health condition. See the Natural Remedy Safety guide.
Frequently asked questions
What are soy foods?
Are soybeans a good source of protein and fibre?
By USDA data, cooked, boiled soybeans have 18.21 g of protein and 6.0 g of fibre per 100 g, and a cup (172 g) has about 31.3 g of protein and 10.3 g of fibre. How much iron and other minerals the body absorbs was not studied in the sources read.
Does soy lower cholesterol?
Is soy good for the heart?
Does soy help with menopause symptoms or hot flushes?
Does soy act like estrogen?
Is soy safe with breast cancer or other hormone-sensitive conditions?
Who should avoid soy because of allergy?
Does soy affect thyroid medicine or the thyroid?
Case reports suggest soy might reduce absorption of levothyroxine tablets, but a randomised crossover study found no difference and a 2023 review thought any effect small. A 2006 review says hypothyroid adults need not avoid soy but should have enough iodine. Ask your prescriber before changing anything.
Can I eat soy foods if I take an MAOI antidepressant?
Is soy safe in pregnancy and breastfeeding?
NCCIH says soy in amounts greater than those commonly found in foods may be unsafe in pregnancy, and little is known about larger amounts while breastfeeding. It does not single out ordinary soy foods. Ask your midwife or doctor.
Are soy foods, soy milk and soy supplements the same?
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Editorial transparency
- Written by
- AlternativeMed editorial team. Research compiled with AI assistance, then checked against the sources listed.
- Medical review
- None. This page has not been reviewed by a physician or pharmacist.
- First published
- 2026-10-26
- Last substantive update
- 2026-10-26
- How we research
- We rebuilt this page from our earlier soy summary, re-checked nutrition against saved USDA FoodData Central data, read the health agency pages (NCCIH, FDA, MedlinePlus, NIDDK) and the US food label rule, and re-read PubMed abstracts for the reviews and cohort studies cited. Only abstracts were read for studies, plus the funding statements of two analyses. Items we could not verify are flagged in the research gaps.
- How we rate evidence
- See "How we rate evidence" in the Evidence tab.
- Independence
- No product is promoted on this page. No affiliate links are shown. Two analyses cited have a link to the soy industry: the 2019 soy protein cholesterol analysis (an author at the Soy Nutrition Institute; many included trials had industry funding) and the 2025 estrogen analysis (funded in part by the United Soybean Board, with an author at Soy Nutrition Institute Global). This is stated where they are used.
Sources 24
Each source was opened and checked. Where we read only the abstract, it says so. The small numbers in the text point here.
- Anderson JW, Bush HM. Soy protein effects on serum lipoproteins: a quality assessment and meta-analysis of randomized, controlled studies.. J Am Coll Nutr. 2011. PMID 21730216. DOI 10.1080/07315724.2011.10719947. (abstract)
- Blanco Mejia S, Messina M, Li SS, et al.. 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. PMID 31006811. DOI 10.1093/jn/nxz020. (abstract)
- Boutas I, Kontogeorgi A, Dimitrakakis C, et al.. Soy Isoflavones and Breast Cancer Risk: A Meta-analysis.. In Vivo. 2022. PMID 35241506. DOI 10.21873/invivo.12737. (abstract)
- Gatta E, Maltese V, Cavadini M, et al.. Interference or Noninterference Between Soy and Levothyroxine: That Is the Question. A Narrative Review of Literature.. Endocr Pract. 2023. PMID 37633413. DOI 10.1016/j.eprac.2023.08.009. (abstract)
- Gillman PK. A reassessment of the safety profile of monoamine oxidase inhibitors: elucidating tired old tyramine myths.. J Neural Transm (Vienna). 2018. PMID 30255284. DOI 10.1007/s00702-018-1932-y. (abstract)
- Hooper L, Ryder JJ, Kurzer MS, et al.. Effects of soy protein and isoflavones on circulating hormone concentrations in pre- and post-menopausal women: a systematic review and meta-analysis.. Hum Reprod Update. 2009. PMID 19299447. DOI 10.1093/humupd/dmp010. (abstract)
- Luan H, Liu Q, Guo Y, et al.. Effects of soy isoflavones on menopausal symptoms in perimenopausal women: a systematic review and meta-analysis.. PeerJ. 2025. PMID 40718787. DOI 10.7717/peerj.19715. (abstract)
- Ma L, Liu G, Ding M, et al.. Isoflavone Intake and the Risk of Coronary Heart Disease in US Men and Women: Results From 3 Prospective Cohort Studies.. Circulation. 2020. PMID 32200662. DOI 10.1161/CIRCULATIONAHA.119.041306. (abstract)
- Messina M, Redmond G. Effects of soy protein and soybean isoflavones on thyroid function in healthy adults and hypothyroid patients: a review of the relevant literature.. Thyroid. 2006. PMID 16571087. DOI 10.1089/thy.2006.16.249. (abstract)
- Naghshi S, Tutunchi H, Yousefi M, et al.. Soy isoflavone intake and risk of cardiovascular disease in adults: A systematic review and dose-response meta-analysis of prospective cohort studies.. Crit Rev Food Sci Nutr. 2024. PMID 36705465. DOI 10.1080/10408398.2022.2163372. (abstract)
- Qiu S, Jiang C. Soy and isoflavones consumption and breast cancer survival and recurrence: a systematic review and meta-analysis.. Eur J Nutr. 2019. PMID 30382332. DOI 10.1007/s00394-018-1853-4. (abstract)
- Spolidoro GCI, Ali MM, Amera YT, et al.. Prevalence estimates of eight big food allergies in Europe: Updated systematic review and meta-analysis.. Allergy. 2023. PMID 37405695. DOI 10.1111/all.15801. (abstract)
- Viscardi G, Back S, Ahmed A, et al.. Effect of Soy Isoflavones on Measures of Estrogenicity: A Systematic Review and Meta-Analysis of Randomized Controlled Trials.. Adv Nutr. 2025. PMID 39433088. DOI 10.1016/j.advnut.2024.100327. (abstract)
- Wiesner A, Gajewska D, Paśko P. Levothyroxine Interactions with Food and Dietary Supplements-A Systematic Review.. Pharmaceuticals (Basel). 2021. PMID 33801406. DOI 10.3390/ph14030206. (abstract)
- Yan Z, Zhang X, Li C, et al.. Association between consumption of soy and risk of cardiovascular disease: A meta-analysis of observational studies.. Eur J Prev Cardiol. 2017. PMID 28067550. DOI 10.1177/2047487316686441. (abstract)
- . US eCFR: 21 CFR 101.82, Health claims: Soy protein and risk of coronary heart disease. . . (full-text)
- . US FDA: Food Allergies (the "Big 9"). . . (full-text)
- . GBIF Backbone: Glycine max (L.) Merr. (usageKey 5359660). . . (full-text)
- . MedlinePlus: Food allergy. . . (full-text)
- . NCCIH (US National Institutes of Health): Soy: Usefulness and Safety. . . (full-text)
- . NIDDK: Gas in the Digestive Tract, Eating, Diet and Nutrition. . . (full-text)
- . PubChem: genistein (CID 5280961), daidzein (CID 5281708), glycitein (CID 5317750). . . (full-text)
- . USDA FoodData Central: Soybeans, mature seeds, raw (FDC 174270, SR Legacy, April 2018). . . (full-text)
- . USDA FoodData Central: Soybeans, mature cooked, boiled, without salt (FDC 174271, SR Legacy, April 2018). . . (full-text)
