This year, 30,000 Scouts ages 12 to 20 and their leaders were required to meet a threshold for body mass index and other health factors before being allowed to participate. Jamboree applicants with a BMI — a measure of body fat determined through height and weight — of 40 or higher were deemed ineligible. Those who fell between 32 and 39.9 faced providing additional health information to Jamboree medical staff.Nationally, about 17 percent of children ages 2 to 19 are considered obese — triple the rate from a generation earlier, according to the Centers for Disease Control and Prevention.“We required a level of fitness in order to come to the Jamboree that we haven’t required before,” McCarthy said. “And that has motivated an enormous return in terms of both kids and adults getting serious about improving their health.”Soon, the Scouts will know why. Besides offering a whole lot of fun, dozens of venues will test their physical skills and fitness. At some point during the Jamboree, every participating Scout will be asked to take a 3-mile trek up a mountain.Their reward: A barbecue waiting at the top.