As the Food and Drug Administration moves to ban trans fat, advertisers are speculating about the possible impact.

The agency released a preliminary ruling that would classify partially hydrogenated oils – the source of trans fat – as not "generally recognized as safe" for use in food. The proposed rule would not affect trans fat that "naturally occurs in small amounts of certain meat and dairy products," and brands would be allowed to petition the FDA for approval to continue using trans fat.

Many food manufacturers had already decreased or cut out the use of trans fat after the FDA mandated in 2006 that the trans fat content of foods be displayed on packaging labels. While the nation's intake of trans fat has since decreased, the FDA noted that many processed foods – such as microwave popcorn, frostings, margarine, frozen pizzas, coffee creamers, and packaged pies – still include trans fat.

"While consumption of potentially harmful artificial trans fat has declined over the last two decades in the United States, current intake remains a significant public health concern," FDA Commissioner Margaret A. Hamburg said in a statement. "Further reduction in the amount of trans fat in the American diet could prevent an additional 20,000 heart attacks and 7,000 deaths from heart disease each year – a critical step in the protection of Americans' health."

If the rule is finalized, the agency would establish a phase-out schedule for various foods. "We want to do it in a way that doesn't unduly disrupt markets," said Michael Taylor, the deputy commissioner for foods.

The FDA's proposal is open for public comment. To preclude the rule from becoming permanent, food manufacturers would have to provide sufficient evidence that partially hydrogenated oils are safe to eat. Given the scientific evidence noted by the agency (like a study by the Institute of Medicine concluding that no safe level of consumption exists for trans fat), any challenge faces significant obstacles.

Local jurisdictions have already instituted similar rules. New York City Mayor Michael Bloomberg established a ban on artificial trans fat in restaurants in 2008; similar rules followed in California, Cleveland, and Philadelphia.

If finalized, the ruling would require changes in product ingredients and labeling, but for advertisers, the impact could be failure-to-warn class actions from consumers. A plaintiff's attorney could argue that brands had knowledge that trans fat was not safe for consumers and sold it anyway, similar to allegations made in tobacco litigation. While many serious obstacles would make the cases a challenge – like establishing the knowledge of food manufacturers – the theory could tempt class action lawyers looking for the next big thing.

To read the FDA's preliminary ruling or comment on the proposal, click here.

Why it matters: While the announcement of the proposal has generated limited controversy in food manufacturing circles, some in the advertising industry have expressed concern that the change could result in class action litigation. Failure-to-warn suits could be based on the theory that companies were aware of the dangers of trans fats prior to the ban and yet continued to manufacture and sell them to the detriment of those that consumed the products.