Thirza van Deuren¹, Ellen Blaak¹, Emanuel Canfora¹

¹Human Biology, School for Nutrition and Translational Research in Metabolism (NUTRIM), Maastricht University Medical Center+, Maastricht, The Netherlands’

Background: Short-chain fatty acids (SCFAs) are believed to improve metabolic health through dietary fiber fermentation. Yet, as indigestible carbohydrates deplete towards the distal colon, gut bacteria shift to protein fermentation, producing potentially harmful metabolites such as branched-chain fatty acids (BCFAs). Research has shown that SCFA administration to the distal colon, rather than the proximal colon, leads to beneficial metabolic alterations. Therefore, we hypothesize that promoting saccharolytic over proteolytic fermentation in the distal colon may offer metabolic health benefits and we aimed to identify a carbohydrate mixture able to induce such a microbial shift.

Methods: The TIM-2 model, an in vitro computer-controlled dynamic model of the human colon, was inoculated with standardized pooled microbiota from individuals with overweight/obesity and a disturbed glucose homeostasis. After an overnight adaptation period, pre-digested proteins were administered together with potato fiber, inulin, or pectin, either individually or in combination, or no fibers were added (protein control). Samples were taken at various time points to assess gut microbiota composition as well as proximal (0–8h) and distal (8–24h) SCFA and BCFA production.

Results: Fiber addition increased total SCFA production compared to protein control (52.11±1.49 vs 27.07±0.26 mmol) whereas total BCFA production was slightly decreased (3.31±0.10 vs 4.18±0.40 mmol). Combining potato fiber and pectin yielded the highest total (59.69±0.09 mmol) and distal SCFA production and SCFA:BCFA ratio compared to protein control (13.32±1.79 vs 2.17±0.53). Additionally, the type of dietary fiber(s) dictated alterations in microbiota composition. To illustrate, relative abundance (at the genus level) of Coprococcus increased (+25.6%) 8 hours after the protein control was administered, whereas for inulin, Bifidobacterium (+23.3%) and Ruminococcus (+15.4%) were increased.

Discussion: The potato fiber and pectin mixture resulted in the most pronounced microbial switch in pooled microbiota of individuals with overweight/obesity. Further research should investigate whether these results can be translated in vivo.