The regulations, originally due in 2011, largely mirror the U.S. Department of Agriculture's proposal from February that limited the fat, salt and sugar content in school snacks and capped portion sizes.
The standards are seen as a critical step in improving students' eating options under a 2010 law revamping school foods. Schools have until July 1, 2014, to implement the new rules.
Though many applauded the new regulations, Sandra Ford, president of the School Nutrition Association, said changing school menus to meet USDA requirements could burden schools already working to offer healthier menus.
"Complex regulations can present unique challenges and unintended consequences when put into practice," Ford said.
Many U.S. children eat more than half of their daily calories at school. The regulations will cover some 50 million children attending more than 100,000 schools that are part of the federal school lunch program.
"This is a significant change in the way young people in this country eat and what they eat, and I think it's going to make a significant difference," Agriculture Secretary Tom Vilsack said on MSNBC.
The standards only apply to foods and beverages sold on school campuses during the day, and limit vending machine snacks to a maximum of 200 calories per item - less than, for example, many regular-sized candy bars.
Food sold at after-school activities, such as sporting events, is not subject to the regulations.
"This is an historic nutrition policy that will do a lot to improve children's diets and address high rates of childhood obesity," Margo Wooten, director of nutrition policy at the Center for Science in the Public Interest, told Reuters.
"Parents won't have to worry their kids are using their money to buy junk foods and sugary drinks instead of buying a healthy lunch," Wooten said.
All foods sold must meet competitive nutrient standards, meaning they must have fruits, vegetables, dairy or protein in them or contain at least 10% of the daily value of calcium, potassium, vitamin D or dietary fiber.
USDA gave the public 60 days to comment after it released its proposals in February. The final guidelines, while mostly unchanged, have incorporated a stricter calorie limit on drinks in high schools.
Twelve-ounce drinks cannot exceed 60 calories, less than the calorie count of most sodas.
And the portion sizes vary between age groups. Younger students will be able to buy water, 100 percent juice, and low-fat and fat-free milk in 8oz. servings, while high school students can also purchase 20oz. calorie-free drinks.
By improving the choices available to U.S. students outside of breakfast and lunch, officials hope to make a dent in childhood obesity in a nation where one-third of those under age 18 are considered overweight or obese.
