Indications for surgery in adolescents have evolved in recent years so that criteria for surgery are now more clearly defined. In the UK, NICE (National Institute for Health and Care Excellence) have provided guidance regarding appropriate patient selection for adolescent bariatric surgery. Adolescent bariatric surgery should be offered in exceptional circumstances to patients who have nearly completed puberty. Their BMI should be between 35 and 40 kg/m² if they have significant comorbidities or above 40 kg/m² without comorbidities. This should be performed in a multi-disciplinary team with paediatric expertise for preoperative and postoperative care. Similar guidelines were also approved by Scottish Intercollegiate Guidelines Network (SIGN) in 2010.

The average age of onset of puberty in the UK is 11.2 years in girls and 11.6 years in boys, with the onset of menarche now 13.06 years [18]. Several records from northern Europe from the 1860s show that menarche at that time was 16–17 years, and sporadic reports at periods since suggest a gradual reduction as body mass has increased [19]. Whilst improved nutrition has begun this process in train, several anthropometric and epidemiological studies and the discovery of leptin (1994) and kisspeptin (1996), all increasingly point towards the obesity epidemic as an important factor in this decline [20–22].

The process of puberty is a fascinating and remarkable stage of life. It is said that primates are the only species to experience it. During this time the skeleton changes, the brain remodels, and the infertile child develops over 2–3 years into the fertile adult. Puberty leads to changes in body composition too, with lean mass in boys increasing to form the ‘android’ shape, and fat mass redistributing in girls to form the ‘gynaecoid’ shape in preparation for child rearing. It is no mistake that evolution has chosen to tie the fates of nutrition and fertility together.

When assessing children and young people, therefore, it is critical to assess their obesity in the context of their stage of puberty. In 1948 Dr James Tanner, a paediatric endocrinologist began a project in Harpenden just to the north of London, studying growth in malnourished children. Over his career that followed, however, his observations led him to characterise the five discrete ‘Tanner’ stages of puberty, and importantly to link these directly to the growth chart. In girls, he noted, the growth spurt begins early in puberty, accompanying thelarche (development of the breast bud), whereas in boys it does not occur until later into puberty (Tanner IV). Clearly, obesity that is identified prior to puberty requires relatively less intervention than that found later on after most growth is complete, as the increase in stature counters the weight to some degree. One way to see this is in BMI; to calculate BMI one must first square the height before dividing it into the weight. This means that changes in height disproportionately affect BMI over changes in weight. Strategies to weight loss in small children with moderate obesity therefore may often seek to maintain weight, rather than actively to lose it until such time as the growth spurt has occurred and allowed the height to ‘catch up’ with the weight.

It must be emphasised that there is only a window of opportunity for this pubertal transformation to occur. In the same way that body composition changes, so too do the androgens and oestrogens that come in puberty causing the skeleton to grow and strengthen. Bone mineral accrual is at its peak at the same time as the growth spurt, though continues on into the third decade, long after epiphyses have fused. This process is uniquely sensitive to nutrition – as evidenced by the secular trend in increase in stature alongside improvements over the last century with sanitation and nutrition. Short stature and ‘stunted’ growth due to starvation in childhood is well described, indeed a key finding of James Tanner’s work [23].

Given this, nutritional interventions in growing children must be carefully considered. Obesity is mistakenly thought of as the complication of excessively wealthy diets but this is undermined by the well-recognised knowledge that obesity is found in greatest prevalence amongst the more deprived groups in society, a finding seen across the world [24, 25]. In fact the cause of obesity is in large part down to diets rich in energy and poor in nutrient. Many children with obesity have very poor quality diets [1, 26]. Calorie restriction as part of a diet must go hand in hand with appropriate supplementation or this will lead to growth restriction. In the adult, calorie restriction typically causes a reduction in the metabolic rate, a switch in metabolism to catabolism (ketosis, lipolysis, proteolysis) and activation of a state of subfertility or infertility mediated through reduction in pulsatility in gonadotropin releasing hormone (GnRH) [27]. Clinically this manifests as bradycardia, hypothermia and hypotension, mood change and secondary amenorrhoea. Patients have muscle wasting and accompanying specific signs of coexisting nutritional deficiencies. In children, however, all this occurs but also growth is affected – starvation paradoxically causes an increase in growth hormone alongside growth hormone resistance and a decoupling of GH-IGF-1 interaction contributing to growth failure [28, 29]. Bone demineralisation occurs as a result of nutrient and vitamin D depletion, and muscle wasting which in turn reduces the strain on bones required for remodelling to occur.

It is for this reason that international centres that consider bariatric surgery in children do not intervene until growth is complete, lest the calorie restriction and metabolic changes that necessarily follow a bariatric procedure prejudice the growth and bone mineralisation in the growing child irreversibly.

The adolescent bariatric team should consist of the following:

It is desirable to also have a paediatric nurse practitioner and physical trainer. Expertise and referral pathways in child safeguarding are essential.

Same surgeries are performed in adolescents as in adults with almost similar results. A meta-analysis of bariatric surgery in adolescents shows that there is moderate weight loss in all patients after surgery. Mean BMI loss at 12 months was −17.2 kg/m² for laparoscopic roux-en-y bypass (LRYGB), −14.5 kg/m² for laparoscopic sleeve gastrectomy (LSG) and −10.5 kg/m² for laparoscopic adjustable gastric banding (LAGB) [30]. In an interventional study comparing adolescents with adults, BMI loss was 32 % and 31 % respectively in adolescents and adults at 2 years follow up. LRYGB has also been shown to improve cardiovascular risks as well as improve quality of life [31]. Surgery is effective in improving obesity related comorbidities. LRYGB and LSG are both effective. Type 2 diabetes (T2DM) remissions occur in almost 95 % of participants while obstructive sleep apnoea improves in 99 % of patients [32]. LRYGB and LSG are also known to improve weight-related quality of life significantly [33]. However, studies have also showed increased risk of micronutrient deficiency with almost 57 % patients having hypoferritinaemia in one study. These patients need long term psychological support too as there is increased risk of addictive substance misuse and attempted suicides.

As bariatric surgery gathers momentum and gains in popularity in adults, the pressure mounts to perform the same procedures on children [34]. The comorbidities of obesity now present at increasingly young ages. It is not uncommon to see small children as young as 2 years with obstructive sleep apnoea. As these cases present, clinicians increasingly resort to these operations at lower and lower ages. The youngest reported case is only 2.5 years of age [35]. In this age group however there is no published data on efficacy, safety or cost effectiveness. By contrast, in small children even with severe comorbidities there is evidence that confident parenting and multidisciplinary support over time can achieve good outcomes [36, 37]. This has led many to question the morality of such an approach given the epidemic nature of obesity across the world [38]. Far beyond the unanswered questions of outcome are also the unexplored ethical issues on whether this intervention respects the child’s autonomy, or is performed with informed consent or assent.