Pilot dietary intervention with heat-stabilized rice bran modulates stool microbiota and metabolites in healthy adults

Heat-stabilized rice bran (SRB) has been shown to regulate blood lipids and glucose, modulate gut mucosal immunity, and inhibit colorectal cancer in animal and human studies. However, SRB effects on gut microbial composition and metabolism and resulting implications for health remain largely unknown. A pilot, randomized-controlled trial was developed to investigate effects of eating 30g/day SRB on the stool microbiome and metabolome. Seven healthy participants consumed a study meal and snack daily for 28 days. The microbiome and metabolome were characterized using 454 pyrosequencing and gas chromatography-mass spectrometry (GC-MS) at baseline, 2- and 4-weeks post intervention. Increases in eight Operational Taxonomic Units (OTUs), including three from Bifidobacterium and Ruminococcus genera, were observed after 2 and 4 weeks of SRB consumption (p < 0.01). Branched chain fatty acids, secondary bile acids and eleven other putative microbial metabolites were significantly elevated in the SRB group after 4-weeks. The largest metabolite change was a rice bran component, indole-2-carboxylic acid, which showed a mean 12% increase with SRB consumption. These data support the feasibility of dietary SRB intervention in adults and support that SRB consumption can affect gut microbial metabolism. These findings warrant future investigations of larger cohorts evaluating SRB effects on intestinal health.