The growing global consumption of soy-based foods has prompted increased scrutiny of their phytoestrogenic compounds, particularly isoflavones, and their potential implications for human health. This review addresses a critical gap in food science literature by systematically evaluating technological strategies for reducing isoflavone content in soy-based products whilst maintaining their nutritional and functional properties.
The significance of this research has been amplified by recent regulatory developments, notably the French Agency for Food, Environmental and Occupational Health & Safety (ANSES) establishment of a toxicological reference value (TRV) of 0.02 mg/kg body weight per day for isoflavones, equivalent to 1.4 mg daily for a 70-kg adult (ANSES, 2025).
This article provides an analysis of scalable interventions specifically designed to mitigate exposure through different food matrices. It proposes evidence-based solutions for food manufacturers, regulators, and public health officials seeking to balance the nutritional benefits of soy consumption with emerging food safety considerations for vulnerable populations, including infants, pregnant women, and individuals with hormone-sensitive conditions.
Isoflavone characteristics and distribution in soy-based foods
Isoflavones represent a class of naturally occurring polyphenolic compounds predominantly found in soybeans, existing primarily as glucosides that undergo conversion to biologically active aglycones through various processing methods or fermentation processes.
These compounds – along with other quality traits of soy, such as protein, oil, fatty acids, and soluble sugars – vary according to plant genotype, location, climate, water availability, and maturity group (do Prado et al., 2022). Consequently, the concentration and bioavailability of isoflavones differ markedly across soy food matrices, processing technologies, and serving sizes, leading to substantial variability in dietary exposure patterns.
Understanding this variability is essential for developing targeted reduction strategies. The heterogeneous distribution of isoflavones across soy products reflects differences in processing intensity, matrix effects, and the degree of protein isolation or concentration employed during manufacture.
Comparative analysis of isoflavone content across soy food categories
| Food Product | Isoflavone Range (mg/100g) | Typical Serving Size | Isoflavone per Serving (mg) | Primary Sources |
|---|---|---|---|---|
| Boiled soybeans | 40–90 | 100g | 40–90 | USDA; Bensaada, 2024 |
| Commercial soy drink | 3–17 | 240mL | 8–40 | Kim, 2022; USDA |
| Firm tofu | 5–30 | 100g | 5–30 | USDA; Bensaada, 2024 |
| Silken tofu | 5–25 | 100g | 5–25 | USDA |
| Tempeh | 20–120 | 100g | 20–120 | Haron, 2009 |
| Miso | 10–60 | 15g (soup portion) | 1.5–9 | Rizzo, 2018; Saeed, 2022 |
| Natto | 40–120 | 50g | 20–60 | Rizzo, 2018 |
| Soy protein isolate | 100–200 | 30g (serving scoop) | 30–60 | USDA |
| Textured soy protein | 20–80 | 100g (cooked) | 20–80 | USDA; Bensaada, 2024 |
The data reveal substantial inter-product variability, with soy protein isolates containing the highest concentrations (100–200 mg/100g) whilst processed products such as tofu demonstrate considerably lower levels (5–30 mg/100g). This variation underscores the potential for technological intervention to achieve meaningful reductions.
Technological strategies for isoflavone reduction
Water-based treatment protocols
Water-based extraction and washing represent the most accessible and economically viable approaches for reduction in both domestic and industrial settings. Research demonstrates that systematic soaking protocols with periodic water renewal, combined with discarding of soak water, can achieve reductions of up to 70% in certain soy-based preparations (Bensaada et al., 2024).
The mechanism underlying this reduction involves the preferential partitioning of water-soluble glucosides into the aqueous phase, effectively removing them from the solid matrix.
The efficacy of water-based treatments can be enhanced through controlled boiling procedures with subsequent disposal of cooking water. This two-stage approach—soaking followed by thermal treatment with water disposal—maximises extraction whilst preserving the structural integrity and nutritional value of the remaining soy proteins.
Coagulation and mechanical processing in tofu manufacture
Tofu production offers particular opportunities for reduction through optimised coagulation and mechanical pressing cycles. During the coagulation process, isoflavones preferentially partition into the whey fraction rather than incorporating into the protein curds.
Systematic optimisation of coagulation parameters, including coagulant type, concentration, and reaction time, combined with enhanced pressing and drainage protocols, enables substantial reductions in final product content (USDA; Bensaada, 2024).
The mechanical pressing stage provides additional opportunities for removal through enhanced whey expulsion. Extended pressing cycles and the incorporation of intermediate rinsing steps during pressing can further reduce levels whilst maintaining desirable textural characteristics in the finished product.
Fermentation: a complex intervention with limited reduction potential
Contrary to common assumptions, fermentation processes do not reliably reduce total content in soy products. Instead, microbial β-glucosidases present during fermentation catalyse the conversion of glucosides into their corresponding aglycone forms, which demonstrate enhanced bioavailability and potentially greater biological activity (do Prado et al., 2022). This biochemical transformation effectively concentrates the biologically active fraction whilst maintaining or potentially increasing total exposure levels.
Fermented products, including tempeh, miso, natto, and tamari, thus represent categories in which alternative mitigation strategies could be applied either prior to or following the fermentation process to achieve meaningful exposure reductions. In these cases, ingredient substitution (e.g., partial replacement of soy with pulses and cereals) may also be considered as a complementary approach to lower isoflavone intake without compromising product quality.
Industrial extraction technologies
Advanced extraction technologies offer the most comprehensive approach to reduction, particularly for specialised applications requiring minimal residual levels. Aqueous extraction protocols, optionally combined with ethanol-based solvent systems, followed by protein recovery and reconstitution, can yield products with dramatically reduced content suitable for vulnerable populations, including infant formula applications.
These industrial approaches require careful economic assessment, as they involve additional processing steps, increased energy consumption, and potential impacts on protein functionality. However, for applications where maximum reduction is required, such as products intended for hormone-sensitive individuals or infant nutrition, these technologies represent viable solutions.
Evidence-based recommendations for food industry implementation
Primary processing modifications
Food manufacturers should prioritise the implementation of water-based protocols as the foundation of reduction strategies. The adoption of systematic soaking with water renewal, combined with disposal of soak and cooking water, represents a scalable intervention that can be readily integrated into existing production workflows with minimal capital investment.
Optimisation of tofu manufacturing protocols
Tofu manufacturers should focus on maximising whey removal through enhanced pressing techniques and the incorporation of intermediate rinsing steps. The systematic optimisation of coagulation parameters, including coagulant selection and processing conditions, offers additional opportunities for reduction whilst maintaining product quality.
Strategic avoidance of fermentation for reduction purposes
Industry stakeholders should recognise that fermentation processes are inappropriate as primary reduction strategies. Where fermented products are desired, alternative techniques should be applied to source materials prior to fermentation, or specialised post-fermentation treatments should be considered.
Development of specialised low-isoflavone product lines
The implementation of advanced extraction technologies should be considered for the development of specialised product lines targeting sensitive populations. These products require dedicated production lines and quality assurance protocols but address specific market needs for minimal-isoflavone products.
Voluntary labelling implementation
The introduction of voluntary content labelling, with clear reference to the ANSES toxicological reference value (TRV), would enhance consumer awareness and enable informed dietary choices. Recommended labelling should also include appropriate guidance for sensitive populations.
Proposed labelling framework:
Total isoflavones: X mg per 100g
Guidance: ANSES (2025) safe daily intake = 0.02 mg/kg body weight/day (≈1.4 mg/day for a 70-kg adult). Sensitive groups (infants, pregnant women, hormone-sensitive individuals) should consult healthcare professionals.
Policy implications and regulatory considerations
The establishment of reference values by ANSES represents a significant development in phytoestrogen risk assessment, with implications extending beyond French regulatory frameworks. The conservative TRV of 0.02 mg/kg body weight per day reflects growing concerns regarding potential adverse effects in sensitive populations and sets an important precedent for a risk-based regulatory approach across various jurisdictions.
The evidence supporting water-based processing as an effective reduction strategy provides policymakers with practical tools for risk mitigation without requiring fundamental changes to existing food systems. The scalability and cost-effectiveness of these interventions make them particularly suitable for implementation across diverse food production contexts.
Regulatory recommendations
Regulatory authorities should consider encouraging industry adoption of validated reduction methods through guidance documents and technical assistance programmes. The development of standardised analytical methods for monitoring would facilitate consistent implementation and compliance assessment across different manufacturers and product categories.
Support for low-isoflavone development in mass catering applications represents an additional policy opportunity, particularly for institutions serving vulnerable populations. This approach would complement individual consumer choice with systematic risk reduction in controlled feeding environments.
Conclusions and future directions
This comprehensive analysis demonstrates that significant reductions can be achieved through readily implementable technological interventions, with water-based treatments representing the most practical and cost-effective approach for widespread industry adoption. The substantial variability in levels across different soy products (ranging from 5–30 mg/100g in processed tofu to 100–200 mg/100g in protein isolates) indicates considerable scope for technological intervention.
The evidence clearly establishes that soaking, boiling, and water disposal represent the most effective scalable methods for total reduction, whilst fermentation processes increase aglycone bioavailability rather than reducing total exposure. Industrial extraction methods may be justified for sensitive-population products, despite higher implementation costs and complexity.
The food industry should give priority to the voluntary indication of isoflavone content on food labels, in comparison with the safety levels established by ANSES. This approach would enhance consumer choice whilst supporting the development of specialised low-isoflavone lines for vulnerable populations.
Dario Dongo
References
- Agence nationale de sécurité sanitaire de l’alimentation, de l’environnement et du travail (ANSES). (2025, March). Avis relatif à l’élaboration de VTR long terme par voie orale pour les isoflavones : Rapport d’expertise collective, Saisine n° 2022-SA-0221. ANSES. https://www.anses.fr/sites/default/files/VSR2022SA0221RA
- Bensaada, S., Peruzzi, G., Cubizolles, L., Denayrolles, M., & Bennetau-Pelissero, C. (2024). Traditional and domestic cooking dramatically reduce estrogenic isoflavones in soy foods. Foods, 13(7), 999. https://doi.org/10.3390/foods13070999
- do Prado, F. G., Pagnoncelli, M. G. B., de Melo Pereira, G. V., Karp, S. G., & Soccol, C. R. (2022). Fermented soy products and their potential health benefits: A review. Microorganisms, 10(8), 1606. https://doi.org/10.3390/microorganisms10081606
- Haron, H., Ismail, A., Azlan, A., Shahar, S., & Peng, L. S. (2009). Daidzein and genistein contents in tempeh and selected fermented soy products. Food Chemistry, 115(4), 1350–1356. https://doi.org/10.1016/j.foodchem.2009.01.053
- Kim, Y., Je, Y., & Giovannucci, E. (2022). Usual intake of dietary isoflavone and its major food sources amongst adults. Nutrients, 14(3), 543. https://doi.org/10.4162/nrp.2022.16.S1.S134
- Rizzo, G., & Baroni, L. (2018). Soy, soy foods and their role in vegetarian diets. Nutrients, 10(1), 43. https://doi.org/10.3390/nu10010043
- Saeed, F., Afzaal, M., Shah, Y. A., Khan, M. H., Hussain, M., Ikram, A., Ateeq, H., Noman, M., Saewan, S. A., & Khashroum, A. O. (2022). Miso: A traditional nutritious & health-endorsing fermented product. Food Science & Nutrition, 10(12), 4103-4111. https://doi.org/10.1002/fsn3.3029
- USDA. (2008). USDA Database for the Isoflavone Content of Selected Foods, release 2.0. Nutrient Data Laboratory. https://www.ars.usda.gov/ARSUserFiles/80400525/data/isoflav/isoflav_r2.pdf
Dario Dongo, lawyer and journalist, PhD in international food law, founder of WIISE (FARE - GIFT - Food Times) and Égalité.
