Effects of defatted rice bran-fortified bread on gut microbiome, cardiovascular risk, gut discomfort, wellbeing and gut physiology in healthy adults with low dietary fibre intake.

2025-06
Clinical nutrition ESPEN 67
- Hwei Min Ng
- Jasjot Maggo
- Catherine L Wall
- Simone B Bayer
- Jane A Mullaney
- Diana Cabrera
- Karl Fraser
- Janine M Cooney
- Catrin S Günther
- Warren C McNabb
- Meika Foster
- Chris Frampton
- Richard B Gearry
- Nicole C Roy

PubMed: 40127766
DOI: 10.1016/j.clnesp.2025.03.045

Study Design

Type: Randomized Controlled Trial (RCT)
Sample size: n = 15
Population: 56 healthy adults with low baseline DF intake
Methods: two-arm, placebo-controlled, double-blind, randomised, crossover study; participants consumed three (females) or four (males) slices of DRB-fortified bread or control bread daily as part of their usual diet for four weeks, with the intervention periods separated by a two-week washout; in a sub-study, 15 participants ingested gas-sensing capsules
Blinding: Double-blind
Duration: four weeks

Background & aims

Inadequate dietary fibre (DF) intake is associated with suboptimal gut function and increased risk of several human diseases. Bread is commonly consumed and is ideal to incorporate cereal bran to increase DF content. No human studies have investigated the effects of defatted rice bran (DRB) in bread, which has triple the DF of white bread, purported hypo-allergenicity and a unique nutrient profile, as a dietary intervention in healthy adults. This study aims to assess the relative abundances of a composite of key faecal microbial genera and species involved in DF fermentation and metabolism following the habitual intake of DRB-fortified bread and its influence on other biological markers of host and microbial interactions, cardiovascular risk profile, patient-reported outcomes, total DF intake, and gut physiology in healthy adults with low baseline DF intake.

Methods

Fifty-six healthy adults with low baseline DF intake (<18 g/day (females), <22 g/day (males)) completed a two-arm, placebo-controlled, double-blind, randomised, crossover study. Participants consumed three (females) or four (males) slices of DRB-fortified bread or control bread daily as part of their usual diet for four weeks, with the intervention periods separated by a two-week washout. Outcomes included faecal microbiota composite (primary outcome); relative abundances (taxa and gene); faecal moisture content and bile acid concentrations; plasma and faecal organic acid concentrations; cardiovascular risk profile; gut comfort, psychological wellbeing parameters; total DF intake; whole gut transit time, and were measured at baseline and following each intervention phase. Additionally, in a sub-study, 15 participants ingested gas-sensing capsules to assess whole and regional gut transit times, and total and regional colonic hydrogen and carbon dioxide concentrations at the same timepoints.

Results

DRB-fortified bread consumption significantly increased total DF intake from 20.7 g/day to 43.4 g/day (p < 0.001). No significant differences were observed in the primary outcome, microbial taxa composite within and between groups (False Discovery Rate (FDR) correction, p > 0.10). As compared to control, the DRB group had increased relative abundances of Faecalibacterium prausnitzii (unadjusted p = 0.04), Bifidobacterium longum (unadjusted p = 0.12), and Bacteroides ovatus (unadjusted p = 0.10); lower relative abundances in Coprococcus genus (unadjusted p = 0.09), Roseburia faecis (unadjusted p = 0.02) and Prevotella copri species (unadjusted p = 0.05). However, no significant differences were observed in the relative abundances of these taxa within and between groups (FDR correction p > 0.10) and for most of the other outcomes between groups (p > 0.05). Only mean serum high-density lipoprotein (HDL) concentrations significantly increased (p = 0.006), and mean total cholesterol (TC) to HDL concentration ratio significantly lowered (p = 0.02) in the DRB group compared to the control group.

Conclusion

This is the first human study to show that a high-DF DRB-fortified bread improved DF intake, HDL cholesterol profiles, and may affect the gut microbiota composition in healthy adults with low DF intake. These findings support the substitution of white bread with DRB-fortified bread as an effective method to improve DF intake, which may have subsequent benefits on gut physiology and metabolic health.

Research Insights

rice bran→Decreased Prevotella Copri Relative Abundance
As compared to control, the DRB group had ... lower relative abundances in ... Prevotella copri species (unadjusted p = 0.05) ... However, no significant differences were observed in the relative abundances of these taxa within and between groups (FDR correction p > 0.10)
Effect
Neutral
Effect size
Small
Dose
Three (females) or four (males) slices of DRB-fortified bread daily
rice bran→Decreased Roseburia faecis Relative Abundance
As compared to control, the DRB group had ... lower relative abundances in ... Roseburia faecis (unadjusted p = 0.02) ... However, no significant differences were observed in the relative abundances of these taxa within and between groups (FDR correction p > 0.10)
Effect
Neutral
Effect size
Small
Dose
Three (females) or four (males) slices of DRB-fortified bread daily
rice bran→Improved Gut Comfort
no significant differences were observed ... gut comfort ... between groups (p > 0.05)
Effect
Neutral
Effect size
Small
Dose
Three (females) or four (males) slices of DRB-fortified bread daily
rice bran→Improved Gut Microbiota Composition
No significant differences were observed in the primary outcome, microbial taxa composite within and between groups (False Discovery Rate (FDR) correction, p > 0.10).
Effect
Neutral
Effect size
Small
Dose
Three (females) or four (males) slices of DRB-fortified bread daily
rice bran→Improved Psychological Wellbeing
no significant differences were observed ... psychological wellbeing parameters ... between groups (p > 0.05)
Effect
Neutral
Effect size
Small
Dose
Three (females) or four (males) slices of DRB-fortified bread daily
rice bran→Increased Bacteroides ovatus Abundance
As compared to control, the DRB group had increased relative abundances of ... Bacteroides ovatus (unadjusted p = 0.10) ... However, no significant differences were observed in the relative abundances of these taxa within and between groups (FDR correction p > 0.10)
Effect
Neutral
Effect size
Small
Dose
Three (females) or four (males) slices of DRB-fortified bread daily
rice bran→Increased Bifidobacterium longum Relative Abundance
As compared to control, the DRB group had increased relative abundances of ... Bifidobacterium longum (unadjusted p = 0.12) ... However, no significant differences were observed in the relative abundances of these taxa within and between groups (FDR correction p > 0.10)
Effect
Neutral
Effect size
Small
Dose
Three (females) or four (males) slices of DRB-fortified bread daily
rice bran→Increased Faecalibacterium prausnitzii Levels
As compared to control, the DRB group had increased relative abundances of Faecalibacterium prausnitzii (unadjusted p = 0.04) ... However, no significant differences were observed in the relative abundances of these taxa within and between groups (FDR correction p > 0.10)
Effect
Neutral
Effect size
Small
Dose
Three (females) or four (males) slices of DRB-fortified bread daily
rice bran→Increased Fecal Lactobacilli
DRB-fortified bread consumption significantly increased total DF intake from 20.7 g/day to 43.4 g/day (p < 0.001).
Effect
Beneficial
Effect size
Large
Dose
Three (females) or four (males) slices of DRB-fortified bread daily
rice bran→Increased HDL Cholesterol Levels
Only mean serum high-density lipoprotein (HDL) concentrations significantly increased (p = 0.006) in the DRB group compared to the control group.
Effect
Beneficial
Effect size
Small
Dose
Three (females) or four (males) slices of DRB-fortified bread daily
rice bran→Increased High-Density Lipoprotein Level
Only mean serum high-density lipoprotein (HDL) concentrations significantly increased (p = 0.006), and mean total cholesterol (TC) to HDL concentration ratio significantly lowered (p = 0.02) in the DRB group compared to the control group.
Effect
Beneficial
Effect size
Small
Dose
3 (females) or 4 (males) slices of DRB-fortified bread per day (providing ~22.7 g/day additional dietary fiber)
rice bran→Reduced Cardiovascular Risk Profile
no significant differences were observed in ... cardiovascular risk profile ... between groups (p > 0.05)
Effect
Neutral
Effect size
Small
Dose
Three (females) or four (males) slices of DRB-fortified bread daily
rice bran→Reduced Low-Density Lipoprotein Level
mean total cholesterol (TC) to HDL concentration ratio significantly lowered (p = 0.02) in the DRB group compared to the control group.
Effect
Beneficial
Effect size
Small
Dose
Three (females) or four (males) slices of DRB-fortified bread daily
rice bran→Reduced Relative Abundance of Coprococcus Genus
As compared to control, the DRB group had ... lower relative abundances in Coprococcus genus (unadjusted p = 0.09) ... However, no significant differences were observed in the relative abundances of these taxa within and between groups (FDR correction p > 0.10)
Effect
Neutral
Effect size
Small
Dose
Three (females) or four (males) slices of DRB-fortified bread daily
rice bran→Reduced Whole Gut Transit Time
no significant differences were observed ... whole gut transit time ... between groups (p > 0.05)
Effect
Neutral
Effect size
Small
Dose
Three (females) or four (males) slices of DRB-fortified bread daily

Adverse Events Reported

rice bran→Overall tolerability
No significant differences were observed in the primary outcome, microbial taxa composite within and between groups (False Discovery Rate (FDR) correction, p > 0.10). ... for most of the other outcomes between groups (p > 0.05).
Finding
Reported