At least one variety of transgenic food, Starlink corn, has not been approved for human consumption. This is not because it has been shown to be dangerous, but only because it has not yet been shown to be safe.
The transgenic protein in Starlink corn, Cry9C, is meant to kill certain insects. It is one of the natural Bt toxins. For humans, it should be a nutrient like almost any other protein. But while most proteins are digested in the stomach within seconds or minutes, Cry9C is digested more slowly.
Neither laboratory animals nor human subjects have shown allergic sensitivity to Cry9C and its amino acid sequence is not similar to any other known allergen. However, because Cry9C is digested slowly, it is difficult to prove that it wouldn't be an allergen for somebody. So although it has not been shown to cause harm, the FDA refuses to allow it to be used except as animal feed. (Experiments with farm animals have shown that Cry9C is digested quickly in their alkaline stomachs.) Testing for safety to humans continues.
Someone should ask Dr. Billings how it can be that a food which is not required to be tested for safety is not allowed to be used for human food.