Soluble, insoluble, and mixed rice bran dietary fibers generated distinct host-microbiota-metabolome responses in DSS-induced colitis, with formulation-dependent remodeling rather than uniform restoration, supporting rational selection and formulation of rice bran fiber ingredients for functional foods.
Key Findings
Results
All three rice bran dietary fiber formulations (RB-SDF, RB-IDF, and RB-MIX) alleviated symptoms, histological injury, barrier dysfunction, endotoxemia, and inflammation in DSS-induced colitis.
The study used a DSS-induced colitis mouse model to compare rice bran soluble dietary fiber (RB-SDF), insoluble dietary fiber (RB-IDF), and their mixture (RB-MIX)
Two doses of each formulation were tested
All formulations showed benefits across multiple endpoints including symptoms, histological injury, barrier dysfunction, endotoxemia, and inflammation
Relative advantages of each formulation varied by endpoint and dose rather than showing uniform superiority of one formulation
Results
RB-SDF showed the greatest histological protection and highest short-chain fatty acid (SCFA) output at high dose.
RB-SDF demonstrated superior histological protection compared to the other formulations
RB-SDF produced the greatest high-dose SCFA output among the three formulations
SCFAs are microbially produced metabolites associated with gut health benefits
This advantage was dose-dependent, being most pronounced at the high dose
Results
RB-IDF produced distinct benefits for barrier-related and metabolic endpoints compared to the other formulations.
RB-IDF showed specific advantages for barrier-related endpoints
RB-IDF also demonstrated distinct benefits for metabolic endpoints
These effects were formulation-specific and not replicated uniformly by RB-SDF or RB-MIX
This suggests insoluble fiber fractions have unique mechanisms of action distinct from soluble fractions
Results
RB-MIX remained effective but did not consistently match or exceed the strongest responses seen with the individual fiber fractions.
Despite combining both soluble and insoluble fractions, RB-MIX did not consistently outperform either individual fraction
The mixture failed to match the strongest endpoint-specific responses of RB-SDF or RB-IDF
This finding challenges the assumption that combining fiber fractions produces additive or synergistic effects
RB-MIX was still effective overall across multiple colitis endpoints
Results
Microbiota profiling and untargeted metabolomics revealed formulation-dependent remodeling of the gut microbiota and metabolome rather than uniform restoration.
Each fiber formulation produced distinct patterns of gut microbiota remodeling
Metabolomic profiles also differed by formulation, indicating formulation-dependent rather than uniform metabolic responses
Untargeted metabolomics was used to characterize metabolic profiles
Disease-axis and factorial analyses revealed partial shifts toward the CONTROL-associated metabolic profile
Analyses showed substantial contributions of fiber formulation and the formulation-by-dose interaction to observed outcomes
Results
Fiber formulation and the formulation-by-dose interaction were identified as substantial contributors to the observed metabolic and microbiota outcomes.
Factorial analyses were used to dissect the contributions of different experimental factors
Both the main effect of fiber formulation and the interaction between formulation and dose made substantial contributions to outcomes
Disease-axis analyses showed partial rather than complete shifts toward the healthy CONTROL-associated metabolic profile
These findings indicate that dose selection interacts with formulation type in determining outcomes
What This Means
This research suggests that not all dietary fiber is the same, even when it comes from the same source. Scientists studying rice bran fiber found that its soluble fraction (which dissolves in water), insoluble fraction (which does not dissolve), and a mixture of both produced meaningfully different effects in mice with gut inflammation similar to colitis. While all three forms of fiber helped reduce inflammation, gut damage, and other disease symptoms, each form had its own particular strengths — the soluble fiber was best at producing beneficial short-chain fatty acids and protecting gut tissue structure, while the insoluble fiber had unique advantages for gut barrier function and metabolism. Interestingly, the mixture of the two did not simply combine the best qualities of each.
The researchers also found that each type of fiber reshaped the gut microbiome and the chemical environment of the gut in its own distinct way, rather than all fibers restoring gut health through the same pathway. The dose of fiber also mattered, and its effects depended on which type of fiber was being used. These findings highlight that the biology of dietary fiber is more complex than previously appreciated, and that choosing between soluble and insoluble fiber fractions — or a mixture — may lead to meaningfully different health outcomes.
This research suggests that food scientists and nutritionists developing functional foods or dietary supplements should consider carefully which fraction of rice bran fiber to use, as the choice of fiber type and dose can produce quite different effects on gut health, the microbiome, and metabolism. Rather than assuming that mixing fiber types is always optimal, this work supports evidence-based selection of specific fiber fractions for targeted health applications.
Fu C, Cheng J, Qiu Z, Ye K, Wang X, Zhou Y, et al.. (2026). Soluble, Insoluble, and Mixed Rice Bran Dietary Fibers Generate Distinct Host-Microbiota-Metabolome Responses in DSS-Induced Colitis.. Journal of agricultural and food chemistry. https://doi.org/10.1021/acs.jafc.6c10465