Figure 1.

Schematic representation of impact of low dietary microbiota-accessible carbohydrates (MACs) on microbiota and gut homeostasis. Consumption of low dietary MACs leads to decreased gut bacterial diversity with outgrowth of mucus-degrading bacteria and decreased levels of MAC-degrading bacteria. The mucus layer will thus become thinner exacerbated by reduced production of Muc2 due to reduced short-chain fatty acids (SCFAs) production. This decrease in production of SCFAs also impairs GPR43 activation on epithelial cells leading to increased production of proTh2 cytokine TSLP and decreased activation of NLRP3, and thus, decreased production of epithelial healing cytokine IL-18. Low SCFAs also impair epithelial barrier function as shown by decreased transepithelial resistance (TER), leading to increased bacterial product translocation into the lamina propria, triggering inflammatory reactions. Finally, due to their key role in immune function, low SCFAs impair regulatory T cell (Treg), Th1 cell, and Th17 cell, while enhancing T helper 2 (Th2) development. Decreased direct activation of B-cells and indirect activation through decreased T follicular helper cells impair IgA and IgG production.