The foods historically highest in trans fat were vegetable shortenings, with some brands containing over 30 grams of trans fat per 100 grams of product. That made anything cooked or baked with shortening, like commercially fried foods, pie crusts, cookies, and pastries, a major source. The U.S. banned the primary source of artificial trans fat (partially hydrogenated oils) with a final compliance date of January 1, 2021, but trans fat hasn’t completely disappeared from the food supply.
Shortening Was the Biggest Source
Vegetable shortening, the solid white fat used in commercial baking and frying, was by far the most trans-fat-dense food ingredient. USDA testing found that different shortening brands ranged from about 10 to 33 grams of trans fat per 100 grams. One soybean-and-cottonseed-oil shortening clocked in at nearly 33 grams, meaning roughly a third of the product by weight was trans fat. These shortenings were the backbone of commercial kitchens because they were cheap, extended shelf life, and gave baked goods a flaky, stable texture.
Any food made with these shortenings inherited a heavy trans fat load. That included pie crusts, biscuits, cake frostings, cookies, crackers, and the oil in deep fryers at fast food restaurants.
Fried Fast Food Ranked High
French fries from fast food chains were among the most common ways people consumed trans fat. USDA analysis of multiple brands showed trans fat levels in french fries ranging from 1 gram to over 5 grams per 100 grams, depending on the frying oil. Fries cooked in vegetable oil that had been partially hydrogenated could get up to 34% of their total fat from trans fat. A single large serving of fries could easily deliver several grams.
Other deep-fried items like chicken nuggets, fried fish, doughnuts, and onion rings carried similar levels when cooked in the same oils.
Packaged Snacks and Baked Goods
Before the ban, microwave popcorn was a well-studied example. Research from UMass Amherst found that as recently as 2013 and 2014, products made with partially hydrogenated oil accounted for about 39% of microwave popcorn purchases in the U.S. The oil gave popcorn its buttery texture and long shelf life at low cost.
Other packaged foods that commonly relied on partially hydrogenated oils included shelf-stable cookies, crackers, frozen pizza dough, refrigerated biscuit dough, stick margarine, coffee creamers, and cake mixes. The pattern was consistent: any processed food that needed solid fat for texture or stability at room temperature was a candidate for high trans fat content.
The Ban Changed Things, But Not Completely
In 2015, the FDA determined that partially hydrogenated oils were no longer safe for use in food. Manufacturers had until 2018 to stop adding them, and products already in distribution were given until January 1, 2021, to clear shelves. In 2023, the FDA followed up by removing outdated references to these oils from its regulations entirely.
Most major food manufacturers reformulated their products well before the deadline, switching to palm oil, fully hydrogenated oils blended with liquid oils, or other alternatives. This dramatically reduced the trans fat in the American food supply. But “reduced” is not the same as “eliminated.”
Where Trans Fat Still Hides
There are three ways trans fat still shows up in food, even after the ban.
First, naturally occurring trans fat exists in meat and dairy from ruminant animals like cows, sheep, and goats. These natural trans fats are present in small amounts in butter, cheese, whole milk, and beef. The levels are much lower than what artificial sources used to deliver, typically 2 to 5% of total fat content.
Second, FDA labeling rules allow manufacturers to list trans fat as “0 g” on the nutrition label if a serving contains less than 0.5 grams. That means a product could contain 0.4 grams per serving and legally say zero. If you eat multiple servings, or eat several of these products throughout the day, the amount adds up.
Third, mono- and diglycerides, which are common emulsifiers in processed foods, can contain small amounts of trans fat. Because they’re classified as emulsifiers rather than fats, the FDA’s ban on partially hydrogenated oils doesn’t apply to them. There’s currently no way to tell from a label how much trans fat these additives contribute. You’ll find them in bread, tortillas, peanut butter, ice cream, whipped toppings, and margarine.
How to Spot Trans Fat on Labels
Check the ingredient list, not just the nutrition facts panel. If you see “partially hydrogenated” anything (soybean oil, cottonseed oil, palm oil), the product contains artificial trans fat regardless of what the label says under grams. This is rare in domestic products now but can still appear in imported foods or older inventory.
Look for mono- and diglycerides in the ingredient list as a secondary flag. Their trans fat contribution is small per serving, but it’s worth noting if you’re trying to minimize your intake entirely.
Why It Matters
Trans fat is uniquely harmful compared to other dietary fats. It raises LDL (the harmful cholesterol) while simultaneously lowering HDL (the protective cholesterol), a combination no other common fat produces. Research from Harvard found a 23% increase in coronary heart disease risk for every 2% of daily calories replaced by trans fat. For someone eating 2,000 calories a day, 2% is just 4.4 grams, an amount that was easy to hit with a single fast food meal before the ban.
The good news is that average trans fat intake in the U.S. has dropped sharply since reformulation began. The biggest remaining sources are natural trans fat in animal products and the small residual amounts hiding behind the 0.5-gram labeling threshold in processed foods.