Trans fat occurs naturally in some meat and dairy products. But artificial trans fat forms when liquid vegetable oils are converted into partially hydrogenated semi-solid fats, such as margarine and shortening, by adding hydrogen to the oils through a process called hydrogenation. ^[1] The hydrogenation process was patented in 1903 and, in 1911, Crisco became the first partially hydrogenated oil widely marketed in the United States. Prior to that time all foods were made without artificial trans fat. Because partially hydrogenated oils allowed for extended product shelf life and greater fry oil stability, they became increasingly popular in the 1950s. ^[2]

As of 2005, naturally occurring trans fat accounted for only 21 percent of total US trans fat intake. The remainder was artificial—found mostly in processed foods, especially baked and fried goods and spreads. For decades, these chemically modified oils entered the food supply without a full evaluation of their effect on people’s health. But in the 1990s, studies began to identify trans fat as a health hazard.

In 2003, the federal Food and Drug Administration (FDA) required that all packaged goods display information on trans fat content by 2006. At the time, the median American intake of trans fat was 2 percent of daily calories. ^[3] The American Heart Association recommended a daily trans fat intake of no more than 1 percent of daily calories—roughly 2 to 2.5 grams of trans fat per day. ^[4] But trans fats were found in a range of popular foods—French fries, bread, donuts, cookies, crackers—which made it difficult to avoid, and meant people were consuming far more than the recommended daily allowance. One McDonald’s order of large fries, for example, then contained 8 grams of trans fat ; a typical Danish breakfast pastry had more than 3 grams; even microwave popcorn had 1.1 grams. ^[5]

The new science and the FDA regulation prompted many food manufacturers to reformulate their products to reduce the amount of trans fat. But the federal regulation did not apply to restaurants, which accounted for one third of daily caloric intake. If the US government would not address the problem, perhaps states would have to take it on. Or, in the case of New York City, the city health department.