9. Having diabetes

If someone has diabetes, his risk of colorectal cancer is increased by 30 percent. Unfortunately, diabetes has also been linked to a worse prognosis for the cancer once it's detected and treated.

10. Being overweight or obese

Experts don't know why being overweight or obese is a risk factor for colorectal cancers, but statistical analyses prove that it is. One recent study showed that obese women were four times as likely to develop colon cancer as those whose body mass index was within the normal range. The risk is highest in those who are "apple shaped," carrying their excess fat around their bellies. The best guess is that it has to do with insulin levels, though researchers are still exploring this issue.