WASHINGTON - The Pentagon is facing a fast-growing national security threat that could prove one of its trickiest challenges yet: the US' obesity crisis. As the epidemic grows, obesity is posing a threat to our nation's security as well," the Council for a Strong America states in its new report. According to the Defense Department, obesity is one of the top reasons why 71 percent of US citizens aged 17-24 do not meet the military's sign up requirements. Encouraging healthy lifestyles early in life will help our nation prepare for future challenges," retired Air Force general Richard Myers said. Of the world's most populous countries, the Unit ed States leads the way in terms of obesity among children and young adults, at 13 percent.