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.
Cancer is one of the largest and growing causes of mortality worldwide, responsible for almost 8m deaths a year, or 13 per cent of the total.
Professor Sir Michael Marmot, chairman of the panel, said: “A third of cancers are diet-related and largely preventable by things we can all do every day of our life through sensible eating and exercise.”
He said the findings reflected the best available knowledge from all published research, in contrast to reports on individual scientific studies that often provided contradictory information.
The recommendations largely mirror the best advice for preventing other diseases. The only exception was alcohol consumption, with cancer studies arguing for total avoidance but cardiovascular research suggesting moderate drinking may help.
Some of the findings reflect existing scientific understanding already widely disseminated, including recommendations from a previous study undertaken on the subject by the Research Fund in 1997, such as limiting the consumption of red meat,
However, Wednesday’s advice also contained new guidelines reflecting changes in understanding. These included the pivotal benefit of being at the lower end of the healthy weight range, with a body mass index of between 18.5 and 25.
It concludes that high doses of dietary supplements could be harmful, and a balanced diet should provide all the nutrients required. It stresses that children should be breastfed to limit the risk of obesity in later life, and breastfeeding reduces mothers’ risk of breast cancer.
It also found that tall people have a greater risk of cancer, which may be partly linked to their diet.
The study did not examine the evidence around the link between smoking and cancer, which Prof Marmot said was already well established.
He estimated that between half and two-thirds of all cancers were caused by environmental factors including diet, smoking and excess weight, while adding that the evidence on how far people could reduce their own risk of contracting cancer by changing their lifestyles was more limited.
David Shuker from the Open University, another author, stressed that cancer prevention measures should be applied throughout peoples’ lives and could have an effect even for those already with a higher risk. “Risk isn’t fate . . . There are simple, everyday changes that reduce your cancer risk.”
The Food and Drink Federation, the UK trade association, said it had worked hard to reformulate food, and added: “The secret of a healthy life is to enjoy a balanced diet, coupled with moderate amounts of exercise.”