The scientific community is continually studying the role of diet in the development of cancer. Many results are preliminary and more is being learned every day. Research is discovering that intake of fruits, vegetables, and cereal grains may interfere with the process of developing cancer of the oral cavity, larynx, esophagus, stomach, colon, lung, prostate, and rectum. In addition to reducing the risk of developing cancer, the risk of developing heart disease, hypertension, obesity, diabetes, and other chronic diseases might also be prevented by eating more fruits and vegetables. There is also evidence that total fat intake of greater than 30 percent of total calories can increase the risk of developing some cancers. This is especially true when total fat intake includes saturated fat and possibly polyunsaturated fat. The Food Guide Pyramid, Dietary Guidelines for Americans, and 5 A Day for Better Health Campaign are good sources for nutritional information.
What foods help to prevent cancer?
Although research studies are inconclusive at this time, preliminary evidence suggests that some components of food may play a role in decreasing the risk of developing cancer, including phytochemicals, antioxidants, and omega-3 fatty acids.
What are phytochemicals (or phytonutrients)?
Phytochemicals are chemicals found in plants that protect plants against bacteria, viruses, and fungi. Eating large amounts of brightly colored fruits and vegetables (yellow, orange, red, green, white, blue, purple), whole grains/cereals, and beans containing phytochemicals may decrease the risk of developing certain cancers as well as diabetes, hypertension, and heart disease. The action of phytochemicals varies by color and type of the food. They may act as antioxidants or nutrient protectors, or prevent carcinogens (cancer causing agents) from forming.
What are specific sources of phytochemicals?
The list below is a partial list of phytochemicals found in foods:
- Allicin is found in onions and garlic. Allicin blocks or eliminates certain toxins from bacteria and viruses.
- Anthocyanins are found in red and blue fruits (such as raspberries and blueberries) and vegetables. They help to slow the aging process, protect against heart disease and tumors, prevent blood clots, and fight inflammation and allergies.
- Biflavonoids are found in citrus fruits.
- Carotenoids are found in dark yellow, orange, and deep green fruits and vegetables such as tomatoes, parsley, oranges, pink grapefruit, and spinach.
- Flavonoids are found in fruits, vegetables, wine, green tea, onions, apples, kale, and beans.
- Indoles are found in broccoli, bok choy, cabbage, kale, Brussel sprouts, and turnips (also known as “cruciferous” vegetables). They contain sulfur and activate agents that destroy cancer-causing chemicals.
- Isoflavones are found in soybeans and soybean products.
- Lignins are found in flaxseed and whole grain products.
- Lutein is found in leafy green vegetables. It may prevent macular degeneration and cataracts as well as reduce the risk of heart disease and breast cancer.
- Lycopene is found primarily in tomato products. When cooked, it appears to reduce the risk for cancer and heart attacks.
- Phenolics are found in citrus fruits, fruit juices, cereals, legumes, and oilseeds. It is thought to be extremely powerful, and is studied for a variety of health benefits including slowing the aging process, protecting against heart disease and tumors, and fighting inflammation, allergies, and blood clots.
Phytochemicals cannot be found in supplements and are only present in food. Foods high in phytochemicals include the following:
- green tea
- Brussels sprouts
- bok choy
- red wine
There is no recommended dietary allowance for phytochemicals. Eat a variety of foods, including plenty of fruits and vegetables, to ensure you are getting adequate amounts in your diet.
What are antioxidants?
Antioxidants are substances that inhibit the oxidation process and act as protective agents. They protect the body from the damaging effects of free radicals (by-products of the body’s normal chemical processes). Free radicals attack healthy cells, which changes their DNA, allowing tumors to grow. Research is underway to investigate the role of antioxidants in decreasing the risk of developing cancer.
- vitamin C (ascorbic acid)
According to the National Cancer Institute (NCI), vitamin C may protect against cancer of the oral cavity, stomach, and esophagus and may also reduce the risk of developing cancers of the rectum, pancreas, and cervix. Also known as ascorbic acid, vitamin C may provide protection against breast and lung cancer.
According to the American Dietetic Association and USDA Nutrient Database for Standard Reference, the following foods are good sources of vitamin C:
§ one medium orange - 69 mg
§ 1 cup orange juice - 124 mg
§ 1 medium raw green pepper - 106 mg
§ 1 cup raw strawberries - 81 mg
§ 1 cup cubed papaya - 86 mg
§ 1 medium raw red pepper - 226 mg
§ 1/2 cup cooked broccoli - 58 mg
The recommended dietary allowance (RDA) for vitamin C has recently been increased to 75 milligrams per day for women and 90 milligrams per day for men. Safe upper limit = 2.000mg. If on high doses of chemo or nephrotoxins, upper limit = 500mg.
- beta carotene
Beta carotene, also known as provitamin A, may help decrease the risk of developing cancer. According to the American Cancer Society, this nutrient may prevent certain cancers by enhancing the white blood cells in your immune system. White blood cells work to block cell-damaging free radicals.
Good sources of beta carotene are dark green leafy and yellow-orange fruits and vegetables. In the body, beta carotene is converted to vitamin A. Eating foods rich in beta carotene is recommended to possibly decrease the risk of developing stomach, lung, prostate, breast, and head and neck cancer. However, more research is needed before a definite recommendation on beta carotene consumption can be made. Overdosing on beta carotene is not recommended. Large doses can cause the skin to turn a yellow-orange color, a condition called carotenosis. High intakes of beta carotene in supplement form may actually cause lung cancer in people at risk, such as smokers, and it is not recommended.
While there is a recommended dietary allowance for vitamin A (safe upper limit = 25,000IU or 15mg), there is not one for beta carotene. Examples of some foods high in beta carotene include the following:
- sweet potatoes
- vitamin E
Vitamin E is essential for our bodies to work properly. Vitamin E helps to build normal and red blood cells, as well as working as an antioxidant. Research is finding evidence that vitamin E may protect against prostate and colorectal cancer. The recommended dietary allowance for vitamin E is 15 milligrams per day. The adult upper limit for vitamin E is 1,000 milligrams per day. Good sources of vitamin E (and the amount each serving contains) include the following:
- 1 tablespoon sunflower oil - 6.9 mg
- 1 ounce sunflower seeds - 14 mg
- 1 ounce almonds - 7.4 mg
- 1 ounce hazelnuts - 4.3 mg
- 1 ounce peanuts - 2.1 mg
- 3/4 cup bran cereal - 5.1 mg
- 1 slice whole wheat bread - .23 mg
- 1 ounce wheat germ - 5.1 mg
Since some sources of vitamin E are high in fat. A synthetic form of a vitamin E is available as a supplement. Vitamin E supplementation is probably not needed for most individuals because vitamin E is a fat-soluble vitamin and is stored in our bodies. Very high doses of vitamin E can also interfere with the way other fat-soluble vitamins work. Also, large doses of vitamin E from supplements are not recommended for people taking blood thinners and some other medications, as the vitamin can interfere with the action of the medication. To make sure you are meeting your needs, eat a varied diet that includes whole-wheat breads and cereals.
There is no recommended dietary allowance for antioxidants. Eat a variety of foods, including plenty of fruits and vegetables, to ensure you are getting adequate amounts in your diet.
What are omega-3 fatty acids?
Researchers are studying the effects omega-3 fatty acids have on delaying or reducing tumor development in breast and prostate cancer. Since our bodies cannot make omega-3 fatty acids, we must get them from food or supplements. The omega-3 fatty acids include:
- alpha-linolenic acid
- eicosapentaenoic acid
- docosahexaenoic acid
Sources and recommended servings of foods high in omega-3 fatty acids include:
- seafood, especially cold-water fish like salmon, mackerel, sardines, herring, halibut, stripped bass, tuna, and lake trout (aim for three to four servings of these fish every week)
- flaxseed oil and beans such as kidney, great northern, navy, and soybeans
The American Cancer Society recommends avoiding omega-3 fatty acid supplements in the following situations:
- if you take anticoagulant medications or aspirin, as omega-3 fatty acid supplements may increase the risk of excessive bleeding
- if you have elevated cholesterol levels, as omega-3 fatty acid supplements may continue to increase your cholesterol levels
- if you are pregnant or breastfeeding (Women should talk to their physicians before taking omega-3 supplements or any dietary supplements.)
- if you are menstruating, as omega-3 fatty acid supplements may increase the tendency of developing anemia