Fiber supplements will kick in and start benefitting your system almost immediately. This is because it’s rough nature functions as a microscopic scrub brush for your intestines and stomach. As your body digests food and pushes the fiber through your system, old waste that may have been stuck to your intestinal walls gets knocked down.
However, it can take between 1-3 days for food to pass through the entire 24 feet of intestines that makes up your digestive system so you may not always notice immediate results. If you’ve been constipated for a day or two the fiber supplement may work in a shorter period of time (typically between 30 minutes and 3 hours).