The requirements are part of the Healthy, Hunger-Free Kids Act of 2010, which seeks to curb child obesity by changing food in schools and promoting healthy eating. The law required the Agriculture Department to set nutrition standards for items sold during the school day, known as "competitive foods."
The agency has jurisdiction since it oversees the federal school-lunch program, which provides low-cost and free lunches in 100,000 public and non-profit private schools. Thirty-nine states already have standards in place governing the foods offered at school, aimed at bolstering nutrition.
"Altogether, the policy and the set of standards that USDA announced is stronger than what exists in any states and most school districts I can think of," Wootan said by telephone.
Children consume as many as half their daily calories in school, where they spend more time than any location except their homes, according to the Pew Charitable Trusts, which underwrites food safety programs. Studies show snacks add 112 calories to the average elementary-school student's daily diet, and those who live in states with strong snack policies gain less weight over three years than those without regulations.
The USDA rules limit salt, sugar and fats, with exemptions for natural products including nuts and seeds, dried fruits and fat-rich seafood. Each item must contain less than 200 calories, including accompaniments, and no trans fats.
There are specific requirements for what is allowed in each item. The first ingredient must be whole grain, vegetable, fruit, dairy or type of protein. Combination foods must have at least one-quarter cup of a fruit or vegetable. If water is first on the label, then one of those ingredients must be second.
There is an exception to the stringent requirements. Foods that provide at least 10 percent of the recommended daily value of calcium, potassium, vitamin D and dietary fiber are also allowed, at least temporarily. Starting in 2016, those nutrients must come naturally, rather than from fortification.
"After a phase-in period, companies won't be able to just fortify foods with cheap nutrients and call them healthy," Wootan said. "It's the difference between fortified junk food and real food."