A new pilot study shows that eating right, exercising and reducing stress may help keep chronic diseases at bay by switching on beneficial genes, including tumor-fighters, and silencing those that trigger malignancies and other ills.

"We found that simple changes have a powerful impact on gene expression," Dean Ornish, founder and president of the Preventive Medicine Research Institute and clinical professor at the University of California, San Francisco (U.C.S.F.), said during a news conference. "People say, 'Oh, it's all in my genes, what can I do?' That's what I call genetic nihilism. This may be an antidote to that. Genes may be our predisposition, but they are not our fate."

Ornish, who has built a reputation on advocating healthy living, and U.C.S.F. colleagues report in the journal Proceedings of the National Academy of Sciences USA that they found the activity of more than 500 genes in the normal tissue of 30 men with low-risk prostate cancer changed after the patients began exercising regularly and eating diets heavy in fruit, veggies and whole grain (supplemented with soy, fish oil, the mineral selenium and vitamins C and E) and low in red meat and fats.

In addition to downing healthier fare, the men also walked or worked out at least 30 minutes six days a week; did an hour of daily stress-reducing yoga-type stretching, breathing and meditation; and participated in one-hour weekly group support sessions.

The subjects had all opted to skip conventional surgical or radiation treatment in favor of a "watchful waiting" approach. The researchers say it is too early to tell whether the lifestyle changes kept the cancer cells in check. But they say the study indicates that exercising, improving nutrition and limiting stress may prompt "profound" differences in the behavior of genes. Among them: some genes believed to be tumor suppressors turned on or became more active, whereas certain disease-promoting ones, including oncogenes (in the so-called RAS family that are implicated in both prostate and breast cancer), were down-regulated or switched off.

The findings were based on changes in levels of RNA (molecules that carry instructions from DNA or genetic material) in samples of noncancerous prostate tissue taken before and three months after the men started the study.

"It is absolutely intriguing this lifestyle change can have as much effect as the most powerful drugs available to us now," U.C.S.F. geneticist Christopher Haqq said during the news conference. "We medical oncologists are always looking for drugs that can do this. It is delightful to find that diet and lifestyle can have profound effects and be complementary to drug therapies—with fewer side effects."

Ornish, who has done extensive research showing that nutritional and other lifestyle changes may prevent and even reverse chronic diseases, says that perhaps the most surprising element of this study was how swiftly the benefits appeared.

"People say, 'Why bother?' But when they see that in just three months these changes can make a difference, they may change their minds," he said. "It is not really so much about risk-factor reduction or preventing something bad from happening. These changes can occur so quickly you don't have to wait years to see the benefits."

Ornish said the findings show that comprehensive lifestyle changes may benefit the general population as well as those with prostate cancer.