Fried foods, particularly those from fast food joints, may contain trans fats. It was once common practice to use trans fats in frying oil intentionally, because those oils last longer in the fryer. But the vegetable oils most chains now use contain small amounts of trans fat, and the more the oil is reused, the more trans fats will be present. Hidden trans fats are just one of the many things fast food companies don’t want you to know about.