Diet experts urge move to poultry, fish and beans after results of long-term study.

A diet packed with burgers, sausage and steak boosts the risk of developing colon or rectal cancer, a study confirms, lending weight to nutritionists' call for a switch to healthier alternatives.

A plethora of previous reports have connected red meat and colorectal cancer, which is the third most common cause of cancer-related deaths in the United States. But some of the results are inconsistent, and few studies have examined participants' diet over long periods, during which eating habits can change.

The new study is one of the most comprehensive so far. Michael Thun of the American Cancer Society (ACS) in Atlanta , Georgia , and his team collected information on the meat-eating behaviour of nearly 150,000 people in the United States in 1982 and in 1992. They divided them into three groups according to the amount of meat they ate, and noted which patients had developed colorectal cancers by 2001.

The group that ate the most processed meat had twice the risk of developing colon cancer compared with those who ate the least, the team found; and those who ate most red meat had a 40% higher risk of getting rectal cancer.

By contrast, those who ate the highest quantity of poultry or fish had a 20-30% lower risk of developing the diseases, the team reports in the Journal of the American Medical Association . This applied even when the researchers took into account other risk factors, such as being overweight, not taking exercise and not eating fruit and vegetables.

Meaty study

The case against red meat still needs back-up from other studies. But for now, people would be well advised to cut back their consumption of red and processed meat, says Marjorie McCullough, an author of the paper, also at the ACS. This might involve removing red meat from a few meals per week, she suggests, or choosing smaller portions.

Members of the high risk group ate around 55- 85 grams of red or processed meat each day, roughly equivalent to a medium sized burger. Red meat includes burgers, meatloaf, beef, liver and pork. Processed meat includes bacon, sausage, hot dogs, ham, salami and lunch meat.

Researchers are not yet clear which ingredient of meat might trigger cancer. Possible culprits include iron, toxins formed during cooking or the nitrates and nitrites used to preserve processed meats.

Replacing red meat with some combination of fish, poultry, nuts and beans will probably help cut your risk of colorectal cancer, says nutritional expert Walter Willett of the Harvard School of Public Health in Boston . "It will have some beneficial effects for reducing heart disease as well," he adds.

"Fortunately, substituting pistachio-encrusted salmon and gingered brown basmati pilaf for roast beef with mashed potatoes and gravy is not a culinary sacrifice," Willett writes in an editorial that accompanies the study.