A vital nutrient we’ve all heard a lot about is fiber. But what is it, exactly, and why is it so important for your health? Dietary fiber is the indigestible parts of fruits, vegetables, beans, nuts, whole grains, and other plant foods. Fiber is what gives celery its crunch, for instance. In your intestines, fiber absorbs water and helps move digestion along; it acts a bit like a broom to sweep out waste. Technically, fiber is a type of carbohydrate, but because it’s mostly indigestible, it passes through you and doesn’t raise your blood sugar.