According to the World Cancer Research Fund (WCRF), four out of ten people (41%) did not know that there is a link between what they eat and the disease.
The poll of 2,000 people found that one in three people knew that eating processed meat increased their cancer risk, but 44% were unaware that being overweight was another risk factor.
However, 42% did know that not taking enough exercise or being physically active increased their risk of cancer.
Research shows that maintaining a healthy weight, which can be achieved through a balanced diet and regular exercise, reduces the risk of six types of cancer including bowel cancer and postmenopausal breast cancer.
Lisa Cooney, head of education for the WCRF, said: 'These results show that there are still millions of people in Britain who are unaware of how they can take simple steps to reduce their cancer risk and are not in a position to make informed lifestyle choices.'
However, the results do show that awareness is improving, with more people saying they knew of the link between diet and exercise than in a similar survey in 2007.