Imagine this: You are a 15 year-old standing in front of a school vending machine, getting ready to satisfy the snack craving you've had since first period. But lo and behold, instead of cookies and chips, every one of the slots behind the glass contains the same healthy stuff your mom and dad fill the cabinets with at home.

That vision could soon be a nationwide reality, thanks to updated nutrition standards from the U.S. Department of Agriculture (USDA), which sets guidelines for the types of foods that are sold in our public schools. The standards are important because students consume about 400 billion calories from junk foods they buy at school every year. This is especially troubling because 33 percent of U.S. children and adolescents are on the way to becoming overweight or obese, and 25 percent of children ages five to 10 exhibit early warning signs for heart disease.

As a retired U.S. Coast Guard admiral and member of Mission: Readiness, a nonpartisan national security organization, I'm especially concerned about the impact of obesity because it’s the leading medical disqualifier for military service; one in four young Americans is now too overweight to join the military. The military recognizes this as a national security issue as our armed forces depend on individuals who are physically fit to serve.

As the "Dadmiral," a nickname coined by my kids, I'm also concerned about the impact on the long-term health of children and young adults. My wife Teresa and I actively strive to instill healthy habits in our children and we will do the same for our first grandchild. Parents and grandparents like us should recognize that sales of junk food and sugary drinks in schools work against family and community efforts to help students develop healthier lifelong eating habits.

We should also work in partnership with educators to help kids be more active. The National Association for Sport and Physical Education recently reported that while nearly 75 percent of states mandate physical activity in K-12 schools, only 4 percent of elementary, 8 percent of middle and 2 percent of high schools offer kids PE on a daily basis.

Many schools cut back on P.E. to allow more time for teaching other core academic subjects despite a wealth of research showing that physical activity can improve cognitive functioning and enhance academic performance. Parents should therefore demand that schools offer at least 30 minutes of P.E. every school day, and they should expect their schools to be accountable for providing this.

Parents and schools should also be aware of the many options for students who aren’t naturally athletic or drawn to competitive sports. Today, educators around the nation are finding innovative ways to make physical education classes engaging to all kids through dance, yoga, bicycling and other non-competitive activities that rely less on athletic ability and more on instilling a love of movement that young people can sustain throughout their lives.

Finally, we should all keep our eyes on what happens as these USDA standards are finalized in the coming months. Special interests will be working hard to make sure that their products, some unhealthy, continue to be available in schools. We saw this previously with updated standards for school meals.

We can avoid a repeat performance by encouraging lawmakers to rely on nutrition experts and support the USDA's efforts to bring these strong standards into practice. It's vitally important to us — the 350 retired admirals and generals who are leading Mission: Readiness's efforts on behalf of national security. And it should be equally important to parents, educators and anyone who wants to get kids on track to live healthy, productive lives.