Sugary soda and other sweet treats are likely not the only foods to blame for the surge in diabetes across the U.S. New research out of Harvard University supports the theory that regular red meat consumption increases the risk of getting type 2 diabetes.

An average of just one 85-gram (three-ounce) serving of unprocessed red meat—such as a medium hamburger or a small pork chop—per day increased by 12 percent the chances a person would get type 2 diabetes over the course of a decade or two. And if the meat was processed—such as a hot dog or two slices of bacon—the risk increased to 32 percent, even though serving sizes were smaller.

The new study, published online August 10 in the American Journal of Clinical Nutrition, is not the first to find the link between red meat and diabetes risk. But it is the largest and one of the first to look separately at unprocessed and processed meats.

"On a gram-per-gram basis, unprocessed red meat is still better," says Frank Hu, a professor of nutrition and epidemiology at the Harvard School of Public Health and co-author of the new paper. "But unprocessed red meat is still associated with a significantly increased risk."

More than 8.5 percent of U.S. adults have been diagnosed with diabetes, and in some counties in the so-called "diabetes belt" in the South, the numbers exceed 11.2 percent. The rates are expected to keep climbing in the coming years.

Hu suggests that based on the analysis there is indeed a "disease burden that can be attributed to consumption of either processed or unprocessed red meat."

It's what's for dinner, for many
A U.S. adult consumes an average of more than 45 kilograms (100 pounds) of red meat a year. "There's no question that consumption of red meat is too high," Hu says, suggesting nuts, whole grains and low-fat dairy products as healthier alternatives. And diabetes is not the only reason to switch to lighter forms of protein. People who ate 113 grams (four ounces) of red meat a day are more likely to die from any cause over 10 years, according to a 2009 Archives of Internal Medicine study of half of a million people.

Of course, eating red meat for a week "is not going to give someone diabetes—we're talking about habitual consumption," Hu says. And for those uncertain about trading in a filet mignon for a fistful of almonds, the researchers behind the new paper also list poultry and fish as alternatives, although Hu cautions that other research also supports the move to a more plant-based diet.

"It really confirms what other studies have suggested," says Elizabeth Seaquist, director of the Center for Diabetes Research at the University of Minnesota, who was not involved in the new study. The new report analyzed health and dietary information from three large-scale cohort studies (the "Health Professionals Follow-Up Study," and the "Nurses' Health Study I and II"), which encompassed some 200,000 adults. It combined that data with previous studies for a meta-analysis that covered a total of 440,000 men and women who were followed for 10 years or more. 

Seaquist puts great confidence in the findings based on the study's sample size, but notes that as an epidemiological study like this one should, it "raises more hypotheses than gives us answers."

The additional incriminating evidence for this category of food seems to swing the pendulum away from refined carbohydrates as the only culprits in advancing diabetes. And the new paper "will heighten awareness of the potential for different dietary components to contribute to diabetes," Charles Burant, director of the Metabolomics and Obesity Center at the University of Michigan Medical School, who also was not involved in the new paper.

For people who have been following the research, however, "the findings are not particularly surprising," Hu says. In fact, despite the big play that sugars and other highly processed carbohydrates have gotten, red meat is actually "one of the most well-established dietary risk factors," he notes.

Size matters
One of the tricky aspects of lifestyle studies like this one is that unhealthful behaviors often go together, making it tough to tease them apart to see if one is having a larger effect than others. And in the studies, those who reported eating the most red meat also tended to have other risk factors for diabetes, such has having a higher body mass index (BMI), smoking and not getting much physical activity. "People who eat a lot of meats tend to gain more weight," Hu says.

So the new findings might be more "a reflection of poor dietary intake by people who eat meat," Burant says. Seaquist explains more plainly that perhaps "people who eat red meat end up eating French fries with it."

Burant is not convinced that red meats—or any other food category in particular—are to blame for diabetes. "My own personal bias is that it's not just what you eat but how much you eat," he says. As obesity is the largest known risk factor for developing type 2 diabetes, "calories are probably the primary driver for the risk for diabetes," Burant says. As a clinician, he says, he tells his patients who might be at risk for diabetes: "I don't care what you eat—just eat less of it."

But, after Hu and his colleagues adjusted their analysis to account for weight gain, they still saw a modest association between red meat and type 2 diabetes. That might mean that there are other factors at work independent of extra pounds, the researchers posit.

One theory is that the type of iron prevalent in red meat, known as heme iron, unlike forms of iron found in plants and nutritional supplements, is readily absorbed by the body and can in fact lead to iron overload. Studies have shown that too much iron can lead to oxidative stress and higher levels of inflammation, both of which can be precursors to diabetes. Seaquist cautions that plenty of people still need to make sure they get enough iron, but adds that, "there is a strong link to iron overload in the body and risk for diabetes."

Another reason for an increase in diabetes risk could be the types of saturated fats in red meat as well as the additives (such as nitrates and sodium) in processed food. But as Hu acknowledges, "it's very challenging to pinpoint the exact components of food that are responsible."

Many researchers are waiting for more evidence. "I don't think we can tell" yet whether red meat can be separated from overall weight gain as a factor for diabetes risk, Seaquist says. But, she notes, the fact that the study was so large and there was still a correlation between red meat consumption and diabetes risk after adjusting for BMI "makes me a little more concerned that maybe there really is something specific about red meat" that pushes the body toward diabetes.

In addition to looking to better understand the mechanisms at work in the body, Hu says, he will be keeping a close eye on other countries where diets are changing.

"It's very important to locate the effects of meat consumption on chronic disease risk in countries that are undergoing nutritional transitions," Hu says. But as in the U.S., the panoply of food and lifestyle choices that people make are difficult to tease apart.

In the meantime, Seaquist says, the best nutritional tactic is akin to good investing: diversify. "We need to watch our total calories," she says. But we also "need to have a broad range of foods in our diet"—especially fruits and vegetables, she says.