Diet and Colon Cancer

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Americans who are non-smokers are more likely to die from colorectal cancer than any other type of cancer. Even higher rates of colorectal cancer are seen in Australia, Canada, the Czech Republic and Austria. The incidence of colorectal cancer in these countries and the U.S. are from 3 to 8 times higher than in countries like China, Colombia, Greece and India. Those who migrate from a low-risk country to a high-risk country experience an increase in risk of colorectal cancer after just a few years. It seems likely that most of the differences in risk seen between populations is probably due to diet.
In most cases cancer of the colon and rectum arise from polyps. These precancerous lesions are an early warning sign that colorectal cancer may develop. Indeed, screening for polyps and surgically removing them when present dramatically reduces the risk of developing and dying from colorectal cancer. Of course it is better to prevent these polyps from developing than it is to have them surgically removed every few years.
What is the best diet?
Early epidemiological research suggested that diets high in fat and low in fruits, vegetables and fiber promoted colorectal cancer. However, the fairly low incidence of colorectal cancer in Greece compared to more northern European countries suggests that a diet high in olive oil does not promote colorectal cancer. This certainly conflicts with the theory that a high-fat diet promotes colorectal cancer. Colorectal cancer is also much less common in Finland than in Germany and other central European countries. The Fins eat a lot more whole grain bread than do Germans and Americans. But is it the increased cereal fiber responsible for the reduced risk of developing colorectal cancer?
Fiber and colon cancer
Two recent studies looked at the impact of dietary changes in people at high-risk of developing colorectal cancer due to the presence of polyps. The Polyp Prevention Trial followed 2079 patients whose colon had been surgically cleared of polyps. Half were provided with intensive counseling and placed on a low-fat (20% fat calories), high-fiber (18g/1000kcal) diet that contained more fruits and vegetables (3 1/2 servings per 1000 kcal). The control group was simply given standard brochures on healthy eating. All patients then underwent colonoscopy after 1 to 4 years. The incidence of polyps was virtually identical in the two groups.1 In the second study, a similar group of 1429 patients were randomly assigned to either a low intake of wheat fiber (2g/day) or a high wheat fiber (13.5g/day) diets. Both groups were then re-examined 3 years later. The recurrence of polyps was 51% and 47% in the two groups, which was not significantly different.2
Lower Meat Intake
The results of these two studies suggest that simply increasing the intake of fruits and vegetables is not going to help prevent the formation of polyps in high-risk individuals. Perhaps a better approach would be to focus more attention on sources of carcinogens in Western diets.
The incidence of colorectal cancer is only 1/8 as common in India as the U.S. In India, much of the population is Hindu and cattle are considered sacred. India has one of the lowest intakes of red meat of any country. All countries where the incidence of colorectal cancer is low also have a low intake of red meats. Meat contains a substance called creatine. At high temperatures, creatine reacts with amino acids to form heterocyclic amines, which are potent carcinogens. Sausages and cured meats contain nitrites, which react with amino acids to form cancer-causing chemicals. A large epidemiological study found an association between red meat intake and the incidence of colorectal cancer.3
Other factors
People who take aspirin regularly have a reduced risk of colorectal cancer. There is some evidence that increased calcium reduces the risk of colorectal cancers.4 Omega-3 fatty acids, found in cold water fatty fish such as salmon and tuna, may inhibit the growth of some cancers by reducing inflammation. People with inflammatory bowel diseases (e.g. ulcerative colitis and Crohn’s disease) have a much greater risk of developing colorectal cancer.
Inactivity and weight gain appear to increase the risk of colorectal cancer. There is also some evidence suggesting that a lack of selenium, folic acid and/or vitamin D may contribute to the development of colorectal cancer. However, there is a need for prospective studies with these nutrients before any firm conclusions should be drawn. Studies with supplements of beta-carotene, and vitamins C and E have shown no reduction in polyp formation.
Bottom Line:
People concerned about the development of colorectal cancer should be advised to cut back on red meats and cured meats, especially ones cooked at high temperatures. These should be replaced in the diet by beans, soy products and some seafood. While an increase in fruits and vegetables didn’t help lower the risk of recurrence of polyps in high-risk patients, this does not mean they may not reduce the risk if consumed throughout life. A low fat diet that is higher in fruits, vegetables, whole grains, sea food and nonfat milk and beans should promote weight loss and will likely reduce the risk of colorectal cancer and many other serious diseases.
By James J. Kenney, PhD, RD, FACN.
References:
1 Schatzkin A, et al. N Engl J Med 2000;342:1149-55
2 Alberta DS, et al. N Engl J Med 2000;342:1156-62
3 Willett W. et al. N Engl J Med 1990;323:1664-72
4 Mobarhan S, Nutr Rev 1999;57;124-9

5 Top Strategies for Lowering the Risk of Colorectal Cancer
1. Reduce your intake of red meats and processed meats. When cooked at high temperatures, these meat products will generate a variety of known and suspected chemical carcinogens (eg, Heterocyclic amines, nitrosamines, benzopyrene). High temperature methods of cooking include frying, broiling and barbecuing. Roasted pan drippings can also contain these carcinogens.
2. Replace red meats and processed meats with seafoods, legumes, nuts and seeds. These foods are good sources of omega-3 fatty acids, folic acid and selenium. Preliminary research suggest that low levels of these 3 nutrients may increase the risk of colorectal cancer.
3. Consume 2-3 servings daily of nonfat milk. It is a rich source of calcium and vitamin D. Epidemiological research suggests that low intakes of these nutrients may increase the risk of colorectal cancers.
4. Eat more fruits, vegetables, and whole grains and cut back on foods rich in refined fats, oils, sugars and grains. Whole foods are rich sources of folic acid, fiber and other phytochemicals that  many studies suggest may reduce the risk of colorectal cancer. This type of diet will help reduce excessive body fat stores, which have been consistently associated with an increased risk of colorectal cancer in the long run.
5. If you have a history of colon cancer, colon polyps or reason to believe you are genetically predisposed to develop colorectal cancer, talk to your doctor about the risk and benefits of talking aspirin or the new COX-2 inhibitor medications to help reduce your risk of developing more polyps or colorectal cancer.

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