Oat fiber comes from the outer hull of oats. It is almost pure insoluble fiber with very few calories or nutrients. People use it to boost fiber content in food or as a supplement, not as a meal replacement. Think of it as a texture and bulk helper, very different from oat bran or whole oats.
Adding it to your routine supports regular bowel movements. The insoluble fiber adds stool bulk, which helps keep things moving. Some people feel a mild increase in fullness, but the effect is smaller than what you get from soluble fibers.
Start with a teaspoon mixed into a smoothie, yogurt, oatmeal, or baked goods. Increase slowly to give your system time to adjust and avoid gas or bloating. Drink a full glass of water with each dose so the fiber can absorb enough liquid and do its job.
Large amounts taken all at once can cause stomach upset. Space any medications at least two hours apart from your oat fiber serving, since the extra bulk may slow absorption.