✓ No active regulatory warningsFDA MedWatch, EMA EudraVigilance, WHO VigiBase, WADA Prohibited List · 2026-05-29
📰Read the full Soy Protein evidence review on GMJ News →Complete clinical article, references and updates on news.gmj.ge. This page is the structured safety summary.⚠ ER+ breast cancer patient — soy FOOD safe; concentrated isoflavone SUPPLEMENTS debated [2]
⚠ Patient on levothyroxine taking soy protein — separate by 4 hours [1]
⚠ Male patient avoiding soy for testosterone concerns — myth; meta-analyses show no effect [1]
⚠ Soy-allergic patient (common in children) — top 8 allergen [1]
🥗 Food first — build your daily Typical 20–50 g
Check the foods you regularly eat — the bar fills toward your daily target.
Soy protein isolate (30 g scoop)27 g protein
Tofu, firm (100 g)17 g protein
Edamame (100 g)11 g protein
Tempeh (100 g)19 g protein
Soy milk (240 mL)7 g protein
Check your regular foods above
🔬 Lab interpreter
Recommended test
No routine monitoring
No routine monitoring
Reference range / target
N/A
N/A
When to test
N/A
N/A
Monitor TSH if on levothyroxine + regular soy intake [1].
Full lab monitoring ↓⚕ For professionals — confirm ranges against your local laboratory.
Clinical verdict
Soy protein is the only plant protein with PDCAAS 1.0 and has an FDA cardiovascular health claim (25 g/day). The isoflavone content makes it unique among proteins — both an advantage (cardiovascular, menopausal) and a consideration (ER+ breast cancer: food OK, supplements debated). The 'soy lowers testosterone' myth is conclusively debunked by two meta-analyses [1] [2].
1 How much do I need?
👤 Adults: Specific dosage data under clinical review
👴 Elderly: Specific dosage data under clinical review
🤰 Pregnancy: See guidance
Soy foods safe and widely consumed. High-dose isoflavone supplements: caution [1].
👦 Pediatric: See guidance
Soy protein is used in infant formula and is safe for children. Soy allergy is among the most common childhood food allergies (usually outgrown by age 10) [1].
🏃 Athletes: Standard dose
⚖️ Obesity: Standard dose
Fat-soluble compounds may require dose adjustment in obesity.
🩺 Renal: Consult specialist
Dose adjustment may be needed in renal impairment.
🌱 Vegan: Standard dose
How to take
🍽 Timing: Post-exercise for MPS. With meals for general protein [1].
💊 With food: No specific requirements [1].
2 Which form?
| Form | Bioavailability | Vegan | Cost |
|---|---|---|---|
| ['Soy protein isolate (SPI, 90%+ protein)', 'standard', 'Highest protein concentration. Used in most studies. Contains isoflavones unless specifically removed [1].'] | Standard | Check label | |
| ['Soy protein concentrate (70% protein)', 'food-grade', 'Higher fiber/carb than isolate. Lower isoflavone content [1].'] | Standard | Check label | |
| ['Textured soy protein (TVP)', 'food ingredient', 'Used in plant-based meat alternatives. Not a supplement form [1].'] | Standard | Check label | |
| ['Fermented soy (tempeh, miso)', 'whole food', 'Fermentation modifies isoflavone bioavailability. Whole food, not supplement [1].'] | Standard | Check label |
3 Common questions
Is soy safe for breast cancer survivors? ▼
Current expert consensus (AICR, ACS): moderate soy FOOD intake (1–2 servings/day) is safe and may even be beneficial for breast cancer survivors. However, concentrated isoflavone SUPPLEMENTS (>40 mg/day isolated isoflavones) are not recommended due to insufficient safety data. The distinction between soy food and soy supplements is critical [2].
Does soy lower testosterone in men? ▼
No. A meta-analysis of 41 studies found soy protein and isoflavones do NOT significantly affect testosterone levels in men. The 'soy feminizes men' claim is not supported by clinical evidence at normal dietary intakes [1].
Is soy protein as good as whey for muscle building? ▼
Soy protein has a PDCAAS of 1.0 and supports MPS. However, it has slightly lower leucine content than whey (~8% vs ~11%). At equal leucine doses, MPS is similar. For muscle building, whey may have a marginal advantage due to higher leucine per gram, but soy is adequate [1].
Should I choose organic/non-GMO soy? ▼
Over 90% of US soybeans are genetically modified. If GMO avoidance is important to you, choose certified organic or Non-GMO Project verified soy protein. From a nutritional/safety perspective, no differences in protein quality or isoflavone content have been demonstrated between GM and non-GM soy [1].
4 Clinical evidence
Strong
Cardiovascular: FDA health claim authorized (1999) based on meta-analyses showing 25 g/day soy protein reduces LDL by 3–5%. EFSA subsequently declined to authorize equivalent claim, citing modest effect size. The American Heart Association endorsed soy protein as part of heart-healthy diet [1]. HIGH
Moderate
MPS: soy protein produces equivalent MPS to whey when matched for leucine content, though leucine content per gram is lower (~8% vs ~11%). Adequate for muscle maintenance [1]. Menopausal symptoms: soy isoflavones within soy protein reduce hot flash frequency in some meta-analyses (similar to red clover — equol producer dependency) [2]. Bone health: some epidemiological data suggest soy intake associated with lower fracture risk in Asian populations [1]. MODERATE
Insufficient
Breast cancer risk: epidemiological data from Asian populations suggest protective effect; interventional data insufficient. Current consensus: moderate soy food intake is safe even for breast cancer survivors, but high-dose isoflavone supplements are debated [2]. Prostate cancer: mixed epidemiological data [1]. Thyroid function: high-dose soy may interfere with levothyroxine absorption and iodine utilization [1]. Cognitive decline: 1 negative RCT in postmenopausal women [1]. LOW
5 Safety, toxicity & adverse events
Absolute contraindications
✕ Soy allergy
Relative
⚠ Hormone-sensitive conditions — isoflavone (phytoestrogen) content; evidence of harm is weak but caution advised
⚠ Levothyroxine — separate dosing (may reduce absorption)
⚠ Chronic kidney disease — protein load
🚩 Red flags
● Soy-allergic patient — top 8 allergen [1]
● Patient on levothyroxine consuming soy within 4 hours — absorption interference [1]
6 Interactions
Drug interactions
Levothyroxine Moderate
Mechanism: Soy protein/isoflavones may reduce levothyroxine absorption and interfere with iodine utilization [1].
Effect: Reduced thyroid hormone levels; increased TSH [1].
Action: Separate soy protein and levothyroxine by ≥4 hours [1].
Supplement synergies
Calcium + Vitamin D · Standard doses
Soy isoflavones + calcium/D3 for bone health in postmenopausal women [1].
Soy isoflavones + calcium/D3 for bone health in postmenopausal women [1].
7 Regulatory
United States (FDA): FDA health claim (1999): 25 g/day soy protein may reduce heart disease risk. Soy is a declared allergen [1].
European Union (EFSA): EFSA did not authorize equivalent cardiovascular claim. Soy is a declared allergen under EU Regulation 1169/2011 [1].
Japan: Soy products classified as Foods for Specified Health Uses (FOSHU) [1].
8 US supplement products
97
on-market products containing Soy Protein (NIH DSLD)
Brands carrying Soy Protein (55)
Click a brand to see its Soy Protein products.
9 Frequently paired with
10 References (4)
[1]FDA. Food labeling: health claims; soy protein and coronary heart disease. Fed Regist. 1999;64(206):57700-57733. GOVERNMENT Accessed: 2026-05-29
[2]Messina M. Soy and health update: evaluation of the clinical and epidemiologic literature. Nutrients. 2016;8(12):754. doi:10.3390/nu8120754 REVIEW Accessed: 2026-05-29
[3]Hamilton-Reeves JM, et al. Clinical studies show no effects of soy protein or isoflavones on reproductive hormones in men: results of a meta-analysis. Fertil Steril. 2010;94(3):997-1007. doi:10.1016/j.fertnstert.2009.04.038 META-ANALYSIS Accessed: 2026-05-29
[4]Reed KE, et al. Neither soy nor isoflavone intake affects male reproductive hormones: an expanded and updated meta-analysis. Reprod Toxicol. 2021;100:60-67. doi:10.1016/j.reprotox.2020.12.019 META-ANALYSIS Accessed: 2026-05-29
11 Cite this page
Vancouver: Pkhakadze G. Soy Protein — safety profile [Internet]. Tbilisi: PHIG; 2026 [cited 2026 Jun 24]. Available from: https://supplement.ge/ingredients/soy/
APA 7th: Pkhakadze, G. (2026). Soy Protein — Safety profile. Public Health Institute of Georgia. https://supplement.ge/ingredients/soy/
📋 Editorial information
Author: Prof. G. Pkhakadze, MD, MPH, PhD
Institution: Public Health Institute of Georgia (PHIG)
Affiliation: David Tvildiani Medical University (DTMU)
First published: January 2026
Last reviewed: 2026-05-29
Next review: December 2026
References: 4 cited sources
COI: SupplementIndex receives no funding from supplement manufacturers. All content independently authored by PHIG.
Process: Systematic literature review
📄 License & reuse
Published under Creative Commons Attribution 4.0 International (CC BY 4.0). You may share and adapt for any purpose with attribution.
Pkhakadze G. "Soy Protein — Safety Profile." SupplementIndex, PHIG, 2026. https://supplement.ge/ingredients/soy/ CC BY 4.0.
GP
Prof. G. Pkhakadze, MD, MPH, PhD
Professor of Public Health · Head of Department, DTMU
Editor-in-Chief, Georgian Medical Journal (ISSN 3088-4322)
Chair, Public Health Institute of Georgia · UEMS Public Health Section
Educational and public health purposes. CC BY 4.0. Consult your healthcare provider before starting any supplement. Corrections: info@accreditation.ge. Publisher: PHIG