HKOS Paediatric Consensus Statements

The definition of obesity in children is controversial as the level of excess adiposity that leads to increased risk of poor health is not well defined as in adults; terminology and measures used in studies of weight and adiposity in children can be complex.

BMI-for-age instead of weight-for-height is used to assess overweight and obesity which is consistent with growth assessment in many countries.

Further studies are required to determine whether overseas guidelines on growth faltering are applicable to the HK population.

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Statement 1: Definition of Obesity in 0-2 years

There is a lack of evidence to define excess adiposity in children 0–2 years so we cannot make any definitive guidance for obesity evaluation and treatment in this age group; however, as a practical approach, we recommend using the HKGS 2020 and WHO 2006 standards as guidance points for tracking weight status. 

WHO 2006

HKGS 2020

Overweight

BMI-for-age >2 SD above the growth standard median

BMI-for-age >98th centile and ≤99.6th centile

Obese

BMI-for-age >3 SD above the growth standard median

BMI-for-age >99.6th centile

Reason for Change:

  • There is a lack of data in defining 'excess adiposity' that is harmful for <2 yrs old and little/no evidence that a high percentile of BW in <2 yrs tracks to obesity in youth or adulthood.
  • As per HKGS Supplementary Information:
    • The CDC and the AAP recommend that weight status in children up to 2 years of age be tracked using the WHO’s weight-for-length, age-, and sex-specific charts.
    • AAP Clinical Practice Guideline wording: ‘does not include guidance for overweight and obesity evaluation and treatment of children younger than 2 years. Children under the age of 2 were not part of the inclusion criteria for the evidence review, because it is difficult to practically define and measure excess adiposity in this age group.’

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Statement 2: Definition of Obesity in 2–5 years

We suggest using the new BMI centile chart from the 2020 Hong Kong Growth Study for children aged 2–5 years, with overweight defined as 99.6th centile ≥ BMI > 98th centile and obesity as >99.6th centile

Overweight

99.6th centile (2.67 SD) ≥ BMI > 98th centile (2.01 SD)

Obese

> 99.6th centile (2.67 SD)

Reason for removal of statement

  • Propose aligning age ranges with international well-accepted definitions rather than a new definition, for example:
    • CPG by AAP, CDC, IOTF and NICE define by 2-19 years.
    • WHO defines obesity differentially for 0-5 and 5-19 years, because WHO 0-5 yrs are growth ‘standards’ (not growth chart).
  • Our HK study only uses a non-gold standard (impedance body composition measurement) to assess body fat, the threshold of which to define obesity in children is also unvalidated. It may turn out to be valid, but we will need to show the cut-offs are valid in terms of correlation metabolic and other co-morbidities, which are not yet available.

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Statement 3: Definition of Obesity in 2–18 years

We recommend using the new BMI-for-age centile chart from the HKGS 2020 to define overweight and obesity in children aged >2 to <18 years.

In clinical assessment, for ease of practical implementation with the HKGS 2020 growth charts, we recommend defining:

  • Overweight clinical cut-off as BMI-for-age >91st centile and ≤98th centile
  • Obesity clinical cut-off as BMI-for-age >98th centile (2.01 SD) or BMI ≥27.5 kg/m2 (the recommended action point for adults), whichever is lower.

Overweight

BMI-for-age >91st centile and ≤98th centile

Obese

BMI-for-age >98th centile (2.01 SD) or BMI ≥27.5 kg/m2 (whichever is lower)

We recognise some countries (eg. the UK) use lower cut-offs than clinical cut-offs for population monitoring purposes (≥85 and <95th centile for overweight, ≥95th centile for obesity), This is to capture children in the population at risk of moving into clinical overweight or obesity categories, to help service planning for the whole population. These lower cut-offs may be useful for public health purposes.

Reason for revision

  • Propose aligning the age ranges with international well-accepted definitions, for example:
    • CPG by AAP, CDC, IOTF and NICE define by 2-19 years.
  • For alignment with the adult consensus, suggest adding BMI ≥27.5 kg/m2 as an action point for intervention for adolescents, as 98th centile BMI is above 27.5 kg/m2 beyond 13yrs of age.
  • For reference, see the paediatric and adult definitions consolidated in the appendix below.

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Statement 4: Other anthropometric measures

We suggest using other anthropometric measures such as waist circumference (WC) and waist-to-height ratio (WHtR) in children as adjuncts to the BMI to evaluate adiposity-related disease risk

Subtext: BMI is the standard method for screening and other anthropometric measures e.g., WC/WHR/WHtR can be used to supplement BMI because they measure central/abdominal obesity, which is linked to high risk of cardiovascular disease