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Defense Plants: Foods That Fight Disease

Susan M. Kleiner, PhD, RD


Have you ever considered sitting down to a plateful of phytochemicals? That's what you do every time you eat a salad, enjoy a vegetable stir fry, or scarf down pizza with tomato sauce. Don't let this unappetizing word scare you: "phyto" comes from the Greek word for "plant," and these substances are just nature's health-giving, disease-fighting chemicals, available in foods you eat every day.

The Best 'Phyto' Foods

Phytochemicals, found only in plant foods, don't provide you with energy, essential vitamins, or minerals—but they have been shown to protect against cancer, heart disease, and other illnesses. Many of the compounds exert subtle drug-like effects and influence the body's biochemistry in positive ways (table 1).

Table 1. Finding Phytochemicals

PhytochemicalFood Source(s)Reputed Benefit

Allyl sulfidesGarlic, onions, shallots, leeks, chivesLower risk of stomach and colon cancers
Sulforaphanes, indoles, isothiocyanatesBroccoli, cabbage, brussels sprouts, cauliflower, kohlrabi, watercress, turnips, Chinese cabbageLower risk of breast, stomach, and lung cancers
CarotenesCarrots, dried apricots and peaches, cantaloupe, green leafy vegetables, sweet potatoes, yamsLower risk of lung and other cancers
Lycopene, p-coumaric acid, chlorogenic acidTomatoesLower risk of prostate and stomach cancer
PhytoestrogensSoy foods, especially tofu, miso, and tempehLower risk of breast and prostate cancers
MonoterpenesCherries, citrus fruit peel oils, caraway, dill, spearmint, lemongrassLower risk of breast, skin, liver, lung, stomach, and pancreas cancers
PolyphenolsGreen teaLower risk of skin, lung, and stomach cancers
Alpha-linolenic acid, vitamin E Vegetable oilsReduce inflammation (eg, from exercise-related muscle damage) and risk of heart disease

There are thousands of phytochemicals in plant foods, but your daily dose may be low if the plant foods you eat consist mostly of grains and other starchy foods. Vegetables and fruits generally contain a wealth of disease-preventing phytochemicals. The following types of foods are good sources:

Allium foods. Garlic, onions, shallots, leeks, and chives belong to the Allium family, which contain allyl sulfides. Besides making your eyes water, allyl sulfides have been shown to inhibit tumors in animals. And studies have shown that people who eat a lot of garlic and onions reduce their risk of stomach and colon cancer. The more pungent the Allium food, the higher its content of allyl sulfides.

The Brassica family. Broccoli, cabbage, and many others belong to the Brassica family of vegetables and contain the important phytochemicals sulforaphane, indoles, and isothiocyanates. Sulforaphane has been shown to prevent breast cancer in lab animals. Indoles work against the dangerously high levels of estrogen associated with breast cancer, potentially reducing the risk. Isothiocyanates have been associated with prevention of stomach and lung cancers.

Carotene-containing foods. Beta-carotene, probably the best known of the phytochemicals and responsible for the color of carrots, is a potent antioxidant. (Antioxidants thwart oxidation, a normal metabolic process that, when left unchecked, can leave the body vulnerable to accelerated aging, cancer, cardiovascular disease, and degenerative diseases like arthritis.) Other carotenes, especially alpha-carotene, have recently been associated with reduced lung cancer risk.

Tomatoes. Tomatoes contain as many as 10,000 phytochemicals. One of the most well-studied is lycopene, an antioxidant that has been shown to help prevent heart disease and cancer. Regular tomato consumption has been associated with a reduction in the risk of prostate and stomach cancers.

Soy. Phytoestrogens are phytochemicals found predominantly in soy foods like tofu, tempeh, and miso. During a woman's childbearing years, phytoestrogens help prevent breast cancer by inhibiting the action of naturally occurring estrogens. Because they also regulate other hormones, phytoestrogens may help prevent cancer of the prostate, another hormone-dependent cancer.

Genistein, another phytochemical in soy, has been shown to reduce the size of LDL-cholesterol particles (harmful cholesterol) and lower the build-up of coronary artery plaque in primates. By consuming about half of your protein in the form of soy (31 to 47 grams per day), you may be able to reduce your risk of heart disease and cancer.

Other sources. Other plant foods—beverages, condiments, seasonings, and vegetable oils—contain substantial amounts of phytochemicals. Monoterpenes, for example, are associated with a reduction in the risks for cancer of the breast, skin, liver, lung, stomach, and pancreas. The polyphenols found in green tea have antioxidant properties, and research indicates that they may be protective factors against cancers of the skin, lung, and stomach.

Vegetable oils contain alpha-linolenic acid and are the greatest source of vitamin E. These nutrients have a dual role as antioxidant phytochemicals. For people who exercise, antioxidants are important because they help guard against the muscle-cell membrane damage and inflammation associated with hard exercise. Compounds in alpha-linolenic acid may also help prevent heart disease.

More Is Better

The wealth of phytochemicals in food—rather than single phytochemicals ground into pills or powders—is what best helps to mobilize the body's own disease-fighting resources. You could never get all of the known phytochemicals (let alone those yet to be discovered) by taking a supplement. By eating plenty of plant foods, you can benefit from the overlapping and possibly interactive effects of multiple phytochemicals. This approach is far better than taking pills formulated to reduce specific risks.

Start with the US Department of Agriculture's food pyramid: Eat at least 3 to 5 servings of vegetables and 2 to 4 servings of fruits every day for a phytochemical feast.

Remember: The above information is not intended as a substitute for appropriate medical treatment.

Dr Kleiner is a private nutrition consultant to athletes in the Seattle area. She is a member of the American College of Sports Medicine; a member of the American Dietetic Association and its practice group, Sports and Cardiovascular Nutritionists (SCAN); and a fellow of the American College of Nutrition.