Harvard researchers come up with a new version of an old song: eating ‘processed’ meats—bacon, sausage and deli meats—causes diabetes. But they ignore the same old reason why.

The consumption of processed red meat is associated with incident type 2 diabetes, according to a new study published online last week in the journal Diabetes Care.

Martin Lajous, D.Sc., from the Harvard School of Public Health in Boston, and colleagues evaluated the association of processed and unprocessed red meat and incident type 2 diabetes in a prospective study of 66,118 French women. Dietary information was collected via validated questionnaires and adjustments were made for a number of key variables, including the intake of calories, fatty acids, carbohydrates, coffee, fiber and fruits and vegetables.

Lajous identified new 1,369 cases of diabetes between 1993 and 2007 and observed a significant association between processed meat intake and incident diabetes when comparing the highest category of processed meat intake (five or more servings a week, with a median consumption of an ounce-and-a-half a day), to the lowest category (less than one serving a week, with a median consumption of five grams a day).

No association was found between eating unprocessed red meat and diabetes.

Now, this isn’t the first time researchers affiliated with the Harvard School of Public Health have gone public with a headline suggesting “processed meat linked to diabetes,” as well as heart disease.

In May 2010, HSPH researchers released a review of some 1,600 medical studies, titled, “Eating Processed Meats, but Not Unprocessed Red Meats, May Raise Risk of Heart Disease and Diabetes.” That review claimed that eating bacon, sausage or processed deli meats was associated with a 42% higher risk of heart disease and a 19 percent higher risk of type 2 diabetes, although no higher risk of heart disease or diabetes from eating unprocessed beef, pork, or lamb.

In the earlier review, as well as in the study of French women’s health status, the Harvard researchers defined processed meat as any meat preserved by smoking, curing or salting or with the addition of chemical preservatives.

Cause-and-effect

Now let’s get to the meat of the matter.

In any associational study, researchers try to link a certain behavior with an outcome. In doing so, they attempt to rule out variables that could affect the integrity of the data, such as prior medical conditions, differences in age, sex, health status, etc.

Then, when they can show a strong association, they posit a theoretical cause-and-effect for why the behavior—in this case, eating processed meats—led to the outcome: an increased risk of developing diabetes.

For heart disease, it might seem obvious that eating processed meats would increase one’s intake of saturated fats and cholesterol, which would explain the greater risk for heart disease. But that would be wrong.

“When we looked at average nutrients in unprocessed red meats and processed meats,” Renata Micha, a research fellow in the HSPH department of epidemiology and the lead researcher in the 2010 study, “we found that they contained similar average amounts of saturated fat and cholesterol.”

So the “too much fat and cholesterol” theory’s out.

What did Micha, et al, turn to next? Nitrates.

“In animal studies, nitrate preservatives can reduce glucose tolerance, which could increase risk of diabetes,” Micha concluded.

Is that correct? Well, sodium nitrate is a salt compound that is an effective preservative when added to cured meats. But it’s a naturally occurring mineral present in all kinds of vegetables, fruits and grains. And yes, sodium nitrate is converted in the body to sodium nitrite. But any time we eat fruits, vegetables or grains, the body produces sodium nitrite, so if sodium nitrite’s a problem, we’d have to back away from the Meatless Mondays theme—substituting “wholesome” fruits and veggies for awful red meat—that Harvard’s public health researchers love to flog as the answer to both the nutritional and ecological challenges inherent in our modern lifestyles.

So what’s the answer? What causes people eating processed meats to increase their risk of diabetes?

I’m going to suggest an obvious answer, but it’s not one that the geniuses at Harvard would likely accept: It’s what’s eaten with the meat that causes the problem.

Think about it. Who eats deli meat or hotdogs by themselves? Yeah, maybe some toddlers like to finger food their way through a few hot dog slices or a piece of sliced ham. But for the adult population, we’re eating such foods as part of a sandwich, between two slices of bread, or in a bun or on top of crackers as a snack, right?

And what’s the common ingredient in all those foods? These days, it’s high fructose corn syrup, or something similar: A high glycemic index carbohydrate—not to mention the white bread and white flour itself—that regularly and effectively spikes the blood glucose levels even in the healthiest of people.

What happens when blood glucose levels become chronically elevated? The body’s ability to properly process all that sugar is compromised, a condition known clinically as diabetes.

Why else would eating unprocessed meats, which contain the same amounts of fat and cholesterol, remember, have no effect on the development of diabetes? It’s not the nitrates—those are present in significant quantities in fruits and vegetables, and anyone wearing a Harvard School of Public Health blazer would NEVER cast aspersions on those foods.

It’s the bread, baby. Face it: All that white bread, all that HFCS, all those refined carbs—that’s the problem.

Cut out those foods, and not only would we effectively diminish the risk of diabetes, we’d deal an effective blow against the ongoing epidemic of obesity.

And guess what’s the No. 1 risk factor for development of diabetes? That’s right. Being overweight.

The opinions expressed in this commentary are solely those of Dan Murphy, a veteran food-industry journalist and commentator.