Artificial trans fat — a common ingredient in many American foods — is now considered so dangerous the government is banning it.

Found in fast foods, pastries and many prepared foods on grocery store shelves, artificial trans fats have been declared unsafe by the U.S. Food and Drug Administration, and now must be removed from foods by 2018.

“They do have a bad effect on the body,” says Catherine Champagne, a dietitian and professor at Pennington Biomedical Research Center. “They started to realize that the trans fats would raise your bad cholesterol and would lower your good cholesterol.”

What is trans fat?

Trans fat is found in many foods. It occurs naturally in small amounts in some milk and dairy products, but that kind doesn’t bother doctors and dietitians much.

Artificial trans fats are found in processed foods that contain partially hydrogenated oils.

“Those are created by an industrial process that incorporates hydrogen into a liquid vegetable oil to make them more solid,” Champagne says.

These oils have helped manufacturers extend the shelf life of foods, but they also alter the taste and texture.

Americans consume far fewer trans fats now than they did a decade ago — in 2003, Americans ate an average of 4.6 grams per day, says the FDA, and by 2012, that had dropped to 1 gram per day. But the nonprofit Institute of Medicine says even 1 gram is too much.

Why are they bad for me?

Over the past decade, scientists have found that trans fats increase bad cholesterol (low-density lipoprotein or LDL) and decrease good cholesterol (high-density lipoprotein or HDL). They also increase the risk of acquiring Type 2 diabetes.

“Those trans fats work very similar to saturated fats in increasing your risk of developing heart disease and stroke,” Champagne says.

Trans fats may also affect your memory.

A 2014 study by doctors at the University of California at San Diego and the National Heart, Lung and Blood Institute found that men under 45 performed poorly on memory tests.

The men who regularly ate trans fats performed worse for every gram of trans fat they consumed daily.

How do I know if I’m eating trans fat?

Since 2006, all prepared foods for sale in the U.S. have had to list the number of trans fats per serving on the label.

Also, any foods that contain artificial trans fats will include some type of partially hydrogenated oil in the ingredients.

“The label is your friend,” Champagne says. “Check the label, because (trans fat) is going to be in a processed food.”

An analysis released in May by the Environmental Working Group found that 37 percent of items in American grocery stores probably contain trans fats. Many fast food restaurants use partially hydrogenated oils, too, and many doughnuts, pastries, cakes, pies and frostings — products made with shortening — will contain them, Champagne says.

Microwave popcorns, coffee creamers, peanut butter and sticks of margarine may contain some sort of trans fat.

Some foods claim zero trans fats on their label even though they include small amounts. Labeling laws allow companies to round the amount down to zero if the product contains fewer than .5 grams per serving.

What’s next?

As artificial trans fats disappear from the American food supply over the next three years, manufacturers will start reworking their recipes.

“It would be interesting to see how well the food supply really changes,” Champagne says. “Some people worry it’s going to taste differently. … People are still going to eat food. They are going to enjoy food as much as they always have.”

When trans fats disappear, there will be other “villains” to avoid in the food supply, Champagne adds.

Prepared foods and restaurant meals contain incredibly high levels of sodium and saturated fat, she says.

“There are so many things that contain sodium that I think the challenge of developing something that tastes good and is low sodium is more difficult than reducing or getting rid of trans fat,” the dietician says.