A study by US researches is one of the first randomized, controlled trials to demonstrate that lifestyle changes may affect the progression of a cancer.
The findings are important as prosate cancer is the second most common cancer in men after lung cancer. It was the most common form of cancer diagnosed among men in the European Union during 2004, representing 15 per cent of male cancers and 238,000 new cases, according to the International Agency for Research on Cancer (IARC).
The team from the University of California in San Francisco recruited 93 men with biopsy-proven prostate cancer who had decided not to follow conventional treatment for the disease.
They were randomly divided into two groups. The first was placed on a vegan diet consisting primarily of fruits, vegetables, wholegrains and legumes. They also received supplements of soy, vitamins and minerals and participated in moderate aerobic exercise, yoga/meditation, and a weekly support group session.
None of the men in this group had conventional prostate cancer treatments such as surgery, radiation, or chemotherapy during the study.
The second group made no changes to diet and lifestyle and six members of this group underwent conventional treatments because their disease progressed.
After one year, PSA levels (a protein marker for prostate cancer) decreased in the group who had changed their lifestyle, the researchers will report in the September issue of the Journal of Urology.
In contrast, PSA levels increased in the comparison group. There was a direct correlation between the degree of lifestyle change and the changes in PSA, said the scientists.
Further, they found that serum from the participants inhibited prostate tumour growth in vitro by 70 per cent in the lifestyle-change group but only 9 per cent in the comparison group.
Again, there was a direct correlation between the degree of lifestyle change and the inhibition of prostate tumour growth.
Patients in the lifestyle-change group also reported marked improvements in quality of life.
"This study provides important new information for men with prostate cancer and all men who hope to prevent it," said study author Dr Peter Carroll, chair of the department of urology at the University of California.
He said it is the first in a series of trials attempting to better identify the exact role of diet and lifestyle in the prevention and treatment of prostate cancer.
"Changes in diet and lifestyle that we found in earlier research could reverse the progression of coronary heart disease may also affect the progression of prostate cancer as well," added co-author Dean Ornish, also founder and president of the non-profit Preventive Medicine Research Institute.
He added that men with prostate cancer who undergo conventional treatments may also benefit from making comprehensive lifestyle changes.
The researchers are continuing to follow the trial patients to determine the effects of their changes in diet and lifestyle on morbidity and mortality.