Effects of non-digestible carbohydrates on gut microbiota and microbial metabolites: a randomised, controlled dietary intervention in healthy individuals

Abstract

The gut microbiome is impacted by certain types of dietary fibre. However, the type, duration and dose needed to elicit gut microbial changes and whether these changes also influence microbial metabolites remain unclear. This study investigated the effects of supplementing healthy participants with two types of non-digestible carbohydrates (resistant starch (RS) and polydextrose (PD)) on the stool microbiota and microbial metabolite concentrations in plasma, stool and urine, as secondary outcomes in the Dietary Intervention Stem Cells and Colorectal Cancer (DISC) Study. The DISC study was a double-blind, randomised controlled trial that supplemented healthy participants with RS and/or PD or placebo for 50 d in a 2 × 2 factorial design. DNA was extracted from stool samples collected pre- and post-intervention, and V4 16S rRNA gene sequencing was used to profile the gut microbiota. Metabolite concentrations were measured in stool, plasma and urine by high-performance liquid chromatography. A total of fifty-eight participants with paired samples available were included. After 50 d, no effects of RS or PD were detected on composition of the gut microbiota diversity (alpha- and beta-diversity), on genus relative abundance or on metabolite concentrations. However, Drichlet's multinomial mixture clustering-based approach suggests that some participants changed microbial enterotype post-intervention. The gut microbiota and fecal, plasma and urinary microbial metabolites were stable in response to a 50-d fibre intervention in middle-aged adults. Larger and longer studies, including those which explore the effects of specific fibre sub-types, may be required to determine the relationships between fibre intake, the gut microbiome and host health.

Keywords: Dietary intervention; Gut microbiota; Humans; Non-digestible carbohydrates; Polydextrose; Randomised controlled trial; Resistant starch; SCFA.

Figure 1.

Flow chart of DISC study design and analytical pipeline. ATIMA, Agile Toolkit for Incisive Microbial Analysis; DISC, Dietary Intervention Stem Cells and Colorectal Cancer; DMM, Dirichlet’s multinomial mixture; PD, polydextrose; RS, resistant starch; SCFA, short-chain fatty acids.

Figure 2.

Effects of supplementation with RS and PD on two metrics of alpha-diversity. Alpha-diversity is represented by both observed operational taxonomic units (OTU) and Shannon Diversity. Panels A and B show the impact of RS supplementation on α diversity measured by observed OTU and Shannon diversity, respectively. Panels C and D illustrate the effects of PD supplementation on the same α diversity metrics. Each point represents individual participants pre- and post-intervention. Lines are coloured if change was > 1 sd, red lines between paired points represent a decrease and blue lines an increase, black lines represent changes of < 1 sd. PD, polydextrose; RS, resistant starch.

Figure 3.

Principal coordinates analysis based on weighted Bray–Curtis distance metrics, illustrating microbial communities pre- and post-intervention in response to both interventions. (a) Impact of RS supplement intervention on microbial community composition. (b) Influence of PD supplement intervention on microbial community composition. PD, polydextrose; RS, resistant starch.

Figure 4.

Effects of supplementation with RS (a and c) and PD (b and d) on the relative abundance of bacteria. Phyla and genera are ordered based on lowest P value. Boxes represent interquartile ranges, with lines denoting median. Abbreviations: PD, polydextrose; RS, resistant starch.

Figure 5.

Dirichlet’s multinomial mixture clustering of participants. (a) Proportional bar plot summarising the number of participants whose enterotype was unchanged and those who changed gut microbial enterotype post-intervention. (b) Movement of participants between the identified clusters (enterotypes) between pre- and post-intervention. Thin lines represent individual participants. PD, polydextrose; RS, resistant starch.