Men who consume more than 10 portions of tomatoes each week reduce their risk by about 20%, according to a UK study.
Prostate cancer is the second most common cancer in men worldwide, with 35,000 new cases and around 10,000 deaths in the UK every year.
Cancer experts recommend eating a balanced diet which is high in fruit and vegetables and low in red and processed meat, fat and salt.
The Bristol team analysed the diets and lifestyles of around 20,000 British men aged between 50 and 69.
They found men who consumed more than 10 portions of tomatoes each week - such as fresh tomatoes, tomato juice and baked beans - saw an 18% reduction in prostate cancer risk.
Eating the recommended five servings of fruit or vegetables or more a day was also found to decrease risk by 24%, compared with men who ate two-and-a-half servings or less.
"Our findings suggest that tomatoes may be important in prostate cancer prevention," said Vanessa Er, from the School of Social and Community Medicine at Bristol University.
"However, further studies need to be conducted to confirm our findings, especially through human [clinical] trials.
"Men should still eat a wide variety of fruits and vegetables, maintain a healthy weight and stay active."
The cancer-fighting properties of tomatoes are thought to be due to lycopene, an antioxidant which can protect against DNA and cell damage.
The researchers also looked at two other dietary components linked with prostate cancer risk - selenium, found in flour-based foods such as bread and pasta, and calcium, found in dairy products such as milk and cheese.
Men who had optimal intake of these three dietary components had a lower risk of prostate cancer, they said.
Commenting on the study, Dr Iain Frame of Prostate Cancer UK said there was not yet enough evidence to make concrete recommendations on which specific foods men should eat to reduce their risk of prostate cancer.
"What we do know is that men shouldn't rely too heavily on one type of food, such as tomatoes," he said.
"A healthy, balanced diet with plenty of fresh fruit and vegetables, together with regular exercise is by far the best option."
Tom Stansfeld of Cancer Research UK added: "While eating foods rich in lycopene - such as tomatoes - or selenium may be associated with a reduction in the risk of prostate cancer, this has not been proven, and this study can't confirm whether there is a link between diet and prostate cancer risk.
"Diet and cancer prevention is a complex issue with few black and white answers; we encourage everyone to eat a balanced diet which is high in fruit and vegetables and low in red and processed meat, fat and salt."
The research, published in the journal Cancer Epidemiology, Biomarkers & Prevention, was carried out in collaboration with the Universities of Cambridge and Oxford.
Eating tomatoes may lower the risk of prostate cancer, research suggests.