July 2000
Fighting the Cancer Battle
By: Andrea Platzman, R.D.
Contributing Editor Cancer, the second most lethal disease in the United States, occurs when cells divide without control or order. Tumorogenesis is a multi-stage process consisting of initiation, promotion and tumor progression. Initiation occurs when a cell's DNA is transformed by random mutation, chemicals, radiation or a virus. This transformation occurs rapidly, but the resultant cell remains dormant for a variable period until activated to tumor progression by a promoting agent.
Although some cancers are promoted by activities such as smoking, many other promoters are tied directly to foods and food compounds. Foods can also play a role in preventing cancer. "Experts estimate that 30% to 40% of cancers worldwide are preventable by dietary means," states Marilyn Swanson, professor and chair, department of food science and nutrition, South Dakota State University, Bookings.
Dietary cancer promotersObesity. Overweight is defined as 10% above the appropriate weight for height, while obese is defined as 20% or more. According to the American Institute for Cancer Research/World Cancer Research Fund, obesity increases the risk of colon, rectum, gallbladder, kidney, endometrial and breast cancers. Alcohol. Heavy alcohol intake is associated with increased risk of developing colon cancer, especially for those deficient in folate. "Some research suggests that moderate drinking may slightly increase the likelihood of cancer development in the mouth, larynx, throat, esophagus and liver," says Mark Kantor, Ph.D., food and nutrition specialist, department of nutrition and food science, University of Maryland, College Park. According to the National Cancer Institute, Bethesda, MD, current guidelines suggest limiting alcohol to less than two drinks a day for men and one drink a day for women. Heterocyclic amines. Long exposure of meat to high heat, especially from grilling, forms heterocyclic amines. "Currently, there are 19 known heterocyclic amines that are mutagenic in the pancreas, colon, breast and prostate," says John Weisburger, Ph.D., M.D., FACN, director emeritus, American Health Foundation, Valhalla, NY. "When any food that contains creatine (meat, poultry, fish) is fried or browned, carcinogens can be initiated." He suggests marinating meat before cooking to stop formation of carcinogens, or microwaving three to five minutes so their precursors are removed. Marinades, especially those with antioxidants such as green tea or vitamin C, also appear to decrease mutagen formation. Nitrites. To maintain color and prevent botulism, nitrites are used in many processed meats. "Nitrites can be converted to carcinogenic nitrosamines in the stomach, which may increase the risk of gastric cancer. Diets high in fruits and vegetables that contain vitamin C and phytochemicals such as phenols retard the conversion of nitrites to nitrosamines," says Weisburger. Fat. "Fat appears to be a cancer promoter, not a cancer initiator. It is recommended, beginning in childhood, to consume only 20% of fat from calories, mainly from monounsaturated fats such as olive and canola oils as well as omega-3 fatty acids," says Weisburger.
Many studies link lower fat intakes with lower cancer rates, but experts aren't sure whether this is due to the obesity-cancer link or if there are specific fatty-acid culprits. Studies have linked certain polyunsaturated omega-6 fatty acids to increased risk of breast and colon cancers. On the other hand, conjugated linoleic acid may inhibit cancer cells, and recent research suggests that omega-3 fatty acids from fish oil protect against breast, mouth, esophageal, gastric, pancreatic, colon and rectal cancers. Cancer protectorsFruits and vegetables. The National Cancer Institute recommends eating at least five servings of fruits and vegetables (combined) per day to lower risk of cancer. Fruit and vegetable phytochemicals appear to increase activity of the enzymes that detoxify carcinogens, as well as protect against certain cardiovascular diseases. Fiber. Fiber may offer protection against breast and colon cancer, the latter by hastening bile excretion and speeding transit time through the colon so that its walls are not exposed for long periods of time to cancer-causing substances. The average fiber intake in the United States is currently 14 grams per day; The National Cancer Institute recommends 25 to 35 grams of fiber per day. Calcium. Some research has suggested that foods high in calcium might help reduce colon cancer in persons previously diagnosed with colon polyps and cancer. The National Cancer Institute and the Dairy Council recommend 1,200 to 1,500 mg of calcium per day. Studies are currently being conducted to determine if a specific type of calcium is most effective based on bioavailability. Soy. "Although the epidemiologic data are inconsistent, those studies that show protective effects indicate that as little as one serving of soy, or 30 to 60 mg of isoflavones per day, is associated with a reduced cancer risk," says Mark Messina, Ph.D., Nutrition Matters, Inc., Port Townsend, WA. "So far, the strongest data are for prostate, lung, breast and colon cancers." Antioxidants. "High doses of vitamin C inhibit the growth of H. pylori, the bacteria responsible for ulcers that are thought to increase the risk of gastric cancer," says Weisburger. Another antioxidant, vitamin E, protects red blood cells and other essential systems against free-radical damage. It's possible that this vitamin reduces cancer risk, though evidence is not conclusive. Carotenoids may also lower risk of cancer. Although a study indicating that beta-carotene may increase lung cancer in tobacco smokers cast doubts on its protective effects, these results may very well have been an anomaly. Lycopene, another member of the carotenoid family, has been found to help lower the risk of prostate, colon and cervical cancer. Tea. "The epidemiological data strongly suggest that both green and black tea help reduce the incidence of skin, gastric, colon and esophageal cancers," says Douglas Balentine, Ph.D., manager, tea research, Lipton, Inc., Englewood Cliffs, NJ. "Drinking three to five cups of either green or black tea, hot or cold, with or without milk, is recommended; however, some decaffeinated teas do have fewer flavonoids depending on the extraction process." Folic acid. Preliminary data suggest that folic acid may reduce the risk of colon polyps and colon cancer. This vitamin is thought to prevent the onset of cancer by preventing DNA damage.
Andrea D. Platzman, a registered dietitian, writes regularly for nutrition publications. She earned a master's degree in nutrition from New York University, and has a culinary and business background.
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