. The main reasons for teenage obesity are – overeating, less activity or inactivity and excess TV viewing. If a teen eats and drinks more than the body needs, the excess energy stores in the form of body fat. And, added to this, if the teen is not doing enough regular exercise, it worsens the problem. Many studies have shown that teens, who have a television in their bedrooms, have the tendency to watch it more. This leads to inactivity, the main culprit of teenage obesity.