SINCE the publication of the federal government’s 1980 Dietary Guidelines, dietary policy has focused on reducing total fat in the American diet — specifically, to no more than 30 percent of a person’s daily calories. This fear of fat has had far-reaching impacts, from consumer preferences to the billions of dollars spent by the military, government-run hospitals and school districts on food. As we argue in a recently published article in The Journal of the American Medical Association, 35 years after that policy shift, it’s long past time for us to exonerate dietary fat.