Being underweight or at risk of being underweight means that your child has a body mass index for his age that is lower than the 5th percentile. This can be normal, especially if your child has been growing and developing normally, has a healthy diet, and is active and energetic. However, being underweight can also be a sign of a problem and deserves a full medical exam, especially if your child is not gaining weight or has recently lost weight, has diarrhea, vomiting, poor appetite, an unhealthy diet, or a low energy level. Children that are underweight can also be at risk of having eating disorders, especially if your child is overly concerned about losing weight, has a poor self body image, exercises excessively, has stopped having periods, or is using laxatives to lose weight. You should see your doctor if you suspect that your child has a medical condition causing him to be underweight or if you suspect an eating disorder.
For adults, a body mass index:
- over 30 is considered obese.
- between 25 and 29.9 is considered overweight.
- between 18.5 and 24.9 is considered a healthy bmi.
- under 18.5 is consider underweight.