In contrast, if the passage of waste is too slow, too much water is absorbed. This results in hard stools and constipation, which often leads to straining. These simple problems occasionally lead to more serious disorders. Also, high-fiber foods expand the inside walls of the colon. This eases the passage of waste.
Fibrous substances pass through the intestine undigested.
They also absorb many times their weight in water, resulting in softer, bulkier stools. Studies show that rural Africans, who eat diets high in fiber, eliminate food waste in one-third the time it takes people from urban westernized cultures. Their stools are larger and softer. Because of the greater bulk and speed of foods through the digestive tract, it is believed that harmful substances are also swept out before they can cause problems. In fact, these rural people have fewer of the digestive tract diseases that plague Western man.