Renal disorders, especially nephrolithiasis, are observed in one-third of patients with Crohn’s disease, probably related to increased oxalate absorption associated with steatorrhea.
HOW? Inflammation or resection affecting the terminal ileum may result in malabsorption of bile acids — this will inevitably affect fat absorption.
Increased intestinal fat binds dietary calcium, which is then unavailable to bind oxalate (a type of salt). Oxalate is free to be absorbed in the GI tract -> Blood stream -> re-deposited in the kidney (hyperoxaluria), where it can form calcium oxalate stones.
Cury DB, Moss AC, Schor N. Nephrolithiasis in patients with inflammatory bowel disease in the community. International Journal of Nephrology and Renovascular Disease. 2013;6:139-142. doi:10.2147/IJNRD.S45466.
Ch 13: Gastrointestinal Disease. Pathophysiology of Disease: An Introduction to Clinical Medicine, 7e. Jason C. Mills, MD, PhD, AGAF; Thaddeus S. Stappenbeck, MD, PhD