Trans Fat and Partially Hydrogenated Oils

Artificial trans fat was once in everything from margarine to microwave popcorn, and it's now largely gone from the US food supply after the FDA ruled that its main source was no longer safe to use. This guide explains what trans fat is, how the ban came about, what "0 g trans fat" on a label actually means, and where small amounts can still appear.

What trans fat is

Fats are made of fatty acids, and "trans" refers to the shape of certain unsaturated fatty acids. There are two sources in food:

• Artificial (industrial) trans fat is created by partial hydrogenation, a process that adds hydrogen to liquid vegetable oil to make it more solid and shelf-stable. The result, partially hydrogenated oil (PHO), was prized for decades because it was cheap, gave baked goods a flaky texture, and resisted going rancid.
• Naturally occurring trans fat is found in small amounts in meat and dairy from cattle, sheep, and goats, formed by bacteria in these animals' stomachs.

Small amounts of trans fat can also form when vegetable oils are refined or heated to very high temperatures, but these amounts are much lower than what PHOs used to supply.

Because of natural trans fat, the Nutrition Facts label on butter, cheese, whole milk, or ground beef may show a small amount of trans fat per serving even though no partially hydrogenated oil was used. That number reflects the animal fat itself, not an added ingredient, and it's one more reason the Dietary Guidelines point to limiting saturated fat from these foods rather than avoiding them entirely.

Fully hydrogenated oil is a different product. Completely hydrogenating an oil turns its unsaturated fats into saturated fat, leaving essentially no trans fat, so fully hydrogenated oils were not part of the FDA's action on PHOs.

Why health authorities targeted it

Research over several decades found that artificial trans fat raises LDL ("bad") cholesterol and lowers HDL ("good") cholesterol, a combination linked to a higher risk of heart disease. Per gram, it has a worse effect on blood cholesterol than saturated fat. The Dietary Guidelines for Americans advise keeping trans fat intake as low as possible, and the WHO has called for eliminating industrially produced trans fat worldwide through its REPLACE initiative, launched in 2018.

The evidence on naturally occurring trans fat from meat and dairy is less clear, and it's consumed in much smaller amounts. Health authorities have focused their efforts on the artificial kind.

How the FDA phased out PHOs

Labeling came first

The FDA required trans fat to be listed on the Nutrition Facts label starting in 2006. Seeing the number on the package pushed many manufacturers to reformulate, and US trans fat intake dropped sharply over the next decade.

The 2015 determination

In June 2015, the FDA issued a final determination that partially hydrogenated oils are no longer "generally recognized as safe" (GRAS) for use in human food. Without GRAS status, PHOs can't be added to food unless the FDA specifically approves them. Manufacturers had until June 18, 2018 to comply. Foods made before that date could be sold until January 1, 2020. For a few specific uses the industry had petitioned for, manufacturing had to stop by June 18, 2019, and those foods had until January 1, 2021 to leave the market, the final compliance date. The FDA estimated that removing PHOs would prevent thousands of heart attacks and deaths each year.

Manufacturers mostly replaced PHOs with oils such as palm oil, fully hydrogenated oil blended with liquid oil, and newer high-oleic versions of soybean, canola, and sunflower oil.

What "0 g trans fat" really means

Under the FDA's labeling rules at 21 CFR 101.9(c)(2)(ii), a food with less than 0.5 g of trans fat per serving may list trans fat as 0 g. That rounding rule made sense for tiny amounts, but it had a loophole when PHOs were legal: a cookie could contain 0.4 g of trans fat per serving and still show "0 g," and eating several servings would add up.

Now that PHOs are no longer allowed as ingredients, that loophole matters much less. A "0 g" product today typically contains only trace amounts from refining or from dairy or meat ingredients. Two quick checks help:

• Read the ingredients list. "Partially hydrogenated" oil should no longer appear on US products. If you see it on an older package or an imported item, that's a sign of artificial trans fat.
• Remember that trans fat has no %DV. There's no safe daily target to aim for, so the goal is simply as little as possible.

What to watch now: saturated fat

With artificial trans fat largely gone, the fat line that deserves your attention on most labels is saturated fat. Some PHO replacements, especially palm oil and palm kernel oil, are high in saturated fat. The Dietary Guidelines recommend keeping saturated fat below 10% of daily calories, and the FDA's Daily Value is 20 g on a 2,000-calorie diet.

Use the 5/20 rule: 5% DV or less of saturated fat per serving is low, and 20% DV or more is high. Swapping foods high in saturated fat for those with mostly unsaturated fats, like nuts, seeds, fish, and liquid vegetable oils, is linked to lower heart disease risk, according to the Dietary Guidelines and the American Heart Association.

How to use this on myfoodfact.com

• Find products that keep saturated fat in check with our low saturated fat list.
• See which products use common PHO replacements on our palm oil and canola oil ingredient pages.
• Get the full picture on vegetable oils in our guide to seed oils and the evidence.

The bottom line

Artificial trans fat is one of the clearest public health success stories in the US food supply. After labeling made it visible and the FDA's 2015 determination removed partially hydrogenated oils from GRAS status, it has largely disappeared from American packaged foods. A "0 g" label today almost always means very little. The more useful number to check now is saturated fat, along with the ingredients list if you're buying older or imported products.

This guide is for general information and is not medical advice. If you have high cholesterol or heart disease, follow the guidance of your health care team.