Combined effects of resistant dextrin and inulin on the reduction of harmful metabolites during in vitro fecal fermentation in older adults.

BACKGROUND/OBJECTIVES: Aging-related dysbiosis is associated with increased production of harmful gut-derived metabolites. Reducing these metabolites by modulating the gut microbiota is important for maintaining health in older adults. This study aimed to investigate whether a combination of resistant dextrin and inulin suppresses the production of harmful metabolites in the gut microbiota of older adults using in vitro fecal fermentation and a metabolomics approach. METHODS: Fecal samples from eight older adults were fermented with resistant dextrin, inulin, their combination, or no saccharides as a control. Potentially harmful metabolites in the fermentation supernatants were assessed by metabolomic analysis. Trimethylamine production was verified by the fecal fermentation with a choline-supplemented medium. RESULTS: The combination group showed a decreasing trend in the production of deoxycholic acid, kynurenine, and trimethylamine compared with the control group. Assessment of trimethylamine production using a choline-supplemented medium revealed that the combination group had a higher proportion of fecal samples with low trimethylamine production (3 of 8 samples) than either prebiotic-alone group. CONCLUSION: Combining resistant dextrin and inulin could reduce the production of some harmful metabolites by the gut microbiota in older adults.