Slim or underweight?
Many parents worry when their child looks thinner than others or eats little. Often there is no reason to: children are built differently, and some are simply slight. Still, there are situations in which a low weight should be looked at more closely. This article explains how underweight is defined in children and how to tell when a visit to the paediatrician makes sense.
How underweight is defined in children
In children and adolescents, weight is not judged against fixed BMI limits but against percentiles. According to the guideline of the German Working Group on Obesity in Childhood and Adolescence (AGA), underweight means a BMI below the 10th percentile of children of the same age and sex. Below the 3rd percentile it is called severe underweight.
This also means that, statistically, ten in 100 healthy children are below the 10th percentile. A value in this range is therefore first of all a prompt to take a closer look — not a diagnosis. The BMI calculator for children and teens shows where your child stands.
The trend is decisive
More important than a single value is the development over time. A child who has grown steadily along the 10th percentile for years and feels well is healthy in the vast majority of cases. It is different if the BMI curve drops markedly, crossing several percentile lines downwards within a short time, or if the child stops gaining weight even though they are growing.
The child health booklet helps here: it records height and weight from all previous check-ups, making it easy to see whether your child is following their curve.
Warning signs to take seriously
If you notice any of the following, make an appointment with your paediatrician soon:
1. The child loses weight unintentionally or their weight has stagnated for months.
2. The BMI is below the 3rd percentile.
3. The child often seems tired or exhausted, or is frequently ill.
4. There is persistent abdominal pain, diarrhoea or other digestive problems.
5. In teenagers: unusual eating behaviour, intense fear of gaining weight, a great deal of exercise or missed periods.
The last point is particularly important. Eating disorders often begin in puberty, and early help significantly improves the outlook.
Possible causes
The most common reason for a low weight is simply genetics: if the parents are slim, the children often are too. But illnesses can also be behind it, such as intolerances, chronic bowel conditions, metabolic disorders or emotional stress. Only a medical examination can establish the cause, so do not try to work it out on your own.
What parents can do
Do not pressure your child to eat more. Pressure at the table often leads to conflict and can make things worse. Shared, relaxed meals and a regular routine help more. Talk to your child respectfully about their body and avoid comments on appearance — that applies to “too thin” just as much as to “too heavy”.
Ideally, bring the child health booklet to the appointment and note down what you have noticed and since when. That way your paediatrician can quickly assess the situation and discuss the next steps with you.
Conclusion
A BMI below the 10th percentile is often harmless, especially if the child steadily follows their curve. But if the curve drops, the value is below the 3rd percentile or warning signs appear, do not wait. The calculator helps with a first assessment — the evaluation belongs with your paediatrician.