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.