Fighting Disease
Using Phytochemicals
April 1998 -- Nutrition Notes

By: Andrea Platzman, M.S., R.D.
Contributing Editor

  Poor diet, unhealthy lifestyles and adverse environmental conditions play major roles in development of certain chronic diseases. As much as 70% of preventable cancers and 33% of cancer deaths are attributable to dietary factors, the scientific community has agreed, based on the findings of several studies. Some foods have been identified as possible cancer promoters and cardiovascular disease initiators; others appear to prevent disease.  Foods showing a protective effect against cancer and cardiovascular disease development include vegetables, grains, fruits, legumes and soybeans. These low-fat foods also contain protective vitamins and phytochemicals.  Phytochemicals encompass various plant-produced compounds, some of which provide the bright colors, flavors and aromas of plants. Other compounds act as antioxidants or exhibit hormone-like actions in plants and in people who consume them. "The rule of thumb is to consume a lot of brightly colored fruits and vegetable products," says Mary Ellen Camire, Ph.D., chair and associate professor at the University of Maine, Orono. "Natural pigments, such as chlorophyll, carotenoids and anthocyanins, appear to have some health benefits."  Numerous phytochemicals are known to exist, along with an accompanying list of professed health benefits: increased activity of enzymes that detoxify carcinogens; altered estrogen activity; and continued smooth and strong artery linings, preventing attachment of cholesterol. "There are hundreds of studies suggesting that a diet rich in fruits, vegetables, grains and beans may lower the risk of some types of cancer, heart disease and other chronic diseases," says Mark A. Kantor, Ph.D., associate professor, department of nutrition and food science, University of Maryland, College Park. "But precisely which individual phytonutrients provide this protection is still far from clear."Listen to mom  Mother was right when she said to eat your fruits and vegetables.  "Including lots of fruits and vegetables in your diet is a good idea, based on so much research, which gets stronger everyday, showing the protective health effects of eating these foods," advises Marion Nestle, Ph.D., chair, department of nutrition and food studies, New York University, New York City.  Cruciferous vegetables, including broccoli, cauliflower, cabbage and brussels sprouts, contain indoles. Indoles have been shown to reduce breast-cancer risk by preventing estrogen overproduction, or by transforming the more cancer-promoting type of estrogen -- thereby also reducing the risk of other cancers. Isothiocyanates, another phytochemical found in cruciferous vegetables, reportedly protect against cancer through effects on enzymes that suppress cellular DNA damage. In addition, broccoli contains flavonoids, which reduce cholesterol levels.  The red, orange and yellow vegetables -- carrots, squash, tomatoes, beets and sweet potatoes -- are rich in carotenoids and flavonoids. More than 600 naturally-occurring carotenoids exist. Of these, about 10% act as precursors to vitamin A. To date, about 800 flavonoids have been identified. Some of the more popular carotenoids include ß-carotene, lutein and lycopene. As antioxidants, the carotenoids protect against heart disease, stroke and several cancers (lung, breast, uterine, colon and prostate). Research indicates these phytochemicals also lower cholesterol levels and enhance the immune response. A decline in carotenoid pigments, especially lutein, is the leading cause of blindness in people ages 65 and older. Consuming lutein-containing fruits and vegetables protects eyesight.  Tomatoes provide a rich source of lycopene, determined to reduce the onset of prostate cancer. Since the human body doesn't produce lycopene, this carotenoid's beneficial effects can only be obtained through diet. Recent studies show that tomato paste is the best source of this powerful phytochemical. This is probably because the body more easily absorbs the fruit's benefits when in paste form. Also, the processing technique used to create paste concentrates the lycopene levels and adds oil, which is vital for the most efficient absorption.  "There are a lot of promising studies being done on lycopene," says F. Jack Francis, professor emeritus, department of food science, University of Massachusetts, Amherst. "However, I am not sure about its acceptance just yet" in the scientific community.  Thiols are found primarily in the alliums, including garlic, scallions, leeks, onions and chives. Two popular phytochemicals in this family are allyl sulfides and organo-sulfur compounds. These compounds have been linked to lowered cholesterol levels, decreased blood-clotting and some anti-bacterial functions. Additionally, increased enzymes found in these foods help rid the body of carcinogenic substances.  Terpenes (limonene being the most common) is found primarily in the rinds of citrus fruits, including lemons, grapefruits and oranges. These phytochemicals help protect lung tissue, inhibit tumor growth, and deactivate carcinogens. Many fruits also contain a form of a potent phytochemical known as phenolic acid. Ellagic acid, a type of phenolic acid, is found in strawberries and raspberries, and reduces the damage caused by carcinogens like tobacco smoke and air pollution. Some research is under way with two not-so-common berries: the elderberry and the bilberry. Found in Europe, the former contains flavonoid anthocyanins. These not only produce the color of the berry, but also have potential pharmaceutical applications. "The latter is a cousin to the blueberry, but the dark color goes all the way through," Camire says. "It is currently being used in drugs in Europe, and has been found to be beneficial to reduce heart and eye disease."  Resveratrol -- found in many foods, including red wine, grapes, some berries and peanuts -- reduces the risk of heart disease, and may possess anti-cancer properties. In the Southeast, muscadines are grown to make juice. Just 2 oz. of this product contains the same amount of resveratrol as 4 oz. of red wine. While many phytochemicals are found in fruits and vegetables, it's not known which provide the greatest disease-prevention benefits. Therefore, it is still recommended that at least five servings of a variety of fruits and vegetables be consumed daily.Countering cancer  Complex carbohydrates provide fiber and many phytochemicals. Whole grains are rich in phenols, lignans, coumarins, phytosterols and protease inhibitors -- all of which lower cholesterol. Recent research has found that a diet rich in whole grains reduces the risk of cancer by suppressing cell mutation, which blocks cancer-causing agents from invading the body or slows progression of the disease. Saponins, found in beans and legumes, may prevent cancer cells from multiplying by influencing the DNA in the cells. Additionally, evidence suggests that these phytochemicals thin the blood and reduce cholesterol.  Soy products -- such as tofu, tempeh and soy milk -- provide isoflavones, the two main types being genistein and daidzein. "Soybeans are high in protein, fiber and phytoestrogens -- phytochemicals that may help protect against breast cancer and, perhaps, prostate cancer," Kantor says. "Soy flour is an ingredient that could provide lots of health benefits. Plus, it's versatile and seems suitable for use in a variety of food products."  These isoflavones are weak phytoestrogens which bind estradiol 17B (the most potent estrogen) to uterine receptors. This means they could potentially inhibit estrogen-promoted breast cancer. Phytoestrogens also might prevent prostate cancer by decreasing testosterone production -- which might slow tumor growth. These isoflavones also help lower the risk of heart disease by inhibiting the formation of blood clots; decrease the risk of osteoporosis by preventing the breakdown of bone matter; and reduce menopausal symptoms, such as hot flashes. In fact, 25 to 50 grams of soy protein per day may be enough to lower cholesterol -- two servings (half a cup) of firm tofu provides almost 40 grams.  Of the polyphenols that are present in the highest concentrations, catechin gallates are the most important. Many epidemiological studies have uncovered a relationship between cancer prevention and green tea. It has been hypothesized that catechin gallates, epigallocatechingallate being the most potent, are anticarcinogenic.  The American Dietetic Association's position is that specific substances in foods may have a beneficial role as part of a varied diet. "In the future," Francis says, "including phytochemicals in food products will have an important nutrition value -- the sky's the limit."  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.Back to top