Diet and exercise may play an important role in keeping prostate cancer at bay, according to a new study. The same lifestyle changes that help prevent heart disease also appear to keep PSA levels in check and may even have an impact on how quickly a tumor grows, researchers from the University of California, San Francisco, report in the September issue of the Journal of Urology.

The study was led by Dean Ornish, MD, who famously discovered that exercising and eating an extremely low-fat diet can actually reverse serious heart disease even without medications. He is a professor at UCSF.

He and his colleagues studied 93 men with early stage prostate cancer who had decided to pursue watchful waiting rather than active treatment with surgery, radiation, or chemotherapy. All of these men were good candidates for watchful waiting -- they had a Gleason score below 7 (indicating a less aggressive tumor) and PSA levels in between 4 and 10 ng/ml.

The men were randomly divided into 2 groups. Men in one group were told to follow their normal lifestyle habits, while those in the other made some big changes. These men went on a strict vegan diet that contained only 10% of calories from fat (most Americans get 30% or more calories from fat), supplemented with soy, fish oil, selenium, and vitamins E and C. They also began getting regular exercise (30 minutes of walking 6 days a week), doing yoga or some other type of meditation, and participating in support groups.

After a year, the researchers measured the men's PSA levels. Men who had followed the diet and exercise plan saw their PSA levels decrease by 0.3 ng/ml (about 4%), while those who followed their usual routine saw their PSA levels increase by 0.4 ng/ml (about 6%). That difference isn't huge, but it is statistically significant, Ornish and colleagues say.

No men who followed the diet and exercise plan had to have additional treatment for prostate cancer, though 6 men in the other group did have to be treated because their cancer appeared to be getting worse.

"This study shows that there may be some benefit to following a strict diet and other lifestyle changes once prostate cancer has been diagnosed," said Len Lichtenfeld, MD, deputy chief medical officer for the American Cancer Society. "There have been similar findings in other studies in other cancers, most recently in postmenopausal women with breast cancer that was not hormone sensitive. The women who followed a low fat diet did better than those who did not."

But the findings aren't conclusive, he noted. The study only measured PSA and other lab results -- it did not look at survival or whether the disease had spread. Also, the follow up period was only a year, which may not be long enough to see all the potential effects of the different approaches.

Ornish and his colleagues acknowledge that their follow up period was brief, and say they are continuing to track the men to look for any differences in survival and other disease outcomes.

Because there were so many aspects to the regimen, it’s not possible to tell how much of an effect (if any) each individual component (vegan diet, supplements, exercise, stress reduction, support group participation) may have had on the PSA level.

The study also couldn't determine whether making these lifestyle changes would actually prevent prostate cancer in the first place.

Although the study focused on men who chose not to treat their prostate cancer, Ornish said the plan may also help men who are having conventional treatment for prostate cancer.

Lichtenfeld notes that the Ornish plan is very strict and may be hard for some people to stick to. In the study, 3 men quit the plan because it was too difficult. Still, eating better and exercising are worthy goals.

"Following a low-fat diet, getting an appropriate amount of exercise, and using stress-reduction techniques isn't bad advice for anyone, whether or not they have prostate cancer," said Lichtenfeld.

Men who do have the disease should talk to their doctor about all their treatment options, he added, and tell their doctor if they plan to follow the type of lifestyle changes described in Ornish’s study. Lichtenfeld said he would not recommend following this plan instead of conventional treatments if they were recommended by a doctor.

Citation: "Intensive Lifestyle Changes May Affect the Progression of Prostate Cancer." Published in the Journal of Urology (Vol. 174, No. 3: 1065-1070). First author: Dean Ornish, MD, University of California, San Francisco.