INS and type 2 diabetes mellitus: Patients in the lifestyle intervention group had higher serum indolepropionic acid levels at the 1-year point of the study, which was associated inversely with T2DM incidence and directly with insulin secretion. A positive correlation was found between dietary fiber intake and serum indolepropionic acid, while a negative correlation was found between high-sensitivity C-reactive protein concentrations and IPA at sampling and study follow-up.