Congress can fight the epidemic of childhood obesity by getting "junk" food out of school stores and snack machines, a parent-teacher group and the American Dietetic Association said on Tuesday.

They backed an overhaul of federal rules so all food sold in schools must meet nutritional standards similar to school lunches. High-fat, high-sugar or high-calorie "competitive" foods now can be sold anytime outside of school cafeterias.

Roughly 17 percent of school-age children are obese, triple the rate in 1980 rate and "an epidemic in the United States," says the Centers for Disease Control and Prevention. Obesity increases the risk of diabetes, heart disease, arthritis and other chronic illnesses.

"The best interests of our children demand that the nutrition standards be modernized," said Byron Garrett of the National Parent Teacher Association during a Senate Agriculture Committee hearing on "reforming nutrition for kids in school."

National standards are needed, the dietitian group said, so all children "have equal opportunity to a healthy school environment."

U.S. child nutrition programs like school lunch and the Women, Infants and Children feeding program are due for renewal this year. They cost $21 billion a year.

School meals comply for the most part with the Dietary Guidelines for Americans, which encourage exercise and more consumption of fruits and vegetables, said Agriculture Committee chairman Tom Harken.

But sugary drinks, candy and high-fat snacks undermine the investment in good food, Harken said, because "on an average day only 62 percent of American kids who could do so eat the federally sponsored lunch."

Sens. Richard Luxar and Amy Klobuchar spoke in favor of national standards during the hearing. Sen. Mike Johanns said he disliked heavy-handed regulation and Sen. Saxby Chambliss said physical exercise should be part of the school day.

Reginald Felton of the National School Boards Association noted that some schools rely on snack sales to help cover costs. He contended that students would buy snack food outside school if it was unavailable inside the building.

Susan Neely of the American Beverage Association said that under a 2006 voluntary guideline, "there has been a 58 percent decrease in beverage calories shipped to schools." She said the guideline should become mandatory. Mars Snackfood US said it supported an update of school nutrition standards and described the work of the nonprofit Alliance for a Healthier Generation to limit fat and sugar content in snack foods.