Psyllium is a viscous, gel forming fibre with properties that have led it to be used for alleviating gastrointestinal discomfort. We have used previously identified fractions of psyllium with differing flow properties. Fraction 1 (F1) forms a non-gelling solution containing rhamnose. galactose, and arabinose. Fraction 2 (F2) forms a fluid-like gel containing mainly xylose and arabinose, Fraction 3 (F3) has almost identical monosaccharide and linkage composition to F2, but forms an insoluble, self-supporting gel. We performed in vitro batch fermentation experiments seeded with human stool. Metabolomics were performed using ¹H NMR, and FISH with calcofluor white and direct red 23 were used to visualise the gels after in vitro fermentation of the fractions. The total amount of gas and short chain fatty acid produced was significantly higher for F1, compared to F2 and F3. F3 gas production was significantly lower than F2, but metabolite production between F2 and F3 did not differ. All fractions preferentially lead to the production of propionate instead of butyrate and were produced in the ratio of 58:35:7, 54:38:8, and 61:33:6 (acetate: propionate: butyrate) for F1, F2, and F3 respectively. Microscopy showed differences in how the fractions broke down and demonstrated the localisation of bacteria on the outer edge of each fraction. These results suggest that for these psyllium fractions the structure is a key factor that determines fermentability. Flow properties may play a role in gas production, suggesting directions for future investigation. Isolated fractions may have clinical benefit above that of unrefined psyllium powder aiding in the treatment of gastrointestinal discomfort.