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updated 8/18/2006 9:30:38 AM ET 2006-08-18T13:30:38

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An estimated 148,000 Americans will be diagnosed with colon cancer in 2006. Having a close relative with colon cancer or an adenoma (noncancerous growth) clearly marks you as someone who needs to be extra watchful. Lack of family history, however, is no reprieve. Seventy-five percent of colon cancer patients seem to have no inherited risk.

Fortunately, many of the factors that increase colon cancer risk are habits you can change. Studies show that change of habit does change risk.

Consider first processed meats, such as bacon, sausage and hot dogs. In one large study, those who ate even 4 to 8 ounces of processed meat per week showed a 13 percent increase in colorectal cancer compared to those who ate no processed meat. In another study, eating nearly three ounces a day raised colorectal cancer risk 42 percent. In these same studies, people who ate more than three to four ounces per day of red meat — beef, pork and lamb — had at least 15 percent more colorectal cancer than those who ate less than 7 ounces a week.

Laboratory studies have suggested several mechanisms by which these meats may raise cancer risk. Nitrites that some processed meats contain may form cancer-causing compounds. Higher cancer risk could come from red meat's higher heme iron — a form of iron especially high in red meats. This iron is associated with damage to the colon lining and stimulating inappropriate cell growth. Meat is also associated with forming cancer-causing compounds in the gut.

Stay away from high fat foods
Another influence on colon cancer risk is the fat you eat. Studies suggest that more saturated fat, from fatty meat, ice cream, high-fat cheese and milk, may trigger increased production of insulin and growth factors that seem to promote colon tumor growth. In contrast, diets high in omega-3 fats found particularly in fish such as salmon, albacore tuna and rainbow trout may decrease inflammation that may lead to colon cancer, and may increase the self-destruction of cancer cells.

Monounsaturated fats like olive oil do not seem to affect colon cancer risk unless you use so much that calorie intake becomes too high to maintain a healthy weight. Excess weight is strongly linked to colon cancer, especially for men, premenopausal women and those with excess fat centered at the waist. If your weight is too high, look for a few simple changes you can adopt for the long-term, such as 25 percent smaller portions, shifting to a plant-based diet with lots of vegetables, cutting back on sweetened drinks and high-calorie snacks, and adding daily physical activity.

Eat your veggies
If you’re not getting five to 10 servings of vegetables and fruits and at least three servings of whole grains each day — all sources of fiber — consider that a risk. Not all population studies show an effect of fiber on colon cancer risk. However, laboratory studies show a variety of ways that fiber may protect the cells of our colon from cancer-causing substances. Also, recent population studies have shown an approximate 25 percent decrease in colon cancer and precancerous growths in those who meet current fiber recommendations. Many researchers have found that eating foods high in fiber, which also supply a wide array of protective vitamins and phytochemicals, provide benefits that adding fiber supplements do not.

Regular moderate activity such as brisk walking for 30 to 60 minutes a day doesn’t just help weight control. Regular exercise brings changes in various hormones and growth factors that lower risk of colon cancer 40 to 50 percent.

Overall lifestyle matters. A study, published in 2003, examined nutritional data collected from more than 76,000 nurses every few years from 1984 to 1994. After following the women through 1996, the study found that the women who most fit the “Western diet” that emphasizes red and processed meats, sweets, and refined grains were 46 percent more likely to develop colon cancer than those who ate this way the least.

Nutrition Notes is provided by the American Institute for Cancer Researchin Washington, D.C.

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