Exercise and diet play a major role in cancer prevention, and should be encouraged through infrastructure and food pricing policies, the report says. (Ryan Jackson/Canadian Press)

An ounce of prevention is worth more than a pound of cure when it comes to cancer, according to an exhaustive international report.

The report by the American Institute for Cancer Research and the World Cancer Research Fund was released Thursday in London, England.

It calls on governments to legislate healthy living, such as:

• Mandate walking and cycling paths that encourage physical activity.
• Support policies for better-priced, healthier food choices for consumers, such as reformulating processed foods to have less sugar, salt and fat.
• Ban ads for sugary drinks and unhealthy foods aimed at children.
• Require schools to provide built-in exercise opportunities for children.

After reviewing 7,000 studies, the report's authors concluded that in countries like Canada, one-third of cancer cases could be eliminated if people ate less fat and sugar, exercised more and reduced obesity.

Another one-third of cancers are due to smoking.

"We should have cancer risk and health as a main value in considering and reconsidering the policies that we already have in place," said Tim Byers, a professor in the school of public health at the University of Colorado and one of the 23 cancer experts who wrote the report.

The authors noted that individuals bear responsibility for health, but lifestyle changes can be difficult to achieve and maintain without support from other sectors of society.

"This is much more far-reaching than in the past, saying that we're recognizing that all of us may be relatively weak when it comes to individual efforts," said Kristan Aronson, a cancer epidemiologist at Queen's University who commented on the report.

"And [it says] governments should encourage healthy food — and discourage unhealthy food — through legislation and pricing. Oh my God, that's huge."

In Canada already, junk food including sugary drinks have been banned in many schools.

The report also included prevention estimates for many types of cancer throughout the world.

For example, eating healthy foods, keeping active and staying trim could prevent 75 per cent of esophageal cancer in the U.K., 52 per cent of endometrial cancer in Brazil and one-third of stomach cancers in China.

With files from the Canadian Press