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.
Propylene glycol was previously a standard ingredient in wet cat food. The FDA had long been aware that this substance could cause Heinz Body formation in cats' red blood cells, but it failed to establish a clear connection between propylene glycol and serious health problems.