In their recent paper, Moreland et al1 showed that obese patients after Roux-en-Y gastric bypass surgery have steatorrhea and hyperoxaluria that were quantitatively correlated. They appropriately explained that hyperoxaluria was due to excess fatty acids in the colon of these patients. Within the colonic lumen, fatty acids and oxalic acids both are present in ionic form and thus are able to be absorbed by the epithelium. After absorption, oxalic acid is excreted in the urine and fatty acids can be injurious to colonic epithelial cells.