Why Standard BMI Doesn't Apply to Children
For adults, fixed BMI thresholds apply (e.g., 25 for overweight). For children and adolescents, this doesn't work because their bodies are constantly changing: growth spurts, puberty, and different development speeds make fixed thresholds useless.
A 10-year-old boy with BMI 20 can be perfectly normal weight, while the same value in a 5-year-old indicates significant overweight.
What Are BMI Percentiles?
Instead of fixed thresholds, pediatricians use percentile charts. These are based on large comparative studies and show how a child's BMI compares to peers of the same age and gender.
- **Below 3rd percentile**: Underweight
- **3rd to 10th percentile**: Mild Underweight
- **10th to 90th percentile**: Normal Weight
- **90th to 97th percentile**: Overweight
- **Above 97th percentile**: Obesity
A child at the 75th percentile has a higher BMI than 75% of peers of the same age and gender, but falls within the normal range.
The KiGGS Study: Reference Values for Germany
In Germany, the percentile charts from the KiGGS study (Child and Adolescent Health Survey) by the Robert Koch Institute are used. These are based on data from over 17,000 children and adolescents.
The Kromeyer-Hauschild reference values are the current standard in German pediatric practices and are documented in the yellow examination booklet (U-Heft).
When to See a Pediatrician?
- When your child's BMI falls below the 3rd or above the 97th percentile
- When the percentile shifts significantly over a longer period (e.g., from the 50th to the 90th percentile within a year)
- When you have concerns about your child's nutrition or weight
Practical Tips for Parents
1. **No diet pressure**: Children should not be pressured to lose weight. Instead, focus on healthy nutrition and exercise.
2. **Regular check-ups**: The U-examinations at the pediatrician include BMI measurement and percentile assessment.
3. **Encourage exercise**: The WHO recommends at least 60 minutes of physical activity per day for children.
4. **Be a role model**: Children model their eating behavior on their parents.