Colon and Rectal Cancers - Dietary Factors

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 based on several 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.

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. Carotenoids have been associated with health protection, although they 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.

Organosulfurs are important food chemicals that are part of the allium family. Studies have reported health benefits from foods containing them. These compounds are found in garlic, leeks, onions, chives, scallions, and shallots. A review of 300 studies concluded that people who eat raw or cooked garlic regularly experience about two-thirds the risk of colorectal cancer as people who eat little or none. Another analysis, however, found the available evidence about garlic to be inconclusive. Garlic supplements, in any case, do not appear to be protective.