“START HOARDING donuts,” a Reason.com blogger declared Thursday. “The FDA is banning trans fats.”

In fact, the preliminary move by the Food and Drug Administration (FDA) to phase out partially hydrogenated oils, the source of most of the trans fat in the food supply, is an insignificant imposition on liberty that would save lives. People won’t lose their doughnuts, french fries, pizza or other indulgences because of it. The FDA should implement its ban as quickly as possible.

Trans fat is about the worst kind of fat you can eat. It increases your LDL — “bad” — cholesterol and is thought to lower your HDL — “good” — cholesterol. It’s worse than the saturated fat in butter. It found its way into Americans’ food because it is a little cheaper than some other oils and has a long shelf life.

In 2006, the FDA began requiring food labels to list trans fat content as a separate item. New York Mayor Michael R. Bloomberg (I) went further, banning the use of large amounts of trans fat entirely. His pioneering effort inspired cities and counties around the country to pass their own restrictions on trans fat.

The combined effect has been a dramatic, but still inadequate, reduction in trans fat consumption, from an average of 4.6 grams per person per day before these policies were phased in to 1.3 grams per day. Haven’t really noticed? That’s because, in most cooking, there are ready substitutes that don’t significantly affect how food tastes. In cases where it’s harder to replace trans fats, companies have invested in finding suitable replacements. So New Yorkers have been able to carry on eating McDonald’s french fries and Kentucky Fried Chicken. Meanwhile, the New York Department of Health and Mental Hygiene found only a slight increase in saturated fat intake, suggesting that restaurants weren’t simply replacing a bad fat with the next worst one on the list.

Applying a national ban would complete this public-health success. People would live longer: The agency reckons that the policy would prevent up to 20,000 cases of heart disease and 7,000 deaths every year. People’s lives would also be better, with fewer people having to cope with the lingering effects of heart attacks, for example, or having to miss work to deal with heart trouble. All that for eliminating one unnecessary ingredient.

The FDA will solicit public comment and work with food companies to determine how to make the transition off trans fats as smooth as possible. It’s unclear how long it might take to wring the stuff out of the food supply. The sooner, the better.