Like vitamins and minerals, many phytochemicals (meaning “plant chemicals”) help promote good health. Some 4,000 have been identified, but only about 150 have been extensively studied—and no one knows how many and how much of them we need. One large class of phytochemicals is the carotenoids, which are pigments that add color to vegetables and fruits such as carrots, red peppers, tomatoes and watermelons. Polyphenols, another large class, include flavonoids, as found in apples, tea, onions, and cocoa.
Many phytochemicals act as antioxidants and have other properties that may help protect against heart disease, cancer and other illnesses. They may do this by lowering blood pressure, inhibiting blood clotting and boosting production of enzymes that detoxify carcinogens, among other mechanisms. It’s not clear which phytochemicals are responsible for the protective effects of this or that food. But they most likely act synergistically—that is, in conjunction with other phytochemicals, as well as with nutrients and other substances in food.
If you follow our advice and base your diet on a wide variety of fruits, vegetables and other plant foods, you will get all the phytochemicals you need.