Newly proposed US nutritional rules would limit the amount of sugar in school meals for the first time, while reducing sodium levels.
The agriculture secretary said the programme, to be rolled out by 2029, is a “national security imperative”.
But critics said the plan would drive students to less-healthy food choices.
The policy is part of a drive by President Joe Biden’s administration to curb childhood obesity, diabetes and nutrition-related diseases by 2030.
“Many children aren’t getting the nutrition they need, and diet-related diseases are on the rise,” Agriculture Secretary Tom Vilsack said in a statement announcing the proposed rule. “We must all step up to support child health.”
The federally subsidised school meals programme serves free or low-cost breakfast to more than 15 million children and lunch to nearly 30 million children every day.
Among several changes, the programme proposed by the Biden administration would limit added sugars from some of the most common sugary school foods, including yogurts, cereals, flavoured milks and desserts, starting in autumn of 2025.
Under one proposal, all public schools would be allowed to serve only 10g of sugar per 8oz of flavoured milk (many popular chocolate milk products contain at least 20g).
Future years would see additional limits on added sugar and sodium.
The new policy is a “step in the right direction”, Dr Selvi Rajagopal, an assistant professor at Johns Hopkins University School of Medicine, told the BBC.
Critics, however, said students would simply leave campus to eat fast food.
“Nutrition is only nutrition if they eat it,” Michael Gasper, nutrition services supervisor for the School District of Holmen, Wisconsin, told Reuters news agency.
The US Department of Agriculture will collect comments on the proposed rule.