>To protect your colon against cancer, you need to take care of your gut. That is why there are so many comercials about probiotics.
Here is a quick tip on what are prebiotics and probiotics.
PREBIOTICS
indigestible carbohydrates, mostly polysaccharides. They promote the growth of microbes in the gut; Lactobacilli and Bifidobacteria.
They key is that any dietary component that reaches the colon intact is a potential prebiotic.
Prebiotics that help the gut include oligosaccharides which ar isolated from wheat, onions, bananas, garlic, soybeans and artichokes.
When you increase your intake of prebiotics, it can promote normal laxation and can protect you from colon cancer.

PROBIOTICS  
Are live microorganisms as in fermented foods such as yogurt, cultured milk,  cheese, pickeled cabbages and tempeh
Probiotic cultures are available pharmaceutically for clinical use.

Keep your gut happy!

Taken in part from: Schlenker,E & Roth, S ( 2011) Williams Essentials of Nutrition and Diet Therapy. St. Louis Mo. Elsevier-Mosby