In the decade since the U.S. began fighting in Iraq and Afghanistan, the frontline of war has been located in the Middle East. That battle zone is now moving closer to home. According to former Joint Chiefs of Staff Chairman James M. Loy, obesity is the single biggest threat facing the United States today. One in four Americans is too fat to serve, and obesity related medical expenses cost the Pentagon over $1 billion each year. A look at the combat against calories.