Despite what you may have heard, not all fats are created equal. Your body relies on healthy fats, like poly- and monounsaturated fats (found in things like fish, avocado, and nuts), to create hormones, produce energy, and absorb certain nutrients. On the flip side, eating artificial trans fat (primarily found in processed foods), can increase your risk of life-threatening diseases. That’s why the World Health Organization (WHO) plans to eliminate artificial trans fats from all foods globally by 2023.

Denmark became the first country to ban trans fats in 2003, and the United States followed suit shortly after. 

But many low- and middle-income countries are still pumping trans fats into their foods. This results in more than 500,000 cardiovascular disease deaths per year, according to the WHO.

“Trans fat is an unnecessary toxic chemical that kills, and there’s no reason people around the world should continue to be exposed,” public health expert Dr Tom Frieden said in an official WHO statement.

So you know trans fats are bad for you-but what exactly are they and what do they do to your body? Here’s everything you need to know about why health experts worldwide want to eliminate them for good.

What is trans fat?

There are two types of trans fats: naturally-occurring trans fats and artificial trans fat. Animals that produce meat and dairy products (like cows) naturally create small amounts of trans fat in their guts. In turn, trace amount of trans fats wind up in the foods they create. However, there’s not enough research out there to determine the impact these types of trans fats have on your health.

Artificial trans fats are a different story, though. These are man-made through a process called hydrogenation, in which hydrogen molecules are added to liquid fats (like vegetable oil) to convert them into solid fats, resulting in the partially hydrogenated oils you’ve heard so much about.

Why is trans fat added to your food?

PHOs are the most common type of trans fat used in processed foods like biscuits, crackers, potato chips and fried foods like hot chips and doughnuts. Very little was known about the health impacts of trans fats before 1990, so companies used them because they were cheap, easy to use, had a long shelf-life, and made food taste better.

How does trans fat impact your health?

Foods rich in trans fat tend to be high in added sugar and kilojoules, so they can pave the way for weight gain and type 2 diabetes.

They’re also bad news for your heart. In a 2015 review and meta-analysis published in the British Medical Journal, Canadian researchers looked at 20 studies that analysed the health impacts of trans fats in several countries. They found that eating artificial trans fats was associated with a 34 percent increase in death from any cause, a 28 percent increase of dying from heart disease, and a 21 percent increase in the risk of developing heart disease.

But why are they so destructive? Trans fats spike your LDL (or the “dangerous”) cholesterol, which clogs your arteries. At the same time, they cause your HDL (a somewhat protective) cholesterol takes a dip, meaning excess cholesterol can’t be transported back to your liver to be flushed from your body, explains dieititan Dana Hunnes. This can pave the way for a blood clot, causing a heart attack or stroke. Trans fats also damage the inner lining of your blood vessels, which hampers their ability to function properly, says Hunnes.

Plus, they’ve been shown to increase at least two inflammatory markers and “we now understand that inflammation is a major driver of many chronic diseases, from diabetes to heart disease and metabolic syndrome,” Hunnes says.

The good news is, research shows that banning trans fats makes an impact. Using data from 2002 to 2013 from the New York State Department of Public Health, a study published in JAMA Cardiology found that hospital admissions for heart attack and stroke dipped by 6.2 percent in people living in counties with restrictions on trans fats compared to counties without restrictions. The decline became most significant between 2007 and 2011, right after New York City banned the use of trans fats in restaurants.

Each year, trans fat intake leads to 500,000 deaths from heart disease.

Are all types of fat bad for you, though?

You should still be diligent about reading nutrition labels. Make sure partially hydrogenated oils are nowhere to be found on the ingredients list. Remember: They are still permitted to be used in trace amounts-and that can be dangerous. When you go to a restaurant, ask about the types of oils they use to fry food or avoid fried foods altogether if they can’t provide nutrition information.

It’s important to note that you shouldn’t confuse trans fats with saturated and unsaturated fats. The National Heart Foundation still recommends that 20 to 35 percent of your daily kilojoules come from fat, with 7 percent stemming from saturated fats. (If you consume about 8,370kJ (2,000cal) a day, 2,100kJ (500cal) can come from healthy fats from whole eggs, nuts, avocado, and olive oil.) If you have high cholesterol or a family history of heart disease, 5 to 6 percent of your daily diet should come from fat.

While you may have heard that saturated fats are also bad for your heart, they’re not as dangerous as trans fats for the average person. However, foods high in saturated fat tend to be processed, salty, or sugary, so limiting your intake is still important, says Hunnes. The best thing you can do is load up on single-ingredient forms of fat-like avocados, nuts, and olive oil-to reap the most benefits.

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