More than a third of cancers are caused by simple, preventable factors including insufficient exercise and poor diet, according to the most comprehensive international scientific study carried out to date.

In a series of recommendations that could hurt the food and restaurant sectors, it advises people to avoid dietary supplements, processed meats and junk food and even to limit their intake of fruit juices.

The findings, co-ordinated by the World Cancer Research Fund and drawing on the skills of 21 leading experts over the past six years, represent the most systematic effort yet to analyse and draw practical recommendations from 7,000 detailed scientific studies.