Dietary supplementation with rice bran or navy bean alters gut bacterial metabolism in colorectal cancer survivors

Abstract

Scope: Heat-stabilized rice bran (SRB) and cooked navy bean powder (NBP) contain a variety of phytochemicals that are fermented by colonic microbiota and may influence intestinal health. Dietary interventions with these foods should be explored for modulating colorectal cancer risk.

Methods and results: A randomized-controlled pilot clinical trial investigated the effects of eating SRB (30 g/day) or cooked navy bean powder (35 g/day) on gut microbiota and metabolites (NCT01929122). Twenty-nine overweight/obese volunteers with a prior history of colorectal cancer consumed a study-provided meal and snack daily for 28 days. Volunteers receiving SRB or NBP showed increased gut bacterial diversity and altered gut microbial composition at 28 days compared to baseline. Supplementation with SRB or NBP increased total dietary fiber intake similarly, yet only rice bran intake led to a decreased Firmicutes:Bacteroidetes ratio and increased SCFA (propionate and acetate) in stool after 14 days but not at 28 days.

Conclusion: These findings support modulation of gut microbiota and fermentation byproducts by SRB and suggest that foods with similar ability to increase dietary fiber intake may not have equal effects on gut microbiota and microbial metabolism.

Keywords: Bile acids; Heat-stabilized rice bran; Navy bean; Short chain fatty acids; Stool microbiota.

Conflict of interest statement

Authors have no conflict of interest to declare for this research.

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Figures

Figure 1

Stool bacterial diversity at days 0, 14, and 28 for SRB, NBP and control participants. All samples were normalized to 1157 sequences for each participant. Sobs = actual number OTUs detected (richness); Chao = estimated number OTUs (richness); SD = Simpson Diversity Index (lower values reflect higher diversity with this index). The table below the graphs lists data for each participant. The asterisk (*) indicates p < 0.05 with student’s t-test comparing time point to day 0.

Figure 2

SRB is associated with decreased Firmicutes:Bacteroidetes ratio at 14 days relative to baseline, but not 28 days. The asterisk (*) indicates p

Figure 3. Predicted differences in stool bacterial functional categories (PICRUSt)

Only KEGG categories found significant using STAMP analysis are shown, p

Figure 4

Changes in stool short chain fatty acids (SCFAs) shown in a) Day 14 and b) Day 28. The asterisk (*) indicates p

Figure 4

Changes in stool short chain fatty acids (SCFAs) shown in a) Day 14 and b) Day 28. The asterisk (*) indicates p