Dietary fiber is also known as roughage. It is found in the cell walls of plants and is felt to fight cancer. Many studies have reported that dietary fiber decreases the chances that a person will develop colon cancer.
One article (1) looked at dietary fiber and its ability to fight colon cancer. It found that dietary fiber adds bulk to the digestive system, decreasing the chances of constipation and decreasing the chances of having colon cancer. By reducing the time that food is present in the colon, fiber can decrease the risk of getting colon cancer.
The US Polyp Prevention Trial, done between 1991 and 1998, was discussed in the article. In the trial, participants with colorectal polyps were subjected to a high fiber diet for a total of four years. Those participants who ate more fiber had a decreased chance of getting colon cancer. Based on this study, those people at risk for developing colon cancer should eat more fiber in order to decrease their risk of colon cancer.
Source: 1.How Fiber Helps Protect Against Cancer. https://www.pcrm.org/health/cancer-resources/diet-cancer/nutrition/how-fiber-helps-protect-against-cancer. Accessed 9/14/16.