Chronic kidney disease is associated with the accumulation of various metabolites, i.e., uremic retention solutes. Evidence is mounting that the colonic microbiota contributes substantially to these uremic retention solutes. Indoxyl sulfate and p-cresyl sulfate are among the most extensively studied gut microbial metabolites, and are associated with cardiovascular disease, overall mortality and chronic kidney disease progression. The most important regulator of colonic bacterial metabolism is nutrient availability and especially the ratio of available fermentable carbohydrate to nitrogen, which can be modified by intake of so-called prebiotics (non-digestible food ingredients). Arabinoxylan oligosaccharides (AXOS) are a recently developed group of prebiotics, and already demonstrated a decreasing effect on intestinal generation of p-cresol in healthy individuals. Whether prebiotics in general, and AXOS more specifically, can influence intestinal generation of microbial metabolites in predialysis patients has not been studied to date. An interventional study with AXOS will therefore be initiated to test the hypothesis that AXOS can decrease intestinal generation and serum concentrations of microbial metabolites in patients with CKD not yet on dialysis.