Impossible Burger at Umami Burger
The veggie burger company said its burger is safe to eat.
REDWOOD CITY, Calif. – A week after closing a $75 million funding round, Impossible Foods, maker of the plant-based Impossible Burger, confronted questions about the safety of a key ingredient that makes the Impossible Burger possible — bioengineered soy leghemoglobin.

The Impossible Burger reportedly looks and tastes like conventional ground beef. But it gets its beef-like attributes from a molecule called heme, which is found in both plant and animal tissues. Impossible Foods found a way to produce heme using yeast cells into which scientists introduced a plant gene encoding a protein called soy leghemoglobin, which can be found in the roots of soy plants.

But it’s the soy leghemoglobin protein that has raised questions about the safety of Impossible Burgers. Impossible Foods is asking that the US Food and Drug Administration (FDA) grant Generally Recognized As Safe (GRAS) status to soy leghemoglobin. However, according to documents obtained from the FDA by the ETC Group, Friends of the Earth and Consumers Union, through a Freedom of Information Act request, revealed the agency’s concern that the ingredient may be an allergen.

“The FDA told Impossible Foods that its burger was not going to meet government safety standards, and the company admitted it didn’t know all of its constituents,” Jim Thomas of ETC Group said in a statement at the time. “Yet it sold it anyway to thousands of unwitting consumers. Responsible food companies don’t treat customers this way. Impossible Foods should pull the burgers from the market unless and until safety can be established by the FDA and apologize to those whose safety it may have risked.”

In a letter posted to the Impossible Foods website, company CEO Pat Brown fired back, saying the company intended to be “…the most open and transparent company in the world.” He added that “only a miniscule fraction” of foods and the molecules and ingredients they contain have been scientifically tested for safety.

“Although there was never a reason to suspect that soy leghemoglobin would pose any more risk than myoglobin, or any of the new proteins we encounter in our diet all the time, we started four years ago to do a deep scientific study of its safety, including any potential for toxicity or allergenicity,” Brown wrote. “The data we collected and our analyses were documented and reviewed by three independent food-safety experts in toxicology, allergenicity and yeast.”

Brown added that an expert panel unanimously concluded in 2014 that, based on all the evidence, that the soy leghemoglobin is generally recognized as safe for human consumption. Impossible Foods then submitted its findings to FDA for review.

“After submitting our GRAS determination, the FDA reviewed it, and had some questions,” Brown explained. “To address them, we conducted additional tests. And the tests turned out just as we expected: no adverse effects in rats consuming leghemoglobin every day for a month at levels more than 200 times what an average American would consume if all the ground beef in their diet were the Impossible Burger, and very low risk of allergenicity. A panel of the world’s leading experts in food safety and allergenicity has reviewed the new data, as well as the data originally submitted. The expert panel has again unanimously concluded that soy leghemoglobin is safe; it is GRAS.”