How what you eat [and how much you exercise] can affect your cancer risk.
In the crusade to prevent cancer, what you eat counts. That’s one of the messages of the latest “American Cancer Society Guidelines on Nutrition and Physical Activity for Cancer Prevention.”
Alcohol — Alcohol consumption should be limited to no more than two drinks per day for men and one drink per day for women. However, regular consumption of even a few drinks of alcohol per week is associated with an increased risk of breast cancer in women. This risk is particularly high in women who do not get enough folate (see next page). Alcohol also increases the risk of cancers of the mouth, pharynx, larynx, esophagus, liver and colo­rectum. Although moderate alcohol intake appears to decrease the risk of heart disease, “from a cancer perspective, no alcohol is best,” says Kushi.
Antioxidants — Along with a number of other defense systems, the body appears to use nutrients known as antioxidants to protect itself against damage to tissues caused by free radicals — unstable molecules within cells that arise constantly as a result of normal metabolism or are introduced in the body by environmental factors. Because free-radical damage is associated with increased cancer risk, the so-called antioxidant nutrients (which include vitamin C, vitamin E, carotenoids and other phytochemicals, or plant-based chemicals) are thought to protect against cancer. Foods rich in antioxidants include orange and red fruits and vegetables and green leafy vegetables, as well as nuts, grains and some meats, poultry and fish.
Aspartame — Current evidence has not demonstrated that aspartame, a low-calorie artificial sweetener, has any link to increased cancer risk.
Beta-carotene — Beta-carotene is an antioxidant and precursor to vitamin A and is found in vegetables and fruits such as carrots, sweet potatoes, cantaloupe and spinach. While consuming fruits and vegetables that contain beta-carotene may be helpful in reducing cancer risk, studies have shown that consuming high-dose beta-carotene supplements should be avoided because they may, in fact, increase cancer risk.
Calcium — A high calcium intake, through diet or supplements, has been associated with lower colorectal polyp recurrence and cancer, but also with increased risk for prostate cancer. Therefore, the guidelines recommend that men and women should consume recommended levels of calcium but avoid excessive intakes. Choose low-fat or nonfat dairy products to reduce intake of saturated fat.
Coffee — While caffeine may heighten symptoms of fibrocystic breast lumps (a type of benign breast disease) in some women, there is no evidence that it increases the risk of breast or other types of cancer.
Fat — Certain types of fat, such as saturated fat, may increase cancer risk. In addition, high-fat diets tend to be high in calories and may contribute to obesity, itself a cancer risk factor.
“We advocate what is called a plant-based diet. That is, fruits and vegetables should make up the bulk of your meal, and animal [based] food should be a side dish instead of the primary part of your meal.”
Fish — Fish is a rich source of omega-3 fatty acids. While animal studies have found that these fatty acids suppress cancer formation or hinder its progression, there is limited evidence suggesting the same benefit in humans.
Folate — Folate is a B vitamin found in many vegetables, beans, fruits, whole grains and fortified breakfast cereals. Folate deficiency may increase the risk of cancers of the colorectum and breast, especially in people who consume alcoholic beverages.
Garlic — Garlic and other vegetables in the onion family (known as allium vegetables) have been widely recognized for their health benefits. However, garlic’s role in cancer prevention is still under investigation.
Lycopene — Lycopene is the red-orange carotene pigment found primarily in tomatoes and tomato-based foods, and to a lesser extent in watermelon and pink grapefruit. While several studies have reported a reduced cancer risk linked to consumption of tomato products, experts are not certain whether lycopene is the micronutrient responsible for this association.
Meat — Unlike the positive attributes of fruits and vegetables, the cards appear to be stacked fairly high against red meats. For instance, the iron content in red meat may generate free radicals in the colon that cause DNA damage. Substances used to process meat such as nitrates/nitrites and salt contribute to the formation of nitrosamines, chemical compounds that can likewise damage DNA. The fat content in meat may also contribute to an increased risk. And substances that cause DNA mutation and cancer are produced by cooking meat at high temperatures and by charcoal grilling.
Olive oil — While consumption of olive oil has been extolled for its heart benefits, it most likely plays no role in causing or preventing cancer.
Saccharin — Although high doses of the sweetener saccharin have been implicated in cancer in rats, there is no evidence of a link in humans. Saccharin has been removed from the list of established human carcinogens by the National Toxicology Program.
Salt — Currently, moderate levels of salt used in cooking or for flavoring have not been tied to cancer risk. But studies in other countries have linked diets containing large amounts of foods preserved by salting and pickling with a higher risk of stomach, nasopharyngeal and throat cancer.
Selenium — Selenium is a mineral that contributes to the body’s defenses against antioxidant damage. It can be found in foods such as potatoes, eggs, whole-wheat bread, tuna, turkey and chicken. Studies in animals have suggested that selenium protects against cancer, and one human trial revealed that selenium supplements might reduce the risk of cancers of the lung, colon and prostate. However, well-controlled studies are needed to confirm the mineral’s benefits in humans.
Soy products — Soy-derived foods are an excellent source of protein and can serve as an alternative to meat. Soy contains several phytochemicals, or compounds derived from plant-based foods, some of which have weak estrogen-like activity and appear to protect against hormone-dependent cancers in animal studies. However, data are limited to support a benefit in reducing cancer risk.
McCullough also warns that high doses of soy may stimulate cell growth in estrogen-responsive cancers and that soy, therefore, should be consumed in moderate amounts.
“If you’re looking for a magic bullet to decrease your risks for cancer, there is none. Ask yourself, does my diet look mostly like plant foods? Moving in that direction will make the most impact.”
To maximize cancer prevention factors, remember that the key to nutrition is variety. A colorful diet in terms of fruits and vegetables will help you get the variety of nutrients you need, McCullough recommends.
“What we are learning about cancer and diet is an evolving process,” she adds. “Many of these foods probably contain many more compounds we have not even discovered yet.”
Aside from tobacco use, for the majority of Americans weight control, dietary choices and activity level are the most important modifiable factors that can impact risk for cancer, according to the new guidelines, which were developed by a national panel of experts in cancer research, prevention, epidemiology, public health and policy. The guidelines were published in the December issue of CA: A Cancer Journal for Clinicians.
Healthy dietary choices not only provide important nutrients that may aid in the prevention of cancer, but can also help individuals maintain an appropriate weight. Research suggests that one-third of the more than half-million U.S. cancer deaths each year can be attributed to factors related to diet and physical activity, including being overweight or obese, while another third are caused by exposure to tobacco products. The last third are due to genetic variations combined with environmental factors as well as other determinants.
Rising to the top of the risk-factor picture is the impact of being overweight or obese, says Lawrence Kushi, ScD, lead researcher and director of etiology and prevention research for Kaiser Permanente in Oakland, Calif., and one of the authors of the guidelines. Roughly two-thirds of Americans are overweight or obese, conditions that are clearly associated with increased risk for developing many malignancies, including cancers of the breast in postmenopausal women, as well as colon, endometrial, esophageal and kidney cancers. Evidence also suggests that obesity may increase risk for cancers of the pancreas, gallbladder, thyroid, ovaries and cervix.
The guidelines, updated every five years, emphasize a diet rich in fruits, vegetables and whole grains, with limited consumption of processed and red meats. Since publication of the last guidelines, “the evidence has become stronger regarding the impact of red meats and processed meats in causing cancer,” says Kushi. “We advocate what is called a plant-based diet. That is, fruits and vegetables should make up the bulk of your meal, and animal [based] food should be a side dish instead of the primary part of your meal.”
Kushi advises against relying on vitamin or mineral supplements to get the benefit of nutrients and antioxidants found in fruits and vegetables. According to the guidelines, some studies have shown that high doses of supplements that isolate specific nutrients have demonstrated no benefit in reducing cancer risk and in some cases may be harmful to your health. “While I wouldn’t recommend avoiding supplements completely, large levels do not appear to have any benefit,” notes Kushi. “Supplements such as a multi vitamin and calcium still appear to be helpful.”
Other dietary recommendations include eating smaller portions, eating fewer high-calorie and high-fat foods, and substituting fruits and vegetables for calorie-dense foods such as French fries, cheeseburgers, pizza or doughnuts.
“Many of the foods people eat in our country are not rich in nutrients and don’t add any nutritional value except empty calories,” says Marji McCullough, ScD, RD, a nutritional epidemiologist for the American Cancer Society and also an author of the guidelines.
Another problem is that two of the most common vegetables consumed in the U.S. are potatoes and lettuce, which are not rich in cancer-prevention properties, notes McCullough.
Ongoing research points to potential cancer-fighting benefits of dark green and orange vegetables; cruciferous vegetables, such as cabbage, broccoli, cauliflower and Brussels sprouts; soy products; legumes, such as beans and peas; allium vegetables, such as onions and garlic; and tomato products.
To maximize dietary benefits, the guidelines recommend eating at least five servings of vegetables and fruits each day. And for improved overall health, consume even higher levels.
“If you’re looking for a magic bullet to decrease your risk for cancer, there is none,” says Kushi. “It’s about your overall dietary pattern. Ask yourself, does my diet look mostly like plant foods? Moving in that direction will make the most impact.”
Along with various lifestyle factors, the new guidelines address some common concerns about the following dietary components: