A strict vegetarian diet combined with relaxation therapy and exercise may be able to control slow-growing Prostate cancer, researchers said on Thursday.

Diet guru Dr. Dean Ornish said his vegan diet program, which some studies have suggested can reverse Heart disease, also seemed to halt the progression of Prostate cancer.

Tests on middle-aged and elderly men who had opted to watch indolent prostate tumors rather than treat them suggested the program slowed the growth of their cancers, Ornish said.

“This is not the definitive study, but it certainly advances the field and it adds new information about how powerful these simple changes can be,” Ornish said in a telephone interview.

Writing in the Journal of Urology, Ornish and colleagues at the University of California San Francisco and the Memorial Sloan-Kettering Cancer Center in New York said they tested 93 men with Prostate cancer. They had an average age of 65 to 67.

Prostate cancer is diagnosed in more than 200,000 men every year in the United States and will kill 29,000 this year, according to the American Cancer Society.

It can sometimes be a slow-growing cancer and men often opt for “watchful waiting” when they have been diagnosed. They get regular tests of prostate specific antigen, or PSA - a compound in the blood that can help indicate prostate health - digital rectal exams and sometimes ultrasounds of the prostate.

Ornish, along with urologist Dr. Peter Carroll at UCSF and other experts, divided their 93 volunteers into two groups. One group was not told anything and the other was put on Ornish’s program.

This includes an ultra low-fat vegan diet with fewer than 10 percent of calories from fat, plenty of fruits and vegetables, as well as whole grains and legumes. “About half their meals were prepared,” Ornish said.

They were also told to exercise daily. “It was mostly walking,” Ornish said. “We asked them to do yoga and meditation.”

There were also group sessions once a week during which they did an hour of yoga, ate a group meal and had a group session.

After a year, on average, PSA levels rose in the group that made no changes but fell in the group that followed the Ornish plan.

PSA is not always directly linked with cancer, but Ornish said it is the best measure available.

In addition, six of the men who made no changes decided in the year to have their prostates removed or to have radiation therapy, compared to no men in who did the Ornish program. Their decisions were based either on a rise in PSA or on exams that suggested the tumors were growing, Ornish said.

Ornish said he does not know which component of his program is more important. “There is no way to factor it out,” he said. “Everything we were doing was to harness the mind-body interactions for the better.”

Ornish said diet alone has not been shown to affect cancer progression. “I think it is difficult for people to change their diet if they don’t change other habits,” he said, noting that people often overeat when stressed, for example.

Diets low in fat and rich in fruits and vegetables, as well as exercise, have been shown to reduce the risk of a range of cancers including breast and Prostate cancer.