Colon and Rectal Cancers - Dietary Factors

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Fiber. Studies have been mixed on whether fiber (found in fruits, vegetables, and whole grains) protects the colon from cancer. For example, three major studies in 2002 and 2003 reported no difference in the development of colorectal polyps or cancer recurrence with high intake of fiber. On the other hand, other studies have been positive. In fact, 2003 results of the European Prospective Investigation into Cancer and Nutrition (EPIC) -- the largest study ever conducted on the role of diet in the development of cancer -- suggested that fiber is protective regardless of its source. However, in the study, the greatest benefits were observed for the left side of the colon and the least for the rectum. In any case, fiber, which is only found in plant products, may be beneficial for the heart and have other health advantages.

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Fats and Oils

The role of fats in inflammatory bowel disease is complex and not fully known. A 2006 study from the Women’s Health Initiative found that a low-fat diet did not help reduce the risk for colorectal cancer. However, the study did not distinguish between types of fat.

• Monounsaturated (olive, peanut, canola oils; avocados, nuts) and omega-3 polyunsaturated (fish, flaxseed oil, walnuts) fats are the healthiest types of fats.
• Saturated fats (red meat, butter, high-fat dairy products) and trans-fats (hydrogenated fat found in snack foods, fried foods, commercial baked goods) are unhealthy types of fats.

Current dietary guidelines recommend that adults limit the total fat in their diet to between 25 – 35% of total daily calories. Saturated fat intake should be less than 7%, and trans fats less than 1%, of total daily calories. (Patients with heart disease or diabetes may need to limit unhealthy fat in their diet even further.) Most fats should come from polyunsaturated and monounsaturated fat sources.

[For more information on fats, see In-Depth Report #43: Heart healthy diet; and #42: Diabetes diet.]

Meat and High-Temperature Cooking

Evidence suggests that red meat raises the risk for colon cancer. Red meat contains dietary iron, which has been associated with a higher risk for colon cancer. In fact, early results in 2000 from the largest study on diet and cancer to date have supported previous studies linking red meat with intestinal tumors.

High-temperature cooking (grilling, broiling, or pan-frying) has been specifically associated with increased risk for colon polyps and colon cancer. Over-cooking meat increases the amount of carcinogens called heterocyclic amines, which has been associated with cancerous changes.