Teens need lots of calories and good nutrients particularly calcium and iron which are important for all the growth and development happening at this stage of life. Calorie requirements for teens vary just like they do for adults but on an average a teenage girl needs between 1800 to 2100 calories a day while boys need between 2200 to 2700 calories daily. That sounds like a lot but remember that teens are growing and their bodies need a lot of fuel to support healthy growth and to get them through their crazy schedules. (Read: Eat and lose weight: 10 food items