FRIDAY, March 5 (HealthDay News) -- Conventional wisdom has dictated that fat from red meat is a risk factor for heart disease, but a new analysis from Harvard researchers finds it's eating processed meat -- not unprocessed red meat -- that increases the risk for heart disease and even diabetes.
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The term "processed meat" refers to any meat preserved by smoking, curing or salting or with the addition of chemical preservatives. The researchers defined "red meat" as unprocessed meats such as beef, hamburger, lamb and pork.
"To lower risk of heart attacks and diabetes, people should avoid eating too much processed meats -- for example, hot dogs, bacon, sausage or processed deli meats," said lead researcher Renata Micha, a research fellow at the Harvard School of Public Health. "Based on our findings, eating up to one serving per week would be associated with relatively small risk."
Micha was scheduled to present the finding Friday at an American Heart Association conference on cardiovascular disease in San Francisco.
For the study, Micha's team analyzed data from 20 studies that included more than 1.2 million participants. Among them, 23,889 had coronary heart disease, 2,280 had had a stroke and 10,797 had diabetes.
The researchers found that people who ate unprocessed red meat did not significantly increase their chances of developing heart disease or diabetes. However, eating processed meat was linked to an increased risk for the two conditions.
In fact, for every 50-gram (1.8-ounce) serving, the risk for heart disease jumped 42% and the risk for diabetes increased 19%.
Though neither unprocessed red meat nor processed meats were linked to an increased risk for stroke, the researchers pointed out that just three studies looked at the connection between eating meat and stroke, so the data was insufficient to draw a valid conclusion.
"When we looked at average nutrients in unprocessed meats and processed meats eaten in the U.S., we found that they contained similar amounts of saturated fat and cholesterol," Micha said. "In contrast, processed meats contained, on average, four times higher amounts of sodium and two times higher amounts of nitrate preservatives."
This suggests that salt and other preservatives, rather than fats, probably explain the higher risk for heart attacks and diabetes seen with processed meats, Micha said.
"Health effects of unprocessed red meats and processed meats should be separately considered," she said. "More research is needed into which factors in meats -- especially salt or other preservatives -- are most important for health effects."
Samantha Heller, a registered dietitian, clinical nutritionist and exercise physiologist in Fairfield, Conn., said that "scientists are looking into why processed meats are so hazardous to our health."
"They may never know the exact reason, but we do know that people should limit their consumption of foods such as bacon, hot dogs, salami and pepperoni to reduce the risk of chronic diseases," Heller said.
"In addition, studies show that eating unprocessed red meat does increase the risk for disease as well," she said. "A study of over 500,000 people found that people who ate the most both red and processed meats had a higher risk of mortality, cancer and cardiovascular disease than those who ate lesser amounts of these foods."
Both red and processed meat and other foods, such as butter and cheese, that are high in saturated fat have been linked to chronic disease, Heller said, adding that people should limit consumption of them as well.
"Going low- or no-fat with dairy products helps lower our intake of saturated fat," she said. "Choosing healthy protein sources -- such as white-meat poultry, low-mercury fish, soy, nuts and beans -- and focusing on moving in the direction of a more plant-based diet will help us all live longer, healthier lives."
Dr. Gregg Fonarow, a professor of cardiovascular medicine at the University of California, Los Angeles, said that "various studies have suggested that higher levels of consumption of red and processed meat is associated with higher risk of heart disease, stroke, diabetes, cancer and premature death."
However, the results have not always been consistent, and some earlier studies have suggested there may be differences in health risk between unprocessed red meat and processed meat, he said. More study is needed to verify the link and explore the mechanisms behind it, Fonarow said.
Although unprocessed red meat might not increase the risk for heart disease or diabetes, it might increase the risk for some cancers, according to a 2007 report from researchers at the U.S. National Cancer Institute.
They found elevated risks for colorectal and lung cancer with high consumption of both processed and unprocessed meats, along with borderline higher risks for advanced prostate cancer. High intake of red meat was also associated with an increased risk for esophageal and liver cancer and a borderline increased risk for laryngeal cancer. And high consumption of processed meat was linked to a borderline increased risk for bladder cancer and myeloma, a kind of bone cancer.
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SOURCES: Renata Micha, R.D., Ph.D., research fellow, Harvard School of Public Health, Boston; Samantha Heller, M.S., R.D., dietitian, nutritionist and exercise physiologist, Fairfield, Conn.; Gregg Fonarow, M.D., professor, cardiovascular medicine, University of California, Los Angeles; March 5, 2010, presentation, American Heart Association's Cardiovascular Disease Epidemiology and Prevention annual conference, San Francisco