With so many people using over- the-counter herbal supplements as a means to promote health, one UW-Madison researcher is wondering why we don”t hunt for health-promoting properties among the ordinary plants we grow for food.
According to Kirk Parkin, a food scientist at the College of Agricultural and Life Sciences, “There’s no reason to believe that exotic botanicals are the only plants that have specific, health-promoting benefits. Domesticated plants do, as well.”
That’s why Parkin has launched a research program aimed at uncovering the healthful properties, such as cancer prevention, of the decidedly unglamorous crop plants cultivated here in Wisconsin, such as garlic, kale, beets, corn and green beans. Not only do common vegetables carry a lower price tag and a safety record spanning thousands of years, but they also contribute to Wisconsin’s economy.
The popularity of exotic herbal supplements with names like echinacea, feverfew, valerian and goldenseal has soared. So have concerns about their effectiveness and safety. Last year, the Food and Drug Administration alerted consumers to the possible liver-damaging effects of kava, a popular herb for relieving anxiety and insomnia. The Secretary of Health and Human Services recently urged mandatory warning labels for the stimulant ephedra. And doctors have begun cautioning about the risks of using herbal supplements in combination with prescription drugs and immediately before surgery.
On the other hand, in a study published in the September 2002 issue of the Journal of Food Science, Parkin”s research group demonstrated that everyday vegetables might indeed play a role in human health beyond simple nutrition. Using a well-known in vitro technique for screening possible cancer-preventive agents, they showed that crude vegetable extracts triggered increases in protective proteins, called phase II enzymes.
Phase II enzymes work in concert with another group of proteins, called phase I enzymes, to detoxify cancer-causing agents in the liver and other organs, and purge them from the body. Due to these activities, high levels of both sets of proteins – but especially phase II enzymes – are thought to help protect against cancer.
Among the vegetable extracts they tested, an extract of sweet corn showed the greatest effect, causing a 13-fold jump in enzyme levels. Kale extract raised the enzymes eight-fold, snap beans increased them five-fold and beets two-fold.
“Our results suggest that commonly consumed vegetables contain components that can elevate phase II enzymes in vitro, and have the potential to be used as dietary sources of cancer chemopreventive agents,” says Parkin. Many of the extracts also showed pronounced antioxidant activities.
But aren”t people already receiving these benefits by eating their veggies? Probably not to the extent they could. In its last dietary assessment of the U.S. food supply, the U.S. Department of Agriculture found that although Americans ate an average of 20 percent more vegetables in 1996 than in 1970, just three types accounted for half of all servings: head lettuce, canned tomatoes, and potatoes, including chips and french fries. Another 15 percent of servings came from dehydrated potatoes, fresh tomatoes, garlic and carrots.
To entice people into eating a wider variety of plant foods, Parkin believes scientists need to continue to pinpoint the health benefits of eating specific vegetables. “The USDA has been advocating all along that eating a diversity of fruits and vegetables in copious quantities will promote health, and I”m convinced it will,” he says. “But I think if you simply tell the public that eating vegetables is good for them, you don”t get much of a response. To change eating habits, you need to give a specific reason why eating certain vegetables will benefit them.”
Research such as Parkin”s could also lead to new vegetable-based dietary supplements for the staunchly veggie-phobic.
Parkin cautions that his research group still has much work to do toward characterizing the specific compounds in vegetables that carry cancer-protective effects, and demonstrating a true health benefit for people. Still, he”s convinced that today”s neglected, humdrum plant foods could be an important part of tomorrow”s preventive medicine.