Result
Also see:
Classification Table for the provided data Why child BMI is different? Classification table What is Z-Score How the calculation is made Curiosities about BMIResult - BMI and Weight Ranges for the Provided Age, Gender, and Height
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≠Why is children's BMI different from adults'?
Constant growth phase: Children and adolescents are in constant development — with rapid changes in height, weight, and body composition.
Classification based on age and gender: BMI during this phase is interpreted using WHO growth curves, which compare the data with reference standards for age and gender.
Use of the Z-score: Instead of fixed ranges, the Z-score is used, which indicates how much a child's BMI deviates from the expected average for their age.
BMI in adults: At 20 years old, the body reaches physical maturity. Therefore, BMI is interpreted using fixed ranges — such as 18.5 to 24.9 for "normal weight".
What is the Z-score?
The Z-score is a statistical measure that indicates how much a value deviates from the expected average for a given age and gender, according to WHO standards.
Why is it important in children's BMI?
- Children and adolescents are in constant growth, and BMI naturally varies with age and between boys and girls.
- The Z-score allows you to compare a child's BMI with an internationally standardized reference.
- It is the most accurate and accepted way by the WHO to classify the nutritional status of young people between 5 and 19 years old.
- With the Z-score, it is possible to make a fairer and more accurate nutritional assessment, respecting the growth phases of each child and adolescent.
How to calculate the Z-score
How to calculate BMI?
Before calculating the Z-score, it is necessary to obtain the BMI of the child using the traditional formula:
\[ BMI = \frac{Weight \, (kg)}{Height^2 \, (m^2)} \]
With this value, we search the WHO table for the average and standard deviation corresponding to the provided age and gender.
How is the Z-score calculated?
The Z-score of BMI is calculated by comparing the child's BMI value with the average and standard deviation (SD) of the reference population of the same age and gender. The formula is:
\[ Z = \frac{IMC_{observado} - IMC_{média}}{DP} \]
In other words, we are measuring how many standard deviations the child's BMI is above or below the expected average for their age and gender.
Tabela de Classificação através do Escore-Z
| # | Classification | BMI Z-score/Age |
|---|---|---|
| 1 | Marked Thinness | Z-score ≤ -3 |
| 2 | Thinness | -3 ≤ Z-score < -2 |
| 3 | Adequate (eutrophy) | -2 ≤ Z-Score ≤ +1 |
| 4 | Overweight | +1 < Z-Score ≤ +2 |
| 5 | Obesity | +2 < Z-Score ≤ +3 |
| 6 | Severe obesity | +3 < Z-Score |
Curiosities about BMI in Children and Adolescents
- BMI in children is interpreted based on percentiles and growth curves.
- The WHO uses age- and sex-specific curves to determine nutritional status.
- The categories include: severe thinness, normal, overweight and obesity.
- Unlike adults, BMI in children varies with growth and sex.
- Boys and girls have different patterns of physical development.
- The same BMI may represent different classifications depending on age.
- The WHO recommends regular assessments of child growth during pediatric consultations.
- High BMI in children can be an early indicator of future disease risk.
- Good eating habits and physical activity are essential in childhood.
- Children may experience "growth spurts" where BMI naturally fluctuates.
- Research shows that childhood obesity can impact cognitive performance.
- Use of tablets and smartphones for long periods is associated with an increase in BMI among teenagers.
- According to the WHO, childhood overweight has drastically increased in recent decades.