Colon and Rectal Cancers - Dietary Factors

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. Any benefits or risks appear to depend on the type of compounds that make up fats (the fatty acids) or other nutrients or substances with fatty acids.

Saturated Fats and Trans-fatty Oils. Some studies had found an association between colon cancer and consumption of saturated fats (found primarily in animal fats). The association is not altogether clear, however, and more recent evidence has not supported a strong link. Some experts suggest that the real hazard is iron from red meat, which is often high in saturated fats and may have confused study results.

Of further interest, however, is a 2001 study that reported a possible link between colon cancer and trans fatty acids, which are partially hydrogenated oils found in stick margarine, fried foods and commercial baked goods. The association is supported by known chemical effects of these manufactured fats, and more research is warranted.

Monounsaturated Fats. Monounsaturated fats are mostly present in olive, canola, and peanut oils and in most nuts. Olive oil, for example, may protect the colon. Some evidence suggests that it reduces levels of deoxycholic acid, an acid found in bile that has tumor-promoting properties.

Polyunsaturated Fats. Polyunsaturated fats are found in both plant and fish oils, and are composed of essential fatty acids including omega-3 and omega-6 fatty acids. These fatty acids may play different roles in colon cancer.

Omega-3 fatty acids are found in oily fish and canola oil, soybeans, flaxseed, and certain nuts and seeds. They have been associated with protection against inflammation in the intestinal tract. It should be noted, however, that not all studies show protection. For example, omega-3 fatty acids in fish are composed of docosahexaenoic (DHA) and eicosapentaneoic (EPA) acids. Some evidence suggests that EPA--although not DHA--may be protective.
Omega-6 fatty acids, found in corn, safflower, soybean, and sunflower oil, constitute most of the oils consumed in the US. Some omega-6 fatty acids are important for health. However, a high intake has been associated with heart disease and certain cancers.