Putting on the pounds 'doubles prostate cancer risk'

Doctors compared the chances of survival of 788 patients against their body mass index - the measure of obesity that takes into account weight and height.

Within five years of diagnosis, the prostate cancer death rate for men with a normal BMI - 25 or under - was less than 7 per cent against 13 per cent for men with a BMI over 25.

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Cancer campaigners said the findings were of "great concern" in the light of the growing obesity crisis.

Every year nearly 35,000 men are diagnosed with prostate cancer in Britain and 10,000 men die from it.

It is the most common cancer diagnosed in men, with at least one person dying from the disease every hour. Many more are thought to have the disease without realising it.

Dr Jason Efstathiou and colleagues from Massachusetts General Hospital, in Boston, studied 788 patients with locally advanced prostate cancer - the form where the cancer has spread outside the prostate gland.

Overall, men who were moderately fat - with a BMI of between 25 and 30 - were 1.5 times more likely to die from their cancer than those with a "normal" BMI of 25, Dr Efstathiou found.

Obese men, those with a BMI higher than 30, were 1.6 times more likely to die from their disease, the researchers report in the journal Cancer.

Body mass index is measured by taking someone's weight in kilograms and dividing it by the square of their height in metres.

Dr Efstathiou, whose team took into account other reasons why the cancer is more deadly for fat men, such as their income, social background and general health, said it was unclear whether losing weight after being diagnosed would alter the course of the disease.

Approximately 12,000 men are diagnosed with locally advanced prostate cancer in Britain each year.

Treatments for prostate cancer include the complete surgical removal of the prostate, radiation and hormonal therapy.

The Prostate Cancer Charity called for more studies into the link between obesity and post-treatment survival.

Ingrid Spickett, senior nurse at the charity said: "This large scale study is of great concern consideringthe rising levels of obesity here in the UK.

"We now need to ask what impact these men's particular treatments may have had on their survival and whether there other factors such as poor diet and lack of exercise may play a role.

"We also need more studies to see whether the same is true of men who are diagnosed with localised prostate cancer and men who have different treatments."

Earlier this month, a major study from the World Cancer Research Fund highlighted the links between diet, obesity and cancer.

Some nutrients - including selenium and lycopene, found in tomatoes - can protect against the disease.