Which foods are most protective against colon cancer?
It is estimated that there are more than 100,000 new cases of colon cancer diagnosed each year in the U.S. alone, and colon and rectal cancers are the third leading cause of cancer-related deaths.1 The American Institute for Cancer Research estimates that forty-five percent of these new cases could be prevented by following a few simple lifestyle habits: avoiding processed and red meat, exercising regularly, maintaining a healthy weight, and limiting alcohol consumption.2 But we can do better – imagine the level of protection if we not only avoided carcinogenic foods, but also focused on eating the foods that work on a cellular level to prevent colon cancer.
So which foods offer us the best protection?
Anti-cancer compounds have been identified in many plant foods: for example cruciferous vegetables, mushrooms, and the onion and garlic family are known to contain substances that can prevent cellular processes involved in cancer development. Certainly, a diet high in fruits and vegetables in general is protective3-5, but many observational studies on diet have not investigated specific food groups, only broad categories like “fruits,” “vegetables,” etc. But there is a wide range of anti-cancer activity in the wide range of plant foods – for example, kale is more protective than iceberg lettuce. Identifying these protective plant foods helps us to construct an anti-colon cancer diet.
A recent study aimed to find some specific foods and food groups that protect against colon cancer. Twenty-six years after reporting information about their diets, subjects were asked whether they had undergone screening colonoscopy, and if so, whether they had physician-diagnosed polyps. The majority of colorectal cancers originate from polyps, so polyps are considered a precursor to the development of cancer. This study was part of the larger Adventist Health Study, which studies relationships between diet and chronic disease in members of the Seventh-day Adventist Church, which emphasizes healthy living in its teachings.
The researchers examined about 25 different foods and food groups. Those that were associated with reduced risk of polyps were cooked green vegetables, dried fruit, legumes (beans, lentils, etc.), and brown rice. All of these displayed dose-dependent effects, meaning that the more of these foods the subjects ate, the more protection they had from colon cancer.6
Green vegetables are rich in folate and isothiocyanates, nutrients with potent anti-cancer properties. Folate is a B vitamin that is involved in turning genes on and off – this is important in preventing the early cellular events that lead to cancer. Adequate folate levels are protective against several cancers, including colon cancer. It is important to note, however, that synthetic folic acid from supplements is not protective.7,8 Isothiocyanates are a group of nutrients found in cruciferous vegetables that have a wide variety of cancer preventive properties – they can detoxify or remove carcinogens from healthy cells, kill cancer cells, have anti-inflammatory and antioxidant effects, and prevent tumors from acquiring a blood supply.9
The protection from beans and other legumes was likely due to their soluble fiber and resistant starch, carbohydrates that are not broken down by digestive enzymes. Intestinal bacteria ferment these carbohydrates, forming short chain fatty acids such as butyrate. Butyrate has a number of anti-cancer effects including disrupting cancer cell growth, increasing levels of detoxification enzymes, limiting DNA damage, and preventing tumors from acquiring a blood supply.10-13
High fiber foods, including dried fruit and brown rice (as well as vegetables and beans) help to reduce transit time of gastrointestinal contents through the colon – this reduces the potential contact between dietary toxins or carcinogens and the cells that line the colon. Reduced transit time is believed to be an important contribution of fiber to the prevention of colon cancer. 14,15 Raisins, probably the most popular dried fruit, have been shown to increase short chain fatty acid production and decrease colon transit time.16,17 In addition to fiber content, dried fruit likely also contributed antioxidant protection of colon cells from DNA damage, which is an early event in the development of cancer.18
Previous studies found a protective effect of berries, citrus fruits, and yellow-orange vegetables, which was likely due to their high concentration of flavonoid and carotenoid antioxidants, respectively.10,19,20Additional studies on specific food groups have also found a reduced risk of colon polyps with high intake of green leafy vegetables (many of which are cruciferous), onions, and garlic.12,19
All of these foods contain known anti-cancer compounds, and of course there are thousands of anti-cancer compounds in plant foods that scientists have not yet discovered. Each of these colorful plant foods contains a spectrum of micronutrients and phytochemicals that work in concert to protect the body against carcinogenic influences. Future studies will continue to reveal these phytochemicals and their anti-cancer properties.
My new book Super Immunity, which will be released September 20, 2011, discusses in depth the connections between diet and cancer.
1. American Cancer Society. What are the key statistics about colorectal cancer? [http://www.cancer.org/Cancer/ColonandRectumCancer/DetailedGuide/colorectal-cancer-key-statistics ]
2. American Institute for Cancer Research. What you need to know about preventing colorectal cancer. http://www.aicr.org/reduce-your-cancer-risk/cancer-site/cancersite_colon_rectum.html. Accessed September 2, 2011.
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15. Gear JS, Brodribb AJ, Ware A, et al: Fibre and bowel transit times. Br J Nutr 1981;45:77-82.
16. Spiller GA, Story JA, Furumoto EJ, et al: Effect of tartaric acid and dietary fibre from sun-dried raisins on colonic function and on bile acid and volatile fatty acid excretion in healthy adults. The British journal of nutrition 2003;90:803-807.
17. Spiller GA, Story JA, Lodics TA, et al: Effect of sun-dried raisins on bile acid excretion, intestinal transit time, and fecal weight: a dose-response study. Journal of medicinal food 2003;6:87-91.
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20. Michels KB, Giovannucci E, Chan AT, et al: Fruit and vegetable consumption and colorectal adenomas in the Nurses' Health Study. Cancer Res 2006;66:3942-3953.