Scientists uncover disease deterrents in everything from amaranth to zucchini

These are salad days for plant foods, a green revolution for those virtuous vegetables, fruits, legumes, grains, seeds and nuts.

It's more than simply that public confidence in animal foods sinks to new depths of misgiving with each outbreak of E. coli O157:H7, salmonella, Mad Cow Disease and others in an apparent bouillabaisse of virulent pathogens.

Consumers are hoisting veggie fare with newfound vigor as medical studies compound like clockwork spotlighting how plant foods promote health and thwart disease. Tim Byers, an authority on the relationship between diet and chronic disease at the Centers for Disease Control and Prevention cites "an explosion of compelling and consistent data" linking plant-rich diets with lower disease risk. The accumulating body of evidence is so overwhelmingly impressive that in a 1995 story heralding the discovery of "yet another class of disease-fighting [plant] nutrients," the journal Science News joked that observers might well suspect a "vegetarian conspiracy against a carnivorous, burger-chomping public."

Thick volumes of epidemiological studies showing that people who eat plant-rich diets generally live longer, healthier lives has spurred researchers to investigate what it is about vegetable matter exactly that is so profoundly beneficial. What they are finding is that foods of plant origin are plush with a whole milieu of protective chemicals that promote human health and safeguard against disease.

Scientists are only just beginning to fathom this vast cornucopia of compounds and their capabilities. There may be literally thousands of such compounds in plant foods that provide health benefits. Of those which have been studied, some have demonstrated the potential to slow or reverse certain steps on the path to cancer. Others may be active in reducing the risk of chronic diseases including heart disease, and stroke. Some plant ingredients will lower blood cholesterol levels while others protect our eyes against cataracts and macular degeneration, bolster the immune system, reduce blood pressure and battle infections.

These incredible, edible protective plant components fall generally into two classes: antioxidants and phytochemicals.

Antioxidants are a family of nutrients with proven disease-fighting prowess. The most prominent and well-studied antioxidants are practically household names: vitamins E and C are routinely in the headlines, as are beta-carotene, folic acid and the mineral selenium.

What distinguishes antioxidants is their uncanny knack for disarming free radicals, highly reactive compounds that have been linked to heart disease and a host of aging-related changes. Antioxidants also reverse the types of DNA damage fomented by free radicals which can foster the development of cancer. "If you don't get enough antioxidants," says biochemist Bruce Ames, PhD, director of the National Institute of Environmental Health Sciences Center at the University of California, Berkeley, "it is the equivalent of irradiating yourself."

Where do free radicals come from? These ubiquitous unstable oxygen molecules are the natural waste products that result from breathing and other routine metabolic processes. Free radicals ricochet around hazardously inside our cells in relentless pursuit of the electrons that will afford them stability. Known as oxidation, this scavenging process ages tissues through cellular damage. (Oxidation is also responsible for things like rusting metal and turning oils rancid.)

Ordinarily our bodies can keep free radicals in check by marshaling an army of antioxidant enzymes. Unfortunately, other free radical promoters are abundant in our world including stress, overexercise, injury, smoking, pollution, ozone, chemotherapy, radiation and certain foods.

It's not possible to completely halt the production of free radicals -- nor would we want to since our immune systems employ some to help fight viruses and bacteria -- but we can minimize their impact. We can choose foods rich in antioxidants (almost exclusively plant foods) while minimizing free radical-rich items like deep-fried foods (at high temperatures, oils, especially polyunsaturated oils, become oxidized), rancid fats and oils and iron-rich foods like meat (iron is a known oxidizer). According to a recent National Research Council study, the overconsumption of fat and calories (of which animal foods are a leading source) are the principal dietary causes of cancer.

Phytochemicals ("phyto" is Greek for plants) are among thousands of biologically active compounds found in plants. Though research in this field is in its infancy, hundreds of individual phytochemicals have been identified including 40 in broccoli, about 50 in garlic and onions, 70 in the herb tarragon and more than 170 in oranges including a tongue-twisting blend of carotenoids, flavonoids, terpenoids, limonoids and glucarates. And scientists readily admit that we are just scratching the botanical surface.

Many phytochemicals function as crucial components in the natural defense system of their host plants, defending against infections and microbial invasion. Other phytochemicals give plants their flavors, aromas and pigments. Presently there are almost 2,000 known plant pigments in our food, including over 800 flavonoids, 450 carotenoids and 150 anthocyanins (reddish pigments found in many fruits).

While fruits and vegetables, especially brightly colored ones, are phytochemical gold mines, so too are whole grains and legumes. Phytochemicals found here include plant sterols, phytates, phytoestrogens, tocotrienols, lignans, ellagic acid and saponins. These substances can reduce the risk of cardiovascular disease and cancer in those who regularly enjoy whole grains. It's important to emphasize the phytochemical advantage of eating whole versus refined grains. Refining wheat, for instance, causes a 200-to-300-fold loss in the phytochemical content.

Like their antioxidant brethren, phytochemicals have impressive disease-fighting resumes that will only grow with time. Scientists now foresee a day in the not-too-distant future when consumers will be able to tailor their eating to include more foods protective against the diseases to which they are personally prone, from arthritis to cancer, says Marc Micozzi, MD, PhD, head of the Philadelphia College of Physicians.

Studies have already linked certain phytochemicals to the prevention and treatment of heart disease, diabetes and high blood pressure. Other phytos support immune function or combat tumors and viruses. Yet others are proven antioxidants. (What separates phytochemicals from true antioxidants is that phytochemicals have no known nutritive value and are not necessary for normal physiologic function as are, for example, vitamins E and C.)

A number of phytochemicals are known to interfere with the cancer process. They accomplish this either by preventing carcinogens from forming in the first place; by blocking various hormonal actions and metabolic pathways associated with cancer's evolution; by stimulating enzymes in the body that flush out, inactivate or metabolize carcinogens; or by suppressing the machinery that allows the growth and division of cancer cells.

Phytochemicals appear destined for stardom. In very short order, they have vaulted into the nutritional spotlight and spawned more activity in food research than in years past. What's more, plants have only just begun to reveal their best secrets.

Nowadays conferees gather regularly to discuss these secrets and the proven disease preventative properties of foods and herbs. At a recent meeting in Chicago topics included "The Anticarcinogenic Effects of Flaxseed," "How Soy Proteins/Isoflavonoids Can Prevent Osteoporosis in Post-Menopausal Women," and "The Cancer Preventative Properties of Isothiocyanates and Fruit Berries." In fact, so keen is the interest in the plant kingdom's treasury of biologically active compounds that the University of Illinois has created the first full-scale scientific program devoted to their study. The Functional Foods for Health Program involves more than 70 researchers scrutinizing the role of foods in preventing disease.

In a society enamored with the idea of simple solutions to complex health problems, it's predictable that researchers are focusing less on ways of getting people to eat more whole plant foods and more on means of encapsulating phytochemicals or fortifying existing products with them. Their aim, of course, is to offer consumers pills or foods souped-up with higher-than-normal levels of certain disease-fighting plant compounds.

It could take generations for scientists to unravel the chemistry inside of foods, however. Each plant harbors a world of individual yet interacting compounds. In the meantime, every tomato slice and spinach leaf contains a multitude of potent antioxidants and phytochemicals perfectly packaged and ready for use.

Ultimately, the greatest promise of phytochemical research might be it's ability to spark a dramatic and widespread shift in the understanding and appreciation of plant foods. When considering how to prevent and treat disease, people may one day soon look to their grocery stores and dinner plates rather than their hospitals and pharmacies.

- Steve Lustgarden