Companies are already removing PHOs from processed foods.
The Food and Drug Administration (FDA) say they have finally determined that partially hydrogenated oils (PHOs) - a major source of artificial trans fat in the American diet - are not "generally recognized as safe" for human consumption.
The regulators are giving food manufacturers 3 years - until 18th June, 2018 - to remove PHOs from food products.
This gives companies time to reformulate products so they do not contain PHOs, or to ask the FDA for permission to use them.
"Following the compliance period, no PHOs can be added to human food unless they are otherwise approved by the FDA," say the regulators.
FDA's Acting Commissioner Dr. Stephen Ostroff says the "action is expected to reduce coronary heart disease and prevent thousands of fatal heart attacks every year."
The FDA announced a preliminary determination to regard PHOs as unsafe to eat in 2013. That followed a review of the scientific evidence and consultation with experts.
The regulators are now finalizing the determination after considering comments from the public.
Director of the FDA's Food Safety and Applied Nutrition Center Dr. Susan Mayne says:
"This determination is based on extensive research into the effects of PHOs, as well as input from all stakeholders received during the public comment period."
While consumption has fallen, 'it is still a public health concern'
Food companies use artificial trans fats to improve the texture, extend the shelf life and increase the stability of processed foods. They are cheaper and more readily available than natural versions from meat and dairy sources.
Since 2006, companies have had to show trans fat content on the nutrition facts labels of food products sold in the US.
The FDA say that while trans fat consumption by Americans has fallen by 78% between 2003 and 2012, the current level of consumption remains a public health concern.
Companies are already removing PHOs from processed foods, and the FDA anticipate that many will achieve compliance before the deadline.
According to the Centers for Disease Control and Prevention (CDC), the main sources of PHOs in the American diet are cakes, cookies, pies, margarines and spreads, fried foods, savory snacks such as microwave popcorn, frozen pizza, ready-to-use frosting and coffee creamers.
Why are PHOs bad for health?
PHOs are made by heating up a food oil such as soybean or cottonseed in the presence of hydrogen and a catalyst. This makes the oil into a semi-solid, partially saturated fatty acid - like margarine - making it easier to use as a shortening in baked goods.
Trans fats are so called because when hydrogenation breaks double bonds between carbon atoms in the long-chain fatty acid molecules, this results in the hydrogen atoms attached to the carbon atoms at a double bond being on opposite sides of the double bond ("trans" means "other side," or "across").
This "trans" configuration is different to naturally occurring versions, which have a "cis" configuration, where the hydrogen atoms attached to carbon at double bonds are on the same side of the double bond.
The trans configuration in the fatty acid molecules of manufactured PHOs is thought to be what makes them bad for health - consuming them lowers "good" cholesterol (high-density lipoprotein, or HDL) and increases "bad" cholesterol (low-density lipoprotein, or LDL) in the body, raising the risk of coronary heart disease.
The CDC say eliminating the use of PHOs in food could prevent 10,000-20,000 heart attacks and 3,000-7,000 coronary heart disease deaths each year in the US.
In November 2014, MNT reported a study of hundreds of healthy working-age men that found higher consumption of trans fats was linked to poorer memory. Speculating on the reason behind the link, the researchers suggested trans fats increase oxidative stress, which affects cell energy.