An unhealthy diet can increase the risk of aggressive prostate cancer almost three-fold, according to new research.
The study found men who gorged on junk food and and fizzy drinks were more prone to life threatening tumours.
However they also discovered that a healthy diet doesn't prevent the disease.
Lead author Dr Adela Castello-Pastor, of the Carlos III Institute of Health, Madrid, said: "Our results indicate avoiding unhealthy dietary habits could be the best nutritional strategy to prevent aggressive prostate cancer."
The findings are based on 15,296 Spanish participants tracked for an average of 17 years.
Those who ate a Western style diet were most likely to develop tumours that spread to other organs. Incidence rose between two and nearly threefold.
Milk and other dairy foods have been found to suppress production of prostate cancer fighting chemicals, said Dr Catello-Pastor.
She said: "Also total and saturated fats and trans fatty acids from red and processed meats, sweets, sauces and convenience food, are suspected to enhance prostate cancer progression through the disruption of hormonal regulation.
"They increase oxidative stress that impairs the repair of DNA damage and lead to inflammation that increases cellular proliferation.
"Also, many compounds that are naturally present or generated when cooking or processing red meat or other products might affect prostate cancer risk by catalysing free radical formation and suppressing the expression of genes involved in cell cycle progression and DNA repair in prostate cancer cells.
"Finally, the high energy profile of the Western dietary pattern contributes to increase body composition, the most important known modifiable risk factor for prostate cancer."
Just over 600 prostate cancer cases were diagnosed during the follow up period. Diets were categorised as Western, Prudent or Mediterranean.
The Western dietary pattern consisted of a high intake of high-fat dairy products, processed meat, refined grains, sweets, caloric drinks, convenience food and sauces and a low intake of low-fat dairy products and whole grains.
The Prudent dietary pattern was characterised by a high intake of low-fat dairy products, vegetables, fruits, whole grains, and juices.
The Mediterranean dietary pattern represented a high intake of fish, vegetables, legumes, boiled potatoes, fruits, olives, and vegetable oil, and a low intake of juices.
While adhering to a healthy diet such as the Prudent and Mediterranean was not enough to prevent prostate cancer, it reduced the risk of the most aggressive forms.
Several studies have shown a link between eating vegetables and a reduced risk of prostate cancer, but results have not been consistent. This is the first to specifically look at the deadliest tumours.
Every year, upwards of 52,300 men are diagnosed with prostate cancer in the UK. The disease claims almost 12,000 lives annually.
The study was published in the journal BJU International.
