DEFINITION OF OBESITY IN CHILDREN
The most appropriate definition of obesity refers to an incremental increase in body fat. The methods to make this diagnosis are the same for adults, with some precise differences due to the fact that it is necessary to use tables and graphs adapted to each age group and sex.
Linear Weight-Height Ratio
This method is widely used in paediatrics. It compares the real weight of the child with the ideal weight that they should have for their height and sex. There are graphs and tables that show different weights (expressed in percentiles) for different heights, defining the ideal weight for height at the 50th percentile.
A child is considered obese if their weight passes the 95th percentile of that which corresponds to their height, or when the ratio between their real weight and their ideal weight for their height and sex (defined as the 50th percentile) is above 120%:
Body Mass Index
This index is useful in evaluating obesity in that in 90% of its variation is due to changes in fat mass. It is obtained using this formula:
In adults this is relatively constant; if the number is above 24.9 it is considered overweight and if it is above 29.9 it is considered obesity.
However, in childhood there are some problems with this formula as an indicator for weight as it does not have a linear evaluation for height; it is very low at the time of birth and increases until one year of life and then progressively descends until the age of 6, when it stably increases until adulthood.
There are tables that that indicate the BMI percentiles for different ages and sexes. A child is considered obese when the BMI is above the 90th percentile for their age group. It can also be expressed as the real BMI of the child in relation to the ideal BMI for a child of their same age and sex. In this case a child is obese when they pass 120% and overweight if they pass 110%.
Subcutaneous Folds
Subcutaneous fat constitutes approximately 50% of total body fat. The measurement for these folds is done through a lipocalibrator, using a simple and precise method with an experienced observer, although if the obesity is very severe this is not a trusted method. Usually the tricipital (most used), bicipital, subscapular and suprailiac folds are measured.
A tricipital fold above the 95th percentile in prepubescent and 85th percentile in adolescents is an accepted method to indicate obesity. In the case that these percentiles are not available, a child with a tricipital fold larger than 20mm can also be considered obese.
Fat Distribution
It is not only important to measure the quantity of body fat, but also to know the pattern of distribution (central/peripheral/generalized) and as in adults, a pattern of central (or abdominal) distribution is related to metabolic anomalies present in obesity (diabetes, hypertension, changes in cholesterol).
Distribution of body fat can be determined using different indexes, with the most utilized being the waist-hip ratio (it is considered central distribution when it is greater than 1 in males and 0.9 in females).