In a victory for everyone from Jamie Oliver to Michelle Obama, the school cafeterias of America are to redesign their menus around strict calorie limits and minimum quotas of healthy food.
Guidelines unveiled by the US Department of Agriculture this week will require schools to offer pupils more whole grains, less sodium and fat, and twice as many fruits and vegetables as before.
But the changes aren't a complete success for health advocates. After extensive lobbying of Congress by the junk food industry, pizza can be classified as one of the two "vegetables" that a child must now be offered each day, on the grounds that it contains tomato paste.
Mrs Obama, who has made tackling childhood obesity her signature issue as First Lady, joined Agriculture Secretary Tom Vilsack at a school in Virginia on Wednesday to unveil what are the first changes to nutritional guidelines in the US for 15 years.
"When we send our kids to school, we expect that they won't be eating the kind of fatty, salty, sugary foods that we try to keep them from eating at home," she said. "We have a right to expect that the food they get at school is the same kind of food that we want to serve at our own kitchen tables."
To illustrate how she hoped the guidelines will be interpreted, Mrs Obama joined 800 children for lunch. In place of the traditional American food of hamburgers and hot dogs, they were served turkey tacos, brown rice, and fresh salsa.
Calorie limits will be calculated on a sliding scale, depending on a child's age. Younger pupils will be expected to consume no more than 650 calories at lunchtime. That figure rises to 700 and then 850 for older teenagers.
The rules apply to all public schools in the nation, and will affect roughly 12 million children. At present, America is by some distance the fattest nation in the world. One in three children between the ages of two and 19 is considered overweight, and around 17 per cent are clinically obese.
But efforts by the Obama administration to limit servings of chips to two per child per week were also derailed, largely at the behest of lawmakers who receive generous campaign funding from potato growers. Margo Wootan, a nutritionist from the Centre for Science in the Public Interest, said she was "disappointed" at the setbacks, but added: "At least the pizza will be lower in sodium and have a whole grain crust and be served with an additional vegetable on the side."
Republicans have voiced opposition to improving children's diets, arguing that imposing strict guidelines on schools represents government over-reach.