The colon is part of the body's digestive system. The digestive system removes and processes nutrients (vitamins, minerals, carbohydrates, fats, proteins, and water) from foods and helps pass waste material out of the body. The digestive system is made up of the esophagus, stomach, and the small and large intestines. The first 6 feet of the large intestine are called the large bowel or colon. The last 6 inches are the rectum and the anal canal. The anal canal ends at the anus (the opening of the large intestine to the outside of the body).

Being age 50 or older is actually the number one risk factor for colon cancer. But other things impact colon cancer development, too. For example, studies indicate that all of these factors can contribute to colon cancer: alcohol, smoking, inflammatory bowel disease, obesity.

A diet high in animal fat and low in dietary fiber, which is the typical American diet today, has been linked to colon cancer. A review of the relationships between diet, exercise, and colon cancer suggests that diets high in vegetables and regular physical activity are the most significant factors in reducing the risk of colon cancer. Strong evidence shows that physical activity can reduce the risk of colon cancer by up to 50 percent. Some scientists hypothesize that fiber (from vegetables) might bind to potential carcinogens and cause them to be excreted before they can cause harm; other suggest that, in enhancing the movement of material through the GI tract, exercise or high-fiber diet reduces the time that carcinogens have to come in contact with colon cells. Other scientists suggest that high levels help protect the GI tract and delay the development of stomach, colon, and rectal cancer. Alternatively, the breakdown products of fiber produced by colonic bacteria, including acids that lower colon pH, might make carcinogens inactive.

Although these logical reasons point to a beneficial effect of fiber, a major study of women fails to support the protective effect of dietary fiber against colorectal cancer. However, a recent study of 400,000 men and women across nine European countries shows as much as a 40 percent reduction in risk.