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updated 9/16/2005 11:10:08 AM ET 2005-09-16T15:10:08

Experts say that our best chance to control colon cancer is to detect and remove – or prevent – a certain type of polyp before it can become malignant. About 95 percent of colon cancers develop from benign (noncancerous) polyps that are easily removed.

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However, less than half of people 50 and older follow national guidelines for colorectal screenings, according to the Centers for Disease Control and Prevention.

Colorectal polyps are extra bits of tissue, generally shaped like a mushroom or a small dome, growing inside the colon (large intestine) or rectum. Polyps are common. An estimated 30 to 40 percent of adults over the age of 50 develop them. Most are benign and will never develop into cancer.

However, one type known as adenomatous polyps, or adenomas, can become cancerous. Genetic changes in these polyps lead to changes in the growth and regulation of their cells, causing them to multiply abnormally. Most adenomas don’t become cancerous, but experts say removing them is an excellent way to make sure they don’t.

Rectal bleeding or blood in the stool, which can make the stool black or streaked with red, can indicate the presence of a polyp. However, most polyps produce no symptoms at all. They are found only with a routine screening test, or a procedure conducted for other reasons that looks into the colon.

Some researchers say that it takes at least five years for a benign polyp to become cancerous, so frequent screenings are unnecessary. Health experts recommend that you begin having colorectal screening tests at age 50, or sooner if you or a family member has a history of polyps or colon cancer.

Your physician can create a screening schedule appropriate for you, based on your individual level of risk. Of course, instead of detecting and removing polyps, it would be better to prevent them altogether. Research suggests that smoking, excessive alcohol consumption, a sedentary lifestyle and overweight all increase polyp formation.

Change your diet, lower your risk
Many studies have been done to see how a person’s eating habits might promote or block the formation of polyps, but specific answers are still lacking.

A fiber-rich diet with plenty of vegetables, fruits, whole grains and beans is commonly associated with a lower risk of colon cancer. Yet in one recent large population study, fiber consumption was unconnected to colon cancer occurrence. No randomized clinical trial – the most convincing type of human study – has shown that increasing people’s dietary fiber decreases the first appearance or recurrence of polyps either.

The problem with the randomized clinical trials so far may be their short duration. None has been more than four years long. It is probable that diet’s affect on colon cancer takes place over a longer period of time.

Despite the lack of supporting evidence from randomized clinical trials, you should still eat the lowfat, mostly plant-based diet researchers recommend to lower colon cancer risk. This eating style might inhibit colon cancer in several ways, such as decreasing polyp formation, slowing the growth of polyps, or blocking their transition from benign to cancerous.

Other steps you could take to decrease the formation of colon polyps include limiting your red meat consumption and meeting the current recommendations for folate.

This nutrient is found in dark green leafy vegetables, orange juice and other plant foods, and it’s often low in Americans’ diets. You should also get enough calcium and vitamin D. Unfortunately, the definition of what constitutes “enough” calcium and vitamin D is still in flux, but it appears that Americans should get more of both.

Most adults can meet current recommendations for calcium and vitamin D by having three cups of nonfat or lowfat milk a day. If you’re over age 50 or don’t drink much milk, consider other fortified foods or supplements.

Nutrition Notes is provided by the American Institute for Cancer Research  in Washington, D.C.© 2005 MSNBC Interactive

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