Dietary Factors

Previous research suggested that diets low in fruits and vegetables and high in meats pose a risk for colon cancer, and that those rich in fruits and vegetables are protective against many cancers.

Fruits, Vegetables, and Whole Grains

There has been a prevailing belief from a number of studies that high intake of fruits and vegetables can lower the risk for colorectal cancer. Studies have been mixed, however, on their benefits. A 2002 study, for example, reported that these foods do not prevent polyps from forming but may help prevent them from becoming cancerous.

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It should be noted that it is nearly impossible to do controlled studies on dietary factors, since people's eating habits can rarely be made consistent. Dietary studies also use a variety of different approaches to obtain results that make comparisons very difficult. To help determine their specific effects researchers are studying the phytochemicals (plant chemicals) in fruits and vegetables and also fiber (which is also found in whole grains.)

Phytochemicals. Many studies have demonstrated the cancer-fighting effects of plant chemicals called phytochemicals. Fruits and vegetables that contain phytochemicals can often be identified by colors:

• Dark green (broccoli, spinach, kale, collard greens, mustard greens). These specific vegetables contain chemicals called isothiocyanates, which have been associated with a lower risk for cancer in general.
• Red (red pepper, tomatoes, watermelon, raspberries, pink grapefruit). Lycopene is a chemical found in these foods that may have strong cancer-protective properties. Cooking tomatoes appears to increase their benefits.
• Yellow-orange (carrots, pumpkin, sweet potatoes, oranges, tangerines). The colors in these foods are due to carotenoids, which have been associated with health protection, although may not have much effect on colon cancer itself.
• Blue-black (many berries). Dark berries appear to have potent chemicals that may be protective against cancer. In one animal study, extracts from black raspberries reduced colon cancer tumors in rats.