Men who follow a vegan diet may cut their risk of prostate cancer, research suggests.
A study found a 35% lower risk of the cancer for those who followed a vegan diet, which is based on plants and includes vegetables, grains, nuts and fruits.
Vegans avoid food that comes from animals, including dairy products, meat and eggs.
The research, funded by the World Cancer Research Fund (WCRF), comes as a separate study suggests men who have radiotherapy to treat prostate cancer could be at risk of secondary cancers of the bladder, bowel area and rectum.
The WCRF study examined data for more than 26,000 men and looked at the relationship between prostate cancer, meat-eating, fish-based diets and vegan diets.
In total, 1,079 cases of prostate cancer were identified among the group. Around 8% of the men studied said they followed a vegan diet.
Researchers from Loma Linda University in California found that men who followed a vegan diet had a "statistically significant protective association", with a 35% reduced risk of developing the disease.
Professor Gary Fraser, who led the study, said: "This new research makes a significant step in linking a vegan diet to reduced prostate cancer risk.
"What we now need is more research into this area to determine to the extent a vegan diet could reduce the number of men developing this cancer."
Prostate cancer is the most common cancer in men in the UK with over 47,000 new cases each year.
More than 10,000 men die of prostate cancer each year.
Dr Panagiota Mitrou, director of research funding at the WCRF, said: "With prostate cancer being the most common cancer in men in the UK, prevention is key if we are to see a decrease in the number of men developing the disease.
"This exciting research has, for the first time, helped fill some vital gaps in our knowledge about eating patterns and the prevention of prostate cancer and could pave the way for future research.
"Although these results are exciting, more studies are needed to demonstrate the strength of the link between a vegan diet and reducing the risk of prostate cancer."
In the second study, published in the British Medical Journal (BMJ), researchers said they had found a possible link between radiotherapy for prostate cancer and an increased risk of developing secondary cancers of the bladder, colorectal tract and rectum.
But they said the absolute rates of these secondary cancers remains very low.
Experts in Canada and the US analysed the results of 21 studies looking at a possible link.
They found an increased risk of cancers of the bladder, colorectum, and rectum, but not cancers of the lung or blood system, after radiotherapy compared with patients having no radiotherapy or surgery.
In an accompanying editorial, Christine Eyler and Anthony Zietman from the Harvard Radiation Oncology Programme in Boston, said the study "confirms our belief that second malignancy should be added to the already long list of avoidable hazards associated with treatment for those men with low risk prostate cancer who simply need no treatment at all".
But they said concern about secondary cancers "should not, however, stand in the way of an effective and well-studied treatment being given to men with higher grade, lethal prostate cancer for whom the potential benefit simply dwarfs the risk."
Jimmy Pierce, spokesman for the Vegan Society, said: "The evidence around the disease-preventative qualities of the vegan diet is now overwhelming. Time and again we are seeing new research showing the vegan diet to be significantly better for our health.
"Still lingering, however, is the perception that eating meat is macho, that it somehow enhances masculinity or virility. Yet it is killing thousands of men in the UK every year.
"Now is the time to reject this outdated notion and embrace plant-based living regardless of gender - for the animals and the planet as well as your health."