Summary:
Dietary fiber is the indigestible component of plant foods that reaches the colon, where it interacts with gut microorganisms. Fermentable fiber is broken down by gut bacteria to produce short-chain fatty acids (SCFAs), including acetate, propionate and butyrate, which support intestinal barrier function, immune regulation and metabolism, while non-fermentable fiber helps maintain bowel regularity by increasing stool bulk. The gut microbiota plays an important role in health, with disruptions linked to conditions including gastrointestinal disorders, obesity and type 2 diabetes. However, few studies have examined the combined effects of fiber on both gut microbiota and bowel function. This randomised controlled study investigated whether four weeks of increased dietary fiber intake could influence gut microbiota composition and bowel-related quality of life in healthy adults. A total of 105 participants consumed either low-fiber foods (2.2 g/day) or fiber-enriched foods (8.2 g/day, including 6.4 g/day fermentable fiber). Researchers assessed changes in gut microbiota alongside bowel function, quality of life, sleep and skin health measures. Compared with the low-fiber group, those consuming higher fiber showed improved bowel-related quality of life and increased levels of beneficial bacteria associated with SCFA production. Effects on sleep and skin health were limited, although some associations with favourable microbial changes were observed. Overall, this study suggests that short-term increases in dietary fiber can improve bowel outcomes and positively modify the gut microbiota, supporting the potential long-term health benefits of higher fiber intake.
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Abstract:
This randomized, double-blind, controlled trial evaluated the effects of 4-week dietary fiber supplementation on gut microbiota, bowel-related quality of life, and secondary outcomes, including sleep and skin condition. A total of 105 healthy adults received either low-fiber foods (2.2 g/day total fiber, 1.2 g/day fermentable fiber) or high-fiber foods (8.2 g/day total fiber, including 6.4 g/day fermentable fiber). Gut microbiota was analyzed by 16S rRNA sequencing. Outcomes included stool diary, JPAC-QOL (Japanese version of the Patient Assessment of Constipation Quality of Life), OSA-MA (Oguri-Shirakawa-Azumi sleep inventory MA version), skin questionnaires, and fecal organic acids. The high-fiber group showed significant improvements in JPAC-QOL and increases in SCFA-associated genera such as Anaerostipes, Bifidobacterium, and Fusicatenibacter. These taxa positively correlated with other beneficial bacteria, including Faecalibacterium, suggesting ecological cooperation. The effects on sleep and skin were limited but correlated with beneficial bacteria, implying possible gut–brain and gut–skin axes involvement. This study demonstrated that short-term fiber supplementation meaningfully improved the bowel-related quality of life and beneficially modulated the gut microbiota in healthy adults. Although the systemic effects were modest, microbial shifts suggest that higher fiber intake may provide broader health benefits with longer interventions. This study was registered in the UMIN Clinical Trial Registry.
Article Publication Date: 05/09/2025
DOI: 10.3390/microorganisms13092068
