The word phytochemicals means plant chemicals. Phytochemicals are not vitamins per se, but plant-based nutrients. Hundreds of phytochemicals are currently being studied. Many are believed to have a major positive impact on human health. Some contribute to the bright and vivid colors found in fruits and vegetables.
The results of studies on specific phytochemicals are not necessarily applicable to the vegetables or fruits that harbor small concentrations of these chemicals. Nevertheless, it is obvious that vegetables and fruits are healthful, which is probably due to some balance of phytochemicals, carotenoids, vitamins, fibers, and minerals rather than to any single substance.
The benefits of individual phytochemical supplements are unproven. Furthermore, they are not regulated. High concentrations of some phytochemicals may behave like drugs and be toxic, possibly even contributing to cancer cell growth.
Xanthophylls contain oxygen and most are found in green vegetables, such as broccoli, cabbage, and kale. They are also in yellow fruits and vegetables. Xanthophylls include lutein and zeaxanthin, which are both stored in the retina of the eye. Neither converts to vitamin A. Both are powerful antioxidants and may be very important for healthy eyes. Cooking may reduce the antioxidant activity of some xanthophylls in foods, although probably not to any significant degree.
Polyphenols and Flavonoids
Polyphenols are important phytochemicals, and flavonoids (or catechins) are members of the polyphenol family that may have significant health benefits. Laboratory (but not human) studies have shown that specific flavonoids suppress tumor growth, interfere with sexual hormones, prevent blood clots, and have anti-inflammatory properties. In general, flavonoids are found in celery, cranberries, onions, kale, dark chocolate, broccoli, apples, cherries, berries, tea, red wine or purple grape juice, parsley, soybeans, tomatoes, eggplant, and thyme. Most common berries contain flavonoids and are particularly rich in potent antioxidants.
Among the important flavonoids are resveratrol, quercetin, and catechin. Evidence suggests that resveratrol (found in red wine, grapes, and olive oil) may be extremely potent. In laboratory studies, reseveratrol increases cell survival and has been shown to increase the lifespan of worms and fruit flies. Catechins are the primary flavonoids in tea and may be responsible for its possible beneficial effects. Flavonoids in dark chocolate may also be health protective.
Isoflavones, commonly known as phytoestrogens, have actions that are similar to the female hormone estrogen. A high consumption of soy, which is primarily composed of isoflavones, may reduce symptoms resulting from estrogen depletion during menopause. However, no evidence to date indicates that phytoestrogen supplements provide any benefit for hot flashes or other menopausal symptoms
Lignan is another phytoestrogen and is found in the fiber layers of whole-grains, berries, some seeds, some vegetables, and a few fruits. In laboratory studies, it seems to have anti-cancer properties.
Review Date: 10/08/2010
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.