Background: Irritable bowel syndrome (IBS) is one of the common gastrointestinal disorders with unknown etiology. In experimental models, it is proposed that soy isoflavones may suppress the clinical and psychological symptoms of IBS by alteration of gut barrier tight junctions.
Methods: We conducted this study to evaluate the effects of soy isoflavones on IBS symptoms and patients’ quality of life. In a randomized double blind placebo-controlled clinical trial, 67 patients with IBS were allocated to consume either soy isoflavones capsules or a placebo for 6 weeks. The primary outcome was a significant reduction in symptoms severity score and the secondary outcome was a significant improvement in quality of life.
Results: 45 participants completed the study. There was no significant changes in mean differences of symptoms severity score between the two groups; however soy isoflavone supplementation could significantly improve the quality
of life scores (p=0.009).
Conclusion: Soy isoflavones supplementation could improve the quality of life in patients with IBS; however it did not suppress the symptoms severity in 6 weeks. Further research with a longer duration is needed to determine the sustained clinical efficacy. 
This study was registered at clinicaltrials.gov as NCT02026518