Considerations when assessing child weight status
Whilst BMI is the main measure through which you can assess a child’s weight status, there are a number of other factors that need to be taken into account. Consideration of these issues in conjunction with the child’s BMI centile will help you decide the best course of action for working with the family.
1. BMI doesn’t measure body composition. Whilst BMI is the best available indicator of unhealthy weight in children, BMI is based on body mass only and does not provide any indication of how much muscle or fat a child has. Therefore a high BMI in a very muscular and active child may be less concerning than the same BMI in an inactive child with a high visual level of fat. It is noteworthy also that BMI centiles can be misleading in children who are naturally very tall (usually with one or more very tall parents), e.g. a child who is on the 98th centile for both height and weight would be on the 91st centile for BMI, but this would likely be due to their genetic height rather than excess weight.
2. Ethnicity. Whilst the child growth charts in this module are recommended for use with all ethnicities, it is important to be aware individuals from Asian backgrounds may accumulate a higher fat mass at lower BMI than other ethnic groups. For further discussion of ethnic considerations around child weight see module on Culture.
3. Lifestyle. When assessing child weight it is important to find out about the child’s current physical activity and dietary patterns. Consideration should also be given to the home environment, parents’ lifestyles and parents’ own weight status, since parental obesity is a risk factor for childhood obesity (particularly if both parents are obese5). For further guidance on discussing physical activity and diet with families see modules Physical activity and Sedentary Behaviour and Nutrition.
4. Growth trajectory. If you monitor a child’s growth over time you will gain a better understanding of the child’s weight issue, and of when additional medical support is required. Monitoring a child’s growth trajectory can also help understand what is “normal” for each child, when compared with a single measurement in time (e.g. if a child has consistently stayed on the 91st BMI centile because they are very tall and have very tall parents this need not cause concern if the child is otherwise healthy). Potential areas of concern include:
- growth retardation (i.e. a child’s height stops increasing or drops down the centiles)
- continuous increases in BMI despite lifestyle change attempts
- early “adiposity rebound” (i.e. a child’s BMI begins to increase at 4 years instead of 5-6 years), which is a risk factor for adult obesity6.
5. Signs of potential syndromes. For the majority of children, excess weight is a result of lifestyle factors (e.g. poor diet and/or insufficient physical activity). There are however rare circumstances in which obesity can be associated with syndromes (e.g. Cushings Syndrome, Prader-Willi Syndrome). Such syndromes are usually associated with distinctive visual signs or behavioural traits. Therefore if any of the following signs are present alongside overweight or obesity, a referral should be made for further medical support:
- developmental delays
- growth retardation (height stopped increasing or dropping down the centiles)
- inappropriately short given parental heights
- insatiable, uncontrollable hunger
- unusual physical characteristics:
- epicanthic folds that are not associated with ethnic origin (this is when the fold of the upper eyelid covers the inner corner of the eye)
- stretch marks on arms and stomach
- face looks puffy and round (“moonface”)
- other abnormal facial features
6. Other medical complications associated with the child’s weight. Whilst pre-school might be too early for some obesity-related co-morbidities to present, children of either over- or underweight may suffer additional medical or psychological complications. Relevant factors in this age group to look out for include continence issues, mobility or breathing difficulties, and anxieties around food or body image.
Health visiting teams only – the attached flow charts provide guidance to help decide when onward referral to the GP is appropriate for children who are overweight or children who have a very low BMI.
5. Whitaker, K.L., Jarvis, M.J., Beeken, R.J., Boniface, D., & Wardle, J. (2010). Comparing maternal and paternal intergenerational transmission of obesity risk in a large population-based sample. American Journal of Clinical Nutrition, 91, 1560-1567.
6. Whitaker, R.C., Pepe, M.S., Wright, J.A., Seidel, K.D., & Dietz, W.H. (1998). Early adiposity rebound and the risk of adult obesity. Pediatrics, 101 (3), e5.