Unfortunately, most kids’ activity decreases dramatically when they enter adolescence. Even with motivation, losing weight for most teenagers can be difficult. According to a Temple University public health study featured on the Huffington Post, this is because teenagers are not very health conscious (their primary concern is losing weight), or are uninformed about healthy eating habits. They studied high school students, 14% of which were obese, and 76% of these claimed they were trying to lose weight. But they have low success rates because they unknowingly adopt the wrong weight loss methods (like skipping meals, smoking, avoiding protein, and increasing intake of junk food etc.)
Obese teens who said that they were trying to lose weight were twice as likely to smoke as obese teens who were not trying to lose weight. And while obese girls who were trying to lose weight were 40 percent more likely to exercise for an hour per day than those who were not trying to lose weight, they were also three times as likely to drink soda every day — undoing many of the benefits of exercising. For obese boys, those trying to lose weight were actually found to be less active than boys who were not trying to lose weight — in fact, they were 47 percent more likely to play video games for three hours each day.
The article touches on the importance of sleep during adolescence. Inadequate sleep (less than 8hrs) boosts weight gain, as it makes us crave unhealthy foods like junk food. This is especially true in children. Parents, (and schools) should try to inform kids of healthy lifestyle and food choices.