Trans Fat: What It is and Why It is Harmful

At 98 years old, biochemist Fred Kummerow sued the U.S. Food and Drug Administration (FDA) to force a ban on the ingredient he had spent decades proving was killing Americans.

Story Snapshot

The FDA required trans fat labels on packaged foods starting January 1, 2006, after science linked the ingredient to dangerous cholesterol spikes.
New York City banned trans fat in restaurants in 2006, years before the federal government acted — and it worked better than labels alone.
In 2015, the FDA ruled that partially hydrogenated oils were no longer safe, effectively banning artificial trans fat nationwide by June 2018.
A loophole let food companies label products “trans fat free” even when they contained up to 0.5 grams per serving — a gap that added up fast.

The Ingredient That Hid in Plain Sight for Decades

Artificial trans fat was everywhere for most of the 20th century. Food makers loved it. Partially hydrogenated oils — the main source of artificial trans fat — made products last longer on shelves, gave baked goods a flakier texture, and cost almost nothing to use. Margarine, crackers, cookies, fast food fries — trans fat was the invisible backbone of processed food in America. Most people had no idea it was there.

The science started turning against it in the 1990s. Researchers found that trans fat raised LDL, the “bad” cholesterol, while lowering HDL, the “good” kind. That combination is a direct road to heart disease. The evidence piled up through the decade, but the FDA did not act on it for years. It took a formal petition from the Center for Science in the Public Interest, a consumer advocacy group, to push regulators off the sideline.

Labels First, Then the Real Fight Began

On July 11, 2003, the FDA published a final rule requiring trans fat to be listed on the Nutrition Facts label of packaged foods, with the rule taking effect January 1, 2006. The idea was simple: tell people what they are eating and let them choose. Awareness did shift. Food companies started reformulating products once shoppers began checking labels. Trans fat intake dropped. But the label rule had a built-in problem that blunted its power.

The FDA allowed companies to round down to zero if a serving contained less than 0.5 grams of trans fat. That meant a product could legally say “0g trans fat” on the label and still deliver a meaningful dose with every serving — especially if a person ate more than one serving. Snack foods exploited this gap routinely. The label told people less than they thought it did, and consumption stayed higher than the numbers suggested.

New York City Showed the Country What a Real Ban Looks Like

While federal regulators moved slowly, New York City moved fast. On December 5, 2006, the New York City Board of Health voted unanimously to ban artificial trans fat in restaurants, giving the food service industry until July 2008 to fully comply. The food industry pushed back hard, calling it government overreach and labeling the city a “nanny state.” The ban held anyway. And it worked. Restaurant food in New York got cleaner, and the city became a model for what direct regulation could do that labels could not.

At ninety-eight, Fred Kummerow sued the Food and Drug Administration.

He was a biochemist at the University of Illinois, born in Germany, and he had been trying to get someone to listen for a very long time.

In 1957 he took samples from the arteries of people who had died of… pic.twitter.com/hi9fr2XZcx

— Sama Hoole (@SamaHoole) July 12, 2026

Research confirmed what New York’s experiment showed. Studies found that labeling alone cut trans fat levels in the food supply by roughly 30 to 50 percent, while outright bans — like Denmark’s in 2004 — eliminated more than 90 percent of artificial trans fat from the food supply. The difference was not small. Labeling informed people. Bans actually removed the ingredient. Those are two very different outcomes, and the data made the gap impossible to ignore.

The FDA Finally Pulls the Trigger in 2015

The federal ban came in June 2015, when the FDA ruled that partially hydrogenated oils were no longer Generally Recognized as Safe. That designation — known as GRAS — had been the legal foundation that allowed trans fat to stay in the food supply without special approval for decades. Stripping it away was a landmark move. Food manufacturers had three years to reformulate or get specific approval for any remaining uses. By June 2018, industrial trans fat was effectively gone from the American food supply.

It is worth noting that the ban only covered artificial trans fat. The small amounts of naturally occurring trans fat found in meat and dairy were never included. That distinction mattered to the food industry and to some researchers, though the public health focus was always on the industrially produced version found in processed foods. The 25-year gap between the first solid evidence of harm and the actual ban is a hard number to sit with — and a reminder of how long it can take for science to become policy when industry has a financial stake in the outcome.