How do phytochemicals work?

Phytochemicals work in many different ways. Some, such as the "phytoestrogens" found in soy beans and their products, interact with hormone receptors, either triggering or inhibiting those receptors and their actions. Phytoestrogens, for example, seem to mimic estrogen's cholesterol-lowering activity while blocking its carcinogenic effect on breast tissue.

Some phytochemicals appear to detoxify or block the action of potential carcinogens, such as free radicals, mentioned above. This helps to prevent precancerous changes in the cell and its genetic material. Other phytochemicals seem to help suppress malignant changes that have already occurred in cells. Cellular damage is associated with artery disease, cancer and other disorders that occur as part of the aging process.

Food sources of phytochemicals

There are dozens of helpful phytochemicals. Since they are found in many different types of plant foods, it is important to include a variety of foods in one's diet. Variety is also important because the research on beneficial phytochemicals is still preliminary; many more may be discovered in the future. Some experts recommend that in addition to consuming five to nine servings of fruits and vegetables a day, people should eat at least three different colors of fruits and vegetables every day to ensure variety. Especially helpful foods include the following:

Cruciferous vegetables: Many studies have suggested that a high intake of cruciferous vegetables helps to prevent cancer. Broccoli, cabbage, brussel sprouts, kale, cauliflower and turnips are found in this group.

Citrus fruits and juices: These contain terpenes, which have been shown to fight cancer in laboratory animals.

Red, orange and yellow fruits and vegetables: The red and yellow plant pigments known as carotenoids live here, as well as in many dark green vegetables such as broccoli and spinach, where they are masked by the chlorophyll. Beta carotine is the most famous, or perhaps infamous, of the hundreds of chemicals in the carotenoid family -- infamous because treatment with beta carotene supplements has been associated with an increased risk of lung cancer in smokers. Despite this association, a positive association with a high intake of carotenoids from foods and lower risk of cancer persists in many studies. Therefore, while beta carotene supplements may be harmful, consuming a wide variety of carotenoid food sources promotes good health. This variety can be found in red, orange and yellow fruits and vegetables, including carrots, sweet peppers, winter squashes, pumpkin, cantaloupe and strawberries. Lycopene, found in tomatoes and tomato products, has been associated with reduced risk of prostate cancer.

Dark green leafy vegetables: The carotenoids lutein and zeaxanthin, found in dark green leafy vegetables such as spinach and kale, have been associated with protection from macular degeneration.

Garlic and onions: Garlic and onions are members of the allium family, along with chives, leeks and scallions. These foods supply helpful sulfer compounds that help reduce the production of cholesterol by the liver. These vegetables are also associated with reduced risk of colon cancer.

Other common fruits and vegetables: Many common fruit and vegetable snacks not mentioned in any of the categories above contain phytochemicals called flavonoids, which help prevent free radical damage and protect against blood clots. Apples, grapes and celery are three of these.

Don't forget the big picture

Eating more fruits and vegetables fits in with the other recommendations for a heart-healthy diet, such as decreasing intake of fats, sugars and salt. The big picture also includes enjoyment of delicious foods. There are many delicious and easy ways to add fruits and vegetables, most of which are naturally low in fat, to a healthful diet. Including a variety of plant foods in one's diet will ensure a healthful intake of phytochemicals and contribute to a heart-healthy lifestyle.



Barbara A. Brehm, Ed.D., is professor of exercise and sport studies at Smith College, Northampton, Mass.

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