How does reducing colonic transit time with fiber prevent colorectal cancer?

Inflammation!: Although the data supports a healthy diet high in fiber with fruits and vegetables improves colonic health - there is some speculation that it may also reduce the risk of colorectal cancer. A diet high in dietary fiber reduces colonic transit time - meaning you go more regularly. The more regular you move your bowels there is less stagnation of stool and decreased inflammation in the colon.

Less contact: The hypothesis is that one factor in colon cancer is potentially ingested carcinogens(cancer causing) that are in the food we eat. The faster the stool moves through the colon, the less time the carcinogen has in contact with any segment of the colon so it's should be less damaging.