Trans fats show up in two places: naturally in meat and dairy from cattle, sheep, and goats, and artificially in processed foods made with partially hydrogenated oils. While the U.S. banned manufacturers from adding partially hydrogenated oils to foods in 2018, trans fats haven’t disappeared entirely from the food supply. Knowing where they still lurk, and how to spot them on a label, matters because even small amounts raise your risk of heart disease.
Processed Foods With the Most Trans Fats
Before the ban, partially hydrogenated oils were everywhere in packaged and fast food. Many products have been reformulated, but some categories still contain residual or low-level trans fats depending on the brand and country of origin. The foods historically highest in trans fats, and the ones most worth checking labels on, include:
- Deep-fried fast food. A four-ounce serving of deep-fat french fries averaged 5.5 grams of trans fat in pre-ban testing, the highest of any common food item.
- Doughnuts. A single doughnut averaged about 3.2 grams.
- Danish pastries and other laminated doughs. One Danish pastry carried roughly 3 grams.
- Corn chips. A one-ounce serving averaged 1.4 grams.
- Boxed cake and pie. A slice of each came in around 1 gram.
- Cookies. A single cookie averaged close to 0.9 grams.
- Stick margarine and shortening. These were the most concentrated household sources, since they were literally solidified vegetable oil.
- Microwave popcorn, crackers, and candy bars. Lower per serving, but easy to eat in large quantities.
Even in countries with bans in place, imported foods, small bakeries, and restaurant fryers can still use partially hydrogenated oils. The World Health Organization has been pushing for global elimination since 2018, and policy coverage has increased six-fold since then, but the effort is not yet complete.
Meat and Dairy Contain Natural Trans Fats
Cattle, sheep, and goats produce trans fats naturally during digestion. Bacteria in their stomachs partially convert unsaturated fats into trans forms, which then end up in their meat and milk. This means beef, lamb, butter, cheese, cream, and whole milk all contain small amounts of trans fat regardless of how the animal was raised.
In cow’s milk fat, trans fats make up roughly 5 to 7 percent of total fatty acids. Grass-fed beef fat contains a similar proportion, around 5 to 8 percent of total fat. The amounts are modest compared to what a doughnut or basket of fries delivered in the pre-ban era, but they add up if your diet is heavy in full-fat dairy and red meat. These naturally occurring trans fats also include conjugated linoleic acid (CLA), which some research treats as a separate category with potentially different health effects than industrial trans fats.
How Trans Fats Form in Processed Foods
Industrial trans fats are created through a process called partial hydrogenation. Manufacturers pump hydrogen gas through liquid vegetable oil (like soybean or cottonseed oil) in the presence of a metal catalyst, usually nickel. The hydrogen atoms attach to the oil’s carbon chain, converting some of the flexible, bent double bonds into rigid, straight ones. That’s the “trans” configuration: the hydrogen atoms end up on opposite sides of the carbon chain instead of the same side.
The result is an oil that behaves more like a solid fat. It has a longer shelf life, a creamier texture, and holds up better in a deep fryer. Those practical advantages made partially hydrogenated oils incredibly popular with food manufacturers for decades. The problem is that the human body handles these artificially straightened fat molecules very differently from natural fats.
Why Trans Fats Are Harmful
Trans fats do something no other type of fat does: they simultaneously raise LDL (“bad”) cholesterol and lower HDL (“good”) cholesterol. Saturated fat raises LDL too, but it at least leaves HDL alone or nudges it upward. In one controlled study, swapping saturated fat for trans fat in otherwise identical diets dropped HDL cholesterol by 21 percent.
That double hit on cholesterol translates directly into heart disease risk. A large analysis from Harvard found a 23 percent higher risk of coronary heart disease for every 2 percent of daily calories that came from trans fat. Two percent of calories sounds small, but on a 2,000-calorie diet that’s only about 4.4 grams, roughly one old-fashioned doughnut’s worth. Trans fats also impair the ability of blood vessels to dilate properly, an early step in the development of atherosclerosis.
The U.S. Ban and Its Limits
The FDA determined in 2015 that partially hydrogenated oils are not safe for use in food. Manufacturers had until June 2018 to stop adding them, with extended deadlines through early 2021 for certain products already in the distribution pipeline. The ban effectively removed the largest source of artificial trans fats from the American food supply.
But “banned” does not mean “zero.” The FDA explicitly noted that trans fat will not completely disappear from foods because it occurs naturally in meat and dairy and is present at very low levels in other edible oils. Refined vegetable oils, even without intentional hydrogenation, can contain trace amounts of trans fats produced during high-heat processing.
How to Find Trans Fats on a Label
The nutrition facts panel lists trans fat, but there’s a catch. FDA rules allow manufacturers to print “0 g” of trans fat if a serving contains less than 0.5 grams. A product with 0.4 grams per serving legally reads as zero. If you eat three or four servings, you could take in over a gram of trans fat from a food you thought was free of it. Serving sizes are sometimes set deliberately small to stay under that rounding threshold.
The more reliable check is the ingredient list. Look for the words “partially hydrogenated” followed by any type of oil (soybean, cottonseed, palm kernel). If that phrase appears anywhere in the ingredients, the product contains trans fat regardless of what the nutrition panel says. “Fully hydrogenated” oil, by contrast, has been completely converted to saturated fat and contains no significant trans fat, though it’s not exactly a health food either.
Shortening and some stick margarines may still list partially hydrogenated oils, particularly store brands or imported products. Baked goods from small or international manufacturers deserve a closer look, since they may not have reformulated. When eating out, you generally can’t check a label, so fried foods and flaky pastries from restaurants remain the hardest sources to track.