Dr. Salhab explains that when you eat, your stomach stretches, sending signals to your brain, which then signals your colon. This causes your colon to contract to make space for more food, triggering the urge to use the restroom. The substances that come out are actually old digested food and water. Heightened reflex People with irritable bowel syndrome (IBS) may experience a heightened gastrocolic reflex. IBS can cause painful abdominal symptoms like constipation, diarrhea, gas, and bloating