They were investigating the impact of lycopene – a bright red chemical found in tomatoes, peppers and water-melons.
A study of 1,031 men, published in the journal Neurology, showed those with the most lycopene in their bloodstream were the least likely to have a stroke.
The Stroke Association called for more research into why lycopene seemed to have this effect.
The levels of lycopene in the blood were assessed at the beginning of the study, which then followed the men for the next 12 years.
They were split into four groups based on the amount of lycopene in their blood. There were 25 strokes in the 258 men in the low lycopene group and 11 strokes out of the 259 men in the high lycopene group.
The study said the risk of stroke was cut by 55% by having a diet rich in lycopene.
Dr Jouni Karppi, from the University of Eastern Finland in Kuopio, said: “This study adds to the evidence that a diet high in fruits and vegetables is associated with a lower risk of stroke.
“The results support the recommendation that people get more than five servings of fruits and vegetables a day, which would likely lead to a major reduction in the number of strokes worldwide, according to previous research.”
He said lycopene acted as an antioxidant, reduced inflammation and prevented blood clotting.
Dr Clare Walton, from the Stroke Association, said: “This study suggests that an antioxidant which is found in foods such as tomatoes, red peppers and water-melons could help to lower our stroke risk.
“However, this research should not deter people from eating other types of fruit and vegetables as they all have health benefits and remain an important part of a staple diet.
“More research is needed to help us understand why the particular antioxidant found in vegetables such as tomatoes could help keep our stroke risk down.”