Conference Reveals Details of Promising Phytochemical Research

American Institute for Cancer Research
Thursday, 2 September 1999

"We are in the middle of rigorous testing of phytochemicals in foods that show great promise as anti-cancer agents," Dr. Richard Rivlin of Memorial Sloan-Kettering Cancer Center told reporters at the 9th Annual Conference of the American Institute for Cancer Research (AICR).

"The end-product of this research into phytochemicals will be powerful and precise tools for reducing incidence of cancer," Rivlin said. "Faced with an individual at risk for a specific kind of cancer, we will be able to prescribe specific foods and perhaps supplements that, consumed together, will significantly reduce that risk."

"Phytochemical" is a catchall term for the vast array of chemical substances found naturally in fruits, vegetables and grains. These substances, with names such as beta-carotene, lycopene and isoflavones, show tremendous potential to fight disease on several fronts.

Focus on Lab Studies

Epidemiological studies, also called population studies, have suggested relationships between a variety of plant foods and low rates of cancer, Rivlin said.

Scientists are now doing laboratory studies to isolate the phytochemicals in these plant foods and determine the "mechanism" by which they work to reduce cancer. Most of the laboratory studies involve animal or cell culture tests.

Researchers at the AICR conference reported on their work with isoflavones in soy, polyphenols in tea, allyl sulfur compounds in garlic and resveratrol in wine, grapes and spices. At another session, the mechanism for cancer prevention in the trace mineral selenium was discussed.

"When we have completed the lab tests on these substances, the next step will be clinical trials in which we test their effect on human beings. Clinical trials require time and considerable funding, but they are essential to determining effectiveness, safety and dosage," Rivlin told reporters.

Dealing With Complicating Factors

Laboratory tests have already taught scientists a lot about the "interaction" of these health-promoting substances. Test results indicate that phytochemicals, vitamins and minerals in plant foods all interact in a manner that enhances or reduces their efficacy as cancer-fighting agents.

"It will be shown at this conference that the action of allyl sulfur compounds in garlic is enhanced by other substances found in an healthy diet. In the presence of selenium and vitamin A, allyl sulfides arrest carcinogenic activity far more effectively than they do in isolation," Rivlin said.

Scientists see interaction as an important factor in understanding phytochemicals. It suggests that specific mixtures of phytochemicals or foods containing phytochemicals will be necessary to reduce cancer risk in humans.

Another significant factor discussed at the conference is the tendency of phytochemicals to act in different ways under different circumstances. For instance, clinical trials have shown beta-carotene reduces incidence of oral cancer, but it increases risk of lung cancer in smokers.

Similarly, phytoestrogens in soy appear to reduce incidence of breast cancer. But preliminary studies suggest it may enhance cancer cell proliferation where the disease is already present.

"Such variances make it clear that considerably more testing and trials must occur before we begin to advise patients about use of phytochemicals," Rivlin said.

Herbal Medicine Considered

On another topic, Rivlin indicated that research into phytochemicals encompasses herbal and alternative medicine. "We are studying the potential of plant substances to fight cancer" he said, "and herbs are plants."

He urged his colleagues to avoid extremes in regard to alternative medicine. "We ought not to embrace it too fast or uncritically. We ought not to reject it out of hand. We need to submit so-called 'alternative' or complementary theories to the same rigorous testing that we use for more conventional approaches."

Rivlin concluded his remarks by saying that at this juncture researchers don't know enough about the nature of phytochemicals and how they work to prescribe particular foods or supplements. The best advice to give patients, he suggested, is to eat a predominantly plant-based diet, rich in vegetables, fruit, whole grains and beans.

"Of the 202 studies on the association between vegetables and fruit and cancer examined by an AICR panel, an astounding 78 percent show those foods to be cancer-preventive. All our research clearly indicates the wisdom of eating a variety of vegetables and fruit daily," Rivlin said.

For more information, or to contact American Institute for Cancer Research, see their website at: www.aicr.org