The additive, called propionate, is actually a naturally occurring fatty acid produced in the gut. When it's used as an additive in processed foods, it helps prevent mold.
But in the new study, researchers found that feeding mice low doses of propionate gradually caused weight gain and resistance to the hormone insulin -- which, in humans, is a precursor to type 2 diabetes.
And when the researchers gave healthy adults a single propionate dose, it spurred a release of blood sugar-raising hormones -- and a subsequent surge in insulin.
None of that proves propionate-containing foods raise the odds of weight gain and diabetes, said senior researcher Dr. Gokhan Hotamisligil, a professor at the Harvard School of Public Health.
"The point is not to say this additive is 'bad,'" he stressed.
Instead, Hotamisligil said, his team is interested in understanding the effects -- good or bad -- of the various "molecules" humans consume in their diets.
"There's a scarcity of scientific evidence on a lot of the things we put in our bodies through food," he said. "Propionate is just one example."
Still, Hotamisligil said, the findings do raise an important question: "Could long-time consumption of propionate in humans be a contributing factor to obesity and diabetes?"
When it comes to processed foods, the concern is usually directed toward ingredients like added sugar, sodium and trans fats. But there's also a host of additives that, according to the U.S. Food and Drug Administration, are "generally recognized as safe."
Despite that "GRAS" status, though, there is typically little known about how those food additives might affect metabolism, according to Hotamisligil.
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