* Obesity a top reason young adults can't join military -experts
* Report: U.S. school kids eat 400 billion excess calories a year
* Retired military leaders push stronger school food rules
By Susan Heavey
WASHINGTON, Sept 25 (Reuters) - Former U.S military leaders have identified a latent threat to the potential for a leaner, more agile fighting force: the school vending machine.
In a report to be released on Tuesday, a group of 300 retired military officers said school-age children are eating 400 billion excess calories a year - the equivalent of 2 billion candy bars - from junk food sold in such machines as well as in snack bars and cafeterias that should be off-limits.
Those extra calories from candy, chips and sugary drinks amount to about 130 calories a day, which over a student's school years can lead to extra pounds.
"The calories add up," the U.S. generals and admirals said in their report, which calls for tougher standards on the snacks schools can sell.
"While limiting the sale of junk food is not a solution by itself for the childhood obesity epidemic, it is part of the solution," wrote the retired officers, who are part of a nonprofit group called Mission: Readiness, focused on youth issues.
Military experts have long been worried that rising obesity is making it difficult to find fit recruits. But the report places new pressure on government officials to revamp nutritional guidelines for foods sold in U.S. schools.
"The folks that are going to enter the military in 2025 are in school right now. So it's up to us to ensure that when those children reach the age of between 17 and 24 that they are ready or eligible to join the military," Retired Air Force Lieutenant General Norman Seip, a member of the group, told Reuters.
The number of overweight or obese children keeps rising and more than one third of American children and teenagers are too heavy, government statistics show. Other data shows that such children are also more likely to be heavier as adults.
"It's a strong reminder of the seriousness and the extent of the obesity epidemic, showing how far reaching it is that even the military is concerned about it," said Margo Wootan, who oversees nutrition policy at the Center for Science in the Public Interest, a consumer advocacy group.
The U.S. Department of Agriculture is considering new standards for so-called "competitive" foods sold outside of traditional school meals. USDA officials have said they are still working on the new rules, which were due in December. They have not said when the rules will be released.
Doctors, public health experts and consumer advocates want the USDA to update limits on calories, fat and sodium in snack foods and to restrict beverage sales to healthier options such as naturally sweetened fruit juices and low-fat or non-fat milk.
Food and beverage manufacturers have said they support efforts to revamp school nutrition guidelines, but they cite lack of exercise and other issues as part of the problem.
30 POUNDS OVERWEIGHT
"Recruiting is always a challenge," said Eileen Lainez, a Defense Department spokeswoman.
Only 25 percent of young U.S. adults qualify to enlist in the military. Among the remaining 75 percent, more than a third have weight-related problems, she said, adding that the military is still meeting its recruiting goals.
It is still alarming that so many are too fat and that future enlistees are likely to follow suit, Seip said.
"And we're not talking a couple pounds here, we're talking about an average of 30 pounds (13.6 kg)," he said of the overweight recruits who do not make the cut.
"The trend is not slowing down," said Seip, a who retired in 2009 after joining the U.S. Air Force about 30 years ago.
Over those three decades, the number of obese American children has more than tripled.
Drinks sold in schools, especially sugary sodas, have been a particular concern.
The beverage industry launched voluntary guidelines in 2005 to limit student access to full calorie sodas that it says is working.
Various studies have shown mixed results on the impact of children's soda consumption. But last week, three published studies offered the strongest evidence yet that sugary drinks play a leading role in expanding U.S. waistlines.
According to Tuesday's report, some students are consuming about 45 fewer calories a day from such beverages on average, even though they are still widely available in many schools.
USDA data has shown students consuming about 177 extra calories from school snacks and sugary drinks, but without such beverages the remaining more than 130 calories a day appear linked to junk food, it said.
Wootan said that reflects the steps a number of school districts have taken to limit sugary drinks. "There has been some improvement in beverages, but for snack foods there hasn't been as much progress," she said.
As for those 2 billion hypothetical candy bars?
Their 400 billion calories would weigh more than the U.S. Navy's longest aircraft carrier, the 70,000-ton Midway, the report said.