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The American Cancer Societyhttp://www.cancer.org/docroot/PED/content/PED_3_2X_Common_Questions_About_Diet_and_Cancer.aspCommon Questions About Diet and Cancer
Developed by the American Cancer Society 2006 Nutrition and Physical Activity Guidelines Advisory Committee and approved by the American Cancer Society National Board of Directors on May 19, 2006.
This section is taken from the Complete Guide—Nutrition and Physical Activity for Cancer Prevention.
Because people are interested in the relationship that specific foods, nutrients, or lifestyle factors have to specific cancers, research on health behaviors and cancer risk is often reported on the news. No one study, however, provides the last word on any subject, and single news reports may put too much emphasis on what appear to be contradictory or conflicting results. In brief news stories, reporters cannot always put new research findings in their proper context. Therefore, it is rarely, if ever, advisable to change diet or activity levels based on a single study or news report. The following questions and answers address common concerns about diet and physical activity in relation to cancer.
Alcohol
Does alcohol increase cancer risk?
Yes. Alcohol raises the risk of cancers of the mouth, pharynx (throat), larynx (voice box), esophagus, liver, and breast, and probably of the colon and rectum. People who drink alcohol should limit their intake to no more than 2 drinks per day for men and 1 drink per day for women. A drink is defined as 12 ounces of beer, 5 ounces of wine, or 1.5 ounces of 80-proof distilled spirits. The combination of alcohol and tobacco increases the risk of some cancers far more than the effect of either drinking or smoking alone. Regular intake of even a few drinks per week is linked to a higher of breast cancer in women, especially in women who do not get enough folate. Women at high risk of breast cancer may want to consider not drinking any alcohol.
Antioxidants
What are antioxidants, and what do they have to do with cancer?
The body seems to use certain nutrients in vegetables and fruits to protect against damage to tissues that happens constantly as a result of normal metabolism (oxidation). Because such damage is linked with increased cancer risk, the so-called antioxidant nutrients are thought to protect against cancer. Antioxidants include vitamin C, vitamin E, carotenoids, and many other phytochemicals (chemicals from plants). Studies suggest that people who eat more vegetables and fruits, which are rich sources of antioxidants, may have a lower risk for some types of cancer. Clinical studies of antioxidant supplements are currently under way but have not yet proven to reduce cancer risk from vitamin or mineral supplements (also see entries for: beta-carotene, lycopene, vitamin E, supplements). To reduce cancer risk, the best advice at present is to get your antioxidants through food sources, rather than supplements.
Aspartame
Does aspartame cause cancer?
Aspartame is a low-calorie artificial sweetener that is about 200 times sweeter than sugar. Current evidence does not show any link between aspartame use and increased cancer risk. People with the genetic disorder known as phenylketonuria should avoid foods and drinks that contain aspartame.
Beta-carotene
Does beta-carotene reduce cancer risk?
Because beta-carotene, an antioxidant chemically related to vitamin A, is found in vegetables and fruits, and because eating vegetables and fruits is linked with a reduced risk of cancer, it seemed to make sense that taking high doses of beta-carotene supplements might reduce cancer risk. But the results of 3 major clinical trials show this is not the case. In 2 studies in which people were given high doses of beta-carotene supplements in an attempt to prevent lung cancer and other cancers, the supplements were found to increase the risk of lung cancer in cigarette smokers, and a third found neither benefit nor harm from them. Therefore, eating vegetables and fruits that contain beta-carotene may be helpful, but high-dose beta-carotene supplements should be avoided.
Bioengineered foods
What are bioengineered foods, and are they safe?
Bioengineered foods are made by adding genes from other plants or organisms to make a plant more resistant to pests and slow spoilage. Some genes improve flavor, nutrient composition, or make the food easier to transport. In theory, these added genes might create substances that could cause harmful reactions among sensitized or allergic individuals. But there is no evidence at this time that the substances found in bioengineered foods now on the market are harmful or that they would either increase or decrease cancer risk because of the added genes.
Calcium
Is calcium related to cancer?
Several studies have suggested that foods high in calcium might help reduce the risk for colorectal cancer, and that using calcium supplements modestly reduces the formation of colorectal adenomas (polyps). But there is also evidence that a high calcium intake, mainly through supplements, is linked with increased risk for prostate cancer, especially for prostate cancers that are more aggressive. In light of this, both men and women should try to get the recommended levels of calcium, mainly from food sources. Recommended intake levels of calcium are 1,000 mg/day for people ages 19 to 50 years and 1,200 mg/day for people older than 50. Dairy products are excellent sources of calcium, as are some leafy vegetables and greens. People who get much of their calcium from dairy products should select low-fat or non-fat choices to reduce their intake of saturated fat.
Cholesterol
Does cholesterol in the diet increase cancer risk?
Cholesterol in the diet comes only from foods with animal sources -- meat, dairy products, eggs, and animal fats such as butter or lard. Although some of these foods (for example, processed and red meats) are linked with higher risk of certain cancers, at this time there is little evidence that this increased risk is specifically related to cholesterol. Lowering blood cholesterol reduces heart disease risk, but there is no evidence that lowering blood cholesterol affects cancer risk.
Coffee
Does drinking coffee cause cancer?
Caffeine may worsen symptoms of fibrocystic breast lumps (a type of benign breast disease) in some women, but there is no evidence that it increases the risk of breast cancer or other types of cancer. The link between coffee and cancer of the pancreas, which got a lot of attention in the past, has not been confirmed by recent studies. There does not appear to be any link between coffee drinking and cancer risk.
Fat
Will eating less fat lower cancer risk?
There is little evidence that the total amount of fat a person eats affects cancer risk. But diets high in fat tend to be high in calories and may contribute to obesity, which in turn is linked with an increased risk of several types of cancer. There is evidence that certain types of fats, such as saturated fats, may increase cancer risk. There is little evidence that other types of fat (omega-3 fatty acids, found mainly in fish), monounsaturated fatty acids (found in olive and canola oils), or other polyunsaturated fats reduce cancer risk.
Fiber
What is dietary fiber, and can it prevent cancer?
Dietary fiber includes a wide variety of plant carbohydrates that humans cannot digest. Specific categories of fiber are "soluble" (like oat bran) or "insoluble" (like wheat bran and cellulose). Soluble fiber helps to reduce blood cholesterol, which lowers the risk of coronary heart disease. Good sources of fiber are beans, vegetables, whole grains, and fruits. Links between fiber and cancer risk are weak, but eating these foods is still recommended. These foods contain other nutrients that may help reduce cancer risk and have other health benefits.
Fish
Does eating fish protect against cancer?
Fish is a rich source of omega-3 fatty acids. Studies in animals have found that these fatty acids suppress cancer formation or slow down cancer growth, but there is limited evidence of a possible benefit in humans.
While eating fish rich in omega-3 fatty acids is linked with a reduced risk of heart disease, some types of fish (large predatory fish such as swordfish, tilefish, shark, and king mackerel) may contain high levels of mercury, polychlorinated biphenyls (PCBs), dioxins, and other environmental pollutants. Women who are pregnant, breast-feeding, or planning to become pregnant, and young children should not eat these fish. People should vary the types of fish they eat to reduce the chance of exposure to toxins.
Research has not yet shown whether taking omega-3 or fish oil supplements produces the same possible benefits as eating fish. .
Fluorides
Do fluorides cause cancer?
Extensive research has looked at the effects of fluorides given as dental treatments or added to toothpaste, public water supplies, or foods on cancer risk. Fluorides have not been found to increase cancer risk.
Folate
What is folate, and can it prevent cancer?
Folate is a B vitamin found in many vegetables, beans, fruits, whole grains, and fortified breakfast cereals. Since 1998, all grain products in the United States have been fortified with folate. Too little folate may increase the risk of cancers of the colon, rectum, and breast, especially in people who drink alcoholic beverages. Current evidence suggests that to reduce cancer risk, folate is best obtained by eating vegetables, fruits, and enriched grain products.
Food additives
Do food additives cause cancer?
Many substances are added to foods to preserve them and to enhance color, flavor, and texture. New additives must be cleared by the Food and Drug Administration (FDA) before entering the food supply. Rigorous testing in animals to look for any effects on cancer is done as part of this process. Additives are usually present in very small quantities in food, and no convincing evidence has shown that any additive at these levels causes human cancers.
Garlic
Can garlic prevent cancer?
The health benefits of the allium compounds contained in garlic and other vegetables in the onion family have been publicized widely. Garlic is currently under study for its ability to reduce cancer risk. There is not enough evidence at this time to support a specific role for this vegetable in cancer prevention.
Genetics
If our genes determine cancer risk, how can diet help prevent cancer?
Damage to the genes that control cell growth can be either inherited or acquired during life. Certain types of mutations or genetic damage can increase the risk of cancer. Nutrients in the diet can protect DNA from being damaged. Physical activity, weight control, and diet might delay or prevent the development of cancer in people with an increased genetic risk for cancer. The interaction between diet and genetic factors is an important and complex topic, and a great deal of research is under way in this area.
Irradiated foods
Do irradiated foods cause cancer?
No. Radiation is used more often to kill harmful organisms on foods in order to extend their "shelf life." Radiation does not stay in the foods after treatment, and eating irradiated foods does not appear to increase cancer risk.
Lycopene
Will lycopene reduce cancer risk?
Lycopene is the red-orange carotene pigment found mainly in tomatoes and tomato-based foods and to a lesser extent in pink grapefruit and watermelon. Several studies have reported that intake of tomato products reduces the risk of some cancers, but whether lycopene is the nutrient responsible is uncertain. Even if lycopene in foods is linked with lower risk for cancer, it can't be concluded that high doses taken as supplements would be either more effective or safe.
Meat: cooking and preserving
Should I avoid processed meats?
Some studies have linked eating large amounts of processed meat to increased risk of colorectal and stomach cancers. This connection may or may not be due to nitrites, which are added to many luncheon meats, hams, and hot dogs to maintain color and to prevent bacterial growth. Eating processed meats and meats preserved by methods involving smoke or salt increases exposure to potential cancer-causing agents and should be reduced as much as possible.
How does cooking meat affect cancer risk?
Adequate cooking is required to kill harmful germs in meat. But some research suggests that frying, broiling, or grilling meats at very high temperatures forms chemicals that might increase cancer risk. Although these chemicals can damage DNA and cause cancer in animals, it is not clear how much they (as opposed to other substances in meat) may contribute to the increased colorectal cancer risk seen in people who eat large amounts of meat in some studies. Techniques such as braising, steaming, poaching, stewing, and microwaving meats produce fewer of these chemicals.
Obesity
Does being overweight increase cancer risk?
Yes. Being overweight or obese is linked with an increased risk of cancers of the breast (among women after menopause), colon, endometrium, esophagus, kidney, and possibly other sites as well. Although research on whether losing weight reduces cancer risk is limited, some research suggests that weight loss does reduce the risk of breast cancer. Because of other proven health benefits, people who are overweight are encouraged to lose weight. Avoiding excessive weight gain in adulthood is important not only to reduce cancer risk but also to reduce the risk of other chronic diseases.
Olive oil
Does olive oil affect cancer risk?
Intake of olive oil is linked with a reduced risk of heart disease, but is most likely neutral with respect to cancer risk. Although olive oil is a healthy alternative to butter and margarine, it is still a dense source of calories and should be used in moderation.
