A rat-feeding study commissioned by Impossible Foods suggested the Impossible Burger’s key ingredient — genetically engineered soy leghemoglobin — caused the rats to develop unexplained changes in weight gain, changes in the blood that can indicate the onset of inflammation or kidney disease, and possible signs of anemia.

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.”

https://childrenshealthdefense.org/defender/impossible-burger-gmos-soy-leghemoglobin/?