What are phytochemicals? |

Protective Role and Abundance

People who eat a diet rich in fresh fruits, vegetables, and whole grains obtain some protection from various diseases because of the phytochemicals that the plants contain. Phytochemicals are not traditional nutrients, such as proteins, carbohydrates, or fats; nor are they vitamins or minerals. Instead, they are substances that plants produce to protect against environmental stresses, such as attack by fungi and other organisms, or to attract animal pollinators or seed dispersers. Many phytochemicals are plant pigments, giving fruits and vegetables their animal-luring colors. There are thousands of phytochemicals, and plant species vary widely in the kinds and amounts that they contain.

Many phytochemicals have antioxidant properties, meaning that they help protect cells from oxidative damage, which has been implicated in cancer, diabetes, heart disease, strokes, and other disorders. Some phytochemicals function in humans in ways similar to the female hormone estrogen.

Although diets rich in plant-based foods have been shown to result in lower incidences of a number of diseases, scientists have had difficulty pinpointing which of the many different phytochemicals are protective. It may be that the interaction of a variety of naturally occurring phytochemicals, rather than any particular ones, is the significant factor in promoting health.

Some Major Kinds

One important group of phytochemicals, the carotenoids, includes many antioxidants. Of the numerous health claims that have been made for these plant pigments, one of the few to be substantiated is that increased consumption of lutein, a carotenoid found in green leafy vegetables such as collards, kale, spinach, and broccoli, is associated with a lowered risk for macular degeneration, an eye disease associated with advanced age.

Flavonoids, pigments that belong to a major class of phytochemicals called polyphenols, are abundant in vegetables, fruits such as blueberries and raspberries, and beverages such as tea, red wine, and fruit juices. Some flavonoids, including the widely occurring group anthocyanins, have antioxidant properties. Flavonoids called isoflavones are plant estrogens plentiful in soy products.

Perspective and Prospects

The discovery that phytochemicals are important to human health was not made until late in the twentieth century, and research is still being done. Scientists do not advise taking dietary supplements of particular phytochemicals; rather, they recommend a diet high in a variety of fruits, vegetables, and whole grains. Taking concentrated forms of phytochemicals might be harmful over the long term.

Bibliography

American Institute for Cancer Research, ed. Nutrition and Cancer Prevention: New Insights into the Role of Phytochemicals. New York: Kluwer Academic/Plenum, 2001. Advances in Experimental Medicine and Biology 492.

Bao, Yongping, and Roger Fenwick, eds. Phytochemicals in Health and Disease. New York: Marcel Dekker, 2004.

Meskin, Mark S., Wayne R. Bidlack, Audra J. Davies, Douglas S. Lewis, and R. Keith Randolph, eds. Phytochemicals: Mechanisms of Action. Boca Raton, Fla.: CRC Press, 2004.

Meskin, Mark S., Wayne R. Bidlack, Audra J. Davies, and Stanley T. Omaye, eds. Phytochemicals in Nutrition and Health. Boca Raton, Fla.: CRC Press, 2002.

Meskin, Mark S., Wayne R. Bidlack, and R. Keith Randolph, eds. Phytochemicals: Nutrient-Gene Interactions. Boca Raton, Fla.: CRC Press/Taylor & Francis, 2006.

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Webb, Denise. “Phytonutrients: The Hidden Keys to Disease Prevention, Good Health.” Environmental Nutrition 26, no. 1 (January, 2003): 1–6.