Dietary fibre modifies gut microbiota: what’s the role of (poly)phenols?

Abstract

The association between dietary consumption of fibre and health-related gut bacteria is essential but not unique. (Poly)phenols are among the most important bioactive components contained in fibre-rich foods. For this reason, the role of (poly)phenols when considering dietary fibres and health outcomes should be taken into account, as synergic or mediating factors contributing to human health.

Keywords:

• (Poly)phenols
• gut microbiota
• dietary fibre

The interesting article of Adamberg et al. (2020) aimed at investigating the association between dietary consumption of fibre and faecal microbiota in a sample of 59 healthy individuals. Authors showed that a diet characterised by high fibre intake was associated with Roseburia, Bacteroides xylanisolvens and Oxalobacter formigenes, while arabinoxylan-, pectin- or inulin-rich foods promoted the growth of several health-related gut bacteria. Although the authors reported that overall dietary fibre intake derived mainly from (whole-grain) cereals, legumes, and vegetables and fruits, they did not mention that (poly)phenols are among the most important bioactive components contained in fibre-rich foods. The most abundant (poly)phenols contained in common cereal grains are glycosylated monomeric flavonoids unsubstituted at position 3 (C3) of the heterocyclic ring (3-deoxyflavonoids), such as flavones (i.e. apigenin and luteolin) (Courts and Williamson 2015), and non-flavonoid phenolic acids (Arranz et al. 2010). Also legumes are rich in flavonoids, namely flavonols, anthocyanins, flavan-3-ols, flavonols, and isoflavones, with a notable variation in the (poly)phenol profile depending on the species and/or cultivar considered (Kalogeropoulos et al. 2010). Vegetables and fruits contain the highest variety of (poly)phenols, including both flavonoids and phenolic acids (Bresciani et al. 2015). These compounds have been demonstrated to exert antibacterial activity, especially against Gram-negative species (i.e. the Enterobacteriaea) and anti-inflammatory activities, possibly through dampening the inflammatory response to bacterial antigens in the colon (Tuohy et al. 2012). It has even been shown that there are synergistic and complementary benefits of diverse (poly)phenol groups derived from various dietary sources (i.e. grain cereals and pulses) with fibre on chronic inflammation and gut health (Awika et al. 2018). In addition, there is evidence that the quality (i.e. specific subclasses), and not only the quantity (i.e. total amount) of (poly)phenols is key for their physiological activities at gut level (Williamson et al. 2018).

The gut microbiota interacts with most of the dietary (poly)phenols reaching the colon, transforming them into possible biologically active molecules efficiently absorbable (Masumoto et al. 2016). However, the ability to produce bioactive colonic metabolites with potential health benefits strictly depends on the microbiota composition, responsible for an important inter-individual variability (Cassidy and Minihane 2017). Moreover, there is evidence that specific gut microbiota profiles may play a role in several chronic non-communicable diseases and health conditions, including inflammatory bowel diseases, obesity and metabolic disorders (Cao et al. 2020; Fan and Pedersen 2020), and cognitive function (Ceppa et al. 2019; Salvucci 2019). On the other hand, among the several exogenous factors modulating gut microbiota, undigested (poly)phenols could contribute to positively modify colonic enterotypes. Interestingly, an inverse relation has been demonstrated, being dietary (poly)phenols able to influence gut microbiota composition (Wu et al. 2018; Chen et al. 2020) and modulate the human gut microbiome community towards a more “healthy” profile by increasing the relative abundance of bifidobacteria and lactobacilli (Cardona et al. 2013; Valdés et al. 2015; Marchesi et al. 2016), or increasing Prevotella/Akkermansiaceae enterotype in mice (Rodríguez-Daza et al. 2020). Thus, the role of (poly)phenols when considering dietary fibres and health outcomes should be taken into account, as synergic or mediating factors contributing to human health. These findings open to the possibility that certain fibre-rich foods may act as functional foods through the regulation of gut microbiota beyond their fibre content, contributing to the health of the host through these compounds (Etxeberria et al. 2013). Not only variation and enrichment of dietary fibre sources should be considered for the modulation of the gut microbiota, as suggested by Adamberg (Adamberg et al. 2020), but also the (poly)phenol composition as it could play an essential role in the health-promoting benefits of certain dietary choices at gastrointestinal level. Further research is needed to better understand the interactions between various (poly)phenols, fibre and other dietary components, as well as the role of individual genetic and microbiota background on this complex picture.

Disclosure statement

No potential conflict of interest was reported by the author(s).