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A major international report warns that medical evidence is stronger than ever that excess weight increases a person's risk for a number of cancers.

"If you're already a bit fat, don't get any fatter, do not put on any more weight," said Dr. Phillip James of the International Obesity Task Force.

 by the American Institute for Cancer Research and the World Cancer Research Fund says carrying excess body fat boosts the risk for cancer of the colon, kidney, esophagus, pancreas, and endometrium, as well as breast cancer in post-menopausal women.

"This report is optimistic because unlike what I was taught at medical school, there is a lot we can do to reduce our risk of cancer," said Dr. Walter Willett of the Harvard School of Public Health.

There is also convincing evidence linking consumption of alcohol, red meat and processed meat to elevated cancer risk, the report concludes.

"This report is a real milestone in the fight against cancer, because its recommendations represent the most definitive advice on preventing cancer that has ever been available anywhere in the world," said Prof. Martin Wiseman, project director of the report.

To avoid excess weight gain, the report recommends:

• Limiting intake of high-fat and sugar-rich foods that are low in fibre, including most fast food.
• Limiting intake of cooked red meat to about 500 grams (1.1 lbs) per week.
• Avoiding completely bacon, ham, sausage and luncheon meats
• Limiting alcohol to no more than two drinks a day for men and one drink a day for women.
• Limiting consumption of salt
• Eating mostly foods of plant origin
• Being physically active every day
• Breastfeeding

But the most important recommendation of all is to be as lean as possible within the normal range of body weight. A BMI (body mass index) of between 18.5 and 25 is generally regarded as "healthy", but the report recommends that an ideal BMI is between 21 and 23.

The  cancer risk increases as people head towards the 25 mark, so everyone should try to be as close to the lower end as possible, the report says.

"We are recommending that people aim to be as lean as possible within the healthy range, and that they avoid weight gain throughout adulthood," said Prof. Sir Michael Marmot, chair of the panel.

"This might sound difficult, but this is what the science is telling us more clearly than ever before. The fact is that putting on weight can increase your cancer risk, even if you are still within the healthy range."

The report says meals should be planned around non-starchy vegetables and fruits, served with such protein sources as poultry, fish or eggs on the side.

"We are recommending five servings or more of vegetables and fruit daily because, like physical activity, they pack a double whammy against cancer,'' panel member Dr. Phillip James said. Fruits and vegetables help reduce cancer risk on their own. And, because they are low-calorie, they help maintain a healthy weight, he noted.

The experts also found convincing evidence that alcohol consumption is linked to cancer of the mouth, pharynx, larynx and esophagus. It is also implicated in colorectal cancer among men and pre-and post-menopausal cancer in women. Drinking alcohol is a probable cause of liver cancer and colorectal cancer in women, they say.

But with many studies concluding that small amounts of alcohol protect against heart disease, the panel decided to recommend limiting rather than avoiding alcohol.

The report is also the first to urge breastfeeding as a way to protect against cancer, arguing that it may reduce breast cancer in the mother and prevent obesity in the child.

The 517-page report, released today in Washington, is the result of the largest-ever study into lifestyle and cancer. There is no new research involved in this document. Instead, nine independent teams of scientists from around the world and hundreds of peer reviewers reviewed 7,000 existing studies over five years.

The experts note that two-thirds of cancer cases are not thought to be related to lifestyle, and there is little people can do to prevent the disease in these cases.

But more than three million of the 10 million cases of cancer that are diagnosed around the world every year could be prevented if the recommendations were followed, say panel members.

With a report from CTV medical specialist Avis Favaro and producer Elizabeth St. Philip