The small pilot study shows for the first time that changes in diet, exercise, stress management and social support may result in longer telomeres - the protective caps on the ends of chromosomes that affect how quickly cells age.
As telomeres become shorter, and as their structural integrity weakens, the cells age and die quicker.
It is the first controlled trial to show that any intervention might lengthen telomeres over time.
Researchers at University of California - San Francisco hope the results will inspire larger trials to test the validity of the findings.
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For five years, all the men were engaged in active surveillance, which involves closely monitoring a patient's condition through screening and biopsies.
Ten of the patients embarked on lifestyle changes that included: a plant-based diet (high in fruits, vegetables and unrefined grains, and low in fat and refined carbohydrates); moderate exercise (walking 30 minutes a day, six days a week); stress reduction (gentle yoga-based stretching, breathing, meditation). They also participated in weekly group support.
The group that made the lifestyle changes experienced a 'significant' increase in telomere length of 10 per cent.
Also, the more people changed their behaviour by adhering to the recommended lifestyle programme, the more dramatic their improvements in telomere length, the scientists learned.
By contrast, the men in the control group who were not asked to alter their lifestyle had measurably shorter telomeres - nearly 3 per cent shorter - when the five-year study ended. Telomere length usually decreases over time.
The researchers said the findings may not be limited to men with prostate cancer, and are likely to be relevant to the general population.
"So often people think 'Oh, I have bad genes, there's nothing I can do about it,'" Ornish said.
"But these findings indicate that telomeres may lengthen to the degree that people change how they live. Research indicates that longer telomeres are associated with fewer illnesses and longer life," he said.
The study was published in the journal The Lancet Oncology.