Obesity is the most common childhood nutritional disorder in the world and is widely acknowledged as being a global epidemic [1, 2]. In the UK the importance of implementing effective strategies for the prevention and treatment of childhood obesity has national significance with the publication of government policy documents [3, 4] as well as evidence based guidelines [5, 6]. The role of the specialist dietitian in the management of childhood obesity has now gained prominence. Dietitians may work with obese children and their families in primary or secondary care, utilising group or individual sessions [7, 8]. Background information, lifestyle advice and the use of behaviour change tools that a specialist paediatric dietitian will require to manage childhood obesity in any combination of these settings are discussed.

The definition of childhood overweight and obesity associates excess body fatness with the clinical relevance of such excess body fat. Body mass index (BMI) is generally recognised as the most appropriate proxy measure for body fat to define and diagnose childhood obesity and overweight [2, 5, 9]. BMI in childhood changes with age and differs between the sexes; therefore it must be plotted correctly on age and sex specific centile charts (UK 1990 data). UK BMI centile charts are available from Harlow Printing Ltd (see Useful addresses) and all dietitians working in the UK with obese children and adolescents should use these charts [10, 11].

There is a debate over the most appropriate centile cut-off points for defining childhood overweight and obesity; however, both the National Institute for Health and Care Excellence (NICE) and Scottish Intercollegiate Guideline Network (SIGN) clinical guidelines recommended ≥98th centile (UK 1990 data) for obesity and ≥91st centile (UK 1990 data) for overweight. For epidemiological studies ≥95th centile (UK 1990 data) defines obesity and ≥85th centile (UK 1990 data) defines overweight [5, 6].

Data on waist circumference centiles for British children [12] are available on the reverse side of the UK BMI centile charts. Currently, with no agreement on the relevant clinical cut-off points for the waist centile charts, they are not recommended for diagnosis of childhood obesity [2, 6, 9] although they have a use in monitoring progress.

Obesity is the accumulation of excess body fat associated with medical consequences (p. 800). The aetiology of all obesity is both complex and multifactorial [13]. It is well recognised that the development of childhood obesity is an interaction between the modern obesogenic environment and family lifestyle choices. Increases in the amount of energy dense foods eaten combined with large portion sizes, more time spent watching television, using computers and playing video games (screen time) with a simultaneous decrease in the amount of physical activity undertaken by children have all been mooted as causes of the current epidemic [2, 14, 15].

There are a number of consequences of childhood obesity that are seen both in childhood and adolescence, and indeed later life. Clustering of cardiovascular risk factors has been reported in children and adolescents including high blood pressure; dyslipidaemia; abnormalities in left ventricular mass and/or function; abnormalities in endothelial function; hyperinsulinaemia and/or insulin resistance. There is evidence that these cardiovascular risk factors are seen in adults who were obese children or adolescents [26, 27]. Hyperinsulinaemia, the metabolic syndrome and type 2 diabetes are also seen in adolescents [28, 29]. Psychological problems, particularly in girls, have been reported in relation to low self-esteem and behavioural problems. There are also long term consequences of social and economic effects, particularly in women achieving a lower income [26, 27].

An important reason why tackling childhood and adolescent obesity is government policy is the evidence that obesity in childhood and adolescence tracks in to adulthood. Risk factors for persistence into adulthood include

• parental obesity (high risk if one parent is obese, higher if both are obese)
  
• level of obesity (increasing risk with increasing level of obesity)
  
• obesity in adolescence [26, 27]

The role of the dietitian, either as a sole professional or as part of a multidisciplinary team, is to educate the child and family on the necessary lifestyle changes while facilitating behavioural change. A dietitian should be positive, non judgemental and empathetic while developing a rapport with the child and parents [30, 31].

For group sessions it is common practice to include some separate child and parents sessions. Practice shows that parents value the opportunity to discuss situations and solutions with other parents without the child being present. For dietitians working with individual children and their families consideration should also be given to seeing the parents alone, as information is often revealed by parents that would otherwise not be discussed in front of their child [7].

Good practice suggests that different age groups require different engagement:

• for preschool and lower primary school age children the intervention, including ownership and responsibility, engagement directly with the parent/carer
  
• for upper primary aged children engagement jointly with the child and parent/carer
  
• for teenagers engagement directly with the adolescent, with the parent in a supporting role

At the first session weight and height should be measured and plotted on child growth centile charts. BMI should be calculated [weight (kg) ÷ height (m)²] and plotted at the correct age on the appropriate centile chart for sex (UK 1990 data). Although used regularly in research in clinical practice, arm anthropometry such as triceps skinfold measurement and mid upper arm circumference are rarely used. Taking the waist measurement can be difficult in obese children, but can be a useful tool in monitoring progress in weight management.