Dietary fibers (DF) are considered as beneficial nutrients for health. Current data suggest that their interaction with the gut microbiota largely contributes to their physiological effects. The FiberTAG project(1) innovates in searching for new biomarkers reflecting the health effect of dietary fibers, including chitin-glucan (CG, extracted from the fungal exoskeleton Aspergillus niger). CG improves metabolic disorders associated with obesity in mice, but its effect on gut microbiota composition and function has never been evaluated in vivo in humans.

CG (KitoZyme, Belgium) was given to healthy volunteers (n = 15), during three weeks (4.5g/day). Volatile Organic Compound (VOC) metabolites released in breath were analyzed using SYFT methodology. Fatty acid (FA) profiling was assessed in stool samples, by gas-liquid chromatography(2). The gut microbiome was analyzed by Illumina sequencing (V5-V6 region of 16S rRNA).

Three weeks of CG supplementation was well tolerated and lead to changes in the kinetics of breath VOC, especially the short-chain fatty acid, alcohols and alkanes. Fecal vaccenic acid, produced upon the bacterial metabolism of fatty acids, was significantly increased by CG. Several bacterial genera were correlated with breath VOC (i.e. 2 methylbutyric acid and RuminococcaceaeUCG005). Moreover, Roseburia, often presented as a butyrate producer, was positively correlated with the production of a rumenic acid isomer “cis-9,cis-11-18:2”.

We show that breath VOC analysis, a non-invasive methodology, reveals characteristics of microbiota-CG interactions. We also show that CG selectively changes the profile of FA metabolites, in favor of vaccenic acid, another bioactive metabolite produced by Roseburia, prone to act on host physiology. This study will help to establish a set of new biomarkers linking insoluble DF and gut microbiota, with focus on their interest in human health.