Children BMI helps detect Obesity in Children and Teenagers

Children BMI Interpretation Differs
From Adults' BMI Interpretation

What is children BMI?

BMI for children is an easy screening tool to identify weight related growth problems in children between 2-20 years of age. The procedure to measure the actual fat content is very inconvenient for the child and is expensive too.

The values obtained on children's BMI correlate reliably to total body fat content. This method of evaluating childhood obesity is cheap and easy.

What is BMI?

BMI, the body mass index, is a simple numeric index of the body fat content; and is not a direct measure of the amount of fat in the body.
It is body weight in kilos divided by the square of the height in meters.

Formula for BMI calculation: BMI = Weight (kg) / [Height (m)]²

The number thus obtained is the person's BMI.
In adults, this BMI number can directly be correlated to weight related problems. See the table given below.

BMI Evaluation in Adults (≥ 20yr)
Sedentary Lifestyle & Average Body Structure

BMI Values

< 16

16 - 18.5

>18.5 - 25

> 25 - 30

> 30 - 35

>35 - 40

> 40

Interpretation

Severely underweight

Underweight

Normal

Overweight

Obese

Very obese

Morbidly obese

Interpretation of Children's BMI

The formula used to calculate children's BMI is the same as given above.
The difference lies in interpreting the values obtained.
In children, the number obtained by using the BMI formula is plotted on BMI percentile chart of CDC.

These charts are sex and age specific They give a comparative position of a child's BMI number among the children of same age and sex:
The percentile position of children BMI.
The percentile position, indicated numerically, is used to interpret the appropriateness of child health in relation to the body weight for height attained at that particular age. (See the table given below)

Children’s BMI
Note: Values are in percentile

< 5th percentile

5th - <85th percentile

85th - <95th percentile

≥ 95th percentile

BMI interpretation in children

Underweight

Healthy

Overweight

Obese

Points to note from BMI interpretation table for children

Any child above 2 years of age, having BMI at 95th percentile or more meets the criterion for obesity; An indication for poor child health.
BMI between the 85th and 95th percentiles is considered in the overweight range.
Underweight children fall below the 5th percentile of BMI.
Terms “overweight” and “risk for overweight” are no more
used to refer obesity in children. They have been changed as per the international definition of childhood obesity.

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Why children's BMI exclude children below 2 years of age?

During the first two year of life normal fat content is high. Consequently, children BMI percentiles charts of CDC do not include children under 2 years of age.

Why are BMI values plotted on BMI percentile charts for children?

Age and sex variation:
Normal fat content in a child varies with age and sex.
The normal body fat content is more in girls than that in boys.

Hence, the children's BMI percentile charts are age and sex specific; and children BMI values need to be evaluated on BMI percentile chart.
Phases of low body fat does not necessarily mean poor child health:
After the second birthday, children’s body fat slowly starts decreasing and continues to do so for about next 4 years. A 6 years old child’s body fat is typically at its lowest, but child is not necessarily under nourished.
Adiposity rebound:
Tween years is the period of adiposity rebound.
During this phase the fat in children's body again starts increasing; and continues to do so through teenage growth spurt til early adulthood.
Same BMI number can conclude different health status at different ages:
A child may have the same BMI number at different ages, but at each age the interpretation of the BMI findings would differ.

Two children (of different age and/or sex) can have the same BMI number, but the numbers may fall in different range of evaluation on BMI percentile chart. Consequently the diagnosis of the two children will also differ: one may be concluded as obese and the other as normal.

Without plotting the BMI number on BMI percentile chart precise interpretation is missed.
Example: 2 boys, one at 10 and the other at 15 years of age. If both have a BMI of 23, then the 15 years old boy is considered healthy, where as 10 year old is obese.
Click here to see the example on children BMI percentile chart.

Why monitor children's BMI?

In chronic childhood diseases:
Frequent monitoring of children's BMI , each at 3 months intervals, is recommended for children suffering of chronic diseases like high blood pressure of childhood, type 1 diabetes, hyperlipidemea etc.
In normal children:
Regular monitoring of weight and BMI percentile is a window to many child health issues. Both should be regularly recorded at each routine health care visit for early diagnosis of nutritional disorders: For example; child's weight gain more than expected for the age, under nutrition and more.