Arabinoxylan (AX) and galactoxyloglucan (GXG) are polysaccharides abundant in the primary cell walls of cereal grains and fruits/vegetables, respectively. In humans, these complex dietary fibres withstand digestion in the stomach and the small intestine, reaching the large intestine, where their fermentation by the resident microbiota is critical in maintaining colonic health. Yet understanding how the gut microbial community alters due to the fermentation of these complex cereal and fruit/vegetable dietary fibres is minimal. Here we investigated the fermentability of purified wheat and rye AX, as well as tamarind GXG using an in vitro batch culture approach, with a human faecal inoculum prepared by collecting human faeces from healthy male (n=3) and female (n=4) volunteers, consuming unrestricted diets. Fermentation proceeded up to 48h, and for each substrate, biomass for microbial community profiling was sampled at the start, then when most of the substrate had disappeared, at one time point in between, and at the end of fermentation. Shotgun metagenomics revealed that during fermentation, an unclassified Lachnospiraceae OTU was promoted by both WAX and GXG substrates. Moreover, for WAX, two additional OTUs (Bacteroides plebeius and a Blautia spp.) were promoted, while GAX fermentation promoted four more OTUs (an unclassified Bacteroidales, Parabacteroides distasonis, Bacteroides uniformis and an unclassified Bacteroides spp.). Ultimately, this study has revealed that differing bacterial communities are essential for the degradation of these cereal and fruit/vegetable complex dietary carbohydrates, and highlights the importance of consuming a varied diet to promote a diverse gut microbiota. Further bioinformatics is being conducted to investigate the functional capabilities of the bacterial communities promoted during the fermentation of these complex dietary carbohydrates.