They say "blood is thicker than water," but what about soy leghemoglobin?

The Center for Food Safety, an advocacy group that promotes "organic, ecological and sustainable alternatives" to industrial food processing, is suing the Food and Drug Administration in an effort to have the agency require more testing of the additive that makes Impossible Burgers appear to "bleed."

Soy leghemoglobin, or heme for short, is what Impossible Foods describes as the "magic ingredient" in its plant-based burgers. It’s what give the meatless burgers their juicy appearance akin to traditional beef burgers. Impossible’s heme is made using yeast genetically engineered with a gene from soybean plant roots, according to the company. But heme is naturally found in all animals and plants.

Soy leghemoglobin, or heme for short, is what Impossible Foods describes as the "magic ingredient" in its plant-based burgers. (Impossible Foods)

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In 2019, the FDA said heme doesn’t require the same certification process as color additives in food, agreeing with Impossible Foods that "there is a reasonable certainty of no harm from this use of soy leghemoglobin as a color additive."

However, the Center for Food Safety wrote in a court filing last week that Impossible Foods didn’t provide enough data to the FDA to prove that its heme is safe. The group also alleged the FDA "failed to properly respond" to its objections to heme approval.   

Bill Freese, science policy analyst at the Center for Food Safety, said in a written statement that a short-term study in rats showed some "troubling" possible effects from eating the modified heme.

"FDA approved soy leghemoglobin even though it conducted none of the long-term animal studies that are needed to determine whether or not it harms human health," Freese said.

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An FDA spokesperson said the agency does not comment on ongoing litigation.

Impossible Foods also declined to comment on the lawsuit. But a company spokesperson said in an email that it "puts health and safety first, and we meet or exceed all pertinent food-safety regulations."

"Impossible has worked closely with the FDA, the nation’s food-safety guardian, and has shared both extensive test data and commercial plans with the government body," the spokesperson wrote.

Impossible Foods further called the Center for Food Safety "an anti-GMO, anti-science organization that has been spreading lies about Impossible Foods for years."

The FDA has said that "there is a reasonable certainty of no harm from this use of soy leghemoglobin as a color additive." (Impossible Foods)

Impossible’s products are widely available at nearly 17,000 supermarkets, and the company has partnered with restaurant chains like Burger King to offer its meatless burgers across the country, Fox Business has reported.

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The Impossible spokesperson also said the company’s products have "undergone rigorous safety testing and meet or exceed all relevant federal requirements."

"We’ve gone above and beyond all regulatory requirements," the spokesperson added.