Resistant dextrin promotes beneficial fecal bacteria in high and low fiber diet populations: a randomized, double-blinded, controlled pilot study

Background and objectives: The average intake of dietary fibers known to beneficially modulate the gut microbiota is below recommendations in high-income countries. This study aimed to evaluate the gut effects of resistant dextrin in healthy male adults with normal weight, consuming high (=25 g/day; HF) or low (=15 g/day; LF) levels of fiber as part of their usual diet. Methods: In this randomized, double-blind, placebo-controlled trial, participants received either 15 g/day of resistant dextrin (NUTRIOSE® soluble fiber) or a placebo (maltodextrin) for 4 weeks. Gut microbiota composition, and especially the relative abundance of the Parabacteroides genus, gut microbiota function, fecal parameters (pH, short chain fatty acids [SCFAs] and secretory IgA), and stool frequency and consistency, were assessed. Results: Overall, 124 subjects were recruited, 62 in each treatment arm; 57 in HF 67 in LF; age: 36.2 ± 11.6 years. The mean relative abundance of Parabacteroides at baseline was similar in the LF (1.5%) and HF (1.3%) subgroups. It increased with the active supplementation and remained stable with the placebo, both in the entire population (5.5% vs 1.4%; p<0.0001) and in the subgroups of dietary fiber intake (HF: 5.5% vs. 1.5%; LF: 5.5% vs. 1.3%; p<0.0001), then returned to baseline levels two weeks later. Among Parabacteroides, P. distasonis showed the highest abundance in the active arm as compared to placebo (2.6% vs. 0.5%; p<0.0001). The Bacillota phylum was less abundant at the end of active supplementation compared to placebo (55.4% vs 59.0%; p=0.0545). Conversely, several species from the Clostridium genus were more abundant. From a functional perspective, resistant dextrin intake tended to increase bacterial genes involved in a- and ß-glucosidase activities, and to decrease those involved in propionate production, especially in the HF subgroup. No treatment effect was found on pH, SCFAs, IgA, stool consistency and frequency. Conclusions: The tested resistant dextrin was effective in modulating the gut microbiota after four weeks of supplementation in healthy male volunteers, favoring the Parabacteroides genus and several related species (especially P. distasonis). The treatment effect was observed in both subgroups of dietary fiber intake, and was even more pronounced in the high-intake subgroup