What people eat and how fast they grow are both significant causes of cancer, but many Americans still incorrectly believe that factors such as pesticides on food are bigger causes, experts reported today.
The American Institute for Cancer Research has released a survey of 1000 US adults that show most do not understand these risks. Only 38 per cent knew of the link between cured and processed meats and cancer, 49 per cent knew that diets low in fruits and vegetables raised the risk of cancer and 46 per cent knew that obesity was a well-documented risk.
But 71 per cent thought that pesticide residue on produce was a cause - something that has never been shown; 56 per cent thought stress causes cancer, again not proven; and 49 per cent believed hormones in beef cause cancer.
"Americans are increasingly likely to attribute cancer to factors over which they have no control, and for which no proven links to the disease exist," the report reads.
"This reflects an 'everything causes cancer' mindset," it adds.
Breastfeeding reduces the risk of cancer for mother and child, and tall people have a higher risk of cancer than shorter people, the report found.
"We need to think about cancer as the product of many long-term influences, not as something that 'just happens,'" Dr Walter Willett, a nutrition expert at the Harvard School of Public Health in Massachusetts, told a news conference.
The report, released jointly by the World Cancer Research Fund and the American Institute for Cancer Research, is the result of five years of study by nine teams of scientists.
They reviewed 7000 studies on diet, exercise, weight and cancer.
Most of what they recommended is in line with what health experts, including governments and the World Health Organisation, have long been advising - that diets based on fruits, vegetables and whole grains and that go easy on red meats, dairy products and fats protect against heart disease, diabetes and cancer.
They found evidence that factors such as hormones that cause the body to grow quickly may be involved in some cancers.
"We found that tallness is also probably linked to increased risk for ovarian, pancreatic and pre-menopausal cancer as well," said Dr Willett. He stressed that tall people are not destined to get cancer but should take care to maintain healthy habits.
The groups make keeping a healthy weight their No. 1 recommendation to reduce the risk of cancer.
"Be as lean as possible within the normal range of body weight," the 400-page report reads. That means keeping a body mass index, they said, of between 21 and 23. BMI is a calculation of height to weight, and the normal range is usually considered to be 18 to 25, with anything over 25 being overweight.
Exercise is also key.
"Be physically active as part of everyday life," is the second of 10 recommendations made by the expert panel. The recommendations also include eating mostly plant foods, such as fruits, vegetables and grains, avoiding calorie-dense foods such as sugary drinks, and limiting red meat, alcohol and salt.
The meat industry quickly denounced the report.
"WCRF's conclusions are extreme, unfounded and out of step with dietary guidelines," said American Meat Institute Foundation Vice President of Scientific Affairs Randy Huffman.