BOSTON — 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.

The guidelines changed how Americans eat. By the mid-1990s, a flood of low-fat products entered the food supply: nonfat salad dressing, baked potato chips, low-fat sweetened milk and yogurt and low-fat processed turkey and bologna. Take fat-free SnackWell’s cookies. In 1994, only two years after being introduced, SnackWell’s skyrocketed to become America’s No. 1 cookie, displacing Oreos, a favorite for more than 80 years.

In place of fat, we were told to eat more carbohydrates. Indeed, carbohydrates were positioned as the foundation of a healthy diet: The 1992 edition of the food pyramid, assembled by the Department of Agriculture, recommended up to 11 daily servings of bread, cereal, rice and pasta. Americans, and food companies and restaurants, listened — our consumption of fat went down and carbs, way up.

But nutrition, like any scientific field, has advanced quickly, and by 2000, the benefits of very-low-fat diets had come into question. Increasingly, the 30 percent cap on dietary fat appeared arbitrary and possibly harmful. Following an Institute of Medicine report, the 2005 Dietary Guidelines quietly began to reverse the government’s campaign against dietary fat, increasing the upper limit to 35 percent — and also, for the first time, recommending a lower limit of 20 percent.