A vegan diet might lower the risk of developing prostate cancer, say researchers.
They have found that men who eat a vegan diet have lower levels of a growth factor that is associated with prostate cancer than either meat-eaters or vegetarians.
The research's publication comes after controversy about claims that dairy-free diets prevent breast cancer.
Earlier studies have suggested that the risk of prostate cancer is increased by high levels of the growth factor IGF-I.
Other research has shown that prostate cancer rates are generally low in countries with a low consumption of meat and dairy products.
The new study, by the Imperial Cancer Research Fund's Cancer Epidemiology Unit in Oxford, reveals IGF-I levels are 9% lower in vegans than in meat-eaters.
Dr Tim Key, senior scientist at the charity, said: "Previous studies have shown that men with prostate cancer have higher levels of IGF-I and that even small differences in the circulating level are predictive of prostate cancer risk.
"Our study shows that the circulating level of IGF-I is different in vegan men than it is in non-vegans, including vegetarians.
"The lower levels of IGF-I found in vegan men might reduce their risk of prostate cancer."
There has been much coverage in the media about the possible effect of a dairy-free diet on breast and prostate cancer risk.
However, until now there has been no scientific evidence to prove the anti-cancer benefits of a vegan diet.
Dr Key said: "More research is needed before it would be possible to say whether having a vegan diet reduces a man's risk of prostate cancer."
The study, carried out in 696 British men, also found IGF-1 levels were slightly lower in vegetarians than meat-eaters.
The men in the study were taken from a larger European study (EPIC), which is looking at the relationship between diet and cancer to follow-up and check for prostate cancer in men with different dietary habits.