Dietary fibre complexity and its influence on functional groups of the human gut microbiota

Abstract

The aim of this review is to provide an overview of the complex interactions between dietary fibre and the resident microbial community in the human gut. The microbiota influences both health maintenance and disease development. In the large intestine, the microbiota plays a crucial role in the degradation of dietary carbohydrates that remain undigested in the upper gut (non-digestible carbohydrates or fibre). Dietary fibre contains a variety of different types of carbohydrates, and its breakdown is facilitated by many different microbial enzymes. Some microbes, termed generalists, are able to degrade a range of different carbohydrates, whereas others are more specialised. Furthermore, the physicochemical characteristics of dietary fibre, such as whether it enters the gut in soluble or insoluble form, also likely influence which microbes can degrade it. A complex nutritional network therefore exists comprising primary degraders able to attack complex fibre and cross feeders that benefit from fibre breakdown intermediates or fermentation products. This leads predominately to the generation of the short-chain fatty acids (SCFA) acetate, propionate and butyrate, which exert various effects on host physiology, including the supply of energy, influencing glucose and lipid metabolism and anti-carcinogenic and anti-inflammatory actions. In order to effectively modulate the gut microbiota through diet, there is a need to better understand the complex competitive and cooperative interactions between gut microbes in dietary fibre breakdown, as well as how gut environmental factors and the physicochemical state of fibre originating from different types of diets influence microbial metabolism and ecology in the gut.

Intrinsic dietary fibers and the gut microbiome: Rediscovering the benefits of the plant cell matrix for human health

“…While all plants share these common aspects of the plant cell wall, their make-up differs depending on the type of plant (e.g. monocots versus dicots; see below), its maturation or ripeness and especially food processing ( 18 , 52 , 58 ). Even within plants, differences in cell types exist between the tissue we consume (such as leaf, root, fruit, stem, seed) and within these tissues ( 52 , 56 ).…”

“…Vegetables, fruits, nuts, seeds and legumes belong to the dicots, that have so-called type I cell walls, while grains are monocots having type II cell walls. Type I cell walls of dicots contain xyloglucan as the most abundant hemicellulose and the hemi-/cellulose network is further stabilized by pectin, which has been reported to make up a third of the cell wall weight ( 18 , 52 ). In contrast type II cell walls of monocots, have no or very low amounts of pectin and the abundant hemicelluloses are β-glucan and arabinoxylan ( 52 , 58 ).…”

“…Current view of dietary fibers: single, isolated components and their impact Dietary fiber is an umbrella term for a group of polymers that are structurally and chemically very different. Numerous sugar molecules, such as glucose, xylose, mannose, galactose, arabinose and rhamnose are linked together by various glycosidic bonds following a specific or random pattern creating linear or branched structures that can be further decorated with phenolic acids or linked to other compounds (18,19). For instance, inulin and starch consist of linear repetitions of a single molecule (fructose and glucose monomers, respectively).…”

Personal diet–microbiota interactions and weight loss

“…Therefore, microbiota diversity is most likely a net result of both intestinal transit time, engraftment of microbes and nutrient availability. The nutrient availability will also depend on the physicochemical characteristics of the dietary fibre, such as whether it dissolves in water (soluble fibre) or not (insoluble fibre), since insoluble fibre (such as cellulose, hemicellulose and lignin) speed up transit time and are generally less available for microbial degradation (36) . The importance of nutrient availability for engraftment of microbes has elegantly been demonstrated in mice.…”

Manipulating the kinetics and site of colonic fermentation with different fibre combinations – a review

“…The main bacterial species promoted by different fibres include Prevotella, Roseburias, E. rectale, Lactobacillus and Bifidobacterium (Louis et al, 2021). Human microbiome researchers (Calatayud et al, 2021;Yao et al, 2022Yao et al, , 2023 have often primarily investigated different fibres individually in relation to the gut microbiota and their metabolites.…”