Rats fed GM yeast-derived protein soy leghemoglobin – the burger’s key ingredient – developed signs of toxicity. Report by Claire Robinson and Dr Michael Antoniou.
The Impossible Burger is a plant-based burger, the key ingredient of which is a protein called soy leghemoglobin (SLH for short), derived from genetically modified (GM) yeast. It's already being sold in restaurants and supermarkets in the US. In 2019 the manufacturing company, Impossible Foods, applied for permission to market the burger in the EU and the UK. However, the results of a rat feeding study commissioned by Impossible Foods and carried out with SLH suggest that the burger may not be safe to eat. SLH is the substance that gives the burger its meaty taste and makes it appear to bleed like meat when cut. The US Food and Drug Administration (FDA) initially refused to sign off on the safety of SLH when first approached by the company. The rat feeding study results suggest that the agency’s concerns were justified. Rats fed the GM yeast-derived SLH developed unexplained changes in weight gain, changes in the blood that can indicate the onset of inflammation or kidney disease, and possible signs of anaemia.
2015: FDA says SLH safety not proven
The company maintains that SLH is safe to eat.[1] It wanted the US Food and Drug Administration to agree with its self-declared conclusion that SLH is “GRAS” (Generally Recognized As Safe), providing reassurance for consumers. But in 2015, in response to Impossible Foods’ first application, the FDA refused to agree that the substance was safe. It responded with tough questions for the company, as revealed in documents obtained under a Freedom of Information request.[2] The FDA was concerned that SLH has never been consumed by humans and may be an allergen. The agency pointed out that the safety information submitted by Impossible Foods was not specific enough: “Although proteins are a part of the human food supply, not all proteins are safe. Information addressing the safe use of modified soy protein does not adequately address safe use of soybean leghemoglobin protein from the roots of the soybean plant in food.”[2] The FDA concluded, “FDA believes that the arguments presented, individually and collectively, do not establish the safety of SLH for consumption, nor do they point to a general recognition of safety.”[2]
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