The obesity epidemic among U.S. children threatens more than their future health, income, and happiness. It’s already impacting America’s strength and security.

More than 18 percent of children ages six to 11 are obese, and more than 21 percent of adolescents ages 12 to 19 are obese. An additional 15 percent are overweight, according to the Center for Disease Control and Prevention.

Less than one-half of boys and one-third of girls in elementary school are getting the daily recommended exercise.

Aerobic conditioning, not weight, is considered the strongest indicator of health — with low aerobic fitness the strongest predictor of death.

A new study, led by the University of North Dakota and the Children’s Hospital of Eastern Ontario, found U.S. kids ranked 47th out of 50 countries studied. The fittest children lived in Tanzania, Iceland, and Estonia — and the least fit were from Mexico, Peru, and Latvia.

The underlying cause is clear: Research led by Harvard Medical School and the Boston Children’s Hospital’s Department of Cardiology showed that 91 percent of U.S. children score poorly on diet standards, and less than half of boys and one-third of girls in elementary school are getting the daily recommended exercise.

By the time they reach high school, only 7.6 percent of U.S. teens ages 16 to 19 get the required 60 minutes of physical activity per day, according to an American College of Sports Medicine study. That is a very low number.

Related: You Can’t Talk to Girls About Their Weight

Sports, traditionally an avenue for developing self-esteem and leadership skills, have been reduced in many schools due to budget constraints and lack of interest. Some sports like baseball are seeing diminished enrollment and have been removed from many high school and college athletic programs. Extracurricular activities are limited when budgets or time are tight for families, too.

[lz_bulleted_list title=”Emotional Toll of Childhood Obesity” source=””]Social stigma|Increased risk of disease|Depression|Emotional eating|Lower-paying jobs|Less likely to marry[/lz_bulleted_list]

Psychologist Dr. James I. Millhouse, of Atlanta, Georgia, believes the situation is crucial — since kids’ physical status affects them psychologically and socially. He says this will eventually be reflected in society as a whole.

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“The impact on their future is enormous,” he told LifeZette. “Our behavior is created from within us, from who we think we are, from our self-worth. In addition to the disastrous physical implications of being overweight, which we all know, the psychological effects can cause decreased ability to take actions that would be beneficial to them.”

In other words — our younger generation could be developing a victim mentality. They may not have the self-worth to be effective in life, but instead find it easier to blame circumstances or other people for their lack of success.

Related: Why Kids’ Sports Aren’t Fun Anymore

Today’s kids lack “grit” and confidence, said Caroline Adams Miller, of Bethesda, Maryland, who writes about children’s development. Grit is defined as perseverance through challenges.

“Grit is important because it predicts who is successful and who drops out,” she said. “Who makes it through Ranger school? Who gets through Teach for America? Who’s not a quitter?”

The lack of fitness is already impacting military might. Recruiters find it more challenging to find young people today who are fit enough for service, and they acknowledge that keeping military youth in shape is a bigger fight.

Our younger generation could be developing victim mentality, where they simply don’t have the self-worth to be effective in life, but find it easier to blame circumstances or other people for their lack of success.

“I often encourage a potential recruit to take the steps to qualify,” said one recruiter for the Army on a large college campus. Ben Smith (not his real name) regularly counsels potential recruits who would excel in the military but don’t meet the standards for weight.

“Most of the time, I never hear back from them. They won’t take the action necessary. The latest studies show more than 70 percent of young people don’t qualify for enlistment,” he noted.

He stresses that the benefits of military service — on-the-job training, adventure, leadership skills, a maturing process, satisfaction from contributing — are good reasons to change bad habits and get in shape, since the incentive to maintain health is part of the program. Enlistees must maintain healthy standards and are tested every six months. If their weight exceeds the standards, they are assigned to a weight control program of exercise and nutrition counseling.

The Army has gradually been relaxing standards in order to fill its ranks. In 2006, 27.1 percent of 18-year-old applicants were overweight, up from 22.8 percent in 1993. If they don’t meet the weight requirements, these young people can qualify with strength tests, but they must meet the physical standards within a year of enlisting.

A less fit military, however, could greatly impact national security — through fitness, but also because many bright, skilled individuals are omitted from serving. Similar standards exist for police officers, firefighters, members of the U.S. Coast Guard, and emergency personnel of all types.

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Schools and communities have to contribute to the solution, said registered dietician Rima Kleiner of Greensboro, North Carolina. But Kleiner said parents are the greatest influence. With more than half of adults overweight or obese, some poor role models are leading the way.

“It’s inherent in young children to want to move a lot and express themselves through their physical movement,” Kleiner told LifeZette. “Parents, caretakers, and educators need to encourage more physical activity in all children — period. And we adults should be engaging in a lot of that physical activity with them, as positive role models and as a way to bond with children and teenagers.”

Pat Barone, MCC, is a professional credentialed coach and author of the Own Every Bite! bodycentric re-education program for mindful and intuitive eating, who helps clients heal food addictions.