The colon is the large intestine. Its major function is to recapture water and fluids that were used to help digest food. If too much of this fluid cannot be recaptured we develop diarrhea. Colon polyps also develop in the large intestine and are known to account for 90% of colon cancers. Frequently, a scoping test of the colon called colonoscopy is used to diagnose colon polyps and cancers.