The Differences in Gut Microbiota Due to Dietary Habits Affect the Onset of Disease Pathology in a Dextran Sulfate Sodium-Induced Colitis Model

Ulcerative colitis (UC), an inflammatory bowel disease (IBD) involving colon ulceration and erosion, is challenging to prevent or stop. The findings highlighted the crucial role of gut microbiota imbalance in IBD development. This study aimed to investigate the influence of five dietary patterns on the onset or progression of UC in a dextran sulfate sodium (DSS)-induced colitis model by altering the gut microbiota. The results showed that the disease condition worsened most significantly in the high-protein diet group, followed by the high-fiber diet group. Before UC induction, these severely affected groups exhibited a higher proportion of Bacteroidota (Bacteroidetes) and a lower proportion of Bacillota (Firmicutes) than the groups in which the condition did not worsen. A reduced Firmicutes/Bacteroidetes ratio has been linked to the onset and progression of IBD. Upon DSS administration, the abundance of Bacteroidota increased in all dietary groups. Analyses revealed that as the disease progressed, the levels of the inflammatory cytokine tumor necrosis factor-α (TNF-α) increased. Specifically, the high-protein group showed elevated expression of interleukin-6 (IL-6) and transforming growth factor β1 (TGF-β1), which are involved in Th17 cell induction, and increased IL-17A secretion, indicating an amplified Th17-mediated inflammatory response. The expression of the tight junction protein occludin was reduced in the high-fiber and high-protein groups. These groups also demonstrated a significant decrease in beneficial short-chain fatty acids, acetate, and propionate. These findings suggest that dietary habits significantly impact the onset and progression of UC, and that the gut microbiota composition before disease onset may play a crucial role in this process.