You can add genetically engineered, purple tomatoes to the list of cancer-fighting foods.

British researchers engineered the fruit to contain nutrients more commonly seen in dark berries, which have been shown to lower the risk of cancer, heart disease and some neurological diseases, Reuters reported.

For the study, cancer-prone mice fed the fruit lived an average of 40 days longer than animals on a standard diet.

"The effect was much bigger than we had expected," Cathie Martin, a plant biologist, said in a news release. "It is enormously encouraging to believe that by changing diet, or specific components in the diet, you can improve health in animals and possibly humans.”

Researchers focused on anthocyanins, a type of antioxidant found in berries such as blackberries and blackcurrants.

The researchers said trials in humans are still a long way off.

The findings are published in the journal Nature Biotechnology.

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