Updated

School cafeterias would have to hold the fries — and serve kids more whole grains, fruits and vegetables — under the government's plans for the first major nutritional overhaul of students' meals in 15 years.

The Agriculture Department proposal to be announced Thursday applies to lunches subsidized by the federal government. The guidelines, which were obtained by The Associated Press and confirmed by department, would require schools to cut sodium in those meals by more than half, use more whole grains and serve low-fat milk. They also would limit kids to only one cup of starchy vegetables a week, so schools couldn't offer french fries every day.

Agriculture Secretary Tom Vilsack said the new standards could affect more than 32 million children and are crucial because kids can consume as much as half of their daily calories in school.

"If we don't contain obesity in this country it's going to eat us alive in terms of health care costs," Vilsack said Wednesday.

While many schools are improving meals already, others are still serving children meals high in fat, salt and calories. The new guidelines are based on 2009 recommendations by the Institute of Medicine, the health arm of the National Academy of Sciences.

The announcement comes just a few weeks after President Barack Obama signed into law a child nutrition bill that will help schools pay for the healthier foods, which often are more expensive.

The subsidized meals that would fall under the guidelines proposed this week are served as free and low-cost meals to low-income children and long have been subject to government nutrition standards. The new law for the first time will extend nutrition standards to other foods sold in schools that aren't subsidized by the federal government, including "a la carte" foods on the lunch line and snacks in vending machines. Those standards, while expected to be similar, will be written separately.

The announcement is a proposal, and it could be several years before and schools are required to make changes.

The new USDA guidelines would:

— Establish the first calorie limits for school meals.

— Gradually reduce the amount of sodium in the meals over 10 years, with the eventual goal of reducing sodium by more than half.

— Ban most trans fats.

— Require more servings of fruits and vegetables.

— Require all milk served to be low fat or nonfat, and require all flavored milks to be nonfat.

— Incrementally increase the amount of whole grains required, eventually requiring most grains to be whole grains.

— Improve school breakfasts by requiring schools to serve a grain and a protein, instead of one or the other.

Some school groups have criticized efforts to make meals healthier, saying it will be hard for already-stretched schools to pay for the new requirements. Some conservatives, including former Alaska Gov. Sarah Palin, have charged that telling children what to eat is a case of government overreach.

Vilsack says he understands the new standards may pose some challenges for school districts, but he believes they are necessary. He compares obesity and related diseases like diabetes to a truck barreling toward a child, and the new guidelines to a parent teaching that child to look both ways before crossing the street.

"You want your kid to be able to walk across the street without getting hit," he says.

According to the USDA, about a third of children 6 to 19 years old are overweight or obese, and the number of obese children has tripled in the past few decades.

The Agriculture Department also is planning to release new dietary guidelines for the general public, possibly as soon as this month. Those guidelines, revised every five years, are similarly expected to encourage less sodium consumption and more grains, fruits and vegetables.