LONDON (Reuters) - A purple tomato genetically engineered to contain nutrients more commonly seen in dark berries helped prevent cancer in mice, British researchers said on Sunday.

Tomatoes of different colors are seen in a bowl in Medford, Massachusetts July 17, 2008. REUTERS/Brian Snyder

The finding, published in the journal Nature Biotechnology, bolsters the idea that plants can be genetically modified to make people healthier.

Cancer-prone mice fed the modified fruit lived significantly longer than animals fed a standard diet with and without regular tomatoes, Cathie Martin and colleagues at the government-funded John Innes Center in Britain reported.

“The effect was much bigger than we had expected,” said Martin, a plant biologist.

The study focused on anthocyanins, a type of antioxidant found in berries such as blackberries and blackcurrants that have been shown to lower risk of cancer, heart disease and some neurological diseases.

While an easy health boost, many people do not eat enough of these fruits, the researchers said.

Using genes that help color the snapdragon flower, the researchers discovered they could get the tomatoes to make anthocyanins -- turning the tomato purple in the process.

Mice genetically engineered to develop cancer lived an average of 182 days when they were fed the purple tomatoes, compared to 142 days for animals on the standard diet.

“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,” Martin said in a telephone interview.

The researchers cautioned that trials in humans are a long way off and the next step is to investigate how the antioxidants actually affect the tumors to promote better health.

But the findings do bolster research suggesting that people can significantly improve their health by making simple changes to the daily diet, other researchers said.

“It’s exciting to see new techniques that could potentially make healthy foods even better for us,” said Dr. Lara Bennett, science information officer at Cancer Research UK.

“But it’s too early to say whether anthocyanins obtained through diet could help to reduce the risk of cancer.”