In recent years, many health claims have been made about dietary and supplemental fiber. However, some reports (eg, those regarding oat bran) have been controversial. A review of scientifically rigorous studies shows that fiber has preventive or therapeutic benefits in irritable bowel syndrome, diverticulosis, colorectal cancer, diabetes, and hypercholesterolemia. It appears to have direct benefit in patients with inflammatory bowel disease, gallstones, and obesity.