Insoluble fiber does not dissolve in water. It travels through the digestive system mostly unchanged, sweeping waste along and bulking up stool. Wheat bran, vegetables, and nuts supply it naturally. You can also buy it as a standalone supplement.
Many people use insoluble fiber to keep bathroom visits predictable when food alone falls short. Take it with a full glass of water and make it part of a balanced eating pattern. Raise the dose slowly and drink enough fluids to cut down on gas and bloating.
Watch out for medication timing. Insoluble fiber can interfere with absorption, so separate it from drugs by at least an hour. Skip these supplements if you have a narrowed digestive tract, strictures, or trouble swallowing, unless a doctor says otherwise.