This article by Sabrina Tavernese explains:
The Food and Drug Administration on Thursday proposed measures that would all but eliminate artificial trans fats, the artery clogging substance that is a major contributor to heart disease in the United States, from the food supply. Under the proposal, which is open for public comment for 60 days, the agency would declare that partially hydrogenated oils, the source of trans fats, were no longer “generally recognized as safe,” a legal category that permits the use of salt and caffeine, for example.That means companies would have to prove scientifically that partially hydrogenated oils are safe to eat, a very high hurdle given that scientific literature overwhelmingly shows the contrary. The Institute of Medicine has concluded that there is no safe level for consumption of artificial trans fats.
Hat tip to Hannah Wolfman-Arent.