Colorectal cancer is the third most common cancer in the U.S. and the second leading cause of cancer death. This year, the American Cancer Society estimates 153,760 new cases will be diagnosed (79,130 in men and 74,630 in women). About 52,180 Americans will die of the disease (26,000 men and 26,180 women).

Risk for colorectal cancer increases with age. The condition is most commonly diagnosed after 50. It's also more common in people with a family history of colorectal cancer and in those with a personal history of the cancer or colorectal polyps. Rates are higher among African-Americans than among those of other ethnic groups. Some other risk factors include: lack of physical activity, high fat diet (especially high in animal fat), obesity, smoking, excessive consumption of alcohol and diabetes.

The Role of Fiber

Fiber is the term used to describe the parts of plant foods the body can't digest. There are two types. Soluble fiber partially dissolves in water to form a gel-like substance. Examples of sources include oatmeal, barley, peas, beans, carrots, broccoli, apples, bananas, citrus fruits and carrots. Insoluble fiber doesn't dissolve in water. It passes through the digestive tract and increases the bulk of stools. Examples include whole grains, seed, nuts, green beans and dark leafy vegetables.

For years, researchers have studied the value of fiber for prevention of polyps, benign growths in the colon and rectum than can turn into cancer. Some studies have suggested that a high-fiber diet can protect against polyps and may decrease the risk for colorectal cancer. Other studies have found no protective effects of fiber against colorectal cancer.

Researchers at the University of Arizona recently compared the results of two large studies of fiber use. Independently, neither of the studies found a beneficial effect of dietary fiber on polyp or colon cancer prevention. However, when the results of the two studies were polled together and analyzed more thoroughly, investigators made a surprising finding: fiber appeared to have a protective effect in men, but not in women.

Elizabeth Jacobs, Ph.D., says no one knows why fiber may not provide any protection against colorectal cancer for women. She theorizes female hormones may somehow interfere with protective effects of fiber. In addition, women are more likely to get polyps on the right side of their colon than men. So, perhaps fiber has more of an effect on left-sided polyps.

The researchers will continue to follow the participants of the two studies to look for longer-term effects of fiber on colorectal cancer risk. In the meantime, Jacobs says fiber has other important health benefits. Studies suggest fiber may help lower cholesterol and blood pressure and decrease the risk of obesity, type 2 diabetes and heart disease. Health experts say adult men should have 30 to 38 grams of fiber every day and women should have 21 to 28 grams of fiber.

For information on fiber:

American Dietetic Association

International Food Information Council

For general information on colorectal cancer:

American Cancer Society

National Cancer Institute