Phytochemicals, Antioxidants, and Omega-3 Fatty Acids for Cancer Prevention

Nutrition to reduce cancer risk

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 certain cancers. In addition to reducing the risk of developing cancer, the risk of developing heart disease, high blood pressure, obesity, diabetes, and other chronic diseases might also be lowered 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. ChooseMyPlate.gov, 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 and 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, red, 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.

  • Lignans 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 may reduce the risk for cancer and heart attacks.

  • Phenolics are found in citrus fruits, fruit juices, dried and fresh plums, raisins, eggplant, cereals, legumes, and oilseeds. They are 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 generally cannot be found in supplements and are only present in food. Foods high in phytochemicals include the following:

  • Broccoli

  • Berries

  • Soy nuts

  • Pears

  • Turnips

  • Celery

  • Carrots

  • Spinach

  • Olives

  • Tomatoes

  • Lentils

  • Cantaloupe

  • Garlic

  • Apricots

  • Onions

  • Seeds

  • Soybeans

  • Green tea

  • Apples

  • Cabbage

  • Brussels sprouts

  • Bok choy

  • Kale

  • Red wine

There is no recommended dietary allowance for phytochemicals. To ensure you are getting adequate amounts in your diet, eat a variety of foods, including plenty of fruits and vegetables.

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 and allows tumors to grow. Research is underway to investigate the role of antioxidants in decreasing the risk of developing cancer.

Antioxidants include:

  • Vitamin C (ascorbic acid). According to the  USDA Nutrient Database for Standard Reference, the following foods are good sources of vitamin C:

    • One medium orange - 70 mg

    • 3/4 cup orange juice - 61-93 mg

    • 1/2 cup raw green pepper - 60 mg

    • 1 /2 cup raw strawberries - 49 mg

    • 1/4 medium, raw, cubed papaya - 47 mg

    • 1/2 cup raw red pepper - 142 mg

    • 1/2 cup raw broccoli - 39 mg

    The recommended dietary allowance (RDA) for vitamin C is 75 milligrams per day for women and 90 milligrams per day for men.

  • 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 help prevent normal cells from becoming cancerous, although it's not yet clear if it can actually help prevent cancer in people.

    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 intake of beta carotene in supplement form may actually increase the risk of lung cancer in people at risk, such as smokers.

    While there is a recommended dietary allowance for vitamin A (900 micrograms a day for men and 700 micrograms a day for women), there is not one for beta carotene. Examples of some foods high in beta carotene include the following:

    • Carrots

    • Squash

    • Collards

    • Spinach

    • 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 - 5.6 mg

    • 1 ounce dry, roasted sunflower seeds - 7.4 mg

    • 1 ounce almonds - 7.3 mg

    • 1 ounce hazelnuts - 4.3 mg

    • 1 ounce peanuts - 2.2 mg

    • 1/2 cup tomato sauce - 2.5 mg

    • 1 tablespoon olive oil - 1.9 mg

    • 2 tablespoons toasted, plain wheat germ - 2.3 mg


    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 overall. 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 may have on delaying or reducing tumor development. 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 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

  • 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 are pregnant or breastfeeding, you should talk to your doctors before eating fish likely to be high in omega-3 fatty acids, or taking omega-3 supplements (or any dietary supplements).

There is no recommended dietary allowance for omega-3 fatty acids. Eat a variety of foods, including plenty of fish and beans, to ensure you are getting adequate amounts in your diet.