The effectiveness of a plant-based milk with fermented brown rice on constipation symptoms via gut microbiota modulation: a double-blind randomized controlled trial.

PURPOSE: To evaluate the effects of a plant-based milk with fermented brown rice on constipation symptoms in patients with functional constipation and to identify post-intervention gut microbial alterations that may underlie potential mechanisms. METHODS: This is a randomized controlled trial among 100 participants with functional constipation. Participants were randomly assigned to the intervention group (plant-based milk with fermented brown rice, 2 bottles/day, 500 ml in total), or the control group (an isocaloric plant protein milk, equivalent dose) for 3 weeks. The primary outcome is complete spontaneous bowel movement (CSBM) rate, while secondary outcomes include score of individual symptoms assessment of constipation, bowel movement frequency (BMF), and gut microbial changes (metagenomics). RESULTS: A total of 99 participants completed the intervention. CSBM and BMF increased, and GSRS scores decreased over time in both groups, with no significant between-group differences. The plant-based milk with fermented brown rice relieved constipation symptoms more than the control group did, with significant between-group differences in straining, bloating and abdominal pain (all P < 0.05). The intervention group showed increases in 8 species, including three beneficial species in the genus Blautia, associated with relief of abdominal pain after the intervention. Meanwhile, machine learning models identified gut microbiota features predicting intervention responders. CONCLUSION: Our study did not find between-group difference in CSBM, while the plant-based milk with fermented brown rice showed greater effectiveness in relieving constipation symptoms and optimizing gut microbiota. Functional species benefiting intestinal health in response to the intervention were also identified. CLINICAL TRIAL REGISTRY: This study has been registered in the Chinese Clinical Trial Registry (https://www.chictr.org.cn/, ChiCTR2400088688).