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A 10-year-old girl, Gemma, has been admitted to the general paediatric unit with an acute asthma exacerbation.

She weighs 70kg and is 1.4m tall.

Her symptoms have improved, and discharge planning has begun. At the end of your round, the consultant asks you to go and discuss Gemma’s weight with her family.

What should you do next?

Although your initial reaction may be to send the intern in to have this often awkward and difficult discussion, identifying and managing childhood obesity is becoming an increasingly important skill for paediatricians and general practitioners.

Obesity is common in Australian children. At least one in twenty kids is obese (Batch and Baur, 2005). When you include data on overweight children, the incidence is 25% (NHMRC 2013b).

So, firstly, it is important to correctly identify overweight and obese children. GPs who use visual clues to determine normal weight children are often incorrect (Spurrier et al., 2006).

Furthermore, even when a practitioner does record height and weight, only on half the occasions do they convert these to BMI (Dettori et al. 2009).

BMI is calculated by dividing weight (in kilograms) by the square of the height (in metres)

BMI then needs to be compared to age and gender-appropriate charts

A child is classified as overweight with
a BMI ≥ 85% of the same age and gender.

Obesity is defined as a BMI ≥ 95% of the same age and gender

How do we define overweight?

In children under 2

  • Overweight is when weight-for-height values are above the 95th centile

In children over 2 years old

  • Overweight is a BMI for age between the 85th and 95th centiles
  • Obese is a BMI for age above the 95th centile

In adolescents

  • Obese is BMI >95th centile or 30mg/kg/m², whichever is lower

Additionally, underweight is a BMI for age below the 5th centile

And how should we calculate the ideal body weight?

The Moore method uses height-for-age growth charts to give a percentile. That percentile is then used to read the ideal body weight from a weight-for-age growth chart.

It is based on the concept that the ideal body weight is the same standard deviation from the mean as the child’s height. So, for example, if a child’s height is on the 95th centile, then you should look at a weight growth chart and work out the weight on the 95th centile for his age. That would be his ideal body weight.

This is easy because you only need a growth chart to calculate the ideal body weight.

The Moore method has its limitations. In particular, it may overestimate the ideal body weight in tall children. Other methods are the McLaren method and the BMI method.

The McLaren method:

  • Plot the height
  • Draw a horizontal line to the 50th centile
  • Look at the age of that 50th centile
  • Look up the 50th centile weight for that age

The BMI method:

Ideal body weight = (BMI at 50th centile for child’s age) x (height in m2)

How can you engage the parents?

Not unexpectedly, evidence suggests that practitioners find it difficult to initiate discussions about children’s weight (Dettori et al. 2009; Gerner et al. 2006; King et al. 2007). Fears regarding offending patients, losing business and alienating clients have all been highlighted as barriers (Dettori et al. 2009; Gerner et al. 2006; King et al. 2007).

Just as with any difficult discussion, it is important to:

  • Pick the right location– A busy emergency resuscitation cubicle is not the correct location. Find somewhere private, quiet and comfortable where everyone can participate in the conversation.
  • Pick the right time – if their child is acutely unwell, parents will not want to discuss chronic problems no matter how concerned they are about them. If not before, these discussions should be part of discharge planning.
  • Ensure you have time – allow time for questions from the parents and the child. Don’t have this discussion five minutes before the weekly grand rounds start.
  • Be informed – explain how you will assess their child’s weight status. Explain how classifications of obesity and overweight are made. Be aware of who will follow them up and what extra services are available in the hospital and community.
  • Consider involving others – interpreters or Aboriginal and Torres Strait Islander health workers may assist (NHMRC 2013a).
  • Be compassionate!

What are the common causes of obesity in Australian kids?

To become overweight or obese, a disparity occurs between energy input and energy expenditure (AIHW 2011). Being an overweight or obese child is caused by a multitude of factors.

  • Sedentary behaviour – overweight and obese children are more sedentary than their peers. (Booth et al. 2006).
  • Diet – Children who consume large amounts of sugary drinks and snack on highly saturated fats, salt and sugar are more likely to be overweight or obese (AIHW 2011). Additionally, children with higher BMI have been shown in studies to have poorer quality breakfast and are more likely to omit meals than their normal-weight peers (Booth et al. 2006).
  • Culture – Acceptable body sizes, food intake and exercise levels are influenced by culture (Cinelli & O’Dea, 2009; Renzaho et al., 2008).
  • Family – Families influence children’s eating habits. Children are more likely to be obese if their mothers are obese (O’Dea 2006).
  • Socioeconomic status – Children from lower socioeconomic status are at greater risk of being overweight and obese (O’Dea, 2006; Wake et al., 2006).
  • Built environment – the community in which one lives, and, therefore, an individual’s access to parks, playgrounds and open public spaces may influence their level of activity (AIHW 2011).

Gemma’s mother states, “She is only a little bit fat. I don’t understand what all the fuss is about.”

What are the consequences of being overweight?

Being overweight and obese influences children’s short- and long-term health and well-being. These children are at higher risk of:

Short term:

Long term

  • Continuing to be an overweight adult
  • Insulin resistance and type 2 diabetes mellitus
  • Fatty liver disease
  • Osteoarthritis
  • Cardiovascular disease
  • Hypertension
  • Hyperlipidemia

(NHMRC 2013a & Williams et al., 2005)

How does obesity affect drug dosing?

In children with obesity, body fat is not equally distributed, and obese children have a higher per cent fat mass and a lower per cent lean mass. Therefore, calculating drug doses according to total body weight can result in overdosing.  Conversely, calculating doses based on ideal body weight can be sub-therapeutic.

Ideal body weight or actual body weight?

For loading doses, the calculation is based on the volume of distribution.

Hydrophilic drugs are based on ideal body weight.

Partially lipophilic drugs are based on an adjusted body metric.

Lipophilic drugs distribute freely into fat, and so in obese and overweight children, a larger dose may be needed. So, these drugs may be calculated on total body weight (but considering toxicity).

Maintenance dose calculations are based on clearance rate. This is determined by renal and hepatic function, and we don’t know the effect of obesity on these functions.

Let’s get down to the specifics.


Most antibiotics should be calculated on total body weight, including – penicillins (maintenance and loading), cephalosporins, vancomycin (maintenance and loading), and carbapenem.

Some require a specific metric of

(0.4[TBW-IBW]) + IBW)

These are ciprofloxacin, gentamicin, amikacin, tobramycin.

For all of these, remember that the total dose should not exceed the adult recommended dose.


Paracetamol, opiates, and ketamine should all be dosed to the ideal body weight.

If the ideal body weight is >40kg, adult dosing is best. The exception may be paracetamol, where mg/kg dosing can be used unless the patient is >65kg (see comments section for more details).


Phenytoin, carbamazepine and benzodiazepines should all be dosed to the ideal body weight. The exception is that for a phenytoin loading dose, use the metric (1.33[TBW-IBW]) + IBW).

How could we manage these obese children?

Few effective BMI reduction programs have been illustrated in the Australian literature (Antoine 2012). No trials have proven an effective GP lead management strategy. However, the HIKCUPS trial showed that a parent-centred dietary program and child-focused exercise approach could be efficacious in BMI reduction (Collins et al. 2011, Okely et al. 2010).

A recent publication from the National Health and Medical Research Council (NHMRC 2013a) recommends the following management strategies:

  • Ask and assess: current dietary intake, level of exercise and medical history. Perform a full examination including – height and weight, looking for signs of complications of being overweight or obese.
  • Advise: Promote the benefits of a healthy lifestyle and diet. Current guidelines recommend at least 60 minutes of moderate daily exercise (AIHW 2011). Children should have no more than two hours of non-educational screen time daily (AIHW 2011). Advise families to make healthy eating choices – have regular meals together in a social atmosphere (NHMRC 2013a).
  • Assist: Provide education on the causes and consequences of obesity.
  • Arrange follow-up and referral as required to allied health members – dietitian, exercise physiologist and psychologist as well as general paediatricians and an endocrinologist.

What about using technology?

We all know that obesity is a serious problem for the paediatric population (Ogden et al, 2014). And we also know that kids love using iPhones (Chiong et al, 2014). So it’s not surprising that there are lots of apps on the app store aiming to help children tackle their obesity.

In fact, there are lots of apps for pretty much any medical problem you can think of. But how useful are these apps? Do they follow accepted medical practice or public health strategies?

A study published in Childhood Obesity looked at this question.

Wearing, J.R., Nollen, N., Befort, C., Davis, A.M. and Agemy, C.K., 2014. iPhone app adherence to expert-recommended guidelines for pediatric obesity prevention. Childhood Obesity10(2), pp.132-144.

The authors scoured the App store for iPhone apps aimed at reducing paediatric obesity which were for children to use. They found 62 apps.  And they compared them against the American Academy of Paediatrics’ Strategy for the Prevention of Childhood Obesity

Strategies from the American Academy of Paediatrics.

Recommended behaviours

  1. Eat five fruits and vegetables per day
  2. Get 1 hour of physical activity per day
  3. Limit screen time to less than 2 hours per day
  4. Limit consumption of sugar-sweetened beverages
  5. Eat breakfast daily
  6. Switch to low-fat dairy products as part of a diet rich in calcium
  7. Regularly eat family meals together
  8. Limit fast food, take-out, and eating out
  9. Prepare food at home as a family
  10. Eat a high-fiber diet

Recommended strategies

  1. Goal setting: Children should set clear goals that reflect progress toward target behaviour (s).
  2. Positive reinforcement: Children should be encouraged for efforts and achievements related to target behaviour (s).
  3. Self-monitoring: Children should be encouraged to record their relevant behaviours, efforts, and progress.
  4. Cognitive restructuring: Negative cognitive patterns should be discouraged and successes, including partial successes, should be highlighted.

They found that apps poorly adhered to the whole guideline, but did tend to focus on specific behaviours. For example, most apps targeted exercise or a particular element of food intake but didn’t focus on the others. In general, while the apps were quite good at dealing with the recommended behaviours, they were poor at implementing or suggesting the correct strategies. The most common strategy used was self-monitoring.

As an interesting side note, there was no correlation between the cost of the apps and how medically appropriate it was – the most expensive app was in fact one of the poorest performing. And strangely, the reviews left on the app store did seem to tally with AAP guidelines adherence.  Perhaps user reviews on the App Store aren’t as irrelevant as we might think…

So whilst there is a future for encouraging your patients to use apps to tackle chronic medical issues, we have no good regulation yet of apps like this on the app store. Check out any apps yourself before recommending them to your patients as there’s a lot of dross out there.

Weight loss is not recommended for most children. Maintaining weight during growth will permit a gradual decrease in BMI (NHMRC 2013a).

Some tertiary hospitals will have weight reduction services or physicians with a special interest in this field.

Involve the General Practitioner – they will likely see the child more frequently than you will. Let them know the management strategies provided to the family and what services you have linked them with.

Selected References

Antoine 2012, ‘Where to from here for Australian childhood obesity’, Australian Medical Student Journal, vol 3, Issue 2, pp 20-23.

Australian Institute of Health and Welfare (AIHW) 2011, Young Australians: their health and wellbeing, AIHW, viewed 28th September 2013, <>.

Batch JA, Baur LA. Management and prevention of obesity and its complications in children and adolescents. Med J Aust. 2005;182:130-5.

Booth ML, Okely AD, Denney-Wilson E, Hardy L, Yang B, Dobbins T. NSW Schools Physical Activity and Nutrition Survey (SPANS) 2004 Summary Report. Sydney: NSW Department of Health 2006.

Chiong C, Shuler C, Learning: is there an app for that? The Joan Ganz Cooney Center at Sesame Workshop, New York, 2012.

Cinelli RL, O’Dea JA. Body image and obesity among Australian adolescents from indigenous and Anglo-European backgrounds: implications for health promotion and obesity prevention among Aboriginal youth. Health Educ Res. 2009 Dec;24(6):1059-68.

Collins CE, Okely AD, Morgan PJ, Jones RA, Burrows TL, Cliff DP et al. Parent diet modification, child activity, or both in obese children: an RCT. Pediatr. 2011;127(4):619-27.

Davis MM, Gance-Cleveland B, Hassink S, Johnson R, Paradis G, Resnicow K, Recommendations for prevention of childhood obesity. Pediatrics. 2007 Dec;120 Suppl 4:S229-53.

Dettori H, Elliott H, Horn J, Leong G. Barriers to the management of obesity in children: A cross-sectional survey of GPs. Aust Fam Physician. 2009;38(6):460-4.

Gerner B, McCallum Z, Sheehan J, Harris C, Wake M. Are general practitioners equipped to detect child overweight/obesity? Survey and audit. J Paediatr Child Health. 2006;42(4):206-11.

Kendrick JG, Carr RR, Ensom MHH. Pharmacokinetics and Drug Dosing in Obese Children. The Journal of Pediatric Pharmacology and Therapeutics : JPPT. 2010;15(2):94-109.

National Health and Medical Research Council (NHMRC) 2013a, Clinical Guidelines for the Management of Overweight and Obesity in Adults, Adolescents and Children in Australia, NHMRC 2013, Canberra, AUS, viewed 28th September 2013, Children in Australia 2013, <>.

National Health and Medical Research Council (NHMRC) 2013b, Obesity and overweight, 31 May, NHMRC, viewed 28th September 2013, <>.

O’Dea JA, Wilson R. Socio-cognitive and nutritional factors associated with body mass index in children and adolescents: possibilities for childhood obesity prevention. Health Educ Res. 2006 December 1, 2006;21(6):796-805.

Ogden CL, Carroll MD, Kit BK, Flegal KM, Prevalence of childhood and adult obesity in the United States, 2011-2012. JAMA. 2014 Feb 26;311(8):806-14.

Okely AD, Collins CE, Morgan PJ, Jones RA, Warren JM, Cliff DP et al. Multi-site randomized controlled trial of a child-centered physical activity program, a parent-centered dietary-modification program, or both in overweight children: the HIKCUPS study. J Pediatr. 2010;157(3):388-94.

Phillips S, Edlbeck A, Kirby M, Goday P. Ideal body weight in children. Nutr Clin Pract. 2007 Apr;22(2):240-5.

Renzaho AMN, Swinburn B, Burns C. Maintenance of traditional cultural orientation is associated with lower rates of obesity and sedentary behaviours among African migrant children to Australia. Int J Obes. 2008;32(4):594-600.

Spurrier NJ, Magarey A, Wong C. Recognition and management of childhood overweight and obesity by clinicians. J Paediatr Child Health. 2006;42:7-8.

Wake M, Hardy P, Canterford L, Sawyer M, Carlin JB. Overweight, obesity and girth of Australian preschoolers: prevalence and socio-economic correlates. Int J Obes. 2006;31(7):1044-51.

Wearing JR, Nollen N, Befort C, Davis AM, Agemy CK, iPhone App Adherence to Expert-Recommended Guidelines for Pediatric Obesity Prevention. Childhood Obesity, 2014, 10(2):1-13.

Williams J, Wake M, Hesketh K, Maher E, Waters E. Health-Related Quality of Life of Overweight and Obese Children. JAMA. 2005 January 5, 2005;293(1):70-6.



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4 thoughts on “Obesity”

  1. Chris Cole @DocOnSkis

    Excellent and thoughtful summary review. My opinion is that while we should go to some pains not to alienate the parents (we need their co-operation if anything beneficial is going to come of the encounter), we should not back away obseqiously, either.

    They need to be told.

    Being polite is the greater of the two possible evils here, I think.

    And the way we do it is important. Joking and colloquially approaching the topic obliquely, and establishing rapport is all well and good, but they need to understand that there is a real, tangible, dangerous problem here, and that we take it seriously. If they don’t perceive us lending a tone of some gravity to the situation, they certainly aren’t going to.

  2. It’s a tough topic to broach and I wonder if some of us pussyfoot around the subject hoping that someone else will do it. There is a big difference between dealing with an overweight 10 year old with the potential self-esteem issues and an overweight toddler/pre-schooler. It is made even harder when the parers are clearly overweight themselves and so have a skewed view of normal.

    For the younger children I try and make sure I always plot their height and weight and give a copy to the parents. Sometimes seeing that their child is on the 90th centile for weight makes a bigger difference than the words we use. Whilst there is no evidence that brief intervention strategies work in an ED setting I think we are missing an opportunity to provide all round patient care if we don’t say something.

    1. Nice link Aaron – thanks. It makes an interesting point – that as parents we set the standard of volume of food intake by plating up the kids’ food. It’s pretty impractical to avoid doing this though – especially until they are a lot older, by which time these problems will be engrained.

      I wonder how much volume of food makes a difference to obesity though, rather than just types of food: fats, nash, fizzy drinks, desserts etc?

      It is difficult to challenge families on obesity – along with parental smoking and choices around immunisations, it is one of the most difficult topics to broach. But if we don’t do it, who will?