A teen's weight issues can fall into one of two categories: either he/she weighs too much or too little. Depending on your teen's weight issue, you'll have a different approach. However, if your teen is suffering from an eating disorder, you'll need to involve professionals to address the underlying emotional and psychological issues triggering the eating disorder. The hints below are simply meant to help your teen either gain or lose weight.
If your teen is underweight, and not suffering from an eating disorder, it's likely that he/she is simply not consuming enough calories to keep up with his/her body and or activities. During adolescence, a teen's metabolism can increase, his/her body is growing, and he/she might be spending more time involved in sports. So the changes you make should focus on getting more (healthy) calories into your teen. You can increase food portions. You can also add some healthy, yet high-calorie foods to his/her diet, such as almonds, walnuts, scoop of sour cream, extra butter, or natural peanut butter. Using whole milk, you can prepare a number of good, yet high-calorie, drinks, such as fruit smoothies and chocolate milk.
If your teen is overweight, he/she is probably already concerned about it. So talk gently with him/her to put a plan together to lose weight. First, make sure he/she has a realistic expectation of how much he/she should lose. Most overweight teens are fairly sedentary, so get them moving. From chores to new lessons (dance, martial arts -- check out your local community center) to just walking to school (does he/she really need you to drive?), you have plenty of options to give your teen. You also want to promote healthy eating habits, so stay away from quick-fix diet fads. As the parent, you do have a lot of control over your teen's food, so use it (in a supportive way). Make sure your teen eats a healthy breakfast, which usually keeps teens from eating too much throughout the rest of the day.