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Consuming large amounts of alcohol is also a diet risk factor in some cancers, such as liver cancer, esophagus and mouth cancer, and, to a lesser degree, breast cancer.
All cancers caused by cigarette smoking and heavy use of alcohol could be prevented completely. The American Cancer Society (ACS) estimates that in 1999 about 173,000 cancer deaths are expected to be caused by tobacco use. This accounts for about one third of all cancer deaths. An additional 20,000 cancer deaths are related to excessive alcohol use, frequently in combination with tobacco use.
What Nutrients Can Do for You
Nutrients can influence cancer on many levels -- from whether it develops at all, to how it proliferates if it does. Most of what we know about nutrition and cancer is based on the results of a variety of medical research studies.
Fat and Calories Although the link between fat intake and cancer is weak at best, some studies have shown that animals on low-fat diets have a lower incidence of cancer and a slower pace of tumor growth.
The research seems to support the idea that monounsaturated fat from sources such canola oil and olive oil may decrease the risk of cancer, while polyunsaturated fat from sources such as corn oil or safflower oil can increase the risk.
In animal studies, the effect of reducing total calories by 30 percent decreased the incidence of cancer in half the control subjects. Cutting calories may be one of the simplest ways to reduce the risk of cancer. However, it may not be such a good idea for people who already have it. Tumor growth can rob a patient of much energy, so it is important to have enough calories in the diet to prevent weight loss and wasting.
Fiber More than 40 studies support the idea that fiber can protect against colorectal cancers. Wheat bran, for example, is a fiber that reduces or dilutes the bile acids that are known to promote cancer in the colon.
On the other hand, corn bran, pectin and agar may increase, rather than inhibit, colon cancer. (Whether a fiber increases or decreases the risk of cancer depends on what bacteria it supports in the colon, and what enzymes these bacteria product that might activate or prevent the initiation of cancer.)
The protective effects of fiber are associated with eating fiber-rich foods and not with taking fiber supplements. To help prevent cancer, get your daily dose of 25-30 grams of fiber from sources like whole-grain foods, fruits and vegetables, and dried beans.
As you increase your intake of fiber, you generally tend to decrease your intake of total fat and calories, perhaps providing an even greater measure of protection against cancer.
The ACS stresses a diet of high fiber foods: at least 6 servings a day. High-fiber foods include whole-wheat breads, macaroni, brown rice, corn, cereals and bran cereals, and air-popped popcorn. Also beans and legumes, such as chick peas, black beans, broad beans, kidney beans, lentils and pinto beans; dried fruits like dates, figs, prunes and raisins; fresh fruits, especially apples, pears, raspberries, blueberries, blackberries and strawberries; and fresh vegetables, particularly squashes, snow peas, uncooked spinach leaves and baked potatoes (with the skins left on).
The key to tolerating high-fiber diets is to first increase your fiber content gradually; otherwise, you may suffer cramps and unpleasant gas. It is also essential to drink at least 8 glasses of liquids per day (water, fruit juices and sodas count, but not tea or coffee because of their diuretic effects.) If you don't, you will likely find yourself constipated, despite the high fiber intake.
Non-nutrient food components Catechins in teas, sulforaphane in foods like broccoli and cabbage, and amyl sulfides found in garlic and onions all have been identified as providing protection against cancer.
Limonoids in citrus fruits, isoflavones in soy foods, lycopenes in tomato and polyphenols in tea also provide a variety of healthful properties in preventing cancer.
Idoles, monoterpenes and isothiocyanates are potential cancer-fighters; they occur naturally in fruits and vegetables, soy products and teas, particularly green teas.
Protein Protein does not seem to be a major factor in cancer once normal protein intake and protein quality have been assured. However, there is a consistent and strong relationship between the consumption of protein-rich red meat and the incidence of cancers of the colon and rectum. It is a good idea to limit red meat consumption on a daily basis and to rely instead on other sources of protein (such as chicken and fish).
Selenium Selenium intakes have been found to be low in cases of various cancers, including breast, gastrointestinal and colorectal cancers, as well as lymphomas and leukemia. Higher levels of dietary intake are associated with decreased risk of cancer in general and of lung, colorectal and prostate cancers in particular.
Selenium is found in seafood, meats (especially organ meats), garlic and whole grains. However, since reducing how much meat you eat is also a cancer-fighting strategy, you may want to get your selenium from an alternative source, like grains. The best way to get enough selenium is to eat foods which contain it or to take a multi-vitamin pill which contains it. The recommended daily amount is 55 micrograms for women and 70 micrograms for men.
An important caveat: Selenium is toxic at even low concentrations (as low as 1000 micrograms a day); in toxic amounts it can cause hair loss, gastrointestinal upset, and peripheral nerve damage. To avoid excessive doses, rely on foods and multi-vitamin sources for selenium; never resort to taking selenium supplements.