June 21, 2000 -- It turns out that eating an apple a day really does keep the doctor away -- but you've got to eat the peel. And no fair skipping the apple altogether in favor of megadoses of vitamins in pill form. Fruits and vegetables in their natural state are better, Cornell University researchers say.
A study published June 22 in the journal Nature offers more evidence that the health benefits of fruits and vegetables are not easily packaged as supplements sold in pharmacies and health food stores. Researchers from Cornell's Food Science and Toxicology Department in Ithaca, N.Y., found that the antioxidant properties of one fresh apple were equal to 1,500 milligrams of vitamin C.
"The pharmaceutical companies will not be happy with me, but I think the consumer gets more health benefits from eating whole fruits and vegetables," lead researcher Rui Hai Liu, MD, PhD, tells WebMD. "You get much more antioxidant activity, you get a variety of antioxidants, and you don't have to worry about toxicity."
The Cornell researchers suggest that a combination of plant chemicals, collectively known as phytochemicals, found mainly in the skin of apples, provide the bulk of the fruit's anticancer and antioxidant properties. The cooperative activity of these phytochemicals, they argue, has health benefits that are superior to those found in single compounds like vitamin C, vitamin E, and beta-carotene, which have been widely studied for their antioxidant activities.
Using colon cancer cells treated with apple extract, Liu and colleagues found that 50 milligrams of apple extracted from the skins decreased the cancer cell growth by 43%, while the same amount of extract from the flesh of the apple decreased cancer cell growth by 29%. Likewise, 50 milligrams of extract from apples with the skin on decreased liver cancer cell growth by 57%, compared to 40% for samples extracted from apples without the skin.
"There is a huge amount of scientific evidence showing that fruits and vegetables lower the risk of cancer and heart disease, but scientists have mostly been isolating single compounds like beta-carotene and vitamin C," Liu says. "Over the years, no single compound has been proven to have a protective effect by itself. An apple could have hundreds of phytochemicals. We think the combination is the important thing."
More than 900 different plant chemicals have been identified as components of different fruits, nuts, grains, and vegetables. Apples are rich in isoflavones and phenolics, but other widely studied phytochemicals include lycopene, found in tomatoes; carotenoids, found in carrots and citrus fruits; and allyl sulfides, found in garlic and onions. It is believed that various phytochemicals help prevent cell damage, prevent cancer cell replication, and decrease cholesterol levels.
Charles Halsted, MD, says evidence is mounting that suggests taking vitamin supplements, even in large doses, does not provide the health benefits of a healthy diet. Halsted edits the American Journal of Clinical Nutrition (AJCN) and is a professor of internal medicine at the University of California, Davis. He was not involved with the study, but reviewed it for WebMD.
"I think the argument that natural sources of antioxidants are better is a pretty sound one," he says, adding that AJCN will soon publish studies showing a diet high in fruits and vegetables to be protective against heart attacks and colon cancer.
"If you look at single compound studies, you see mixed results," Halsted says. "For example, the early studies of beta-carotene suggested that it protected against lung cancer, but later studies found that it increased lung cancer risk. Single supplements may not be able to provide the benefits of a healthy diet."
The Cornell study was funded, in part, by the New York Apple Research Development Program and the New York Apple Association, and Liu is an eager spokesman for their favorite fruit.
"You should eat an apple every day," he says. "Everybody in my family gets an apple a day. We go through several thousand apples a year."
- Many of the antioxidants in an apple are in the skin, which might have cancer-fighting properties.
- Researchers think it's better to get antioxidants from fruits and vegetables than from dietary supplements. These naturally occurring plant chemicals, or phytochemicals, may work together to fight cancer and other disease.
- As scientists study antioxidants, many say they are beginning to believe it's the combination of different phytochemicals working together that bring good health.