Part One: Do Not Talk About Weight
How to talk to your teenager about dieting:
Answer: Don’t.
Don’t use the “D” word. Talking about diets or even weight is bad for all teenagers.
Do not talk about their weight or your weight. 
Unless they are the ones to bring it up. What if they want to go on a diet to lose weight? If they are the ones to bring up the topic, then listen. Listen and don’t interrupt. As you focus on listening, it is okay to ask questions related to how they feel about their body and why they feel that way. For example, “Did someone tell you that you needed to lose weight?”… or…”Did someone suggest that your body is not okay?” If you do ask such questions, let these questions take a back seat to actually listening to them and their answers to these questions.
Many teens turn to dieting to try and change their bodies and feel better about themselves. They often do this in response to others’ negative comments about their weight.
We can help protect teenagers from the emphasis society puts on appearance and weight, and help them develop a healthy perspective, healthy thinking, and healthy habits.
If you are the one who wants your teen to lose weight, don’t tell them that. Don’t coax or pressure them to lose weight. Don’t comment on their weight or their eating habits.
Poor body image can lead to an eating disorder. Parents should not encourage dieting efforts. When families and/or a doctor is very weight-focused, the child or teen tends to become very fixated on reaching a certain weight. If they do lose weight, they usually regain any weight that was lost.
The brain uses various mechanisms to keep the body in a certain weight range.
After losing weight, the body’s regulatory systems do everything they can to get the weight to return to its original point. This principle is referred to as “set point”. For example, when a person eats less than their body wants, the body produces more hunger-inducing hormones, and the person finds eating more rewarding. Furthermore, the more rapid the weight loss, the greater the chance of regaining the weight and regaining it quickly. In addition, the greater and more rapid the weight loss, the greater the chance that the person will go to a weight that is even higher than before – when this happens, the body now has a new “set point”, a new higher weight. The regulatory systems will then try to keep the body’s weight at the new “set point”.
Willpower does not work, because the body’s mechanisms and regulatory systems will eventually override the person’s “willpower”.