You might expect your child to gain weight if he's eating unhealthy foods and not exercising, but sometimes weight gain occurs for other reasons. It's normal for children to gain weight as they grow -- and gain even more during puberty -- but you'd normally expect him to stay within the same weight percentile. If he's jumped from the 30th percentile to the 80th, and you haven't noticed a major change in diet, it's time to address the problem.
If your child is taking medication on a daily basis, the weight gain could be stemming from this, particularly if it started happening soon after she started the medication. Antidepressants, anti-seizure medications, antipsychotics and steroids commonly list weight gain as a side effect. These are by no means the only medications that can cause weight gain, though. Talk to your child's doctor to see if this could be the cause and whether or not there's an alternative. If not, you may find that the benefits of the medication are worth the negative effects of weight gain. It's all about balance.
Though uncommon, certain illnesses can cause your child to gain weight. If he's insulin-resistant, for example, his body isn't properly processing the sugars he eats, causing the weight gain. Careful diet changes, such as reducing or eliminating refined sugars, can help. Some studies have also shown that low leptin levels can cause weight gain by hindering the body's ability to tell when it's full, according to the American Academy of Pediatrics. Hypothyroidism reduces metabolism and could be the cause if your child doesn't seem to be eating more but is still gaining weight.
Many people eat for reasons other than being hungry. Your child might be eating because she's anxious or stressed. She may also have an eating disorder like bulimia. In many cases, your child knows that this type of eating is "wrong" and may hide it from you, keeping a stash of candy and chips hidden in her room. She may only eat these foods alone, during the day when you're at work or late at night. It may seem like she's eating a healthful diet because she eats normally in front of you, but she's getting the extra calories when you're not around.
Tracking for the Doctor
Your child's doctor will take note of a large weight gain at your child's annual exam. If the weight gain is occurring in the middle of the year, though, don't hesitate to make an appointment. To prepare for this visit, take careful notes about what your child is eating and how the weight gain has occurred. For example, it's more worrisome if your child experienced a 20-pound weight gain in a month rather than over a period of three months. Help your child keep a food diary for a few days, including the specific foods he has eaten, along with portion sizes. This will show, for example, that he is either eating within the normal range or that his appetite has either increased or decreased, which could be important in diagnosing the problem.