The U.S. Food and Drug Administration is beginning a process to ultimately ban the use of artificial trans fat in processed foods, saying the fats are no longer "generally recognized as safe" for consumption.

The agency announced Thursday it was taking steps to require the food industry phase out the use of partially hydrogenated oils, which are the primary source of trans fat in processed foods.

FDA Commissioner Dr. Margaret A. Hamburg said eliminating artificial trans fat would help protect Americans and could prevent as many as 20,000 heart attacks as well as 7,000 deaths from heart disease each year.

Many food makers have stopped using trans-fat-containing oil in recent years, but the fat can still be found in some processed foods such as microwave popcorn, margarines, frosting and coffee creamers.

"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," Hamburg said in a statement.

In its announcement, the FDA did not specify a timeline for when it wanted all trans fats out of processed foods, but said it would collect comments for two months before determining how long the phase-out should take.

Different foods might have different timelines, the agency said, depending on how easy the fat is to substitute. But it noted that numerous manufacturers "have already demonstrated that many of these products can be made without trans fat."

In Canada, trans fats are still found in many processed foods and many have criticized Health Canada for not taking a tougher stand on the issue.

In June 2007, the federal government said it was giving the food industry two years to reduce the amount of trans fat in its products, and promised government monitoring of trans fat levels every six months in the interim.

In late 2009, the agency quietly released its final monitoring results and released a report showing that high levels of the fats still exist in many foods sold in Canada.

The Heart and Stroke Foundation said after that report that it was disappointed that so many products continue to contain "disturbingly high amounts" of trans fat.

"Trans fat levels are still too high, especially in baked goods. The verdict is in. Canada urgently needs trans fat regulations to protect our children and all Canadians," the foundation said in a January, 2010 statement.

Since then, there has been no further action from Health Canada on trans fat.

Artificial trans fats were introduced into the food supply in the 1970s as a means of extending the shelf life of food products. The FDA has allowed the use of the fats saying they were "generally recognized as safe," a legal category that also permits the addition of salt and caffeine into foods

But research in recent years has shown that consuming trans fat raises low-density lipoprotein (LDL), or "bad" cholesterol, which increases the risk of heart disease.

The Institute of Medicine, which advises both the FDA and Health Canada, has concluded that there is no safe level of consumption of artificial trans fat.

The FDA's planned phase-out of trans fat affects only the artificial trans fats found in partially hydrogenated oils, not the trans fat that naturally occurs in small amounts in certain meat and dairy products.

On Thursday, the American Heart Association lauded the FDA for its plans for a ban.

"We commend the FDA for responding to the numerous concerns and evidence submitted over the years about the dangers of this industrially produced ingredient," the AHA's Nancy Brown said in a statement.

The AHA also urged the FDA to go further and revise labelling for "trans fat-free" foods. Current policy allows food products with less than 0.5 grams of trans fat to round down and list 0 grams on the Nutrition Facts Panel.

A similar food labelling policy exists in Canada.