For seven years, the Healthy, Hunger-Free Kids Act required America's schools to serve children plenty of fruits, vegetables and whole grains, and kept tight limits on added sugar and sodium in their lunches. These rules were a signal success of the Obama administration: According to one estimate, they would have prevented almost 2 million new cases of childhood obesity.

That's "would have," because Agriculture Secretary Sonny Perdue has rolled them back. In deference to the food industry — most particularly the dairy industry, which has a sizable school market — he softened the standards for whole grains, and reopened the door to sweet chocolate milk and sodium-heavy cheeses. A bunch of states are now suing to get this change reversed. They deserve to succeed, because Perdue's reasoning was weak.

Schools needed more "flexibility," he said, because the higher standards were costing them money, and children just don't like healthy foods. "If kids aren't eating the food and it's ending up in the trash, they aren't getting any nutrition," he said.

But the food didn't end up in the trash — no more, anyway, than school meals ever did. It's true that when the healthier foods were introduced, children complained. Some unsubsidized customers started bringing their own lunches, which temporarily hurt lunchroom revenue. And children served the healthier food reportedly threw some of it out. Yet when researchers looked more closely, they found that kids were actually tossing out less food than before and eating more fruits and vegetables. These salutary changes happened especially when schools made a point of encouraging them. (Hardly surprising: As any parent knows, good habits don't develop spontaneously.)

Only a few schools had trouble sourcing the required foods or preparing lower-sodium dishes. By 2014, the great majority had brought their meals up to the new standards.

Perdue's changes flout the federal Dietary Guidelines for Americans and ignore the alarming reality that nearly 1 in 5 children in the U.S. are obese. The American Heart Association, the Academy of Nutrition and Dietetics and 98% of those who formally commented on his intervention opposed it.

With luck, the states will prevail in the courts. If not, and in the meantime, schools should operate as if Perdue's changes never happened, and maintain good nutritional standards regardless.

FROM AN EDITORIAL ON BLOOMBERG OPINION