People who eat lots of red meat may have a higher risk of some types of kidney cancer, suggests a large U.S. study.
Researchers found that middle-aged adults who ate the most red meat were 19 percent more likely to be diagnosed with kidney cancer than those who ate the least. A higher intake of chemicals found in grilled or barbecued meat was also linked to increased risk of the disease, they reported in the American Journal of Clinical Nutrition.
"Red meat is an important source for iron (and) it has protein," said Dr. Mohammed El-Faramawi, an epidemiologist from the University of North Texas Health Science Center in Fort Worth, who has studied diet and kidney cancer risks but wasn't involved in the new study.
"You should not stop eating red meat because there is an association between red meat and renal cancer," he told Reuters Health. Instead, eating a limited amount of meat while following dietary recommendations is a good idea, he said.
U.S. guidelines call for limiting high-fat foods including processed meat, and instead eating more lean meat and poultry, seafood and nuts.
Eating red meat in large amounts—even if it doesn't necessarily lead to kidney cancer—increases the risk of a host of health problems, such as plaque buildup in the arteries, El-Faramawi added.
Previous studies examining the link between red meat and kidney cancer arrived at mixed conclusions, according to Carrie Daniel, from the National Cancer Institute in Rockville, Maryland, and her colleagues.
To try to clear up that picture, they used data from a study of close to 500,000 U.S. adults age 50 and older, who were surveyed on their dietary habits, including meat consumption, and then followed for an average of nine years to track any new cancer diagnoses.
During that time, about 1,800 of them—less than half a percent—were diagnosed with kidney cancer.
On average, men in the study ate two or three ounces of red meat per day, compared to one or two ounces among women. Participants with the highest consumption of red meat—about four ounces per day—were 19 percent more likely to be diagnosed with kidney cancer than those who ate the smallest amount, less than one ounce per day.
That was after accounting for other aspects of diet and lifestyle that could have influenced cancer risks, such as age, race, fruit and vegetable consumption, smoking and drinking and other medical conditions including high blood pressure and diabetes.
When the researchers looked at the most common types of kidney cancers, they found that the association between red meat and cancer was stronger for so-called papillary cancers, but there was no effect for clear-cell kidney cancers.
People who ate the most well-done grilled and barbecued meat—and therefore had the highest exposure to carcinogenic chemicals that come out of the cooking process—also had an extra risk of kidney cancer compared to those who didn't cook much meat that way.
The study doesn't prove that eating red meat, or cooking it a certain way, causes kidney cancer. And, El-Faramawi pointed out, some people who eat lots of red meat won't develop cancer, while others that hardly eat any will.
Daniel and her colleagues said more research is needed to figure out why red meat may be linked to some types of kidney cancers but not others.
But for now, meat-related cooking chemicals "can be reduced by avoiding direct exposure of meat to an open flame or a hot metal surface, reducing the cooking time, and using a microwave oven to partially cook meat before exposing it to high temperatures," Daniel told Reuters Health in an email.
"Our findings," she concluded, "support the dietary recommendations for cancer prevention currently put forth by the American Cancer Society—limit intake of red and processed meats and prepare meat by cooking methods such as baking and broiling."