Unhealthy fats — for decades a slippery slope in the American diet — are finally falling out of favor.

The Food and Drug Administration ruled in November that partially hydrogenated fats don’t meet the criteria for their “generally recognized as safe” category, starting the process to dramatically reduce trans fats from the food supply.

The American Heart Association supports eliminating partially hydrogenated fats because too much can increase bad (LDL) cholesterol, lower good cholesterol (HDL) cholesterol and increase the risk of heart disease, the No. 1 killer of all Americans.

Avoiding foods with partially hydrogenated fats could prevent 10,000-20,000 heart attacks and 3,000-7,000 heart disease deaths each year in the U.S., according to the Centers for Disease Control and Prevention.

Alice H. Lichtenstein, D.Sc., received her first grant from the American Heart Association in the mid-1980s and has spent years as a strong advocate for eliminating trans fats from the nation’s food supply. Her work developing science-based policies has shaped the debate from how food companies develop their products and how shoppers pick their groceries to what children are offered in the school lunch line.

“I was interested in the impact of diet and cardiovascular risk and trans fats turned out to be an important component of it,” said Lichtenstein, who is the Gershoff Professor of Nutrition Science and Policy, director and senior scientist at the Cardiovascular Nutrition Laboratory at Tufts University in Boston and a long-time association volunteer.

The food industry has long used partially hydrogenated fats to boost the texture and shelf life of a wide variety of foods such as cookies, cake mixes, doughnuts and snack foods. Trans fats come from two sources: animal fats (meat and dairy fat); and partially hydrogenated fat (traditional margarines and cooking shortenings made from vegetable oil). Before trans fats were added to labels in 2006, you could only recognize them under the alias “partially hydrogenated oil” on the ingredient list.

Partially hydrogenated fats were first developed in the late 19th century as a cheap substitute for butter, Lichtenstein said. They gained increased popularity in the 1960s and 70s, when partially hydrogenated fat was promoted as a logical substitute to saturated fat because it was made from vegetable oil, which was thought to be healthier than butter.

It was an assumption that was wrong, “but well-founded at that time,” Lichtenstein said.

Fast-forward to the early 1990s, when it was observed that trans fats increase LDL cholesterol concentrations, similar or worse than saturated fat. It was then a new fight for Lichtenstein and many others.

Lichtenstein said a small study that compared corn oil to partially hydrogenated corn fat, which is higher in trans fat, resulted in higher LDL cholesterol concentrations than corn oil.

Momentum built from there. A large study using a wider range of partially hydrogenated fats published in 1999 confirmed these findings.

“This is one of the few situations that the data were extremely consistent in terms of increasing cardiovascular risk. All the investigators came up with the same conclusion,” Lichtenstein said. “It wasn’t particularly controversial. And so began a gradual movement to eliminate partially hydrogenated fat from the food supply.”

That same year, the FDA first proposed that manufacturers be required to declare the amount of trans fats on Nutrition Facts labels, which became law one year later. In 2005, the Institute of Medicine released a report saying that trans fats in the diet should be as low as possible.

Then in 2006, the same year the labeling regulation went into effect, New York set a precedent as the first city to eliminate trans fats from restaurants. Lichtenstein said the city’s ban — which included a multilingual helpline and resources for how to make healthier substitutions and where to buy alternate fats — was a good blueprint for how to legislate a widespread health change.

Consumers were getting smarter and local municipalities listened, Lichtenstein said. Two years later, California banned trans fats in fast food restaurants, with more places to follow.

In addition, few foods made with partially hydrogenated fat are being introduced into the market.

“Industry has really risen to the challenge,” she said. “They’ve heard that consumers don’t want to see partially hydrogenated fat in the ingredient label or anything other than 0g trans fat in the Nutrition Facts panel, so they’ve become innovative.”

The American Heart Association hopes the FDA will finalize the November ruling and remove partially hydrogenated fat from the GRAS list, which will make it difficult for companies to use it in food preparation. Currently food products with less than 0.5 grams of trans fat are allowed to round down and list zero grams on the Nutrition Facts Panel.

While some foods are notoriously high in trans fats, including pie crusts, sticks margarines, cookies and crackers, Lichtenstein cautioned not to assume that a particular food is bad for you. Many of those foods are now reformulated. She advises reading labels, checking out websites and looking over nutrition information on restaurant menus.

“You’re going to have to do a little bit of detective work, but it shouldn’t be overwhelming,” she said.

She also points out that people need to live overall healthy lives.

“It’s the whole picture,” Lichtenstein said. “You can’t be virtuous by focusing on one aspect of the diet or lifestyle behaviors, but ignoring the other.”

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