In 2006, New York City passed a law banning artificial trans fats, also known as partially hydrogenated fats, in all restaurant foods. The law was first applied to fried foods—but not fried bread products like donuts—before taking effect for all restaurant foods in July 2008. A study released on Wednesday in the Journal of American Medical Association Cardiology found that the law, criticized by some as evidence of a “nanny state”, actually lead to a six percent decline in hospitalizations and strokes. To understand why, it helps to know what trans fats are and what they do in the body.

It’s been known since the 1950s that eating a lot of saturated fats is associated with heart attacks and poor cardiovascular health. Saturated fats are a kind of fat found primarily in animal…