Trans fats are found in two places: naturally in small amounts in meat and dairy, and artificially in processed foods made with partially hydrogenated oils. While the U.S. banned the major source of artificial trans fats in 2018, trace amounts still show up in the food supply, and many packaged products reformulated with replacement fats still deserve a closer look.
How Trans Fats End Up in Food
Most trans fats in the food supply have been artificial, created through a process called partial hydrogenation. Manufacturers pump hydrogen gas into liquid vegetable oils, which converts some of the oil’s natural molecular bonds into a different shape. The result is a semi-solid fat with a higher melting point, better stability, and a longer shelf life. That made partially hydrogenated oils extremely useful for commercial baking, frying, and food processing for decades.
A small amount of trans fat also occurs naturally. Bacteria in the stomachs of cows, sheep, and goats produce trans fats during digestion, so beef, lamb, and full-fat dairy products contain them. These naturally occurring trans fats typically make up 1 to 8% of the total fat in ruminant animal products. The dominant one is vaccenic acid, which behaves differently in the body than industrial trans fats and can actually be converted into a form of conjugated linoleic acid. The amounts are low enough that they aren’t considered a meaningful health concern at normal dietary levels.
Foods That Contain (or Contained) Trans Fats
Before regulations tightened, these were the biggest sources of artificial trans fats in the American diet:
- Commercial baked goods: cakes, cookies, pies, and pastries relied on shortening made from partially hydrogenated oils for texture and shelf stability.
- Fried foods: french fries, doughnuts, and fried chicken were often cooked in partially hydrogenated frying oils that could be reused many times without breaking down.
- Stick margarine and spreads: the solid consistency of stick margarine came directly from partial hydrogenation.
- Frozen pizza: the crust and cheese layers frequently contained partially hydrogenated oils.
- Microwave popcorn: the buttery coating was a common hiding spot for trans fats.
- Refrigerated dough: biscuits, rolls, and crescent dough in tubes used these fats for flakiness.
- Nondairy coffee creamer: both powdered and liquid versions relied on partially hydrogenated oils as a base.
- Shortening: the classic baking fat was essentially pure partially hydrogenated oil.
Many of these products have been reformulated since the FDA ban took effect, but older recipes, imported products, and smaller manufacturers may still use ingredients that contribute small amounts of trans fat.
Why Trans Fats Are Harmful
Trans fats earned the reputation as the worst type of dietary fat because they hit your cholesterol from both directions. They raise LDL (the type that deposits cholesterol in artery walls) while simultaneously lowering HDL (the type that helps clear it away). Saturated fat raises LDL too, but it doesn’t suppress HDL the way trans fats do. That double effect is why even modest intakes are linked to a significantly higher risk of heart disease.
The World Health Organization considers any intake above 1% of total daily calories from trans fat to be associated with increased risk of coronary heart disease and death. For someone eating 2,000 calories a day, that threshold is just over 2 grams, roughly the amount that used to be in a single serving of microwave popcorn or a couple of commercially fried doughnuts.
The U.S. Ban and Its Limits
In 2015, the FDA determined that partially hydrogenated oils were no longer “Generally Recognized as Safe.” Manufacturers had until June 2018 to stop adding them to foods, with a final compliance date of January 1, 2021, to allow existing products to clear store shelves. In 2023, the FDA issued a follow-up rule removing outdated references to partially hydrogenated oils from food regulations entirely.
The ban addressed the artificial source, but trans fat hasn’t disappeared from the food supply. It occurs naturally in meat and dairy and is present at very low levels in other edible oils, including fully refined vegetable oils. Globally, the effort is still uneven. The WHO launched its REPLACE initiative in 2018, calling for worldwide elimination of industrial trans fats. Coverage of best-practice elimination policies has increased more than sixfold since then, but the WHO is still pushing for full global adoption by 2025.
The Labeling Loophole to Watch
U.S. nutrition labels can legally list “0 g” of trans fat if a serving contains less than 0.5 grams. That means a product with 0.4 grams per serving appears trans-fat-free on the label. If you eat multiple servings, which is common with crackers, cookies, or popcorn, you could be consuming a gram or more without realizing it.
The more reliable check is the ingredient list. If you see “partially hydrogenated” anything (soybean oil, cottonseed oil, palm kernel oil), the product contains artificial trans fat regardless of what the nutrition panel says. Since the ban, this has become rare on U.S. shelves, but it’s still worth checking on imported foods, products from smaller brands, or anything sitting in the back of your pantry from before 2021.
What Replaced Trans Fats in Processed Foods
When manufacturers reformulated, most switched to palm oil, fully hydrogenated oils blended with liquid oils through a process called interesterification, or high-oleic versions of soybean and sunflower oil. Fully hydrogenated oils are different from partially hydrogenated ones: complete hydrogenation converts all the double bonds, producing a saturated fat rather than a trans fat. These replacement fats eliminated the trans fat problem but introduced more saturated fat into some products. The long-term health profile of interesterified fats is still being studied, so “trans-fat-free” on a package doesn’t automatically mean the product is heart-healthy. Checking total saturated fat on the label gives you a more complete picture.