Though many people would love to lose a few pounds, weight loss when you aren't actually trying to lose weight is troublesome. An unintentional weight loss in your teen could signify an underlying problem, rather than a reason to rejoice. If she's lost more than 10 pounds or 5 percent of her body weight within six to 12 months without trying to lose weight, it's time to visit the doctor, according to the Mayo Clinic.
Unexplained weight loss is a symptom present in a wide variety of medical problems. It could be from cancer or AIDS, diabetes, Crohn's disease, celiac disease or hyperthyroidism, for example. If you suspect that there might be a medical problem for the weight loss, consider other symptoms your teen has, as these will help narrow down the problem. Stomach troubles with weight loss might point to celiac disease, while excessive thirst might point to diabetes.
Some teens respond to stress or depression with a change in appetite. It might seem that your child is eating normally, but she might be picking at her food at the table and not eating as many in-between snacks as she used to. This will result in unintentional weight loss. Worry about this if your teen is crying more frequently or just seems down all the time, wanting to spend time alone.
The teenage years are when many kids first get braces. This makes eating more difficult and painful, so the child eats less overall. You may also find that due to the pain or trouble of certain foods getting stuck in his teeth, he's making healthier choices; if chips are a problem, for example, he might reach for a yogurt instead.
Body Image Problems
Disordered eating is another problem that tends to crop up in the teenage years. Your teen may seem to eat in front of you, but is actually hiding her eating disorder. She might purge her food after dinner, throw away the food you packed for her lunch or use laxatives improperly. Take note if she seems happy with her sudden weight loss or is constantly talking about wanting to lose weight.
Teens also start becoming more active as they get involved in school activities. You might expect to see weight loss if your child is participating in a sport, but it may seem strange if he's working on the yearbook or staying late for science club. Even though he may not be getting as much physical activity, he's also not sitting at home in front of the TV, a prime time for indulging in unhealthy snacks. He could simply be too busy for eating out of boredom.