The guide

Trans fat: mostly gone, not all

By GyroscopeUpdated November 14, 202612 sources

The artificial trans fat from partially hydrogenated oils is out of US food. After June 18, 2018, manufacturers couldn’t add those oils for most uses, and the last ones had to be gone by January 1, 2021. A small amount of natural trans fat remains in milk, butter, cheese and meat.

A lot of people still scan labels for trans fat, and a lot of others assume it vanished completely. Neither is quite right. The worst source is gone, so there’s no need to hunt for trans fat anymore. But a little is still in foods people eat every day, and the label is allowed to call small amounts zero.

How did trans fat get into everything?

In 1903 the German chemist Wilhelm Normann patented a way to harden liquid oil with hydrogen. In June 1911 Procter and Gamble’s Crisco, a shortening made by hardening cottonseed oil, reached American grocery shelves. The name came from “crystallized cottonseed oil”, and by the winter of 1911 the company had shipped it to about 15,000 retailers.

The appeal was easy to see, since a cheap liquid oil could now stand in for lard. Through the 1960s, common margarines and shortenings were rich sources of the trans fat this process made, as the researchers who recovered the Minnesota diet trial’s data later pointed out.

Partial hydrogenation doesn’t only fill in kinks with hydrogen. It also twists some of the remaining kinks into a different shape, called trans, and a trans kink lets the chain lie almost straight.

What does a trans kink do?

It makes an unsaturated fat behave like a saturated one. Oleic acid, about three quarters of the fat in extra virgin olive oil, has one natural kink and melts at about 56 to 61 °F (13 to 16 °C). Elaidic acid has the same atoms with the kink in the trans shape, and it melts at about 108 to 111 °F (42 to 44 °C). That’s solid on the counter, which is exactly what the shortening makers wanted.

In your blood it acts worse than saturated fat. In 1990 two researchers at Wageningen in the Netherlands, Ronald Mensink and Martijn Katan, fed 59 young adults three diets for three weeks each, in random order. The diets were the same except that 10% of the calories came from oleic acid, from trans fat or from saturated fat. Compared with the oleic acid diet, the trans fat diet raised LDL and also lowered HDL, the cholesterol carrier people think of as the good one. The saturated fat diet raised LDL too, but its HDL was the same as on the oleic acid diet.

The margarines of that era were full of trans fat, and that’s a large part of why people still distrust margarine today. The margarine myth covers what’s in a tub now.

How did the US get rid of it?

• 2015. The FDA found that partially hydrogenated oils were no longer “generally recognized as safe”, the status that let them be added to food without approval.
• June 18, 2018. After this date manufacturers couldn’t add them to foods for most uses.
• January 1, 2021. The final date, after the FDA gave products already made time to clear the shelves.

The FDA says taking them out of processed foods “is estimated to be preventing thousands of heart attacks and deaths each year”. The newest US cholesterol guideline, from 2026, still lists trans fat with saturated fat as the fats to replace with unsaturated ones.

Where is trans fat now?

It’s mostly in milk fat and beef fat now. The FDA says trans fat “occurs naturally in food products from ruminant animals”, cows, sheep and goats, in milk, butter, cheese and meat, and its ban didn’t touch these. Here’s how much, from the USDA’s tables.

Those numbers are small next to the saturated fat in the same foods. A tablespoon of butter has 7.2 g of saturated fat and less than half a gram of trans. The National Academies recommend keeping trans fat “as low as possible without compromising the nutritional adequacy of the diet”. There’s no Daily Value for it on the label.

Why does the label say 0 g?

The label follows a rounding rule. Under US labeling law, trans fat is rounded to the nearest half gram, and “if the serving contains less than 0.5 gram, the content, when declared, shall be expressed as zero.” A tablespoon of butter, at about 0.46 g, can say 0 g of trans fat.

For one serving that’s a small amount. The rounding hid more when partially hydrogenated oil was in packaged foods, since three servings that each said zero could add up to more than a gram. With those oils gone, the rounding mostly hides the natural trans fat in dairy and meat.