The most comprehensive study ever undertaken on the association between cancer and obesity concludes that excess body fat triggers many types of the disease, as does the consumption of even moderate amounts of alcohol, red meats and processed meats.
The study, released yesterday in Washington by the American Institute for Cancer Research and the World Cancer Research Fund, shows food, nutrition and lack of exercise appear critical in causing many cases - perhaps up to one-third - of all cancers. That means controllable lifestyle factors associated with diet and weight have about the same impact on cancer rates as smoking.
"The most striking finding in the report is that excess body fat increases risk for numerous cancers," said Phillip James, one of the study's authors and chairman of the British-based International Obesity Taskforce.
The international team of medical experts, which conducted an exhaustive, five-year review of more than 7,000 research papers that investigated whether food, nutrition or lack of physical exercise had an impact on cancer incidence, made 10 recommendations for preventing the disease. They include eating diets containing large quantities of vegetables and fruits and, most important, staying as thin as possible within the normal range of a person's body weight.
More Front Page Stories
"Cancer is preventable. There are changes you can make in your daily life that will reduce your chances of developing cancer," Dr. James said. "Let's get more vegetables, fruits. ... Let's get off our backsides, however and whenever we can."
Among the cancers convincingly linked to excess body fat, particularly if it is carried around the waist, are colon, kidney, pancreas, uterine, adenocarcinoma of the esophagus, and postmenopausal breast cancer.
The new research also made some unusual findings about cancer. One is that there is convincing evidence linking being tall to a higher risk of colorectal and postmenopausal breast cancer. Another is that an association exists between high birth weight and increased risk for premenopausal breast cancer - probably due to body fat.
Although many medical researchers have presented studies before linking cancer to weight and diet, the new study makes the case even more convincingly because it draws together most of the available evidence on the subject. The AICR published a previous study on cancer and body mass 10 years ago, and, at the time, the evidence was only strong enough to link it to uterine cancer - indicating how much scientific research has uncovered in the last decade.
"This report today is showing us that the evidence is becoming more and more clear about the relationship between how we live, what we eat, and our individual risk of developing cancer," said Heather Logan, a spokesperson for the Canadian Cancer Society in Toronto.
The cancer society has long advocated that Canadians do what they can - through diet, smoking cessation, and sensible sun exposure - to reduce the odds of developing the illness. Although not all cancers are caused by such lifestyle factors - others are due to genetics, environmental contaminants and as yet unknown factors - a significant portion appear to be.
Based on the findings, millions of cancer deaths in industrialized countries could be avoided if the public paid more attention to diet, exercise and weight. In Canada alone this year, about 160,000 people will be diagnosed with cancer and about 73,000 will die from the disease.
Given the association between excess weight and cancer, it is likely that many types of the disease linked to body fat will remain at elevated levels unless the public makes a major effort to lose weight. The study said the prevalence of overweight people doubled in many wealthy countries between 1990 and 2005.
Among the recommendations, the study threw cold water on the idea that people should try to prevent cancer by taking supplements, an approach that has been advanced by many in the health food industry. Except for a few isolated examples, such as the need for taking vitamin D, the study said people should get their nutrients through diet alone.
Although there is evidence that high-dose supplements can reduce some types of cancer, the study concluded that, for otherwise healthy people, "the best source of nourishment is foods and drinks, not dietary supplements."
For those who have had cancer, the study advises the best course is to follow the recommendations on weight, diet and exercise in the hopes of preventing further bouts of the disease.
