Excess body fat increases a person's risk of developing cancer, according to a new report by the American Institute for Cancer Research and the World Cancer Research Fund.

The report, called Food, Nutrition, Physical Activity, and the Prevention of Cancer: A Global Perspective, urges people to stay at a healthy weight, which means having a body mass index (or BMI, a ratio of weight to height) between 18.5 and 24.9. And it recommends regular physical activity as a way to control weight.

"The recommendation reflects what the science is telling us today," says W. Phillip T. James, MD, DSc, a member of the panel that wrote the report. "Even small amounts of excess fat, especially if carried at the waist, increase risk."

The report also makes recommendations for eating more healthfully to reduce cancer risk. It says people should eat mostly foods from plants, limit red meat and alcohol, and avoid processed meats like bacon, sausage, and lunchmeat.

This new report confirms what the American Cancer Society has been telling the public for years, says Colleen Doyle, MS, RD, American Cancer Society director of nutrition and physical activity.

"These recommendations are consistent with the American Cancer Society's 2006 update of its Nutrition and Physical Activity Guidelines for Cancer Prevention, as well as the Society's 2006 Guide to Informed Choices for Cancer Survivors," she says. "There is no question that if you do not smoke, the most important lifestyle goal to work toward to reduce your cancer risk is to maintain a healthy weight."

ACS guidelines recommend eating a diet rich in plant-based foods, and limiting alcohol, red meat and processed meats. They also call for people to get at least 30 minutes of physical activity on 5 or more days per week.

"People should try to keep their Body Mass Index between 18.5 and 24.9, and if you start to see it increase -- even if you are still within that healthy weight range -- you should limit the amount of calories you consume and increase your activity level," says Doyle. "Being physically active and eating a healthy diet that emphasizes vegetables, fruits and whole grains are also important for reducing cancer risk, both in a direct way and indirectly, by helping to control weight."

The newly published report also says the strongest evidence on methods of food preservation, processing, and preparation shows that salt and salt-preserved foods are probably a cause of stomach cancer, and that foods contaminated with aflatoxins are a cause of liver cancer.

The report includes a review and evaluation of an estimated 7,000 pieces of research on diet, physical activity and weight management and their effect on risk for 17 different types of cancer.