Effects of Dietary Fibers on Short-Chain Fatty Acids and Gut Microbiota Composition in Healthy Adults: A Systematic Review

Abstract

There is an increasing interest in investigating dietary strategies able to modulate the gut microbial ecosystem which, in turn, may play a key role in human health. Dietary fibers (DFs) are widely recognized as molecules with prebiotic effects. The main objective of this systematic review was to: (i) analyze the results available on the impact of DF intervention on short chain fatty acids (SCFAs) production; (ii) evaluate the interplay between the type of DF intervention, the gut microbiota composition and its metabolic activities, and any other health associated outcome evaluated in the host. To this aim, initially, a comprehensive database of literature on human intervention studies assessing the effect of confirmed and candidate prebiotics on the microbial ecosystem was developed. Subsequently, studies performed on DFs and analyzing at least the impact on SCFA levels were extracted from the database. A total of 44 studies from 42 manuscripts were selected for the analysis. Among the different types of fiber, inulin was the DF investigated the most (n = 11). Regarding the results obtained on the ability of fiber to modulate total SCFAs, seven studies reported a significant increase, while no significant changes were reported in five studies, depending on the analytical methodology used. A total of 26 studies did not show significant differences in individual SCFAs, while the others reported significant differences for one or more SCFAs. The effect of DF interventions on the SCFA profile seemed to be strictly dependent on the dose and the type and structure of DFs. Overall, these results underline that, although affecting microbiota composition and derived metabolites, DFs do not produce univocal significant increase in SCFA levels in apparently healthy adults. In this regard, several factors (i.e., related to the study protocols and analytical methods) have been identified that could have affected the results obtained in the studies evaluated. Future studies are needed to better elucidate the relationship between DFs and gut microbiota in terms of SCFA production and impact on health-related markers.

Flavonoid Intake in Relation to Colorectal Cancer Risk and Blood Bacterial DNA

“…Indeed, our data show that higher anthocyanidin and flavanone intakes are associated with a reduction of evenness indices of microbiota composition, which reflects a different passage of bacteria into blood through the intestinal barrier, especially considering rare bacteria abundances. No previous studies have investigated this issue, but a few recent intervention studies on another dietary component, i.e., fiber, mainly coming from food sources similar to those of flavonoids, reported decreased alpha–diversity indices in fecal samples upon dietary fiber treatment [ 46 ].…”

Microbiome-based interventions to modulate gut ecology and the immune system

“…In addition to impacting the composition of the microbiome, fibre supplements can influence the production of microbial-derived metabolites that influence immune responses (see section on diet). SCFA production is dependent on the fibre type and species present in the host microbiome 104 , providing a framework for directing SCFA production by utilising different fibres 139 (for a recent review see Vinelli et al 146 ).…”

Endotoxemia and Gastrointestinal Cancers: Insight into the Mechanisms Underlying a Dangerous Relationship

“…Several studies have investigated how to inhibit this multistep process at different points, starting from BT. Indeed, dietary interventions can reduce LPS translocation [ 144 ]: microbiota production of SCFAs from dietary fibers regulates intestinal inflammation [ 145 ], reinforces TJs integrity in case of intestinal dysbiosis [ 146 ] and inhibits NF-kB activity [ 147 ], while alcohol consumption and HFD are known to be associated with the development of serrated colorectal polyps, recognized as precancerous lesions [ 148 ]. Moreover, in the animal model of NASH, high-fructose feeding is associated with an increased risk of HCC development [ 149 ].…”