Researchers found that combining a diet low in fat and rich in fruit and vegetables with regular moderate exercise seems to switch on genes that fight disease, while effectively turning off others that can promote cancer.
The evidence that genes are not your fate, undermining what the authors call "genetic nihilism," comes from a study of men with early stage prostate cancer but could be of relevance to a wide range of cancers, such as breast cancer advertisement.
This is accoring to Dr Dean Ornish, founder and president of the non-profit Preventive Medicine Research Institute and clinical professor of medicine at the University of California, San Francisco.
Inspired by studies that show prostate cancer is rarer in parts of the world where people eat a predominantly low-fat plant-based diet, he devised a vegan diet for patients, along with exercise, and a resulting "striking" effect on the way genes are used in the body is reported in the Proceedings of the National Academy of Sciences by Prof Ornish, working with Dr Christopher Haqq and Prof Peter Carroll.
An earlier randomised control study by his team on 93 men with early stage prostate cancer who make intensive changes in diet and lifestyle showed it may stop or perhaps even reverse the progression of their illness.
The new pilot study shows, for the first time, that men with low-risk prostate cancer who made improvements in fitness, stress management and nutrition - one linked with benefits when it comes to other diseases too - altered the use of genes that have a role in tumour progression.
The team studied gene expression - use - in biopsies taken with a needle from 30 men who were diagnosed with low risk prostate cancer and who had decided not to undergo conventional treatment for reasons unrelated to the study. The researchers studied the genes again three months later, after participants had made significant, prescribed lifestyle changes.
The use of over 500 genes was beneficially affected in normal tissues, so they believe the benefits could apply to women as well. Around 50 disease preventing genes were upregulated, or turned on, and certain disease-promoting genes, including genes involved in prostate cancer and breast cancer, were downregulated, or turned off.
"It is striking there are so many changes, and to such a degree," said Dr Haqq, adding that the effects on cholesterol were comparable to those achieved with a drug.
The findings complement earlier work that showed that, after a year PSA levels (a protein linked with prostate cancer) decreased in men in the group who made comprehensive lifestyle changes but increased in the comparison group. There was a direct correlation between the degree of lifestyle change and the changes in PSA.
Also, they found that blood serum from the participants inhibited prostate tumour growth in the test tube by 70 per cent in the lifestyle-change group but only nine 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.
Understanding the mechanisms of how comprehensive lifestyle changes alter the ways genes are used may strengthen efforts to develop effective prevention and treatment strategies for prostate cancer, they conclude, adding that bigger studies are now needed.
Ed Yong, health information manager at Cancer Research UK, said: "People often think that their odds of getting cancer are written in their genes. But studies like this suggest that changing your lifestyle can change the activity of your genes, and that nature can be changed by nurture.
"This study tells us that men with low-risk prostate cancers can change the levels of certain genes that are relevant to cancer by making positive lifestyle changes, like keeping active, eating a healthy, balanced diet and managing their stress levels.
"These steps helped to turn on some cancer-preventing genes and turn off other cancer-promoting ones. But, importantly, the study hasn't yet shown whether these genetic changes will actually stop their tumours from developing further, and it will be interesting to see if they do.
"Long term, it will also be interesting to see if combining specific lifestyle advice with the emerging knowledge of the genetic variations that affect a man's risk, will allow doctors to give tailored advice to men at highest risk, allowing them to minimise their chances of developing prostate cancer."
Prof Ornish believes "an ounce of prevention really is worth a pound of cure" and has found that two principles help: the first is to make small, incremental changes such as walking 2,000 steps more per day and to consume 100 calories less per day. Over time, these small changes add up and make a meaningful difference.
A second approach is to motivate people to make more intensive changes in diet and lifestyle. Paradoxically, some people find it easier to make big changes than small ones because when they make comprehensive changes in diet and lifestyle, they often feel so much better, so quickly, that it "reframes the reason for making these changes from fear of dying to joy of living."
Healthy diet and lifestyle
A vegan diet consisting primarily of fruits, vegetables, whole grains, and legumes supplemented with soy, vitamins and minerals. Low fat regime with only 10 per cent of calories from fat, and low refined flour and sugar.
Moderate aerobic exercise, such as walking for half an hour a day, an hour a day of yoga/meditation, and a once weekly support group sessions.
However, when it comes to prostate cancer the largest study of its kind to investigate the role of diet (European Prospective Investigation into Cancer and Nutrition) found no effect of fruit and vegetables, or dietary fat.
Unhealthy diet and lifestyle
High red meat, low fruit and vegetables; high saturated fat, salt and dairy; and sedentary lifestyle. However, Prof Orinish and his team stress that individual's fat intake (and other lifestyle factors) varies based upon his/her personal health.
"For example, an individual in good health might have different nutritional plans (including fat intake) and exercise and stress management versus an individual who is fighting a specific disease."
-By Roger Highfield, Telegraph Science Editor