The word "fiber" may bring many thoughts to our minds. Helping us "stay regular" would be the most prominent thought for most of us. This is certainly true; however, fiber plays a much larger role in the prevention and reversal of disease, as Dr. Neal Barnard points out in this ten minute video.
Fiber is the indigestible substance which is resistant to digestive enzymes. Its role in removing toxic waste products is an important one. Carcinogens, for example, found in meat and dairy products, are moved along more quickly when sufficient fiber is available. This shortens the time it has to damage the lining of the intestines, which helps us avoid colon cancer. This would explain one reason why colon cancer rates are much lower in those consuming a plant-based diet.