Any food item, which has good amount of fiber. Papaya fruit is quite beneficial to regulate the bowel. Husk of whole wheat, Sat-Isabgol, a natural vegetable product, derived from seeds of Ispagul( Plantago Ovata), is commonly used in India as a natural laxative. It is purified by milling process and packaged.
It helps if you have a systematic and regular life, timely meals, healthy diet and exercise. Avoid greasy and junk food.