Phytochemicals: Guardians of Our Health
Author: Winston Craig, MPH, PhD, RD.
The optimal diet recommended by most health organizations is a low-fat, high-fiber diet characterized by a regular consumption of vegetables, fruit, whole-grain breads, rice and pasta. The World Health Organization recommends that we consume at least 14 ounces of fruits and vegetables every day, including at least 1 ounce of legumes, nuts and seeds.
Such a plant-based diet is naturally low in fat, saturated fat, cholesterol, and sodium, and rich in potassium, fiber, the antioxidant vitamins (vitamins A, C and E), and phytochemicals. Persons consuming this type of diet enjoy a reduced risk of chronic diseases such as heart disease and cancer.
The "5-a-Day for Better Health" program is a nationwide campaign designed to encourage the consumption of at least five servings a day of fruit and vegetables. The average American eats less than two servings of vegetables per day and less than one serving of fruit per day. A recent survey of American eating habits showed that only 1 in 11 Americans met the guidelines for eating at least 3 servings a day of vegetables and at least 2 servings a day of fruit. According to another survey, two out of every three Americans said they thought that only one or two servings were sufficient for good health.
Many studies have revealed that a regular consumption of fruits and vegetables provides a significant protection against breast, colon and other types of cancer. The risk of cancer is typically reduced by about 50 percent or more in those regularly eating many servings of fruit and vegetables every day compared with those eating few servings.
Different fruits and vegetables may provide protection against cancer at certain locations. For example, the use of carrots and green, leafy vegetables provide substantial protection against lung cancer, while broccoli, cabbage, and cauliflower provide useful protection against colon cancer. The regular consumption of cabbage has been shown to decrease the risk of colon cancer by 60 to 70 percent, while the regular use of onions or garlic can decrease the risk of stomach and colon cancer by 50 to 60 percent. Recently, regular consumption of tomatoes and strawberries was found to substantially protect against prostate cancer.
The National Cancer Institute has identified about 35 plant foods that possess cancer-protective properties. The foods and herbs with the highest anticancer activity include garlic, soybeans, cabbage, ginger, licorice root, and the umbelliferous vegetables (including carrots, celery, coriander, parsley, and parsnips). Additional foods with cancer-protective activity include onions, flax, citrus, turmeric, cruciferous vegetables (broccoli, Brussels sprouts, cabbage and cauliflower), tomatoes and sweet peppers, brown rice, whole wheat, oats, barley, various herbs (such as mints, rosemary, thyme, oregano, sage and basil), cucumber, cantaloupe and berries.
Scientists have identified a host of cancer-protective phytochemicals in these foods (see Table 1). These beneficial substances inhibit various hormone actions and metabolic pathways that are associated with the development of cancer.
The many flavonoids in fruit, vegetables, nuts and grains have extensive biological properties that promote human health and help reduce the risk of disease. Flavonoids act as antioxidants; protect cholesterol from oxidation to the unsafe cholesterol oxides; inhibit the formation of blood clots; and have anti-inflammatory and anti-tumor action. One study found that men with the highest consumption of flavonoids had 60 percent less mortality from heart disease and 70 percent lower risk of stroke than the low flavonoid consumers.
The Miracle Bean
Chinese having a regular consumption of soybeans and/or tofu have only one-half as much cancer of the stomach, colon, breast and lung compared with those Chinese who rarely consume soy or soy products. Soybeans contain fairly high levels of several compounds with demonstrated anti-cancer activity, including a high content of isoflavonoids, such as genistein. These isoflavonoids have been shown to inhibit the growth of both human breast and prostate cancer cells. In addition, regular use of soy protein (soybeans, tofu, soy nuts, soy beverage) can lower blood cholesterol and triglyceride levels by 10 to 15 percent, especially in persons with elevated lipid levels.
Benefits Of Flax
Flour derived from flax seed provides a nutty flavor to bread and bakery products as well as increasing the health-promoting properties of the product. The use of flax seed can lower blood cholesterol levels due to its very low saturated fat content and rich source of omega-3 fatty acids. Flax seed can also enhance immune function and promotes anti-inflammatory action It has been used in the treatment of lupus and arthritis. Flax seed, and other oilseeds such as sesame, are very rich sources of lignans, which are converted in the colon to cancer-protective substances. These estrogen-like metabolites can bind to estrogen receptors and inhibit the growth of estrogen-stimulated breast cancer, similar to the action of genestein in soy.
Protection From Whole Grains And Nuts
Many of the cancer-preventive phytochemicals found in fruit and vegetables are similar to those found in whole grains and nuts. The phytochemicals are concentrated in the bran and the germ of the kernel, so that the health benefits of grains are maximized when the whole grain product is consumed. Cereal grains and nuts contain substantial levels of tocotrienols (a form of vitamin E with powerful antioxidant activity), which strongly inhibit tumor growth and elicit a significant reduction in blood cholesterol levels.
Grapes are Good for You
Red grape juice and red wine contain a significant level of flavonoids and red anthocyanin pigments that act as antioxidants. These substances protect cholesterol from oxidation, reduce blood lipid levels, and inhibit blood clot formation, thereby providing protection against heart disease. It is the trans-resveratrol (a flavonoid) content of red wine, rather than the alcohol content, that has been shown to reduce the tendency of blood clots to form. Substantial levels of trans-resveratrol and other antioxidant compounds are found in the grapes and unfermented grape juice, clearly safer sources than the red wine.
The regular use of raisins (3-4 ounces./day for 2 months) has been shown to lower blood cholesterol and LDL cholesterol levels, improve bowel function and possibly lower the risk of colon cancer. In addition to fiber, the raisins contain the active phytochemical tartaric acid.
Pigments Are More Than Just Color
There are about 4000 known plant pigments in our food, including thousands of flavonoids, and hundreds of carotenoids and anthocyanins. These pigments do more than provide color to our foods. They also protect us from disease.
Anthocyanins are the water-soluble, reddish pigments found in many fruits, such as strawberries, cherries, cranberries, raspberries, blueberries, grapes and black currants. Since anthocyanins inhibit cholesterol synthesis these fruits provide protection against heart disease.
Carotenoids are the pigments found in yellow-orange vegetables (carrots, pumpkins, and sweet potatoes) and leafy, green vegetables (kale, broccoli and collard greens) and the red and yellow-orange fruits (mangoes, pineapple, peaches, oranges, pink grapefruit, tomatoes, strawberries, watermelon, cantaloupe) known to possess significant anti-tumor activity. The carotenoids are also known to enhance immune function. Persons with high blood levels of carotenoids have a reduced risk of heart disease and cancer.
Protection From Seasoning Herbs
Garlic, onions and other members of the Allium family are rich in sulfides and other protective substances. Garlic is known to decrease the tendency of blood clots to form, significantly lower blood cholesterol levels and decrease the risk of cancer at different sites. Terpenoids are responsible for the flavors of many common herbs and seasonings. Many of these substances are reported to be useful cancer chemopreventive agents. A diet in which herbs are generously used to flavor the food will provide a variety of substances that promote health and protect against chronic diseases.
The regular consumption of foods that are naturally high in antioxidants (fruits, vegetables, whole grains, nuts and seeds, legumes and herbal seasonings) is associated with substantial health benefits. Those consuming modest to high levels of these foods would ingest substantial levels of a variety of active phytochemicals and thereby have a decreased risk of cancer and heart disease. According to the USDA Food Guide Pyramid, for good health it is recommended that adults daily consume 3-5 servings of vegetables (especially the green and yellow vegetables) and 2-4 servings of fruit. Since many of the phytochemicals are reasonably heat stable and most are not water soluble they are not appreciably lost during conventional cooking methods. This means that one does not have to eat raw food in order to receive the health benefits of the foods that are rich in phytochemicals.
|Allyl sulfide||Onions, garlic, chives, leeks|
|Carotenoids||Yellow-orange vegetables and fruits; green, leafy vegetables; red fruits|
|Flavonoids||Most fruit, vegetables, grains and nuts|
|Indoles & isothiocyanates||Broccoli, cabbage, cauliflower, Brussels sprouts|
|Lignans||Soybeans, flax seed|
|Phenolic acids||Berries, grapes, nuts, whole grains|
|Phthalides & polyacetylenes||Carrots, parsnips, parsley, coriander, cilantro|
|Terpenes||Cherries, citrus, herbs|
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