Beyond purified dietary fibre supplements: Compositional variation between cell wall fibre from different plants influences human faecal microbiota activity and growth in vitro

Abstract

Dietary fibre is a major energy source for the human gut microbiota, but it is unclear to what extent the fibre source and complexity affect microbial growth and metabolite production. Cell wall material and pectin were extracted from five different dicotyledon plant sources, apples, beet leaves, beetroots, carrots and kale, and compositional analysis revealed differences in the monosaccharide composition. Human faecal batch incubations were conducted with 14 different substrates, including the plant extracts, wheat bran and commercially available carbohydrates. Microbial activity was determined for up to 72 h by measuring gas and fermentation acid production, total bacteria (by qPCR) and microbial community composition by 16S rRNA amplicon sequencing. The more complex substrates gave rise to more microbiota variation compared with the pectins. The comparison of different plant organs showed that the leaves (beet leaf and kale) and roots (carrot and beetroot) did not give rise to similar bacterial communities. Rather, the compositional features of the plants, such as high arabinan levels in beet and high galactan levels in carrot, appear to be major predictors of bacterial enrichment on the substrates. Thus, in-depth knowledge on dietary fibre composition should aid the design of diets focused on optimizing the microbiota.

Dietary fibre optimisation in support of global health

“…While grass seeds are believed to have been part of the hunter‐gatherer diet, grains (especially wheat and rice) became major staple foods, alongside other crops and farmed animals (Tannock, 2024 ). Grains are Monocotyledon plants with large cell wall compositional differences to Dicotyledon fruits and vegetables (Louis et al., 2021 ), consequently promoting the growth of different gut bacteria (Solvang et al., 2023 ). The picture of microbiome differences between different contemporary lifestyles (hunter‐gatherer, traditional agrarian, industrialised, rural/urban, etc.)…”

“…What effect the physicochemical properties of fibre have on the microbiota is not well understood (Puhlmann & de Vos, 2022 ), but it is to be expected that eating a diverse whole plant‐based diet is more beneficial than even a mixture of several refined fibre components. The insoluble plant particles provide surfaces for biofilm formation, which could foster interactions between different microbes, for example, synergistic actions in complex fibre breakdown or cross‐feeding of breakdown intermediates or fermentation products between microbes (Solvang et al., 2023 ). Complex insoluble fibre is also likely to be more slowly fermented, leading to more sustained microbial activity and production of health‐promoting metabolites further into the distal gut, where most gut diseases occur.…”