Eating better, exercising regularly and cutting stress apparently can slow the progression of early prostate cancer, according to the first study to provide direct evidence that lifestyle changes can fight the common malignancy.

The study of 93 prostate cancer patients found that those who adopted a series of lifestyle changes that included a primarily vegan diet, regular moderate exercise, and yoga and other relaxation techniques scored better on a standard blood test used to monitor prostate cancer growth a year later. They were also less likely to require additional treatment, and their blood showed signs of being able to inhibit prostate cancer cells in lab tests.

Many studies have suggested that adopting healthful lifestyles can have a host of health benefits, including reducing the risk for various cancers. But the new research is the latest in a series of recent studies that have found that factors such as diet, exercise and stress reduction may have a powerful effect on cancer patients' prognoses.

"Diet and other lifestyle changes play an important role in the development of many health problems," said Dean Ornish of the University of California at San Francisco, who led the new study, being published in next month's issue of the Journal of Urology. "Now we have evidence it can slow the progression of prostate cancer."

Other researchers said many more studies will be needed to explore which components of the lifestyle changes may be important, and to demonstrate whether the effects translate into a reduced risk of dying.

"There's a building body of evidence that lifestyle may affect cancer progression," said Peter Greenwald of the National Cancer Institute. "This is a very important area, and this is one more important lead that indicates a crucial direction for more research."

But given that a healthful diet and regular exercise can have other benefits, several researchers said there is no reason patients should not consider adopting them in addition to their standard care.

"The take-home message is that an active lifestyle combined with a healthy diet definitely decreases the risk of many types of cancer, and in the case of early nonaggressive prostate cancer, it may slow disease progression," said Durado Brooks of the American Cancer Society.

Prostate cancer strikes 232,000 American men each year and kills about 30,000, making it the leading cause of cancer among men and the second-leading male cancer killer, after lung cancer.

Ornish and his colleagues studied 93 men who had been diagnosed with early prostate cancer. The men had opted not to seek treatment immediately but, instead, to closely monitor their tumors.

Half the men adopted a regimen that included a vegan diet -- primarily fruits, vegetables, whole grains and legumes but no meat, eggs or dairy products -- supplemented with soy, vitamins and minerals.

That same group of men also started moderate aerobic exercise, such as walking 30 minutes six days a week; participated in a one-hour support group meeting once a week; and began using stress-management techniques, such as yoga, breathing exercises and meditation for an hour a day.

When the study began and then a year later, the researchers gave both groups of men the prostate-specific antigen (PSA) blood test, which is widely used to monitor the progression of the cancer. Those on the diet and exercise regimen saw their PSA levels drop by an average of 4 percent, while those in the other group saw theirs rise an average of 6 percent, the researchers found.

In addition, blood from the men in the diet and exercise group appeared to inhibit prostate cancer cells in laboratory tests, indicating that something in their diet or their bodies' response to the regimen was inhibiting their cancer, Ornish said.

Moreover, none of those who made the lifestyle changes needed any cancer treatment during the study period, whereas six of those in the other group did.

"This is the first randomized trial showing that the progression of prostate cancer can be stopped or perhaps even reversed by changing diet and lifestyle alone," said Ornish, who stressed that the changes should be considered only as an addition to standard treatment and not a substitute.

Two recent studies found that breast cancer patients who ate low-fat diets and exercised regularly were less likely to suffer recurrences, Ornish noted. "We think we may be able to give many people new hope and new choices that they didn't have before," he said.

Other researchers were cautious, saying the study had not yet demonstrated that the lifestyle changes help people live longer, and it was difficult to pinpoint which aspects of the regimen might be beneficial.

"So many variables were changed in the experimental group that it is not possible to sort out which of the many lifestyle factors . . . or combination thereof, was responsible for the observed effects," Howard L. Parnes of the National Cancer Institute wrote in an e-mail.

In addition, the changes were so dramatic that it is unclear how many men could sustain them, Parnes said. "Although the findings appear to support the hypothesis that dietary and lifestyle factors can potentially alter the natural history of prostate cancer, there are many caveats."

In comments accompanying the article, Paul H. Lange of the University of Washington said the study would likely trigger follow-up research.

"Even if scientific evidence is still meager, complementary medicine approaches have strong appeal in practicing the medical art since they give the patient an active role in his care and promote an attitude of optimism and hope," he wrote.