Recently, an issue concerning a 6 year-old girl’s weight went viral over the Internet, after being reported by NBC News.

In summary, the news story reports the mother receiving a school letter stating that the results of the [State Mandated] Health Screening and Evaluation had revealed that her daughter’s Body Mass Index (BMI), was high and “could be severely detrimental to her health and academic performance if it went untreated”.

The mother was furious on two counts.

  • Her daughter, Charley, regularity goes to their primary pediatrician and has always gotten a clean bill of health and
  • The incident had caused her daughter to ask if she was fat and was there something wrong with her?

This story highlights a number of concerns about the validity of BMI evaluation in schools.

Dueling Definitions and The Reliability of Results

How come the school’s health screening and evaluation differed from that of Charley’s pediatrician?

Perhaps it was because they were using different BMI Charts?

Unlike the fixed BMI values used to classify adults, children’s BMI is classified using ‘thresholds’ or ‘cut offs’ that vary to take into account the child’s:

  • Age, to account for the changing BMI as children develop and
  • Gender because the growth patterns of boys and girls are different. (1)

The data collected for the creation of these ‘thresholds’ was gathered by weighing and measuring a large number of children; the ‘reference population’ with an average taken to provide a BMI value for a boy or girl at a particular age. This means that an individual child can be compared to the ‘reference population’ and the degree of variation from the expected value can be calculated. (2).

Sounds good, right?

The thing is various organizations, such as the World Health Organization (WHO), U.S. Centers for Disease Control and Prevention (CDC 2000), International Obesity Task Force (IOTF) and the British 1990 Growth Reference (UK90) have created different BMI charts with different thresholds and cut-offs because of their varying definitions of overweight and obesity in children and adolescents (see table).

The variation in definitions might be explained by the fact that each organization used a different ‘reference population’.

See the table below.

Organization Definition of Childhood Obesity
World Health Organization WHO Child Growth Standards (birth to age 5) (2)

  • Obese: Body mass index (BMI) > 3 standard deviations above the WHO growth standard median
  • Overweight: BMI > 2 standard deviations above the WHO growth standard median
  • Underweight: BMI < 2 standard deviations below the WHO growth standard median

WHO Reference 2007 (ages 5 to 19) (3)

  • Obese: Body mass index (BMI) > 2 standard deviations above the WHO growth standard median
  • Overweight: BMI > 1 standard deviation above the WHO growth standard median
  • Underweight: BMI < 2 standard deviations below the WHO growth standard median
U.S. Centers for Disease Control and Prevention CDC Growth Charts (4)
In children ages 2 to 19, BMI is assessed by age- and sex-specific percentiles:

  • Obese: BMI ? 95th percentile
  • Overweight: BMI ? 85th and < 95th percentile
  • Normal weight: BMI ? 5th and < 85th percentile
  • Underweight: BMI < 5th percentile

In children from birth to age 2, the CDC uses a modified version of the WHO criteria (5)

International Obesity Task Force
  • Provides international BMI cut points by age and sex for overweight and obesity for children age 2 to 18 (6)
  • The cut points correspond to an adult BMI of 25 (overweight) or 30 (obesity)


So depending on the BMI chart used, you are quite likely to get a different result…

For example, in preschool girls, the World Health Organization Body Mass Index’s ‘cut offs’ for overweight and obesity are much higher than those of the International Obesity Task Force.

A recent Czech study found that by using the International Obesity Task Force ‘cut off’, about 15 percent of 5-year-old girls were overweight however with the World Health Organization cut-off, only about 3 percent were overweight. (3)

Quite a big difference!

12% potentially incorrectly defined, but which 12%?

So which chart is ‘right’?

Given it seems that the powers that be can’t align on the definitions and with the various ‘charts’ giving different estimates for overweight and obesity how valid is the use of the Body Mass Index for…

  • Determining a child’s weight as ‘underweight’, ‘normal’, ‘overweight’ or ‘obese’?
  • Raising awareness of the importance of a ‘healthy’ weight?
  • Tackling childhood obesity?

And could this potentially misleading ‘tool’ do more harm than good?

Despite there being extensive evidence showing the adult BMI lacks accuracy for calculating an individuals body fat or healthy weight, and whilst the various versions for children seem to have the same problem, it is being used to do just that.

Whilst these charts may have some value for evaluating the pattern of children’s growth, trends in weight and the prevalence of obesity in a population – are they really suitable for defining the individual child?

An individual child may not follow the ‘Average’ BMI for their age but still be perfectly healthy however they could get wrongly categorized and if a child was evaluated just before a growth spurt – when weight gain is common – the child could be deemed overweight.

Both [erroneous] results could lead to unnecessary interventions, which may damage the child’s physical health.

The Negative Impact of Labeling

Charley Cacdac - Categorized as overweight by school in Florida
 Charley Cacdac – Categorized as overweight by school in Florida

How helpful is it to label any child ‘overweight’ or ‘obese’ rightly or wrongly?

Due to our cultural obsession with thinness and our fear of fat many ‘overweight’ children (truly or ‘wrongly’ diagnosed) tend to be stigmatised, bullied and teased, which has a negative psychological impact on them, causing low self esteem, body dissatisfaction and eating disorders.

The majority of the women I work with in eating disorder recovery can trace the start of their problem back to being told there were ‘fat’.

With rates of eating disorders skyrocketing and the alarming 119% increase in the number of children under 12 being hospitalized from 1999 to 2006 due to an eating disorder (4), is school screening and evaluation really the way to go? And is the Body Mass Index really the tool to use given its inaccuracy?

Whilst “no exact cause for eating disorders has yet been found” some common characteristics for their development have been established; low self esteem, fear of being fat, dieting and being in an environment where weight and thinness are emphasized, all of which are being cultivated with this type of government directive.

So whilst childhood obesity needs tackling, what perhaps we really need to be doing is finding an accurate alternative to the BMI charts and looking at some of the real culprits…

  • Poor eating habits and consistent ‘unhealthy’ food choices; Eating on the go and fast foods, rather than cooking from ‘scratch’
  • Pervasive Cultural messages as Professor Gately from Leeds Metropolitan University says: ‘It starts early — people ask about babies: “Is he a good feeder?” We are developing an over-active appetite from a young age; we bottle-feed babies so they finish a bottle rather than take as much as they need from the breast. ‘We tell them to eat up or they won’t get a pudding and we allow them to snack, which is not going to do anything to help them develop healthy eating habits’.(5)
  • The manufacture of many of our food products – highly processed and lacking in nutrients.
  • The way advertising is used to target children creating a desire for fast food, fizzy ‘health’ or ‘sports’
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