One, the fact that an increasing numbers of teens are overweight is an issue for serious concern. The first question is... why are so many teens overweight?
The answer in its most basic form is very simple... they aren't getting enough exercise, they eat too much of the wrong things, and they have little knowledge of nutrition. The real answer, however, is much more complicated.
First, a large contributor to teen overweight is the disappearance of physical exercise programs and after school activities that are the first to fall under the ax when budget cuts are near. Extra-curricular sporting activities are too expensive, and fall by the wayside. Students, in some cases, are no longer even obliged to take physical education classes.
Secondly, teens are more and more often participating in sedentary activities. Instead of coming home, grabbing a snack, and going out to shoot a few hoops, or play road hockey, or whatever, teens are grabbing a snack, and firing up the PlayStation. Calories burned? None!
Third, parents are working longer and longer hours. Often there's no one home to cook proper balanced meals. So to alleviate their guilt for not being there, parents buy thier kids everything they ask for. Since most teens know little about nutrition, popular dinners include pizza pops, fries, pizza, and burgers. Lots of fat, lots of high glycemic carbs, and lots of calories. If you eat like this long enough... you'll get fat! Parents, if you're buying your kids this stuff, you're not doing them any favours.
Hordes of overweight teens may be disturbing, but not nearly as disturbing as those who are not overweight, and are desperate to lose a few pounds. The possibility that something like this could spiral into anorexia or bulemia would scare the heck out of me, if I were a parent. In fact, unless your teen has a very serious weight problem, I'd tread very carefully indeed. At an age where self esteem is easily damaged, it's important you let your teen know they're marvellous no matter what they weigh.
If teen weight loss is a concern...
Your best bet is to try your best to ensure there are always nutritious meals available for your teens - pre-cook and freeze them if possible. That's the quickest and most efficient road to teen weight loss.
Teens, don't measure yourself against what you see on T.V. - that is not reality. Don't deprive your body of the proper nutrition you need to build the foundation for a healthy body. What you do now will affect you for the rest of your life - so eat well. Yes, that means eat your veggies - they are good for you!
To sum up, I'd say that unless a teen is severely overweight, teen weight loss boils down to the very basics -- nutritious meals, no junk. Oh, yes, and regular exercise. No rocket science here! :-)