By the late 1940s, the American Heart Association’s rise coincided with funding from Procter & Gamble—a company whose major products included the hydrogenated vegetable oil Crisco.

Soon after, the AHA promoted dietary advice favoring vegetable oils and discouraging saturated fat, while other factors—like ultra-processed foods—were swept under the rug.

The result was a widespread belief that dietary fat—especially saturated fat—raised cholesterol levels, which were assumed to cause heart disease.