December 1, 2005

4 Min Read

It’s possible that your market’s produce department may look a little sparse right now—except for the bright, sunny citrus section. Grapefruit, oranges, lemons, and other citrus are at their peak during winter, offering an abundance of valuable vitamins and phytochemicals. Put your knowledge to the test and find out why you should give citrus the squeeze this winter.

Per serving, all citrus fruits pack the same amount of vitamin C.
False. Of all citrus, the orange family—which includes Mandarins, clementines, satsumas, tangelos, Minneolas, and Ugli fruit—delivers the highest levels of vitamin C per serving. Just one medium orange provides the recommended daily requirement of 75 mg for women. Aside from its historical role in preventing and treating scurvy, vitamin C regenerates vitamin E levels in the body, helps maintain a healthy immune system, may shorten the duration of colds, and when consumed as part of the diet (but not from supplements) may lower the risk of cancers of the mouth and esophagus (Nutrition and Cancer, 2002, vol. 39, no. 2).

Researchers are looking at vitamin C’s potential for preventing atherosclerosis, age-related macular degeneration, and osteoarthritis. In one study, 640 men and women underwent a thorough knee evaluation and dietary analysis; those with a daily intake of at least 152 mg of vitamin C had more knee cartilage and a significant threefold reduction in the risk of osteoarthritis progression compared with those consuming only 81 mg of vitamin C each day (Arthritis and Rheumatism, 1996, vol. 44, no. 4).

Citrus has nutrients not found in any other fruits.
True. Although every plant food offers a unique nutritional profile, the citrus family contains an array of phytochemicals not found in other foods—and they are currently receiving a lot of attention for their role in disease prevention and healing. Of the 4,000 known flavonoids in fruits and vegetables, certain citrus flavonoids exhibit anti-inflammatory effects, stimulate liver enzymes responsible for detoxification, and may help prevent cancer.

According to John Manthey, PhD, a researcher for the U.S. Department of Agriculture (USDA), two main classes of citrus flavonoids—flavonoid glycosides and polymethoxylated flavones—may offer protection from cancer. “Animals have a lower risk of cancer when fed glycosides in laboratory studies,” Manthey says, “and the polymethoxylated flavones have been shown to block cancer in animal trials and kill human cancer cells in test tube experiments.” Researchers are now trying to determine just how protective these compounds are when eaten as part of a healthy diet.

Scientists are also investigating yet another group of citrus-exclusive chemicals, called limonoids, for their ability to prevent, slow, and even halt the growth of several types of human and animal cancer cells. One class in particular, limonoid glucosides, excites researchers for several reasons. “Limonoid glucosides are readily available—that is, easily absorbed—from a glass of orange juice, and they display promising cancer-protective properties based on animal and cancer cell laboratory tests,” says Gary D. Manners, PhD, a chemist with the USDA’s agriculture research service. “In fact, tests with breast cancer cells have shown these compounds, and related citrus limonoids, to be as effective as tamoxifen [a drug treatment for breast cancer] in inhibiting cancer growth.”

The juice is citrus fruit’s most beneficial part.
False. All parts of citrus fruits contain healthy nutrients, but a strong case can be made for eating the peel and pith, the white layer just beneath the peel. The phytochemical d-limonene, which is largely responsible for giving citrus its mouth-puckering quality, is found abundantly in the oils (peel) of oranges, grapefruit, lemons, and limes. In a recent study of Arizonans, those consuming higher levels of limonene, as measured by eating citrus peel, had a 34 percent lower risk of developing squamous cell carcinoma, a type of skin cancer (Nutrition and Cancer, 2000, vol. 37, no. 2).

Although more bitter than the inner fruit, both citrus peel and pith contain more limonenes than any other part of the fruit, so it’s worth adding citrus zest (grated peel) and even shredded pith to recipes in small amounts whenever you can. Keep in mind that citrus peel readily absorbs pesticides, so organic citrus is always your best choice.

Including citrus fruits in your diet on a regular basis may not only protect against disease but also help to heal what ails you. Perhaps it was a freshly picked orange that inspired Hippocrates to advise, “Let thy food be thy medicine and thy medicine be thy food.”

Photos: Leigh Beisch; food styling by Merilee Bordin; prop styling by Sara Slavin

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