TUESDAY, June 17 (HealthDay News) -- Genes may not fully control your destiny when it comes to cancer risk, according to a new study of men with prostate cancer.

New research suggests that stringent dietary changes, getting more exercise and practicing stress reduction can change the expression of hundreds of genes. Some of the changes positively affect genes that help fight cancer, while others help turn off genes that promote cancer development, according to the study, which is in this week's issue of the Proceedings of the National Academy of Sciences.

"These findings are very exciting. They counter the genetic nihilism I hear so often. People say, 'It's all in my genes, there's nothing I can do,' but actually you can do quite a lot," said the study's lead author, Dr. Dean Ornish, president of the Preventive Medicine Research Institute and a clinical professor of medicine at the University of California, San Francisco.

Previous epidemiological studies have found that the incidence of prostate cancer is significantly lower in areas of the world where people eat a more plant-based, low-fat diet instead of the higher-fat, higher-protein diet often consumed in the United States. Because of these findings, Ornish and his colleagues initially set out to see if altering diet and lifestyle could decrease the amount of prostate-specific antigen (PSA) in men who'd been diagnosed with early prostate cancer. PSA is a blood marker for prostate growth.

In September 2005, they reported that after intensive lifestyle changes -- consuming a vegan diet with about 10 percent of calories from fat, walking 30 minutes six times a week, and practicing stress management one hour daily -- men with early prostate cancer lowered their PSA scores by 4 percent, while men in the control group saw their PSA score rise by 6 percent.

But, the researchers didn't know what the mechanism behind the change was, according to Ornish. The current study was designed to elucidate the reasons behind the improvement.

Thirty men diagnosed with early prostate cancer were enrolled in the study. The men were predominantly white (84 percent), with an average age of 62.3 years, and an average PSA score of 4.8 nanograms per milliliter (ng/ml). Their Gleason scores -- another measure of the severity of the cancer -- were an average of six.

All of the men had already declined immediate surgery, hormonal therapy or radiation. Instead, they chose to have their tumors periodically monitored to ensure that they remained slow-growing.

The lifestyle interventions began with a 3-day residential retreat, followed by weekly telephone consultations and a one-hour group support session each week. The study participants were provided all of their food and were asked to follow a plant-based diet containing about 10 percent of calories from fat. They were also told to walk for 30 minutes a day, six days a week.

Additionally, the study volunteers practiced stress management for 60 minutes a day. Stress management techniques included yoga-based stretching, breathing exercises, meditation, imagery, and progressive relaxation. The study volunteers were also given additional soy, three grams of fish oil, 100 units of vitamin E, 200 milligrams of selenium and 2 grams of vitamin C daily.

The researchers compared genetic expression from baseline samples to those taken after three months of study intervention and found positive changes in more than 500 genes, according to Ornish.

"I thought younger people with milder disease would show the most improvement, but neither age nor disease severity made as much difference as adherence," said Ornish. That means that the more people are able to change, the better. And, these findings suggest that you're never too old to make changes that can positively affect your health.

"It's encouraging to see that by going on a very low-fat diet that you can change gene expression in the prostate itself, but just because changes can happen, you don't yet know if it would mean anything for cancer risk," said Dr. Simon J. Hall, director of the Deane Prostate Health and Research Center, and the chairman of urology at Mount Sinai School of Medicine in New York City.

Hall said he'd like to see them follow these men for a long time to see what these genetic changes eventually mean.

Ornish said this study's findings were "very unexpected, and we've raised more questions than we've answered."

In any case, Hall added, it's clear that if you can make lifestyle changes like those in the study, you can definitely improve your cardiovascular health.

More information

To learn more about how food and exercise can affect your cancer risk, visit the American Cancer Society.