Is it healthy for a teenager to diet?

Dieting is a good practice for all people. Dieting means a controlled amount of food intake. It does not mean that you skip some meals. It means that if you are eating 3 hamburgers for lunch, you can reduce it into 1 or 2. That's a normal diet. The most efficient way to lose weight is to do physical exercise coupled with a proper diet.

I don't believe in diets for anyone, in the sense that you're limited to what you can eat, when etc, and are only allowed certain food groups. "healthy", "balanced" lifestyle and food habits are what I support, which basically means breakfast, lunch and dinner and a few healthy snacks (fruit, dried fruit, nuts, juice, water) throughout the day coupled with exercise (walking is truly the best, for general fitness, cardio and losing weight). Make sure to get in all the food groups and eat your energy/carb foods in the morning and not at night (which means cutting down on pastas and breads with dinner if they're a common part of your diet, as they usually don't have time to be worked off by this time). I like to have a bowl of cereal or a few slices of toast (multigrain bread) in the morning, with some water and Yakult, followed by a salad/wrap/sandwich (capsicum, tomato, lettuce, cheese, mayonnaise - just not too much -, and ham/tuna/salami if I want a meat) are my usual ingredients, and a healthy dinner with lots of fresh vegetables and a lean meat. Healthy eating and living is actually really quite enjoyable, once you're adapted - and don't feel like you have to completely give up your pleasures like chocolates, cookies etc - don't binge, allow yourself to have them daily if you like, but cut down the quantities, and up the exercise =)