“Even when I was a graduate student,” says Enig, who didn’t return to school until she had raised three kids and was in her thirties, “I couldn’t understand why all these scientists, as well as the American Heart Association and the like, were all blaming saturated fats for the rise in heart disease.” After all, she reasoned, heart disease started going up just as Americans were cutting back on butter. Enig figured the answer must lie elsewhere, possibly lurking in the foods Americans had been steered toward as a supposedly healthy alternative to butter: vegetable oils, margarine, more processed foods. “The trans fat question was just out there,” she remembers, “and no one was studying it.”

Trans fats came to America from—of all places—Germany, the land of pork sausage and Muenster cheese, a land famously unafraid of fat in all its glorious, natural variations. In 1901, after a French chemist had devised a way to alter matter by bombarding it with hydrogen atoms, a German scientist figured out how to apply that technology to convert oils into solids. These solid oils, called “partially hydrogenated,” contain trans fats, and their debut as a food product came in the form of margarine. (Small amounts of trans fats are found naturally in foods like dairy pro­ducts and meat, but they are chemically different and occur in such small amounts as to be almost negligible.)

Margarine did not get a warm welcome in this country in the early 1900s. The dairy and meat industries weren’t keen to have it supplant butter and lard, then staples of the American diet. Many states responded to industry pressure by passing “margarine laws” that limited the sale and distribution of this new rival. Even the pleasant yellow color of margarine, made to mimic butter, was prohibited. (Early margarines came in white blocks, to evade the color ban, with a dye capsule that you had to knead into them.) But margarine, unlike butter, didn’t melt on hot days and was, above all else, cheap. Following President Truman’s abolition of the margarine laws, in 1950, margarine manufacturers began selling it as it appears today, in quantities that, since about 1970, have been twice those of butter.

One boon to margarine manufacturers was the growing consensus in the 1970s that saturated fats cause heart disease. Butter and lard were out. For the multitude of packaged products with saturated fats on the ingredient list, a replacement had to be found, and trans fats became the solution. They gave products both a long shelf life and the rich mouthfeel, as the industry calls it, that consumers like. Moreover, trans fats gave products an edge because they were cholesterol-free, another dietary priority to emerge in the ’70s. Margarine manufacturers used the slogan “Healthy for Your Heart” and marketed the product like a drug to doctors.

How is it this line of thinking went unquestioned for so long? In Europe, Canada, and the U.S., a scattering of people pursued trans fats research from the 1960s on, but the studies were very expensive and, according to one researcher, “not very glamorous.” More importantly, those taking on this stepchild of a topic had to deal with the tidal wave of industry pressure unleashed against them at meetings, conferences, and events. Their papers were rebutted with unusual ferocity, and their research funding was scarce.

Dr. Thomas Applewhite and Dr. J. Edward Hunter, industry scientists employed, respectively, by Kraft and Procter & Gamble (which held the original U.S. patent for trans fats), were the principal forces behind this criticism. Given that they worked for two food giants, the potential for bias was apparent, but their ability to fund research (as well as their own encyclopedic knowledge of the field) meant they could exercise considerable influence.

“Applewhite and Hunter worked behind the scenes,” says Dr. Randall Wood, a professor emeritus at Texas A&M University who has researched trans fats. “I would say they had ways of finding out if a paper was going to be reviewed on a subject. There were papers, ironclad, indisputable evidence, and the reviews would be so negative. You’d get paranoid.”