Effects of Defatted Rice Bran Fortified Bread on Gut Microbiota Composition of Healthy Adults with Low Dietary Fibre Intake: Protocol for a Crossover Randomised Controlled Trial (Preprint)

BACKGROUND Inadequate dietary fiber (DF) intake is associated with several human diseases. Bread is commonly consumed, and can increase its DF content by incorporating defatted rice bran (DRB). OBJECTIVE This first human study on DRB fortified bread, primarily aims to assess the effect of DRB bread on the relative abundance of a composite of key microbial genera and species in stool samples. Secondary outcomes include clinical (cardiovascular risk profile), patient-reported (daily bread consumption and bowel movement, digestive comfort, general well-being, total DF intake), biological (stool microbiota gene abundances, stool and plasma metabolites). Exploratory outcomes include physiome (whole gut and regional transit time, and gas fermentation profiles) outcomes in healthy adults with low DF intake. METHODS The BREAD (Bread Related Effects on Microbial Distribution) study is a two-armed, placebo-controlled, double-blind, randomized, crossover study. The study duration is fourteen weeks: two weeks lead-in, four weeks intervention per phase, two weeks washout, and two weeks follow-up. Sixty healthy adults with low DF intake (<18g/day (females), <22g/day (males)) were recruited in Christchurch, New Zealand between June and December 2022. Randomized participants consumed three (for females)/ four (for males) slices of fortified bread per day, then placebo white bread and vice versa. The DRB fortified bread provided 8 g (for females) and 10.6 g (for males) of total DF, while the placebo (a matched commercial white toast bread) provided 2.7 g for females and 3.6 g for males of total DF. Before and after each intervention phase, participants provided stool and blood samples to assess biological responses; completed a three-day food diary to assess usual intakes; online questionnaires to assess gut symptoms, general and mental well-being, daily bread intake and bowel movement via an app; underwent anthropometry and blood pressure measurements; drank blue food dye to assess whole gut transit time. In addition, 15 participants from the cohort ingested Atmo gas-sensing capsules to assess gut regional’s fermentation gas profile. RESULTS At the time of writing, data was still being analysed. Results will be published as separate manuscripts. CONCLUSIONS This study will offer insights into the prospect of consuming DRB fortified bread to effectively modulate health-promoting gut microbes and their metabolism, and DF intake in healthy adults with low DF intake. CLINICALTRIAL ACTRN12622000884707