Of all the advance cancer experts give, eating more fruits and vegetables is the most palatable. Picture your farmers market brimming with ruby-red peppers; cabbage with delicate taste and crunchy texture; and broccoli as sweet as freshly picked peas.
Or how about the tempting tomatoes on the vine, or baskets of succulent blueberries your supermarket produce counter offers this time of the year? The best part is that as you indulge in this late summer harvest, you’re not only getting great flavors, but nutritional ammunition in the battle against cancer.
Fruits and vegetables contain dietary fiber and vitamins, such as A, C, folate, and E; carotenoids including beta carotene, lutein, lycopene, and zeaxanthin; and hundreds of known and unknown phytochemicals. All are potential cancer fighters. How strong is the link? "The epidemiological evidence through culture, society, and immigration studies is so strong. Eighty percent of the studies show an inverse relationship between fruits and vegetables and cancer," says Jeffrey Blumberg, Ph.D., Professor of Nutrition at Tufts University in Boston.
The Harvard Report on Cancer Prevention even suggests which cancer risks have the greatest potential of being reduced. According to the report, "Diets high in fruits and vegetables may have a beneficial effect in reducing the risk of several types of cancers. This finding is most firmly established for cancers of the lungs, stomach, esophagus, and larynx."
The American Institute for Cancer Research (AICR), which studies the link between diet and cancer, looked at 4,500 cancer research papers from around the world. Its recently published Food, Nutrition and the Prevention of Cancer: A Global Perspective, makes the following points: diets high in fruits and vegetables may reduce the incidence of cervical cancer by 10 to 20 percent; breast cancer by 10 to 20 percent; pancreatic cancer by 33 to 50 percent (if alcohol is also eliminated); laryngeal cancer by 33 to 50 percent; and cancer of the esophagus by 50 to 75 percent (if alcohol is also eliminated). Sounds like stunning victories are possible. However, scientists always use cautious words such as may, possibly, or potentially, when they discuss the link between fruits and vegetables and cancers.
Here’s why: Increasing your consumption of fruits and vegetables is one of several things you should do. Others include getting frequent exercise, such as a 30-minute walk every day, maintaining a normal weight, cutting back on fat, especially the saturated types, and avoiding or reducing alcohol consumption. And if you smoke, stop. It’s hard to single out one lifestyle factor as the one that prevents cancer. Also, no one is sure how substances in plant foods fight certain cancers. Blumberg sees a strong general correlation that weakens when it comes to examples. "I think the data is very consistent on fruits, vegetables, and cancer. Once you break it down, [linking] certain fruits and vegetables to certain cancers is difficult. It’s difficult to say ‘eat more broccoli and get less breast cancer,' " he says.
For example, researchers would have to find a large group that could be followed for years. One set of people would be given vegetables; the other placebos. This would have to be duplicated with hundreds of fruits and vegetables and thousands of people. And it would have to be done in such a way that no one would know who ate what. Blumberg is also concerned that consumers might focus on one fruit or vegetable as the preventive factor for a certain cancer and ignore the rest. "There’s no magic fruit. Diversity, moderation, and balance in the diet [are key]."
Down To Basics
Although nutrition experts recommend variety, the scientific community is honing in on specifics, targeting individual foods and components. At the University of Illinois, which has one of the country’s best phytochemical research programs, scientists discovered that wild blueberries have a potentially valuable antioxidant capacity. Nutritionists there hope to learn the mechanisms of hundreds of phytochemicals in fruits and vegetables. Harvard researchers made headlines with their announcement that cooked tomatoes might reduce the risk of prostate cancer. They pinpointed lycopene, a carotenoid in tomatoes, as the protective element.
Recently the Agriculture Research Service (ARS) of the USDA launched a Phytonutrients Laboratory at the Beltsville, MD, Human Nutrition Research Center. Its goals are to identify plants with benefits; find out what dosage or serving size is protective; and to learn how phytochemicals work to improve health. (Some people use the term phytochemicals which covers all plant chemicals, others prefer phytonutrients since it refers to the beneficial substances in plants.) "So far the strongest evidence [for the cancer-fighting properties of plant foods] is epidemiological. ARS wants to go into controlled feeding studies where we know exactly what people are eating," says Beverly Clevidence, Ph.D., the scientist leading the lab investigations. "This goes back to the way we studied heart disease. People who ate a lot of saturated fat had heart disease. People who eat a lot of fruits and vegetables are protected from some cancers, heart disease, and macular degeneration. We want to see how much [produce] it takes to overcome cancer. We believe that you can take someone who is healthy with no signs or symptoms of cancer and over time, if they eat fruits and vegetables their risk of cancer is lowered. They have little assaults on their bodies, but can interrupt the assaults with a diet high in fruits and vegetables," she says.
The challenge will be to measure biomarkers in subjects. Biomarkers are molecular, biochemical, or physiological changes that can be used to gauge effectiveness of some activity, such as fruit and vegetable consumption. "It’s one thing to say a food is high in a phytonutrient, but we need to know if we can find it in [blood] plasma or in tissue. And, if we can find it, we want to know how the phytonutrient works. What is the mechanism?" Clevidence asks. "For example, we know that some phytonutrients turn on enzymes in the body that are healing. Broccoli has sulforaphane that turns on enzymes that detoxify substances in the liver that might be carcinogenic. It [the reaction] is being done in the lab. How can we test it in humans? We can’t take a piece of someone’s liver to test," she says.
But don’t wait for scientists’ answers before indulging in fruits and vegetables. "Epidemiological studies show that it doesn’t take that much. If people would actually eat five servings a day of fruits and vegetables they’d be fine. Actually people are eating more fruits and vegetables [than in previous years] but they’re only eating two servings of deep green and two servings of deep yellow vegetables. We’re eating a lot of potatoes," Clevidence says.
Eating a wide selection of fruits and vegetables is AICR’s advice as well. "Different fruits and vegetables have different nutrient and phytochemical profiles. For example, you can have strawberries and oranges. Both are high in Vitamin C, but their phytochemical profiles are different and you’ll have different benefits," says Melanie Polk, a registered dietitian who works with the organization. "Try a wide selection of vegetables as well. Cruciferous vegetables like broccoli and Brussels sprouts have phytochemicals that are different than those in the allium family of onions and scallions." She also recommends using more than one food preparation technique. "Lycopene [a carotenoid that may reduce prostate cancer risk] is a little more available in cooked tomatoes. Does that mean we should only eat cooked tomatoes? No. Eat a variety of foods, that’s the important thing."
FOODS THAT FIGHT BACK
Here’s a quick look at vitamins and phytonutrients that according to AICR reports show some potential as cancer fighters, along with the fruit and vegetable sources for them.
(Such as beta carotene, lutein, lycopene, and a-carotene)
Found in apricots, broccoli, carrots, dark leafy greens such as spinach and kale, mangoes, red and yellow bell peppers, red grapefruit, sweet potatoes, and tomatoes.
Probable evidence that carotenoids reduce the risk of lung cancer when taken from a food source. Possible evidence for stomach, colon, rectum, breast, cervix, and esophagus cancer reduction.
Found in broccoli, cabbage, citrus fruit, kiwi fruit, mangoes, papayas, red bell peppers, potatoes, strawberries, and tomatoes.
Probable evidence that it lowers the risk of stomach cancer; possible evidence for mouth, lung, pancreas, and cervix cancers.
Found in avocados, mangoes, and sweet potatoes.
Possible evidence that it lowers the risk of lung and cervix cancers.
Found in fortified flour and cereal products, artichokes, asparagus, broccoli, green cabbage, leafy greens, oranges, and papaya.
Possible evidence that it lowers the risk of lung, stomach, breast, and cervix cancer. (Harvard researchers add colon cancer to the list.)
Found in onions, garlic, scallions, and chives. Possible evidence allium compounds lower the risk of stomach cancer.
Note: Other phytochemicals that might have potential, but haven’t been sufficiently studied, include terpenoids, most often found in citrus fruit peel; potent antioxidant flavonoids in berries (especially high in blueberries), grapes, tomatoes, potatoes, broccoli, and onions; and isothiocyanates in broccoli and cauliflower.
Written by: Bev Bennett
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