Last week was a momentous one for the future of genetically engineered foods, both in the U.S. and in Europe. On July 24, the U.S. Food and Drug Administration approved the Impossible Burger, an all-veggie burger that "bleeds" and sizzles just like meat. The burger's star ingredient — a protein called heme that renders blood red and helps make meat a carnivore's delight — was granted GRAS (generally recognized as safe) status. In 2015, the FDA had required that the $400 million Silicon Valley startup, Impossible Foods, demonstrate that their heme, made by genetically modified yeast, was safe. But across...