Oat fiber and regular oat dietary fiber, while both derived from oats, differ significantly in their composition and properties. Oat fiber is essentially the pure, insoluble fiber extracted from the outer hull of the oat, making it calorie-free and with minimal nutritional value. Regular oat dietary fiber, on the other hand, includes both soluble and insoluble fiber, primarily beta-glucan, found within the oat groat itself, and offers various nutritional benefits.