But surprisingly, science has only been against trans fats for the past few decades. Through the late 1980s, animal fat substitutes like Crisco and margarine were all the rage, and for a brief moment were even considered a health product. Here’s the story of how America fell in love with, and then quickly slid away from, hydrogenated oils.

In 1902, the scientist Wilhelm Normann found that adding hydrogen to vegetable oil would make it solid, creating trans fats in the process.

From the start, trans fats’ earthy origins were a selling point over that of their rivals, beef fat and butter. When Procter & Gamble debuted Crisco in 1911, it was billed: “It’s all vegetable! It’s digestible!” The shortening was also kosher, leading to the even better (worse?) slogan: “The Hebrew Race has been waiting 4,000 years for Crisco!”

A 1961 Time magazine article railed against the dangers of saturated fat (the kind found in butter and lard), and eventually some consumers began to view margarine and shortening as healthier alternatives.

Oddly, some health groups also trumpeted hydrogenated oil’s benefits.

In the 1980s, some scientists began to associate heart disease with saturated fats, and in response, groups such as the Center for Science in the Public Interest and the National Heart Savers Association (NHSA) began to hound manufacturers for “poisoning America … by using saturated fats,” and as a result “nearly all targeted firms responded by replacing saturated fats with trans fats,” as David Schleifer wrote in 2012 for the journal Technology and Culture.

At the time, many restaurants used beef fat for frying, which groups like CSPI believed was far worse than hydrogenated oils, based on the research of the time. Schleifer writes:

[CSPI’S 1986] Fast-Food Guide specifically criticized Taco Bell, Arby’s, Hardee’s, and Wendy’s for frying in beef fat and tropical oils (that is, coconut and palm oils). But it praised Burger King for switching to vegetable shortening in 1986, which it described as “a great boon to Americans’ arteries.”  The guide also praised KFC, writing that the chain was “fortunately” frying in “partially saturated soybean oil . . . that is much less saturated than beef fat.”

Two years later, the same group released the report Saturated Fat Attack, which described trans fats as “more healthful” than saturated fats, Schleifer wrote.

In 1990, a New York Times food writer said CSPI’s campaign prompted fast-food chains to “slim down” by switching to frying in shortening.

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In the 1990s, the health risks of trans fats began to eclipse those of the saturated variety. A 1990 New England Journal of Medicine found that they raised “bad” cholesterol levels. A 1993 Harvard study found that eating partially hydrogenated vegetable oils increased the risk of heart attacks. Today, it’s estimated that trans fats contribute to thousands of early deaths each year.

The food industry even funded its own study with the goal of proving that trans fats were perfectly safe. However, it only confirmed the earlier findings, and food manufacturers quickly began developing alternatives to hydrogenated oils. Today, even Crisco has changed its recipe, and it now has less that half a gram of trans fat per serving. Which means zero, if you use FDA-label math.

Surprisingly, it was the same organization, CSPI, that later urged the FDA to add trans fats to food labels, and nutrition panels have been required to list the substance since 2006. Though American consumption of trans fat has declined precipitously in recent years, it’s still common in food such as microwave popcorn, margarine, and some coffee creamers. But probably not for much longer.