Why Red Meat May Lead to Colorectal Cancer
Colorectal cancer is the second most common cancer worldwide with an estimated 80 percent of cases attributable to diet. Previous research indicates that individuals who regularly eat processed or red meat are up to 50 percent more likely to develop colon cancer than individuals who avoid these foods altogether.
Researchers in London recently examined what it is about red meat consumption that increases colorectal cancer risk. In the study, healthy volunteers consumed a controlled vegetarian, red meat, or red meat with high fiber diet for 15 days. Individuals on the high red meat diet (15 ounces per day) had significantly higher colon levels of N-nitrosocompounds—compounds that can alter DNA and increase the risk of developing colon cancer—when compared with those consuming the vegetarian diet. Consumption of the red meat, high fiber diet resulted in lower levels of N-nitrosocompounds than the high red meat diet, but not as low as the vegetarian regimen. Investigators suggest that fiber may have played a protective role in the red meat, high fiber group as it can help repair damaged DNA and decrease the amount of time harmful compounds such as N-nitrosocompounds stay in the colon.
While researchers did not investigate the effects of white meat on colon cancer risk, they did note that chicken may contain high levels of heterocyclic amines (HCA), known carcinogens. In addition, earlier studies among Seventh-day Adventists have indicated that those consuming white meat, particularly chicken, have approximately a threefold higher colon cancer risk, compared with vegetarians.
Fraser GE. Associations between diet and cancer, ischemic heart disease, and all-cause mortality in non-Hispanic white California Seventh-day Adventists. Am J Clin Nutr. 1999;70(suppl):5325-5385.
Lewin MH, Bailey N, Bandaletova T., et al. Red meat enhances the colonic formation of the DNA adduct O6-carboxylmethyl guanine: implications for colorectal cancer. Cancer Res. 2006;66:1859-
Smoking Linked to Colon Cancer
The link between cigarette smoking and lung cancer is undeniable and well known. Now research has implicated the dangerous habit in the development of colon cancer as well. Two large prospective studies, including both men and women, found that smoking for 35 years was associated with higher colon cancer rates. Another study examined the type of tumors present in colon cancer patients and found that those who smoked were more likely to have microsatellite instability tumors (MSI), which contain unstable DNA.
"It provides support for the idea that lifestyle factors can cause tumor mutations," says University of Utah epidemiologist Martha Slattery. Researchers found the strongest links between tobacco use and MSI among people who smoked the longest and started at a young age.
Slattery ML, Curtin K, Anderson K, et al. Associations between cigarette smoking, lifestyle factors, and microsatellite instability in colon tumors. J Nat Cancer Inst 2000;92:1831-47.
Cancer-Fighting Ingredients in Apples and Carrots
Two new studies confirm the cancer-fighting power of plant foods. Scientists at Cornell University performed laboratory tests on human colon cancer cells and found that apple skin inhibited the growth of cancer cells by 43 percent. Tests on liver cancer cells were even more effective. Researchers believe it is the combination of phytochemicals in plant foods that reduces cancer.
It's no surprise that the second study also found carrots to be high in antioxidants, compounds that prevent free radicals from damaging cells and causing diseases such as cancer. However, scientists found that cooking and puréeing carrots increases their antioxidant level more than three times. Researchers report that heating and softening the carrot's tissue allows cancer-fighting phenolic compounds attached to the cell wall to be released. And, keeping the outer skin on carrots, as with other vegetables and fruits, retains numerous extra cancer-fighting compounds.
Eberhardt MV, Lee CY, Liu RH. Antioxidant activity of fresh apples. Nature 2000 22;405:903-4.
Don't Thank Fiber; Blame Meat and Milk
The very low rate of colon cancer among blacks in South Africa compared with whites is probably not due to a high fiber intake but rather to a very low intake of animal products, according to a recent study in the American Journal of Gastroenterology. Colon cancer affects only 1 in 100,000 South African blacks and is 17 times more common among whites. The cornmeal-based diet common among South African blacks is not particularly high in fiber and is low in calcium. According to Stephen J.D. O'Keefe and colleagues at the University of Capetown, the healthfulness of the diet comes from the absence of "aggressive" factors such as animal protein and fat. Osteoporosis, which is also linked to diets rich in animal protein, is also extremely rare among South African blacks.1
The American Journal of Clinical Nutrition published results of a 65-year follow-up study showing dairy consumption affects biological pathways associated with carcinogenesis. They found a diet rich in dairy products during childhood is associated with a greater risk of colorectal cancer in adulthood. High childhood total dairy intake was associated with a near-tripling in the risk of colorectal cancer compared with low intake, independent of meat, fruit, and vegetable intakes and socioeconomic indicators. Milk intake showed a similar association.2
O'Keefe SJ, Kidd M, Espitalier-Noel G, Owira P. Rarity of colon cancer in Africans is associated with low animal product consumption, not fiber. Am J Gastroenterol 1999;94:1373-1380.
van der Pols JC, Bain C, Gunnell D, Smith GD, Frobisher C, Martin RM. Childhood dairy intake and adult cancer risk. 65-y follow-up of the Boyd Orr cohort. Am J Clin Nutr. 2007;86(6)1722-1729.