Soy protein

Also called soy protein isolate, soy protein concentrate, soybean protein, textured soy protein, soya protein.

Best grade B across 6 graded outcomes Other Last checked Oct 25, 2026

The short answer

From 13 sources

Soy protein is a plant protein powder. A meta-analysis of 43 trials found a median 25 g a day lowered LDL cholesterol by about 4.8 mg/dL over a median 6 weeks. For muscle, nine studies with 266 people found soy and animal protein gave similar strength and lean mass gains with resistance training.

Every graded outcome on this page

6 rows · line = participants

Grade BStrength and lean body mass with resistance trainingSoy protein vs animal protein supplementsn 266
Grade BLDL and total cholesterolSoy protein vs non-soy proteinn 43
Grade CBlood pressure in postmenopausal womenSoy protein (with isoflavones)n 1,551
Grade CLean body mass and strength in young adultsWhey or soy protein concentrate or isolaten 261
Grade CCirculating reproductive hormonesSoy protein or isoflavonesn 47
Grade DBreast cancer survival and recurrence (observational)Dietary soy and isoflavone intake, highest vs lowestn 37,275
3 more graded outcomes, in the evidence chapter

Key facts

LDL cholesterol: Median 25 g/day for a median 6 weeks: LDL -4.76 mg/dL and total cholesterol -6.41 mg/dL vs non-soy protein (43 trials)²
Muscle vs animal protein: Soy and animal protein gave similar strength and lean mass gains with resistance training (9 studies, 266 participants)³
Blood pressure: In postmenopausal women, 25 g/day or more lowered systolic pressure by 4.62 mmHg (12 trials, 1,551 women)⁵
Hormones: Soy or isoflavones lowered FSH and LH by about 20% in premenopausal women; in postmenopausal women estradiol showed only a non-significant 14% rise (47 studies)⁶
Protein quality: Mean DIAAS 84.5 and PDCAAS 85.6 across soy products; isolate scored below soymilk⁸
Label claim: FDA proposed revoking the soy protein and heart disease health claim in October 2017; it remained listed as authorized on FDA's page last updated March 2024¹⁰

What it is

Soy protein is the protein from soybeans, sold as isolate or concentrate powders; it also carries some soy isoflavones.

How it works

Proposed

The NIH fact sheet notes that soy protein lacks the essential amino acid methionine and may lose some cysteine and lysine in processing, yet a quantitative review scored soy products at a mean DIAAS of 84.5. Its cholesterol effect is small and its mechanism is not settled; the blood pressure benefit in one meta-analysis was linked by the authors to the isoflavone component.^1,5

Forms, side by side

2 forms named in our sources. The rest show what our data holds, and say plainly where it holds nothing yet.

Soy protein forms compared

2 forms

Soy protein forms compared: 2 forms by 3 attributes. Empty cells are labelled No data yet, or Not graded in the evidence row.
2 forms	Isolate	Concentrate
Absorption in people	The NIH fact sheet says soy lacks the essential amino acid methionine and may lose some cysteine and lysine in processing. In a quantitative review, isolate scored below soymilk on DIAAS, and heat or moisture during processing could raise or lower scores.^1,8	Ranked just below soymilk for DIAAS among the soy products in the quantitative review; scores varied widely within each group.⁸
GI tolerance	No product-specific safety signal in the cited meta-analyses.^2,3	Not reported separately in the cited abstracts.⁸
Studied for	Cholesterol (median 25 g/day) and muscle with resistance training	Protein quality comparisons; used alongside isolate in muscle trials

Soy protein isolate
Absorption in people
The NIH fact sheet says soy lacks the essential amino acid methionine and may lose some cysteine and lysine in processing. In a quantitative review, isolate scored below soymilk on DIAAS, and heat or moisture during processing could raise or lower scores.^1,8
GI tolerance
No product-specific safety signal in the cited meta-analyses.^2,3
Studied for
Cholesterol (median 25 g/day) and muscle with resistance training
Soy protein concentrate
Absorption in people
Ranked just below soymilk for DIAAS among the soy products in the quantitative review; scores varied widely within each group.⁸
GI tolerance
Not reported separately in the cited abstracts.⁸
Studied for
Protein quality comparisons; used alongside isolate in muscle trials

What the human research says

Human trials only, one row per outcome. The form line shows what each trial actually tested. Grades follow our evidence-grading policy.

Trial map

6 graded outcomes, largest study first

6 graded outcomes: 2 improved, 2 mixed, 2 no effect. The largest, a 2019 meta-analysis of 37,275 people on breast cancer survival and recurrence (observational), found mixed results.

By sizeTable

1Breast cancer survival and recurrence (observational)

Mixed · Grade D · Meta-analysis, 37,275 people, 2019

Women with breast cancer in 12 observational articles (37,275 women)

Dose, result and source

Every graded outcome on this page, largest study first
Outcome	Found	People	Study	Who was studied
Breast cancer survival and recurrence (observational)	Mixed	37,275	Grade D · Meta-analysis, 2019	Women with breast cancer in 12 observational articles (37,275 women)
Blood pressure in postmenopausal women	Improved	1,551	Grade C · Meta-analysis, 2017	Postmenopausal women in 12 randomized trials
Strength and lean body mass with resistance training	No effect	266	Grade B · Meta-analysis, 2018	Participants in 9 studies of at least 6 weeks; 5 compared whey with soy and 4 compared soy with beef, milk or dairy protein
Lean body mass and strength in young adults	No effect	261	Grade C · Meta-analysis, 2026	Healthy adults aged 18 to 30 doing resistance training, 12 studies
Circulating reproductive hormones	Mixed	47	Grade C · Meta-analysis, 2009	Pre- and postmenopausal women in 47 trials of 4 weeks or longer (11 premenopausal, 35 postmenopausal, 1 perimenopausal)
LDL and total cholesterol	Improved	43	Grade B · Meta-analysis, 2019	Adults with baseline LDL cholesterol of 110 to 201 mg/dL in the 46 controlled trials FDA identified (43 had usable data)

Every graded row

6 rows

Form tested

Showing 6 of 6 outcomes. Human trials only.

Grade BStrength and lean body mass with resistance trainingPerformanceNo effectMeta-analysis
n 266 · 2018

Both groups gained strength with no difference between them (bench press p = 0.90; squat p = 0.64). Lean mass change did not differ between whey and soy (p = 0.96), and soy vs other proteins also showed no difference (p = 0.80).

Design: Meta-analysis, n = 266, 2018
Population: Participants in 9 studies of at least 6 weeks; 5 compared whey with soy and 4 compared soy with beef, milk or dairy protein
Form: Soy protein vs animal protein supplements
Dose: Varied by study
Duration: 6 weeks or longer
Source: Reference 3 · PubMed 29722584 (opens PubMed)

Grade BLDL and total cholesterolHeartImprovedMeta-analysis
n 43 · 2019

LDL fell by 4.76 mg/dL (95% CI -6.71 to -2.80; I2 = 55%) and total cholesterol by 6.41 mg/dL (95% CI -9.30 to -3.52; I2 = 74%). About 75% of trials showed an LDL reduction, though only a minority were individually significant; there was no dose-response.

Design: Meta-analysis, n = 43, 2019
Population: Adults with baseline LDL cholesterol of 110 to 201 mg/dL in the 46 controlled trials FDA identified (43 had usable data)
Form: Soy protein vs non-soy protein
Dose: Median 25 g/day
Duration: Median 6 weeks
Source: Reference 2 · PubMed 31006811 (opens PubMed)

Grade CBlood pressure in postmenopausal womenHeartImprovedMeta-analysis
n 1,551 · 2017

Overall, systolic pressure fell 3.03 mmHg (95% CI -5.03 to -1.02) and diastolic 0.71 mmHg. At 25 g/day or more the drops were 4.62 and 1.63 mmHg; below 25 g/day there was no significant effect. The authors link the benefit to isoflavones.

Design: Meta-analysis, n = 1,551, 2017
Population: Postmenopausal women in 12 randomized trials
Form: Soy protein (with isoflavones)
Dose: 25 g/day or more in the benefit subgroup
Duration: Varied by trial
Source: Reference 5 · PubMed 28675204 (opens PubMed)

Grade CLean body mass and strength in young adultsPerformanceNo effectMeta-analysis
n 261 · 2026

Neither whey nor soy significantly changed lean body mass. Protein supplements raised peak plasma essential amino acids, and whey improved bench press (MD 8.87) and squat (MD 9.60); the abstract gives no soy strength result.

Design: Meta-analysis, n = 261, 2026
Population: Healthy adults aged 18 to 30 doing resistance training, 12 studies
Form: Whey or soy protein concentrate or isolate
Dose: Varied by study
Duration: Varied by study
Source: Reference 4 · PubMed 41454445 (opens PubMed)

Grade CCirculating reproductive hormonesHealthy agingMixedMeta-analysis
n 47 · 2009

In premenopausal women estradiol, estrone and SHBG were unchanged, FSH and LH fell about 20% and cycle length rose 1.05 days. In postmenopausal women there were no significant effects, with a non-significant 14% rise in total estradiol (p = 0.07).

Design: Meta-analysis, n = 47, 2009
Population: Pre- and postmenopausal women in 47 trials of 4 weeks or longer (11 premenopausal, 35 postmenopausal, 1 perimenopausal)
Form: Soy protein or isoflavones
Dose: Varied by trial
Duration: 4 weeks or longer
Source: Reference 6 · PubMed 19299447 (opens PubMed)

Grade DBreast cancer survival and recurrence (observational)Healthy agingMixedMeta-analysis
n 37,275 · 2019

Pre-diagnosis intake was linked to a lower risk of death (HR 0.84, 95% CI 0.71 to 0.98) but not breast cancer-specific death. Post-diagnosis intake showed no significant link with overall survival (HR 0.80, 0.62 to 1.04); both were linked to lower recurrence.

Design: Meta-analysis, n = 37,275, 2019
Population: Women with breast cancer in 12 observational articles (37,275 women)
Form: Dietary soy and isoflavone intake, highest vs lowest
Dose: Dietary intake, not supplements
Duration: Observational follow-up
Source: Reference 7 · PubMed 30382332 (opens PubMed)

What the numbers add up to

Each point is worked out from the data and the sources numbered on this page, with the arithmetic shown under it. It adds no new data and is not medical advice.

A small cholesterol effect, not a drug

The 43-trial analysis found a drop of about 3 to 4% in LDL, with most but not all trials favoring soy and no dose-response. FDA proposed revoking its heart claim in 2017 over what it saw as inconsistent LDL results in these trials.^2,10

For muscle, soy matches animal protein rather than beating it

Soy and animal protein produced similar strength and lean mass gains, and in older adults a network analysis ranked whey first for muscle mass, handgrip and walking speed.^3,9

Blood pressure results may be about isoflavones

The blood pressure drop appeared only at 25 g/day or more, and the authors attributed it to the isoflavones that come with soy protein.⁵

Studied doses

Doses used in research, shown against the official limits. They describe the studies, not a recommendation for you.

Studied doses in research, not advice. These are amounts used in research, not personal advice. Your clinician or pharmacist can say what fits you.

Doses studied in human trials

NIH ODS updated Apr 1, 2024

Doses studied in human trials ranged from about 25 g of soy protein a day (the median in the cholesterol meta-analysis, over a median 6 weeks); the muscle trials lasted 6 weeks or longer and their doses are not given in the abstracts. These are research doses, not advice.^2,5,3

Intake reference: Protein RDA: 0.8 g/kg/day for healthy adults and 0.85 g/kg/day for adolescents. The NIH fact sheet notes that athletes may need more; it does not set an upper limit for protein.¹ The Food and Nutrition Board has not set a UL for protein but advises caution with high intakes from foods plus supplements because data on adverse effects are limited. NIH ODS fact sheet (updated April 1, 2024).

Interactions and safety

Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.

What Soy protein meets

1 cited row

Medicines 1

Soy protein1 medicine · 0 supplements

Supplements and foods 0

No supplement rows in our sources.

Drug label or FDA notice

Interactions

1 agent

Published interactions, grouped by kind
Agent	What the source says	Evidence
Medicines1
Levothyroxinee.g. Thyroid hormone tablets such as Synthroid	The levothyroxine label lists soybean flour among foods that may bind levothyroxine in the gut and decrease its absorption, which can require dose adjustment. Soy protein powder itself was not tested; people on thyroid hormone should ask their prescriber about timing.¹³	Drug label

Check with what you take

Kept on this device only

Add what you take. We list every interaction our evidence profiles cite between Soy protein and your picks, and between your picks.

Add a supplement or medicine

Most cited:

Add a supplement or medicine you take to check it against Soy protein.

Starting from one medicine? The interaction checker rates how serious each pair is, on a curated list of 19 entries for 11 medicines. This cabinet has no severity rating: it lists every interaction row our supplement pages cite.

Who should be careful

4 groups

Soy allergy: Soybeans are a major US food allergen, and labels must name soy as the allergen source. People with a soy allergy should avoid soy protein products.¹¹
Hormone-sensitive conditions: Soy products contain isoflavones and changed FSH, LH and cycle length in premenopausal women in a meta-analysis. The breast cancer data are observational and about dietary soy, not powders, so anyone with a hormone-sensitive condition should ask their care team.^6,7
Kidney disease: A systematic review in healthy adults found protein above the RDA consistent with normal kidney function in the short term, but it excluded people with kidney disease and most studies ran under 6 months.¹²
Pregnancy, breastfeeding and children: No soy protein supplement studies in these groups were found in the sources reviewed.¹

How to read the label

What to check on the Supplement Facts panel.

How to read the label

4 checks

Check protein grams per serving

The cholesterol meta-analysis used a median of 25 g of soy protein a day, so compare grams of soy protein, not scoop size.²

Read the allergen statement

FDA requires packaged foods and dietary supplements to declare soy, in the ingredient list or in a 'Contains' statement.¹¹

Read heart-health wording carefully

FDA proposed in October 2017 to revoke its authorized soy protein and heart disease claim, saying the evidence no longer met its standard; the claim was still listed on FDA's page updated March 2024.¹⁰

Look for a blend

The NIH fact sheet notes that many protein products combine sources; soy lacks methionine, which other protein sources in a blend can supply.¹

Label X-RayPhotograph a bottle's Supplement Facts panel and see each line, soy protein included, beside the doses and forms the trials used

Frequently asked questions

Short answers to common questions; the numbers link to the sources below.

Common questions

6 answers

Does soy protein lower cholesterol?

Modestly. A median 25 g a day for a median 6 weeks lowered LDL by 4.76 mg/dL in a 43-trial meta-analysis, roughly 3 to 4%.²

Is soy protein as good as whey for muscle?

In a nine-study meta-analysis (266 people) soy and animal protein gave similar strength and lean mass gains with resistance training. In older adults a network analysis ranked whey first.^3,9

How much soy protein did studies use?

The cholesterol analysis used a median of 25 g a day; the blood pressure benefit appeared at 25 g a day or more. These are research doses, not advice.^2,5

Does soy protein affect hormones?

In a 47-study meta-analysis, soy or isoflavones lowered FSH and LH about 20% in premenopausal women; in postmenopausal women estradiol rose a non-significant 14%.⁶

Is soy a complete protein?

The NIH fact sheet says soy lacks the essential amino acid methionine, although quality scores still averaged DIAAS 84.5 across soy products.^1,8

Can soy protein carry a heart health claim?

FDA authorized the claim in 1999 and proposed revoking it in October 2017. It was still listed as authorized on FDA's page last updated March 2024.¹⁰

Sources

13 sources: trial abstracts, NIH fact sheets and reference databases. Numbers in the text link here.

Sources cited on this page

13 sources

1Exercise and Athletic Performance: Health Professional Fact SheetFact sheet NIH Office of Dietary Supplements, 2024 · ods.od.nih.gov
2A Meta-Analysis of 46 Studies Identified by the FDA Demonstrates that Soy Protein Decreases Circulating LDL and Total Cholesterol Concentrations in Adults.Meta-analysis J Nutr, 2019 · PMID 31006811
3No Difference Between the Effects of Supplementing With Soy Protein Versus Animal Protein on Gains in Muscle Mass and Strength in Response to Resistance Exercise.Meta-analysis Int J Sport Nutr Exerc Metab, 2018 · PMID 29722584
4The Impact of Whey and Soy Protein Supplementation on Resistance Training in Young Adults: A Systematic Review and Meta-Analysis.Meta-analysis J Diet Suppl, 2026 · PMID 41454445
5Effect of soybean protein on blood pressure in postmenopausal women: a meta-analysis of randomized controlled trials.Meta-analysis Food Funct, 2017 · PMID 28675204
6Effects of soy protein and isoflavones on circulating hormone concentrations in pre- and post-menopausal women: a systematic review and meta-analysis.Meta-analysis Hum Reprod Update, 2009 · PMID 19299447
7Soy and isoflavones consumption and breast cancer survival and recurrence: a systematic review and meta-analysis.Meta-analysis Eur J Nutr, 2019 · PMID 30382332
8Protein quality of soy and the effect of processing: A quantitative review.Review Front Nutr, 2022 · PMID 36238463
9Comparative Efficacy of Different Protein Supplements on Muscle Mass, Strength, and Physical Indices of Sarcopenia among Community-Dwelling, Hospitalized or Institutionalized Older Adults Undergoing Resistance Training: A Network Meta-Analysis of Randomized Controlled Trials.Meta-analysis Nutrients, 2024 · PMID 38612975
10Authorized Health Claims That Meet the Significant Scientific Agreement (SSA) Standard (lists 21 CFR 101.82 soy protein and CHD, with the October 2017 proposal to revoke it)Fact sheet U.S. Food and Drug Administration, 2024 · fda.gov
11Food Allergies (soybeans are one of nine major food allergens; allergen source must be declared on packaged foods and dietary supplements)Fact sheet U.S. Food and Drug Administration, 2026 · fda.gov
12A Systematic Review of Renal Health in Healthy Individuals Associated with Protein Intake above the US Recommended Daily Allowance in Randomized Controlled Trials and Observational Studies.Systematic review Adv Nutr, 2018 · PMID 30032227
13SYNTHROID (levothyroxine sodium) tablets: prescribing information (7.9 Drug-Food Interactions)Label AbbVie via DailyMed (U.S. National Library of Medicine), 2024 · dailymed.nlm.nih.gov

What changed

Every dated change to this page: what changed, who made it and why.

Change log

2 entries

Dated changes to this page
Date	Change	Who and why
Oct 25, 2026interactions	Adversarial review: added the levothyroxine interaction from the Synthroid label (section 7.9 lists soybean flour among foods that decrease absorption; label read via openFDA, effective 2024-02-20). Hormone key fact and FAQ now report the non-significant 14% estradiol rise in postmenopausal women instead of "no change"; heart-claim insight reworded to the reason FDA gave. FDA health-claims page re-opened (content current as of 2024-03-28).	Writer: Kymata Health EditorialTrigger: adversarial review
Oct 17, 2026all	Initial editorial evidence review. Every PMID checked against NCBI E-utilities esummary (title, year, journal) and each cited abstract read; figures taken from the abstracts. Regulatory status from FDA's authorized health claims page (content dated 2024-03-28) and its allergens page (2026-03-11); the final-rule status of the 2017 revocation proposal was not confirmed beyond that page.	Writer: Kymata Health EditorialTrigger: new page

Supplement & Nutrient Encyclopedia. Educational information only; it is not medical advice and does not replace a clinician. Dietary supplements are not intended to diagnose, treat, cure or prevent any disease. Statements about supplements have not been evaluated by the FDA.

Soy protein

Medicines 1

Supplements and foods 0

Levothyroxine