Doctors led by Paolo Boffetta at the Mount Sinai Medical Center, New York, studied eight years of data between cancer risk and food, involving 470,000 volunteers
Between 1992 and 2000, more than 30,000 of the participants were diagnosed with cancer.
Boffetta's team found that high consumption of fruit and vegetables had little effect against cancer.
While researchers found some benefit against cancer, it was much smaller than previously thought.
The UN's World Health Organisation (WHO) issued a recommendation in 1990 suggesting that five servings of fruit and vegetables per day helped prevent cancer and other diseases.
"Worldwide, low intake of fruits and vegetables is estimated to cause about 19 per cent of gastrointestinal cancer, about 31 per cent of ischaemic heart disease and 11 per cent stroke," the WHO says on its website.
The new study appears online in the Journal of the National Cancer Institute, published by Britain's Oxford University Press.
