Our long-term goal is to mechanistically understand how dietary fibers promote gut bacterial shifts that effectively translate into health benefits to humans. In this sense, we have shown that key bacteria associated with reduced inflammation and enhanced gut barrier function, theClostridiumclusters IVandXIVa, are better supported withfermentable insoluble fibers and matrix-entrapped soluble fibers than soluble fibers alone. The former cell wall-type fibers are abundant in whole food sources, which are reduced in modern Western diets and are often replaced with isolated soluble fibers, like inulin, in processed foods.Our aim is to compare whole food fibersversusinulin for support of butyrogenicClostridiumclusters IV and XIVagrowth, and to evaluate associated health biomarkers. Whole food fibers and whole food fiber mixtures will be fermentedin vitroand analyzed for increase inClostridiumclusters IVandXIVaandbutyrate production. Based onin vitrofecal fermentation results, a whole food dietary fiber mixture will be selected for a crossover human trial to compare whole food dietary fibersversusinulin and monitored forimproved gut and systemic health biomarkers.