Propylene glycol was once a common ingredient in soft moist cat food. According to the FDA "It was known for some time that propylene glycol caused Heinz Body formation in the red blood cells of cats (small clumps of proteins seen in the cells when viewed under the microscope), but it could not be shown to cause overt anemia or other clinical effects.
In the past, propylene glycol was frequently used as an ingredient in soft, moist cat food. The FDA had previously noted that this substance could lead to Heinz Body formation in feline red blood cells, although it did not demonstrate a direct link between propylene glycol and severe health issues.