Red meat has long been cast as a bad player in heart disease and diabetes. But a new analysis from Harvard suggests that processed red meat - think bacon, salami, and hot dogs - may be the true dietary villain.

Renata Micha of the Harvard School of Public Health and her colleagues systematically reviewed more than 1,500 studies about the relationship between red meat, processed meat, and total meat consumption and heart disease, stroke, and diabetes. They selected 20 studies involving more than 1.2 million participants from 10 countries who were followed for up to 18 years. More than 23,000 people developed heart disease, more than 2,200 had strokes, and more than 10,000 had diabetes.

Pooling the study results, the researchers found that eating unprocessed red meat was not associated with heart disease or diabetes. But people who ate at least one serving a day of processed red meat - one hot dog or two deli slices - had a 42 percent higher risk of heart disease and a 19 percent higher risk of diabetes than people who did not eat processed red meat.

Total consumption of processed and unprocessed meat fell in between, with a 12 percent increased risk of diabetes compared to non-meat eaters. Results for heart disease were not conclusive. Neither kind of meat was tied to stroke, but because only 3 of the 20 studies looked at stroke, the sample was too small to draw statistically valid conclusions, the authors said.

Recommendations to cut down on red meat usually focus on the fat and cholesterol they contain, which can clog coronary arteries. But both processed and unprocessed meat contain similar amounts, the researchers found. People who ate the two kinds of meats were alike when it came to smoking, exercise, and other lifestyle factors.

The researchers say the salt and preservatives found in processed meat may account for the difference. Some processed meat has four times the salt that unprocessed meat has, and salt is a known contributor to high blood pressure, which can cause heart disease. Processed meat preservatives such as nitrates have been linked to lowered glucose tolerance, which is a factor in diabetes.

The American Meat Institute Foundation took issue with the study. “At best, this hypothesis merits further study. It is certainly no reason for dietary changes,” James H. Hodges, the trade group’s president, said in an e-mailed statement. “The body of evidence clearly demonstrates that processed meat is a healthy part of a balanced diet. Meat contains protein, amino acids and essential nutrients like iron and zinc that are the keys to good health.”

The Harvard analysis, published online today in the journal Circulation, doesn’t prove cause and effect between processed meat and these diseases, but it does make a compelling argument for studying processed and unprocessed meat separately. And unprocessed meat isn’t off the hook, having been linked in other research to higher rates of colon cancer.

“People should not use this finding as an excuse to eat all the unprocessed meat you like,” Micha, a research fellow in epidemiology, said in an interview. “We know fruits, vegetables, whole grains, and fish are associated with lower risk. People should put more emphasis on increasing foods in their diet that are shown to be protective.”

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Posted by Elizabeth Cooney
Harvard University