Over 40% of breast and bowel cancer cases in rich countries are preventable through diet, physical activity and weight control alone, experts say.
Globally, each year there are millions of these preventable cancer cases, the World Cancer Research Fund estimates.
Its report makes recommendations for “clean living” policies.
According to the report, about a third of the 12 most common cancers in high-income countries and about a quarter in lower income countries could be prevented through diet, exercise and weight control.
This include cancers of the throat, lung and bowel.
The figures do not take into account the impact of smoking, which alone accounts for about a third of cancers.
The panel of 23 experts who compiled the report say urgent action is needed to avert a crisis, with cancer rates set to increase.
Professor Martin Wiseman, project director, said: “We are expecting a substantial increase in cancer rates with the ageing population, obesity rates soaring, and with people becoming less active and increasingly consuming highly processed and energy dense foods and drinks. The good news is that this is not inevitable.”
Panel chair Professor Sir Michael Marmot said: “This report shows that by making relatively straightforward changes, we could significantly reduce the number of cancer cases around the world.”
The report says all sections of society “from governments to households” should make public health, and cancer prevention in particular, a higher priority.
Among the 48 recommendations is the advice for schools and workplaces to actively encourage physical activity and ban unhealthy food.
Governments should require widespread walking and cycling routes to encourage physical activity.
And the people who do the weekly food shopping for their family should check food labels to make sure the food they buy is healthy.
Professor Mike Richards, National Clinical Director for Cancer, said: “The evidence linking diet, physical activity, obesity and cancer has become stronger over the last decade and this report can play a part in people adopting healthier lifestyles.
“After not smoking, it is clear that diet, physical activity and weight are the most important things people can do to reduce their cancer risk.”
Major step forward
Dr Francesco Branca, Head of Nutrition at the World Health Organization, called the report a major step forward in understanding how policies and actions can help prevent cancer and other chronic diseases.
He said: “The recommendations will inspire policy-makers and decision-takers to act in a way that will play an important role in the fight against cancer.”
Richard Davidson, of the charity Cancer Research UK said around 13,000 cancer cases in the UK were linked to being overweight or obese, and even more were linked to poor diet, drinking too much alcohol and not doing enough exercise.
He said: “Doing nothing could be disastrous.
“There is no magic bullet, no one single fix to the problem. If we are to tackle the situation we need individuals, business and government to work together to encourage healthy lifestyles by promoting things like cycle lanes and food labelling.” BBC News