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Plant foods to the rescue

Posted - Aug. 11, 2004 at 6:40 a.m.



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The cherries and plums in a traditional still-life painting might appear to be, at first glance, well, still. Nestled in a bowl, these fruits don't seem terribly energetic.

Scientists who study nutrition paint a very different picture.

A growing body of research shows that, once inside the body, fruits and vegetables spring into the role of superheroes, fighting cancer and other diseases in at least eight simultaneous ways. And, like the Superfriends, they seem to work better as a team.

Some phytochemicals, or plant chemicals, knock out carcinogens and fight inflammation. Some regulate how quickly cells reproduce and spur old, damaged cells to self-destruct. Other plant chemicals perform ''routine maintenance'' on DNA, says Jeff Prince, vice president for education at the Washington-based American Institute for Cancer Research.

Doctors caution that recent research indicates that fruits and vegetables may not provide as much protection against cancer as once believed. In the past five years, studies have shown that weight control may be more crucial, says Walt Willett, chairman of the nutrition department at the Harvard School of Public Health.

Yet most experts agree that the body needs a variety of these phytochemicals -- there are more than 25,000 of them -- to stay in top form. That's why so many nutritionists no longer stress individual ''power foods,'' Prince says, but instead promote a ''plant-based'' diet of fruits, vegetables, whole grains, beans and nuts. Preliminary research indicates these foods bring out the best in each other and magnify their protective effects.

At the cancer institute's annual scientific conference in July, researchers from the University of Illinois-Urbana described their research feeding tomatoes and broccoli to lab rats that had prostate cancer. The tumors of rats that were fed both vegetables shrank far more than those of animals who ate either food alone. Researchers stressed, though, that people do not necessarily react the same way as animals and that many larger studies need to be done to confirm these results.

''The take-home message is not that experts recommend tomatoes and broccoli,'' Prince said at the conference. ''We're not going to find a single source that fights disease. What's important is the interaction of thousands of plant chemicals.''

Humans evolved to depend on a rich diet of 800 plant foods, says David Heber, director of the University of California-Los Angeles Center for Human Nutrition. Today, he says, most people eat three, and those are often french fries, ketchup and iceberg lettuce.

Yet some potentially potent plant foods, experts say, are exotic varieties that Americans rarely sample: herbs such as ginseng; spices such as turmeric, used in Indian cooking; and Reishi and Maitake mushrooms from Japan.

Heber suggests that people select their five to nine recommended daily servings of fruits and vegetables from seven color groups, such as purple grapes or yellow squash, whose colors are produced by disease-fighting chemicals called carotenoids.

Scientists have identified only a handful of the thousands of potentially beneficial plant chemicals, says Daniel Nixon, author of The Prostate Health Program and president of the Institute for Cancer Prevention in New York. People who would rather pop dietary supplements instead of eating the real thing may miss out on proven health promoters such as fiber, as well as compounds that scientists have yet to discover, Nixon says.

Last week, the American Heart Association published an advisory finding that antioxidant supplements do not prevent heart disease. In some studies, supplements with beta carotene -- the chemical that colors carrots orange -- increased the risk of cancer.

Plants vs. disease

Plant foods, however, may help prevent a number of diseases, says Rachel Brandeis of the American Dietetic Association. Antioxidants found in vegetables neutralize dangerous molecules called ''free radicals,'' which are produced by smoking and radiation, as well as everyday activities of the body. Left to themselves, free radicals attack healthy cells and may lead to plaques in the arteries and even Alzheimer's. They also can damage DNA in ways that lead to cancer.

As plants evolved, they developed antioxidants to fight free radicals, Heber says. Humans grew to depend on fruits, vegetables and nuts to provide these vital defenses. That may explain why, without a rich plant diet, people are more vulnerable to disease.

Diets rich in plant compounds, on the other hand, may prevent a variety of ailments.

At a meeting of the Alzheimer's Association last month, for example, researchers presented the results of a six-year study of 3,000 senior citizens. In the study, people who consumed lots of vitamin C and carotenoids, both through food and supplements, scored higher on reasoning tests. Carotenoids are found in squash, strawberries and other fruits.

According to another study presented at the meeting, vegetables such as spinach and broccoli -- which contain vitamin C and carotenoids, as well as the vitamin folic acid -- were found to slow cognitive decline.

Other things that appear to lower the risk of Alzheimer's include vitamin E, found in wheat germ, and fatty fish, such as salmon and mackerel, which are rich in omega-3 fatty acids, according to the Alzheimer's Association.

Scientists say they still have many questions about antioxidants: Can they fight cancer at any stage of the disease or at any age? Or do people benefit only if they consume these foods from infancy? Under which circumstances might antioxidants promote disease, rather than healing?

Scientists have identified at least a handful of the ways that plant foods appear to fight disease, says Cheryl Rock, a professor of nutrition at the University of California-San Diego Cancer Center.

* By mopping up free radicals, antioxidants such as the beta carotene in sweet potatoes or the vitamin E in almonds prevent cell damage. Another class of chemicals called flavonoids have been shown to activate the body's natural DNA repair system.

* Fruits and vegetables often are high in potassium, which can help control blood pressure.

* Antioxidants may interrupt a process leading to inflammation, which appears to play a role in cardiovascular disease and cancer. Vitamin B6, found in bananas, and folic acid, found in broccoli and leafy greens, both lower levels of homocysteine, which has been linked to hardening of the arteries, heart attacks, strokes and dementia.

* Chemicals such as beta carotene also help regulate the natural cycle of cell birth and death, telling cells when to divide, differentiate into new types or recycle themselves. Keeping this process under tight control can prevent cancer, Rock says.

* Phytochemicals in foods such as Brussels sprouts, red cabbage and kale may help prevent cancer by activating enzymes that break down carcinogens.

Antioxidants vs. angiogenesis

* Emerging research suggests that antioxidants may shut down a process called angiogenesis, by which tumors recruit blood supplies that help them grow and spread, says William Li, president of the Angiogenesis Foundation. Scientists are investigating links between angiogenesis and compounds found in foods such as licorice, blueberries and garlic, Li says.

Researchers who studied tumors in mice were able to cut back the number of new blood vessels by 70% simply by replacing their water with green tea, Li says. Scientists have not proved this link in humans.

* Plant foods such as whole-grain cereals and oats are loaded with fiber. In a study of 40,000 male health professionals, high-fiber diets reduced the risk of coronary heart disease by 40%. Diets filled with cereal fiber also may help prevent diabetes and a painful intestinal inflammation called diverticular disease.

''Mother Nature is cleverer than all of us and has laced many of our favorite foods with things that can be helpful,'' Li says. ''Ancient cultures have long recognized that your diet can be healing, and scientists are only now beginning to understand why.''

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