What Are Hydrogenated Fats? Plus, Learn How to Identify and Avoid Them in Foods

We've all heard the terms "trans fat" and "hydrogenated fat," and the vast majority of us now they should be on our personal "do not eat" lists. But what are these fats and where might they be unexpectedly hiding? Here, we explain everything you need to know about trans and hydrogenated fats and remind you why it's so important to read labels when you're grocery shopping. What's more, you can also consider this a refresher course in which oils are healthiest for cooking.

What Are Trans Fats, and How Do They Impact Our Health?

First, it's important to have some context. Trans fats can be natural (coming from meat/dairy products) or artificial. These artificial trans fats occur thanks to a manufacturing process called hydrogenation, according to the FDA. This process adds hydrogen to liquid vegetable oils in order to make them solid at room temperature, explains the Mayo Clinic. This is beneficial for businesses, as it makes the fats more stable, lengthens shelf life, and is cheaper.

While trans fats may be good for business, they're not good for our health. They not only increase "bad" (LDL) cholesterol, but they also reduce "good" (HDL) cholesterol—that's a double whammy of negative heart consequences. Overall, a diet that's high in trans fats can put you at risk of heart disease and increase your risk for heart attacks, strokes, and even type 2 diabetes.

The Big Change

In 2015, after years of research, the FDA determined partially hydrogenated oils (aka "PHOs") to no longer be "generally recognized as safe." This led to the FDA banning the manufacturing of PHOs in foods, with an initial compliance date in 2018 (this was extended to 2020 and even 2021 in some petitioned cases). These PHO's were a major contributor of artificial trans fats within the U.S. food supply, so now that this ban is in effect, our overall consumption of trans fats should be on the decline. However, Thea Bourianne, a Registered and Licensed Dietitian at product data provider Label Insight, whose clients include the FDA and USDA, points out these FDA compliance dates just refer to manufacturing, and if a product was already on a store shelf, it didn't have to be removed. "This detail is critical because some products, such as sprinkles, often contain PHOs and can have up to a five-year shelf life," says Bourianne.

Prior to the recent regulations, trans fats could be found in some more obvious products, like shortening or stick margarine, but they could also found in more unexpected products, like baked goods, refrigerated pre-made doughs, various fried foods, frozen pizzas, or bags of microwavable popcorn, according to the Mayo Clinic and American Heart Foundation. Bourianne adds, "Trans fats are also commonly found in snack cakes, chocolate bars, confection products, and packaged cookies." Currently, Bourianne reports that in the Label Insight database, there are over 10,500 food products that contain PHOs. Over 3,300 of those were for sale in stores within the last year, according to IRI data, she added.

Read the Label

Any nutritionist will tell you that reading labels is key—and there's no exception when it comes to trans fats. Your label-reading skills are especially important here: Due to some sneaky rounding rules, a food that contains under 0.5 grams of trans fats per serving is able to round down and list 0 grams. While 0.5 grams is by no means a huge quantity, the issue is that if you consume multiple servings of that food, that 0.5 can add up to something larger and more impactful very quickly. Bourianne also points out, "Consumers will notice there is no percent daily value listed for trans fat, because there is no established recommended intake for trans fat."

The moral of the story? The 0 grams trans fat on your food's label may not be telling the full story. Be your own detective and look out for "partially hydrogenated oils" in the ingredient list. And remember, the FDA only banned partially hydrogenated oils, so there are still fully hydrogenated oils on the market; Bourianne notes that "while they are still processed fats (and may not be "healthy"), they are, in fact, nearly free of trans fats."

What Fats Should You Eat?

When it comes to fats, the unsaturated variety is your best bet. The American Heart Association recommends using naturally occurring, unhydrogenated vegetable oils (think canola, olive, safflower, or sunflower oils), rather than oils high in saturated fats (think tropical oils like coconut or palm). They also recommend substituting soft margarine as a butter substitute, rather than hard stick forms of margarine. If you're stuck on which oils are best, check out our guide to choosing healthy oils.

So, does the average home cook have trans fats hiding in their kitchens? Bourianne says it's possible (after all, we're not too far past the FDA's compliance deadlines and IRI data shows thousands of products with PHOs still in stores within the last year): "There are still products that likely contain PHOs in the ingredient statements in peoples' pantries." While trans fats may not be totally extinct yet, overall, if you're eating a balanced, wholesome (not super processed) diet full of various fruits and vegetables, whole grains, and lean proteins, you're likely well on your way to a trans fat-free diet.