Feeding the Mind: Cognitive Effects of Soy

By Ajla Bristina, BS and Naiman Khan, PhD, RD

Supporting brain health and cognitive function is vital to success and well-being throughout life. From academic achievement in youth to maintaining independence and quality of life in older adulthood, cognitive function supports our ability to learn, respond, and adapt to dynamic environments. The brain is a metabolically demanding organ that is sensitive to environmental and lifestyle influences. Growing research highlights the significant role of nutrition in supporting its function. Nutrients and bioactive compounds found in foods—such as monounsaturated fats, antioxidants, and phytoestrogens—have shown promise in enhancing cognitive health.  

Soy Supports Brain Health and Cognition  

A significant body of research has examined how soy foods and soybean components may influence brain function. Soy foods are an excellent dietary source of high-quality protein and are uniquely rich sources of isoflavones.^1–3 Soy isoflavones (daidzein, genistein, and glycitein) are phytoestrogens that can interact with estrogen receptors (ERs).^4–6 They have been studied for a variety of potential benefits, including protection against metabolic syndrome, cardiovascular diseases, and obesity. Since brain structure, development, and cognitive function rely on the health of other organ systems, the potential cardiovascular and metabolic benefits of soy may indirectly support brain health and cognitive performance. On the other hand, soy isoflavones preferentially bind to and activate ER‑β, which is abundant in the hippocampus and prefrontal cortex; brain structures vital for memory, learning, and decision making.  

Isoflavones and the Brain: A Closer Look at the Science 

Previous systematic reviews and meta-analyses provide insight into the potential of soy foods and soy isoflavones to elicit cognitive benefits.^7,8 A meta-analysis of 16 randomized controlled trials (RCTs) conducted among 1,386 adults found small but significant cognitive improvements from soy isoflavone consumption.⁹ The meta-analysis included trials focusing primarily on postmenopausal women; study duration ranged between six to 130 weeks. Effects were observed across several cognitive domains but primarily on memory.     

One of the earliest RCTs to be conducted examined the effects of a dietary soy intervention in healthy adults on attention, memory, and frontal lobe function.¹⁰ Participants were allocated to either a high-soy isoflavone (100 mg/d) or an isocaloric low-soy (0.5 mg/d) diet for 10 weeks. The high-soy diet resulted in significant cognitive improvements with effects observed on short-term memory, long-term memory, and mental flexibility. Another relatively small, double-blind study evaluated a 12-week soy isoflavone intervention in 36 postmenopausal women.¹¹ Participants consumed 60 mg/d of encapsulated isoflavones while the control group received identical placebo capsules. Results from this study show that women consuming the isoflavones had significant improvement in long-term recall of pictures, mental flexibility, attention, and planning. Additionally, a different study demonstrated that cognitive function in men improved following soy isoflavone supplementation. Forty healthy men receiving daily encapsulated supplements comprising 116 mg of isoflavones in a 12-week double-blind placebo-controlled cross-over trial demonstrated enhanced spatial working memory.¹² When compared to the placebo group, treatment group participants had fewer attempts and errors, as well as less time needed to correctly identify information.  

More recently, the benefits of soy foods and isoflavones have been extended to brain structural and functional outcomes. For example, a cross-over RCT among 23 healthy older participants (60-70 years) showed that soynut intake over 16 weeks improved psychomotor speed as well as cerebral blood flow in four brain clusters including temporal and frontal lobes.¹³ The soynut intervention provided ~25. 5 g of soy protein and 174 mg of isoflavones daily, whereas during the control period, no soynuts were consumed. Further, in a large-scale, observational study focused on the intake of total isoflavones and brain morphology, higher isoflavone intake was selectively associated with a lower decrease in hippocampal volume among older adults.¹⁴ This study utilized longitudinal data from 1,325 adult men and women, with the highest isoflavone intake group consuming 70.5 ± 24.0 mg/d of isoflavones.  

Understanding the Variability in Research Findings  

Although the literature overall points to a small but positive effect, the evidence supporting the role of soy and isoflavones on cognitive function is not consistent. For example, in a two-and=a-half year double-blind RCT involving 350 healthy postmenopausal women who consumed either 25 g/d isoflavone-rich soy protein (91 mg isoflavones) or milk protein, there were no differences between groups on a battery of neuropsychological tests.¹⁵ Possible explanations for the inconsistency could be due to differences in demographic characteristics of populations studied, habitual soy food and isoflavone intake, isoflavone dose, and study duration.   

Another factor to consider is equol producer status. Equol is a metabolite produced by certain gut microbiota from the soy isoflavone daidzein; it is more biologically active than its parent isoflavone.¹⁶ Following soy consumption, ~50% of Japanese individuals convert daidzein to equol, whereas ‘producer status’ within the U.S. population is estimated to only be 20-30%.^17-21 Equol producer status should be considered when investigating the effects of soy consumption.   

Exploring Soy’s Role in Childhood Brain Development 

Work testing the effects of soy foods or isoflavones on brain health and cognitive function has been limited to adults. Given the significance of establishing healthy eating habits early in life,^22–24 it is important to determine the health effects of soy consumption in childhood. Nutrition in childhood and adolescence predicts long-term physical and cognitive health.^25,26 Adolescence is marked by the development of brain regions responsible for crucial cognitive processes (e.g., executive function).²⁷ Executive functions have demonstrated importance for academic success, specifically within math and reading achievement.²⁸ Research shows that isoflavones are more bioavailable in children versus adults²⁹ and nutritional habits in childhood track into adulthood; therefore, the absence of studies involving children may be a missed opportunity to optimize neurocognitive development.  

To address this gap in the literature, the Neurocognitive Health Behavior Laboratory at the University of Illinois is conducting a RCT investigating the effects of daily soy consumption on child health outcomes. The Plants Optimizing Development Study will examine effects on cognition, metabolic health, reproductive hormones, and body composition following a three-month dietary intervention in children (N=96) ages 8–11 years. Treatment group participants will consume a daily mix of soy foods (e.g., soy milk, soynuts, tofu) with the target isoflavone intake goal being 50 mg/d, whereas control group subjects will consume isocaloric plant-based alternatives (e.g., pea milk, chickpeas). This study is registered at ClinicalTrials.gov under the number NCT6276426.  

Conclusion

Intriguing evidence indicates that because they contain isoflavones, soy food intake has the potential to improve brain function and cognitive performance. However, further research is needed to determine the overall efficacy of consuming soy foods across different populations and to establish appropriate soy consumption recommendations to elicit effects for brain health and cognitive function.

REFERENCES

1. Hughes, G. J., Ryan, D. J., Mukherjea, R. & Schasteen, C. S. Protein digestibility-corrected amino acid scores (PDCAAS) for soy protein isolates and concentrate: criteria for evaluation. J Agric Food Chem 59, 12707–12 (2011). 

2. Messina, M. J. Legumes and soybeans: overview of their nutritional profiles and health effects. Am J Clin Nutr 70, 439S-450S (1999). 

3. Murphy, P. A., Barua, K. & Hauck, C. C. Solvent extraction selection in the determination of isoflavones in soy foods. Journal of Chromatography B 777, 129–138 (2002). 

4. Duncan, A. M. Soy Beans: Dietary Importance. in Encyclopedia of Food and Health 43–47 (Elsevier Inc., 2015). doi:10.1016/B978-0-12-384947-2.00639-5. 

5. Kuiper, G. G. et al. Comparison of the ligand binding specificity and transcript tissue distribution of estrogen receptors alpha and beta. Endocrinology 138, 863–70 (1997). 

6. Kuiper, G. G. et al. Interaction of estrogenic chemicals and phytoestrogens with estrogen receptor beta. Endocrinology 139, 4252–63 (1998). 

7. Cui, C. et al. Effects of soy isoflavones on cognitive function: A systematic review and meta-analysis of randomized controlled trials. Nutr Rev 78, 134–144 (2020). 

8. Lehert, P., Villaseca, P., Hogervorst, E., Maki, P. M. & Henderson, V. W. Individually modifiable risk factors to ameliorate cognitive aging: a systematic review and meta-analysis. Climacteric 18, 678–89 (2015). 

9. Cui, C. et al. Effects of soy isoflavones on cognitive function: a systematic review and meta-analysis of randomized controlled trials. Nutr Rev 78, 134–144 (2020). 

10. File, S. et al. Eating soya improves human memory. Psychopharmacology (Berl) 157, 430–436 (2001). https://pubmed.ncbi.nlm.nih.gov/11605103/.  

11. Duffy, R., Wiseman, H. & File, S. E. Improved cognitive function in postmenopausal women after 12 weeks of consumption of a soya extract containing isoflavones. Pharmacol Biochem Behav 75, 721–729 (2003). https://www.sciencedirect.com/science/article/abs/pii/S0091305703001163?via%3Dihub.  

12. Thorp, A. A., Sinn, N., Buckley, J. D., Coates, A. M. & Howe, P. R. C. Soya isoflavone supplementation enhances spatial working memory in men. British Journal of Nutrition 102, 1348–1354 (2009). 

13. Kleinloog, J. P. D., Tischmann, L., Mensink, R. P., Adam, T. C. & Joris, P. J. Longer-term soy nut consumption improves cerebral blood flow and psychomotor speed: results of a randomized, controlled crossover trial in older men and women. Am J Clin Nutr 114, 2097–2106 (2021). 

14. Nakamoto, M. et al. Isoflavone intake is associated with longitudinal changes in hippocampal volume, but not total grey matter volume, in Japanese middle-aged and older community dwellers. Eur J Nutr 64, 151 (2025). 

15. Henderson, V. W. et al. Long-term soy isoflavone supplementation and cognition in women: a randomized, controlled trial. Neurology 78, 1841–8 (2012). 

16. Setchell, K. D. R., Brown, N. M. & Lydeking-Olsen, E. The Clinical Importance of the Metabolite Equol—A Clue to the Effectiveness of Soy and Its Isoflavones. J Nutr 132, 3577–3584 (2002). 

17. Sekikawa, A. et al. Potential Protective Mechanisms of S-equol, a Metabolite of Soy Isoflavone by the Gut Microbiome, on Cognitive Decline and Dementia. International Journal of Molecular Sciences vol. 23 Preprint at https://doi.org/10.3390/ijms231911921 (2022). 

18. Sekikawa, A. et al. Effect of S-equol and Soy Isoflavones on Heart and Brain. Curr Cardiol Rev 15, 114–135 (2019). 

19. Jackson, R. L., Greiwe, J. S. & Schwen, R. J. Emerging evidence of the health benefits of S-equol, an estrogen receptor β agonist. Nutr Rev 69, 432–448 (2011). 

20. Setchell, K. D. R. & Cassidy, A. Dietary Isoflavones: Biological Effects and Relevance to Human Health. J Nutr 129, 758S-767S (1999). 

21. Setchell, K. D. R. & Clerici, C. Equol: History, Chemistry, and Formation. J Nutr 140, 1355S-1362S (2010). 

22. No authors listed. Guidelines for school health programs to promote lifelong healthy eating. J Sch Health 67, 9–26 (1997). 

23. Birch, L. L. Development of food acceptance patterns in the first years of life. Proc Nutr Soc 57, 617–24 (1998). 

24. Mennella, J. A. & Beauchamp, G. K. Flavor experiences during formula feeding are related to preferences during childhood. Early Hum Dev 68, 71–82 (2002). 

25. Mikkilä, V., Räsänen, L., Raitakari, O. T., Pietinen, P. & Viikari, J. Consistent dietary patterns identified from childhood to adulthood: the cardiovascular risk in Young Finns Study. Br J Nutr 93, 923–31 (2005). 

26. Fruh, S. et al. A practical approach to obesity prevention: Healthy home habits. J Am Assoc Nurse Pract 33, 1055–1065 (2021). 

27. Walk, A. M. et al. Adiposity is related to neuroelectric indices of motor response preparation in preadolescent children. International Journal of Psychophysiology 147, 176–183 (2020). 

28. Best, J. R., Miller, P. H. & Naglieri, J. A. Relations between executive function and academic achievement from ages 5 to 17 in a large, representative national sample. Learn Individ Differ 21, 327–336 (2011). 

29. Halm, B. M., Ashburn, L. A. & Franke, A. A. Isoflavones from soya foods are more bioavailable in children than adults. British Journal of Nutrition 98, 998–1005 (2007).