Distinct effects of supplementation with resistant starch and polydextrose on plasma and faecal bile acid profile and associations with gut microbiota: a randomised, controlled intervention in healthy participants

PURPOSE: Dietary fibre may influence bile acid (BA) metabolism via interactions with gut microbiota. We hypothesised that dietary fibres with distinct fermentative properties, resistant starch (RS) and polydextrose (PD), would differentially alter BA profiles in plasma and faeces through gut microbiota-mediated mechanisms. METHODS: Ultra™ (PD) for 50 days. The intervention effects of RS and PD on BA profile were investigated using general linear models and beta regression models. Genus abundances derived from 16 S rRNA gene sequencing were used to investigate fibre-specific microbial correlations with BA profiles. RESULTS: Supplementation with RS, but not PD, increased a range of conjugated BAs and deoxycholic acid (FDR < 0.05). Concentrations of taurochenodeoxycholic acid (FDR = 0.027) and taurine conjugated BAs (FDR = 0.049) in plasma correlated positively with Akkermansia abundance in response to RS. Although neither RS nor PD altered BA concentrations in faeces, RS decreased (p = 0.032) and PD increased (p = 0.012) faecal proportions of primary BAs. PD reduced secondary BA transformation ratios (p < 0.05), along with shifts in related microbial associations. There were negative correlations between plasma primary conjugated BAs and faecal secondary BAs in response to RS specifically (p < 0.05). CONCLUSION: RS increased plasma BAs, particularly conjugated BAs, whereas PD reduced faecal secondary BA transformation. The distinct impacts of RS and PD on BA profiles and fibre-specific microbial associations may underlie their differential metabolic effects. Trail registration The DISC Study was registered with https://clinicaltrials.gov/ (Identifier NCT01214681) in 2010.