The current system of
Body Mass Index (BMI) is biased among young children, and may categorize tall
pre-pubescent children as overweight or obese, according to a new study. An
Australian study into children's health and lifestyles has found that tall
pre-pubescent children are being incorrectly classified as overweight or obese.
Lead author Richard Telford, an Australian National University (ANU) adjunct
professor, says that using BMI to calculate the body size of pre-pubescent
children is skewing results.
The results of the study highlighted that six to 12 percent of eight-year-olds
are misclassified when BMI is used to determine body size or adiposity, he adds.
Telford claims that BMI could incorrectly classify significantly tall and short
eight-year-old children, as the adiposity measurements of BMI and percent body
fat are both related to height.
"BMI is biased as a measure and unfairly would predict a taller child to be
fatter than he or she is," ABC Online quoted him as saying.
Giving an example of two eight-year-old girls with a 19 cm difference in their
heights, he said that, if calculated by current measurement system, the taller
girl's BMI would be 1.6 points higher and her percent body fat value would be
3.8 points higher.
"That would easily tip a girl from being normal into the mid-range of being
overweight," he said.
According to Telford, the biggest drawback of the bias is that medical staff
using BMI to measure young patients "may be giving misinformation".
"If a child is told they are overweight [when they are not] that can have
serious consequences," he said.
However, the researchers admitted that the height bias could easily be overcome
by changing the formula by which adiposity is calculated.
The team have now proposed a new system for measuring eight-year-olds called
body mass function, which is body weight divided by height cubed. On the other
hand, BMI is calculated by dividing body weight by height squared.
The four-year Lifestyle of our Kids project (LOOK), funded by the Commonwealth
Institute, is following the health, academic achievement and physical activity
of 830 Canberra schoolboys and schoolgirls from the age of eight years.