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. Eat dark-colored greens, red fruit and vegetables, and blue and purple berries.

Dark green broccoli, spinach, kale, collard greens, and mustard greens contain chemicals called isothiocyanates, which have been associated with a lower risk for cancer in general.

Red peppers, tomatoes, watermelon, raspberries, and pink grapefruit contain lycopene, which may have strong cancer-protective properties. Cooking tomatoes appears to increase their benefits.

Yellow-orange carrots, pumpkin, sweet potatoes, oranges, and tangerines contain carotenoids. Carotenoids have been associated with cancer prevention, although they may not have much effect on colon cancer itself.

Blue-black assorted 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 multiple health benefits, including cancer protection, from foods containing them. These compounds are found in garlic, leeks, onions, chives, scallions, and shallots.

According to the American Institute for Cancer Research, the dietary fiber found in plant-based foods helps protect us against cancer, specifically colorectal cancer. The insoluble fiber found in fruits and vegetables may be protective against cancers of the mouth, esophagus, stomach, and rectum.

The American Cancer Society recommends that most of our fat intake should come from the heart-healthy unsaturated fats, which are found predominantly in nuts, seeds, fish, soy products, avocados, and oils such as olive, canola, and peanut oil. There is scientific evidence that foods containing healthy fats (such as salmon, which is rich in omega-3s), may have a protective effect on inflammatory bowel disease.

Research has found that even moderate coffee consumption (one to two cups per day) is associated with a decreased risk for colorectal cancer. Consumption of green tea is also linked to cancer prevention.

There is evidence that the B vitamin folate (called folic acid) is cancer-protective, though excessive supplementation is not recommended. Both folate and vitamin B12 convert the amino acid homocysteine to methionine, a chemical that protects certain genes that help prevent cells from becoming cancerous. Folate is found in beans, citrus fruits, and green vegetables.

Antioxidants are chemicals that help eliminate harmful particles called oxygen-free radicals, which have been associated with cancerous changes. Some studies suggest an association between supplements of the antioxidants selenium and vitamins A, C, D, and E with lower colon cancer risk, but most studies reported by the National Cancer Institute have found no protective effect.