Many factors contribute to the development and maintenance of childhood obesity, although parental obesity appears to be one of the strongest risk factors for persistence of obesity in children. This underpins the need for family-based change if successful weight management is to be achieved in the child.

Obesity occurs because energy intake exceeds energy requirement. Our understanding of factors that influence this energy balance equation is incomplete, but important considerations include:

• Lifestyle factors include increased sedentary activities such as watching television and computer gaming, less time partaking in physical activities and increased access to energy-dense foods (such as those containing high levels of sugar and/or fat).
  
• Genetic factors (susceptibility genes) may contribute to the development of obesity, although given that the gene pool changes slowly, lifestyle changes are more likely to be responsible for the recent increases in obesity prevalence. Single-gene disorders (e.g. leptin deficiency) are extremely rare.

Children with exogenous (non-medical) obesity are usually of normal intellect and either of normal or tall stature.

• Hormonal and metabolic factors: Endocrine causes are rare and are usually associated with growth failure (see chapter 25, Endocrine conditions page 319).
  
• Syndromal causes are often recognised by the presence of a significant developmental/ intellectual disability and less frequently by dysmorphic features. Clues to syndromal or endocrine causes of obesity include

– Height <50th centile (or less than genetic potential)

– Dysmorphic features

– Developmental/intellectual disabilities

– Hypogonadism.

Definition

A simple, clinically useful definition that reflects excess body fat is the body mass index (BMI). However, it does not reflect body composition and thus very well-muscled individuals may have a high BMI. This is usually clinically apparent.

In children, BMI changes with normal growth; an initial rise in BMI over the first year is followed by a nadir before gradually increasing to normal adult levels (see growth charts, Appendix 1). The initial rise after the nadir is termed the adiposity rebound and usually occurs around the age of 6 years. The timing of the adiposity rebound may be important for later risk of obesity.

Plot BMI on a BMI centile chart, now included in standard growth charts:

• Overweight is defined as a BMI between 85th and 95th centile for age and sex.
  
• Obesity is defined as a BMI >95th centile for age and sex.

Once obesity is diagnosed, the aim is to identify:

• Contributing factors for that individual
  
• Any underlying medical causes
  
• Individuals at high risk of associated disease
  
• Complications and co-morbidities.

History

A detailed personal, family, developmental and past (including perinatal) history, complemented by a thorough dietary history, activity history and a detailed physical examination, is sufficient in most cases.

Clues in a standard history may suggest an underlying cause for the obesity such as poor postnatal feeding and hypotonicity during infancy (Prader–Willi syndrome) and medications (e.g. long-term steroid use).

Explore risk factors suspicious of associated co-morbidities, document family history of obesity, heart disease, diabetes, hypertension, dyslipidaemia and other complications of obesity. Ethnicity is also important as children from certain ethnic backgrounds (e.g. Australian indigenous peoples, Pacific islanders, Asians and Indians) have a higher tendency for weight gain and display greater levels of co-morbidity for a given level of obesity.

An age-appropriate developmental approach is required. Parents can be the exclusive agents of change for preschool children, whereas adolescents should be offered the chance to be seen separately from their parents. It is important to address body image and ensure the young person has realistic, appropriate healthy weight goals.

Examination

• Plot height, weight and BMI on percentile charts.
  
• Document pubertal and developmental status.
  
• Assess the body build, posture and distribution of adiposity.
  
• Measure the waist circumference (at midpoint between lowest ribs and iliac crests – be sure to include any apron of abdominal fat).
  
• Measure the blood pressure with an appropriate-sized cuff.
  
• Look for acanthosis nigricans (velvet pigmentation on the neck and/or axilla).
  
• Look for clues to a syndromal/endocrine cause:

– Height <50th centile (or less than genetic potential)

– Dysmorphic features

– Cushingoid features (including abdominal striae)

– Developmental/intellectual disability

– Hypogonadism.

Investigations

• For aetiology.
  
• For underlying cause, if clinically indicated (see chapter 25, Endocrine conditions).
  
• For complications:

– Hyperlipidaemia – full lipid profile

– Type 2 diabetes – formal oral glucose tolerance testing is preferred although fasting glucose and insulin provide useful information if this cannot be performed.

– Hepatic steatosis – liver function tests ± liver ultrasound scan.

Screening for complications should be considered in children where obesity is resistant to lifestyle change and where there are risk factors for these conditions. These include a positive family history of type 2 diabetes and particular ethnic groups. Puberty is associated with a significant reduction in insulin sensitivity in normal individuals and investigation for type 2 diabetes is therefore further warranted in these children.

Other investigations, such as sleep studies in those with significant obstructive sleep apnoea, should be performed as clinically indicated.

The goal is to diminish morbidity and mortality risk, rather than to achieve an ideal body weight. Emphasis should be on improved fitness, health and social functioning rather than an aesthetic ideal. The primary objective is usually to maintain weight over time so that with normal longitudinal growth, the weight falls back into the healthy weight range. The exception to this is children and adolescents with severe obesity where a degree of actual weight loss may be required.

Successful maintenance of a healthy weight is best achieved through long-term family-based interventions that include a component of behavioural change. The aim is a shift in the child’s energy balance. Ideally, the following should be provided by a multidisciplinary team.

• Provision of professional input which is:

– Encouraging, empowering and understanding.

– Non-judgemental and avoids use of pejorative language: consider not using the word ‘obese’, but rather ‘above the child’s healthiest weight’.

• Education of families about:

– Medical complications of obesity – current and future health risks.

– The concept of energy balance.

– Healthy eating and interpreting food labels (see below).

– Appropriate physical activities (see below).

• When approaching the family:

– Identify the family’s readiness to change – this will guide whether the goal of the consultation is just to raise awareness or actually explore behaviour change.

– Explore ways to involve all family members and caregivers.

• Aim for permanent lifestyle changes, as opposed to short-term diets or exercise programmes that are aimed at rapid weight loss:

– Severely energy-restricted diets are contra-indicated in the majority of obese children/adolescents.

– Self-monitoring of diet and physical activities help maintain these changes.

Physical activity

Any increase in activity is an improvement!

• Aim for ‘lifestyle’ exercise: using the stairs, walking to school, walking the dog.
  
• Involve the whole family (everyone can benefit, regardless of weight status).
  
• Use after-school time to get outdoors and be active.
  
• Decrease screen-based activities (TV, computer, electronic games).
  
• Have bikes, helmets and balls ready to go, right beside the door.

Nutrition

Not forgetting drinks!

• Water is the best drink for kids: cut out cordial, soft drink, fruit juice.
  
• Better to eat fruit rather than drink fruit juice.
  
• Low-fat (2% fat) milk (<500 mL/day) is preferred for children >2 years of age.
  
• Importance of breakfast, regular meals and healthy snacks.
  
• Basic food label reading and awareness of the ‘traps’ e.g. ‘no fat’ might mean large amounts of sugar and therefore the same number of kilojoules.
  
• Serving sizes – does the 5 year old get served as much as mum or dad? (see chapter 6, Nutrition, p. 91).
  
• Planning ahead, avoiding regular take-away meals.

Referral to a specialist

This may be indicated when there is:

• Suspicion of a pathological cause.
  
• Presence of complications.
  
• Lack of progress in weight maintenance.
  
• Severe and progressive, or early-onset, obesity.
  
• Parental or patient request.

Some specific medical therapies are now beginning to be assessed for their use in obese children:

• Metformin may be useful in reducing obesity-associated insulin resistance.
  
• Studies assessing orlistat and sibutramine in adolescent populations are under way and they may be used more in this population in the future, particularly in those with severe or resistant obesity. They should only be prescribed from specialist centres and must be used in conjunction with an ongoing lifestyle-modification intervention.
  
• Gastric banding is also being trialled in adolescents and this may become a useful tool in the future to aid weight loss in severely obese adolescents or those with major obesity-related co-morbidities.