Phytochemical Power
June 1999 -- Nutrition Notes

By: Andrea Platzman, R.D.
Contributing Editor

  Unlike vitamins, phytonutrients may not be essential for life, but researchers believe they may very well be essential for optimal health. So what exactly are phytochemicals? Says Patricia Murphy, Ph.D., professor, department of food science and human nutrition at Iowa State University, Ames, "Any chemical produced by a plant can be classified as a phytochemical."

  Phytochemicals may protect against a wide range of ailments, such as abnormal heart rhythm, coronary heart disease, stroke, diabetes, hypertension and osteoporosis, as well as certain cancers and various gastrointestinal disorders. They also appear to increase the activity of enzymes that detoxify carcinogens, alter estrogen activity and keep arterial linings smooth and strong (thereby not allowing cholesterol to become attached).

  Currently, there are 11 classes of phytonutrients, according to Gary Beecher, Ph.D., research chemist at the USDA's ARS Food Composition Lab, Beltsville, MD. These classes, some of which contain hundreds of different phytochemicals, are as follows: carotenoids; dietary fiber; glucosinolates, indoles and isothiocyanates; inositol phosphates; phenols and cyclic compounds; phytoestrogens; plant sterols; polyphenols; protease inhibitors; saponins; and sulfides and thiol-containing compounds.

  Phytochemicals are found in a variety of foods - major sources include vegetables, fruits, grains, nuts, soybeans and tea, with many foods containing more than one class of phytonutrient.

Carotenoids

  Thanks to beta-carotene, carotenoids may be the class with which the public is most familiar. However, over 560 carotenoid structures have been identified, and even more structures are possible if geometric isomers are included. About 10% of these act as vitamin-A precursors, including alpha-carotene and beta-carotene.

  Carotenoids are found in red, orange and yellow foods. They act as antioxidants, protecting against heart disease, stroke and certain cancers, as well as boosting the immune system. There are two types of molecules in the carotenoid family. The first type, which includes the carotenes, is chemically classified as hydrocarbon carotenes, while the second type, which is classified as oxygenated xanthophylls, includes the carotenoid alcohols and ketocarotenoids. Xanthophylls appear to protect vitamins A and E from oxidation.

  Lutein, a carotenoid, appears to protect against lung, colorectal, breast, uterine and prostate cancers. Since carotenoids are tissue-specific in their response, a diverse mix of these phytonutrients provides the greatest protection against certain cancers.

Tomatoes, which are a rich source of lycopene, another carotenoid, have been linked to a reduced risk of prostate cancer. "Lycopene becomes more active and potent via heating, and the best source of this phytonutrient is tomato paste," says Murphy.

Phenolic compounds

  Certain phenols inhibit the formation of nitrosamines, thus helping resist cancer development. Phenols also inhibit enzymes that can mutate critical genes and cause cancer. Included in the phenol category are flavonoids, of which anthocyanins and flavones are subgroups.

  Isoflavones are found in high amounts in soybeans. Genistein and daidzein are the major isoflavones, found in amounts ranging from 1,600 to 2,400 mg in dry soybeans. "I recommend consuming a variety of foods, and a variety within each food group; for instance, don't just have soy milk - consume tofu, tempeh and soy nuts as well, that way you'll be sure to get all of the phytochemical benefits," says Murphy. Isoflavones seem to help lower the risk of heart disease by inhibiting the formation of blood clots. They also decrease the risk of osteoporosis by preventing the breakdown of bone matter, as well as reduce menopausal symptoms such as hot flashes.

  Many epidemiological studies have found a relationship between cancer prevention and both green and black teas. There are numerous polyphenols found in the teas, but catechin gallates appear to be the most important. It has been hypothesized that catechin gallates, epigallocatechin gallate being the most potent, are anticarcinogenic, inhibiting the onset of cancer development associated with oxidative stress.

  Resveratrol, a phenol found in foods such as red wine, grapes, some berries and peanuts, reduces the risk of heart disease and may have anticancer properties. In the Southeast, muscadines are grown to make juice - just two oz. of this product contain the same amount of resveratrol as four oz. of red wine.

  New research is focusing on elderberries and bilberries. The former, found in Europe, contain flavonoid anthocyanins, and have some potential pharmaceutical applications. The latter are a cousin to the North American blueberry, but the dark color goes all the way through the fruit. They are currently being used in medications in Europe, and have been found to be beneficial in reducing heart and eye diseases.

Other major players

  Terpenes, specifically the limonoids found primarily in the rinds of citrus fruits such as oranges, grapefruits and lemons, help protect lung tissue, interfere with carcinogenic action and inhibit tumor growth.

  Indoles are powerful phytochemicals found primarily in cruciferous vegetables such as broccoli. Indoles help reduce the incidence of breast cancer by either preventing the overproduction of estrogen, or transforming the more cancer-promoting estrogen into a less active form.

  Alliums such as onions, shallots, garlic, leeks and chives, contain thiols, which decrease cholesterol levels as well as stimulate a detoxification enzyme called glutathione-S-transferase.

  Foods categorized as complex carbohydrates provide fiber and many phytochemicals, including phenols, lignans, coumarins, phytosterols and protease inhibitors. Lignans are antioxidants, and they appear to suppress cell mutation, while coumarins block cancer-causing substances before they can develop. Phytosterols help destroy cancer-causing estrogen hormones, and protease inhibitors appear to lower cholesterol and have been shown to slow cancer formation.

  "There are literally hundreds of phytochemicals - we just do not yet know what they all do at this time. The many potential relationships between improved health and food make the study of phytochemicals very challenging and so exciting," says Swanson.

  Andrea D. Platzman is a registered dietitian who is a consultant to the food industry, and regularly writes for nutrition publications. She earned a master's degree in nutrition from New York University, and has a culinary and business background.

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