Former military leaders say one of the biggest threats to the national security of the United States is not another country or even terrorism, it's obesity.

A new report by 300 retired military officers finds one in four young adults are too overweight to join the U.S. military. The report also finds school-age children are eating 400 billion excess calories a year.

The non-profit group Mission: Readiness published the report this week. The organization's members include Richard Myers, the former Chairman of the Joint Chiefs of Staff and James M. Loy, former Deputy Secretary of Homeland Security.

"The calories add up," the retired generals and admirals said in the report. "While limiting the sale of junk food is not a solution by itself for the childhood obesity epidemic, it is part of the solution."

The U.S. Department of Agriculture is working on new standards for items sold at schools that are not part of traditional meals such as chips and snacks.

Mission: Readiness supported the Healthy, Hunger-Free Kids Act of 2010. The law updated the nutrition requirements for the first time in 15 years.

The changes require more fruits, vegetables, whole grains, fat-free and low-fat milk in school meals. The law also updated calories limits for the National School Lunch Program.

Doctors and public health experts want the USDA to also update limits on calories, fat and sodium in snack foods and encourage the sale of alternatives to soda and sugary drinks.

*Information from Reuters was used in this report.