HCAR2 and inflammatory bowel disease: Another example is HCAR2 (GPR109a) which was upregulated in CD and UC patient biopsies (log2fc = 6.15 [CD] and 4.51 [UC]) while its competing modulators, nicotinic acid and trigonelline were depleted and enriched, respectively, in IBD patients’ stool (Fig. 3c; Supplementary Data 2).