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.