L15 Metabolism Childhood obesity

Overview

Childhood obesity affects nearly one in three New Zealand children aged 2 to 14, with much higher prevalence among Pacific and Māori children and in the most deprived areas. The lecture sets out why it matters (obesity tracks into adulthood and carries metabolic, mechanical and psychosocial complications), why the drivers are largely environmental rather than individual, and how a clinician should respond using the Ministry of Health 2016 four-stage pathway: Monitor, Assess, Manage, Maintain. It then goes deep on one lifestyle behaviour that is easy to forget, sleep, showing the epidemiological link to obesity, the proposed mechanisms and an experimental crossover trial demonstrating that sleep restriction increases energy intake. It closes on communication (person-first, non-blaming language) and on the doctor’s realistic role: refer, advocate and support population-level prevention.

Scale of the problem in New Zealand

• Overweight and obesity together affect nearly one in three children aged 2 to 14. Latest survey figure: prevalence 31.5%, an estimated 269,000 children.
• Population reporting by the Ministry of Health uses the International Obesity Taskforce growth chart, not the NZ-WHO chart.
• Obesity prevalence (2023/24 data, values read from an unlabelled bar chart so approximate): boys about 13%, girls about 12%; age 2 to 4 about 11%, 5 to 9 about 12%, 10 to 14 about 13%; Māori about 15%, Pacific about 38%, Asian about 5%, European/Other about 9%; least deprived households about 5% rising in steps to about 22% in the most deprived.
• Overweight plus obesity combined: boys about 32%, girls about 31%; age 10 to 14 highest at about 37%; Māori about 39%, Pacific about 58%, Asian about 23%, European/Other about 26%; least deprived about 24% rising to about 42% in the most deprived.
• Children in the most deprived areas are three times as likely to be obese as those in the least deprived areas.
• Time trend: obesity prevalence has been roughly flat at about 30 to 33% (overweight plus obesity) across 2011/12 to 2024/25. Sex-specific obesity trends fluctuate between about 8 and 13% from 2006 to 2019, with a survey methodology break around 2020 to 2022; after the break boys decline from about 15% to about 12% by 2024 while girls sit around 11.5 to 12%.
• B4 School Check data show a reduction in obesity in four-year-olds, declining steadily both before and after March 2020, with males (about 18% falling to about 15%) consistently higher than females (about 13.5% falling to about 11%).

Why childhood obesity matters

• Childhood obesity tracks into adulthood, and confers increased risk of high blood pressure, type 2 diabetes and abnormal lipids at a younger age.
• Complications wheel (Lakshman et al 2012), read as intermediate process leading to comorbidity:
  • Insulin resistance leads to type 2 diabetes.
  • Hypertension and dyslipidaemia lead to cardiovascular disease.
  • Increased mechanical load leads to sleep apnoea and orthopaedic pain.
  • Low self-esteem leads to psychosocial problems.
  • Influence on puberty leads to impaired fertility.
  • Increased risk of some types of cancer, and physical disability, are shown without a separate intermediate label.
  • Adult obesity sits in the ring and a dashed arrow loops from it back around, meaning adult obesity in turn increases the likelihood of all the other comorbidities.
• Other associations listed in the guideline background: obstructive sleep apnoea, musculoskeletal problems, asthma, body dissatisfaction, poor self-esteem, depression and other mental health problems, bullying (which further damages self-esteem), and attention problems that can affect learning.
• Two caveats the lecturer stresses: not everyone living with obesity in adulthood had obesity as a child, and health behaviours matter for wellbeing regardless of weight. This is why population approaches are needed alongside individual guidance.

The obesogenic environment

• Diet, excess weight and physical inactivity in the context of an obesogenic environment are the major modifiable risk factors contributing to early death, illness and disability in New Zealanders.
• The lecture illustrates the food and marketing environment with images of fast-food advertising (celebrity and sports sponsorship, meal deals), food delivery services, traffic and car dependence, supermarket snack aisles and screen use by young children.
• Cost comparison worked through in class: a McDonald’s “Mates Hunger Buster” meal for two at $29versusasupermarketbasketofingredients(tomatoes,cucumber,lettuce,breadrolls,beetroot,cheeseslices,onions,potatoes,beefmince)totalling$40.38. The takeaway option is the cheaper one.
• Other environmental and external factors raised: geographic location and food swamps, the minefield of nutrition information including social media, family dynamics, and socio-economic status.
• New Zealand food environment benchmarking (Vandevijvere et al 2018, INFORMAS):
  • 13.7 fast food and takeaway outlets per 10,000 people in the most deprived areas versus 3.7 in the least deprived.
  • 12.7 convenience stores per 10,000 people in the most deprived areas versus 4.5 in the least deprived.
  • 53% of sport and recreation centres sell sugar-sweetened beverages.
  • 2.4 convenience stores and takeaway outlets within 500 m of urban schools, more around the most deprived schools (2.4) than the least deprived (1.8).

Warning

Several slides in this section carried no title or caption text (the advertising collage, the single fast-food advert, and the supermarket cart screenshot). Their intended message is inferred from the images and from the following “Takeaway vs Supermarket” slide rather than stated in the slide text.

The four-stage weight management pathway

The Ministry of Health 2016 Clinical Guidelines for Weight Management in New Zealand Children and Young People cover ages 2 to 18 and present a four-stage cycle, drawn as a ring running clockwise and looping back to the start:

1. Monitor measure and plot growth regularly to catch trends early.
2. Assess full history and examination for those over the 98th centile.
3. Manage slow weight gain using Food, Activity and Behavioural strategies (FAB).
4. Maintain long-term follow-up to hold onto positive changes.

Practitioners may not have time to work through the whole pathway in one consultation; brief motivational advice with follow-up at later visits, and referral where needed, is acceptable. The guidelines are a statement of best practice and do not replace clinical judgement; individual clinical state, age, comorbidities and family/whānau preferences all count. The 2016 update is a limited evidence review of the 2009 guidelines, with no formal GRADE analysis; the new evidence generally supported or strengthened the 2009 recommendations, and the notable addition is the role of sufficient sleep.

Stage 1: Monitor

• Rationale: regular monitoring identifies early those who need extra support. The key recommendation is to act on a BMI trending towards or over the 91st centile rather than waiting until a child is over the 98th centile.
• Body mass index is an indirect measure of adiposity, in contrast to direct measures such as dual-energy x-ray absorptiometry (DXA), doubly labelled water or MRI, which are not practical for all children.
• Weight status is determined using an age- and sex-specific BMI centile, because body composition changes with normal growth and maturation and varies by sex. Children’s BMI cut-offs differ for each age and are not the adult cut-offs.
• Recommended steps:
  1. Measure height and weight to calculate BMI for all children over two and young people up to 18, ideally at least annually.
  2. Under five years, measure and plot height/length and weight per the Well Child / Tamariki Ora schedule, and use the weight-height BMI conversion chart to get the BMI centile.
  3. Aged 5 to 18, calculate $BMI=\frac{\text{weight (kg)}}{{\text{height (m)}}^2}$ and plot on the NZ-WHO growth charts (one male, one female, based on the WHO growth reference for 5 to 19 year olds).
• Cut-offs on both the 2 to 5 and the 5 to 18 NZ-WHO charts: overweight is over the 91st centile, obesity is over the 98th centile.
• One-off measurements do not give the whole picture; repeated measurements are needed to see the trend.

Next steps by centile band

BMI	Action
Under the 91st centile and stable	Monitor opportunistically, ideally annually, or per the Well Child / Tamariki Ora schedule
Under but trending towards the 91st centile	Brief food and activity advice; monitor ideally six monthly
Between the 91st and 98th centiles	Discuss current and long-term health risks with family/whānau, brief food and activity advice; monitor ideally six monthly
Over the 98th centile	Discuss current and long-term health risks and proceed to Stage 2, Assess

Is BMI good enough?

• The concern is that BMI cannot discriminate fat from lean tissue. The lecture makes the point with two elite rugby players whose BMIs are 30.3 and 29.4.
• Guideline meta-analysis (Javed et al 2015): commonly used paediatric BMI cut-offs for obesity are good at identifying children who truly have lower body fat (specificity 93%) but only moderate at identifying those with higher body fat (sensitivity 73%).
• Lecture figures from 11 DXA studies in more than 25,000 children (Obes Rev 2016):
  • Obesity: sensitivity 90% (of those with high body fat had high BMI), specificity 94%.
  • Overweight: sensitivity 77%, specificity 92%.
• Waist circumference is not recommended for diagnosing childhood obesity: there is no clear threshold associated with morbidity outcome in children, and it can be a confronting measurement, particularly for teenagers.
• There is no clear consensus on the best supplementary measure to BMI. For children BMI remains the only realistic screening tool.
• Where this leaves practice: BMI is a good screening tool but not perfect for every individual; also look at family history and other indices of health such as blood pressure, lipids and psychosocial health; do not focus only on childhood obesity because many adults with obesity did not have it as children; individual guidance plus population approaches promoting healthy lifestyles for all, which is more strengths-based and reduces stigma.

How we talk about weight

Important

Ask permission before measuring anyone’s weight or height, including a child’s, and ask permission before discussing weight with a family. If you are going to measure BMI and talk about weight, follow up with actual help rather than just telling them to lose weight, eat better or exercise more.

• Do not blame the individual, child or parent, and avoid any language implying it is their fault.
• Use person-first language and promote appropriate use of imagery (the World Obesity Federation publishes language guidelines and a non-stigmatising image bank).
• Examples: say “person or individual with obesity” not “obese person”; “subject or participant with obesity” not “obese subject”; “children with obesity” not “obese children”.

Health literacy and cultural competence

• Health literacy is a person’s ability to obtain, process, understand and act on basic health information and services to make appropriate health decisions, including navigating the health system, understanding health messages, medicine labels and nutrition information, and filling in forms or talking with a doctor or nurse. It applies to services as well as to users of services.
• For weight management specifically, practitioners should establish long-term trust relationships with patients and family/whānau to build shared understanding of values, priorities and strategies; routinely review weight management plans; use relevant support services to address identified barriers; and develop collaborative partnerships with Māori health providers, Whānau Ora providers and other community organisations so that advice is consistent, timely and comprehensive.
• Culturally competent practitioners are aware of cultural diversity, engage effectively and respectfully with people of different backgrounds, and acknowledge their own biases and how those manifest in treatment. In general practice the approach should extend to the whole practice including reception and nursing staff.
• Good practice points for engagement, monitoring stage: a welcoming environment (friendly greeting, waiting space for family/whānau, information in te reo Māori or another appropriate language); acknowledge the role of the broader family/whānau but always ask rather than assuming their involvement is wanted; spend time getting to know the family; listen and explain at a pace that allows individual contribution, taking cues from the family/whānau; acknowledge when you are uncertain about cultural processes; know who to contact for support, translation and cultural advice.
• Good practice points at the assess stage: avoid jargon and explain health terms, consider a translator where English is a second language; use thoughtful individualised communication and reflect on your own body language, words and tone; consider training in how to talk about weight (for example Healthy Conversation Skills); use the “teach back” technique, asking the patient to explain back what you have told them.

Stage 2: Assess

Assessment applies to children with a BMI over the 98th centile. It should determine current health risks, identify lifestyle habits susceptible to positive change, identify barriers, enablers and contributing factors, and exclude endocrine and genetic causes. It must take account of the eating habits, lifestyle, attitudes and practices of the individual family/whānau.

History

• Current physical consequences (snoring, joint problems, abdominal pain, breathing difficulties) and social consequences (isolation, bullying, behaviour problems, depression) of body size.
• Family history of obesity, early cardiovascular disease or dyslipidaemia; precipitating events that may have contributed to weight gain; actions the family/whānau have already taken; readiness of the individual and family to make lifestyle changes.
• Medications that may contribute to weight gain.
• Food and drinks: assess the contribution of high fat (especially saturated fat), added sugar and salt foods and drinks by asking how often they eat fast food, takeaways or ready-to-eat high fat/sugar/salt items (donuts, pies, hot chips); how often they drink sugary drinks (soft drinks, energy drinks, cordial, juice); what snacks they eat between or after meals; whether vegetables and/or fruit feature at each meal; how many times a week they eat breakfast; what they usually eat for lunch; whether dinner is eaten as a family/whānau; whether the child helps prepare and cook food. The 2002 National Children’s Nutrition Survey estimated energy-dense, nutrient-poor foods and drinks contributed 20% of total energy intake in children’s diets, likely higher now.
• Alcohol use in young people.
• Physical activity and sedentary behaviours: usual activity levels (time playing outside is a good indicator in younger children), sport participation, screen time, and whether there is a television in the bedroom.
• Sleep: usual length and patterns, regular sleep and nap times, disturbed sleep, and sleep hygiene (temperature, crowding, noise, light).
• Other factors: growth and pubertal status, and possible pregnancy.

BEARS mnemonic for sleep history

• B Bedtime issues: “Does your child have any difficulty going to bed or falling asleep?”
• E Excessive daytime sleepiness or excessive disruptive symptoms: “Is your child difficult to wake in the morning? Do they act sleepy, or are they overactive, inattentive or easily frustrated?”
• A Awakenings at night: “Does your child have trouble with waking up at night?”
• R Regularity and duration of sleep: “What time does your child go to bed and get up on schooldays? And on weekends?”
• S Snoring or sleep-disordered breathing: “Does your child have noisy breathing, or snore on most nights?”

Adapted from Chamness 2008. The New Zealand Guidelines for the Assessment of Sleep-Disordered Breathing in Childhood give more detail on assessing obstructive sleep apnoea and obesity, with a supporting questionnaire.

Clinical examination

Consider, as appropriate to the history:

• Blood pressure with an appropriate cuff size (hypertension).
• Hip or knee pain, limited hip motion, or lower leg bowing (slipped capital femoral epiphysis, or Blount’s disease / tibia vara).
• Poor linear growth (hypothyroidism, Cushing syndrome, Prader-Willi syndrome).
• Dysmorphic features (genetic disorders such as Prader-Willi syndrome).
• Tonsillar hypertrophy (can cause sleep apnoea).
• Abdominal tenderness or hepatomegaly (non-alcoholic fatty liver disease).
• Skin: striae (Cushing syndrome), intertrigo (rash in flexures or body folds), acanthosis nigricans (velvety light-brown to black markings, usually neck, axillae or groin, suggesting insulin resistance), skin infections such as cellulitis or carbuncles.
• Undescended testicle (Prader-Willi syndrome).

Secondary causes to exclude

• Endocrine: hypothyroidism, Cushing’s syndrome.
• Genetic or congenital: Prader-Willi syndrome, Trisomy 21 (Down’s syndrome), and rare syndromes such as Alström, Carpenter and Cohen. These are typically associated with other clinical signs including short stature, delayed growth and sexual maturation, and cognitive impairment.

Laboratory studies

Where indicated by history and examination:

• Fasting lipid profile (total cholesterol, triglycerides, HDL cholesterol, calculated LDL cholesterol).
• HbA1c (average blood glucose over the previous 8 to 12 weeks, indicating longer-term control).
• Overnight sleep study using pulse oximetry (non-invasive monitoring of blood oxygen levels).

What is realistic in clinic

A dietitian’s first appointment often takes around 45 minutes just to begin understanding where a family might be able to make changes and to set realistic goals. The lecturer’s practical questions are: clinical examination, laboratory studies and medications; food, exercise, sleep; mental health; whānau situation; socio-economic situation; and what barriers make healthy behaviours hard. This is a very complex issue and too much to cover in a 15-minute consultation.

Stage 3: Manage

The aim is for the child or young person to decrease the rate of weight gain and grow into their weight, not to lose weight. Any plan must involve parents, caregivers and family/whānau, with realistic goals jointly agreed between practitioner, individual and family, and review ideally every three to six months.

Refer to a multidisciplinary team, appropriate specialist or specialist service (for example paediatrician or dietitian) if there are significant comorbidities or complex needs. Questions the lecturer poses before managing: is there a medical reason for the excess body fatness; is this a behavioural or environmental issue; who is best placed to deliver this advice; and do you have the time and skills to help this whānau. Ensure advice is evidence-based and from reputable sources, refer to a dietitian where weight management support is needed, and build relationships with Māori, Pacific and community health providers.

Interventions should encompass multiple approaches together: changes in eating and drinking, increased physical activity, and behavioural strategies. Combined, a healthy diet, increased physical activity, less sedentary activity, sufficient sleep and behavioural strategies are the first line of treatment. Changes must be made by the whole family/whānau, not just the individual, and must become firmly established long-term habits.

F: Food

• No single eating pattern (low-glycaemic, low-fat, low-carbohydrate, increased protein) has been shown to be consistently more effective than another for weight management in the short and medium term, and there is insufficient evidence on long-term efficacy or safety of many of these approaches. Long-term compliance with whatever change is made is what is required.
• Energy restriction should be moderate and intake nutritionally balanced, to preserve growth and development. A healthier lifestyle for the whole family must be led and maintained by parents/caregivers.
• Healthy eating pattern: plenty of vegetables and fruit; grain foods, mostly whole grain and naturally high in fibre; some milk and milk products, mostly low and reduced fat; some legumes, nuts, seeds, fish and other seafood, eggs, poultry and/or red meat with the fat removed. Choose mostly whole or less processed foods low in saturated fat, added sugar and salt. Make plain water the first choice of drink. Alcohol is not recommended for children or young people. Whole nuts are not recommended before age five because of choking risk.
• Practical changes, aimed at what parents/caregivers buy: do not buy sugar-sweetened drinks, offer mostly water plus two or three glasses of milk per day; have takeaways no more than once a week or choose healthier options; provide healthier snacks such as fruit or cheese and crackers rather than chippies and snack bars.

A: Activity

• Meta-analyses support including exercise and physical activity in weight management plans. The goal here is to increase energy expenditure and resting metabolic rate.
• Under five years: provide lots of opportunities to be active inside and outside in ways that develop fundamental movement skills (running, jumping, throwing, catching, skipping, balance); be active as a family/whānau; enable safe exploration and play appropriate to developmental stage.
• Aged 5 to 18 and not regularly active: start with 5 to 10 minutes of aerobic activity a day and increase weekly (skateboarding, dancing, running, cycling, swimming, fast walking, ball sports, tag), or split activity into smaller bouts totalling at least 60 minutes per day (10-minute walks, stair climbing, active play, activity-based virtual reality games, household chores).
• Progressively increase to at least 60 minutes of moderate to vigorous intensity each day. Moderate intensity makes breathing harder than normal but you can still talk (brisk walking on the flat, cycling under 16 km/h, active play, dancing, kapa haka); vigorous intensity makes breathing a lot harder and talking difficult (brisk walking uphill, cycling over 16 km/h, running, fast swimming, team sports).
• Include muscle-strengthening and bone-strengthening activity (trampolining, skipping, climbing trees or play equipment, gymnastics, running) at least three days a week. Formal strength training is unnecessary, especially for children; young people who want to should seek professional advice. Power lifting, body building and maximal lifts must be avoided until physical and skeletal maturity. Warn families that muscle-strengthening activity may cause an initial weight gain as muscle size increases.
• Encourage active transport such as walking or cycling to school and other activities.

Reducing sedentary time

• Meta-analyses show interventions aimed mainly at reducing TV or other screen time reduce sedentary time and subsequently BMI.
• Under five years: provide activity breaks to limit time sitting without moving (for example stopping at a playground to break up long car trips); discourage screen time entirely for under-twos and limit it to less than one hour per day from age two.
• Aged 5 to 18 years: aim for less than two hours of recreational screen time per day.

B: Behavioural strategies

• Behavioural strategies help plan, implement and reinforce lifestyle change. Unless new habits are acquired, long-term weight management is unlikely.
• Children’s eating and activity behaviours are largely shaped by parents/caregivers, who do the shopping, control what is eaten and where, control sedentary time and sporting opportunities, and act as role models. Young people are more independent and need skills to make healthy choices themselves, so strategies are developed in consultation with them; interventions should be adapted to maturity level.
• Six behaviour change techniques identified as likely effective (Martin, Chater and Lorencatto 2013): providing information on the consequences of behaviour to the individual; environmental restructuring; prompt practice; prompt identification as role model or position advocate; stress management or emotional control training; general communication skills training.
• Implementation: identify problem behaviours and the circumstances in which they occur; identify what the family wants to work on first; encourage problem-solving and goal-setting with goals that are specific, measurable and modest; monitor target behaviours, usually by the child and parents; consider behavioural contracts (for example five minutes of active play daily in week one rising to ten in week two); encourage appropriate non-food rewards for meeting goals; treat unmet goals as opportunities to learn about the barriers the family faces.

The five behavioural tools

1. Self-monitoring the child or parents record food intake (amounts and types) and physical activity. Key first step, because it builds awareness of patterns that can then be adjusted.
2. Stimulus control behaving one way in the presence of a stimulus and another in its absence (chippies in the cupboard get eaten, chippies absent do not). Modifies behaviour by limiting exposure to high-risk situations.
3. Problem solving identifying, planning and implementing the healthier alternative then evaluating the outcome; identify weight-related problems, brainstorm solutions, choose one, and treat setbacks as learning (“what did we learn from this attempt and how else can we achieve what we want to?”).
4. Contingency management or contracting planned use of rewards for specific beneficial activities, from parents or self-administered. A review of monetary incentives for weight loss found no effect, so rewards should be intrinsically valuable to the person (family/whānau time, a new pet, music downloads).
5. Cognitive restructuring actively changing how one thinks, managing unrealistic goals and inaccurate beliefs about weight loss and body image, and encouraging rational responses to negative thoughts. Example: reframe “I blew my eating plan by eating a pie this morning, I may as well eat what I like for the rest of the day” into “Well, I ate that pie this morning, but I can still eat in a healthy manner at lunch and dinner”.

Other management options

• Support services and programmes range from nutrition and healthy-eating services to exercise and weight-loss programmes, some publicly funded through the Ministry of Health or DHBs, ideally with multidisciplinary input. Examples: dietetic services; whānau planning services through Whānau Ora providers and collectives; Active Families, an exercise and nutrition programme for families; community-funded physical activity services for Māori and Pacific communities such as church groups, Zumba and youth exercise programmes; whānau-based programmes such as Triple P (Positive Parenting Program).
• Orlistat is a gastrointestinal lipase inhibitor: it binds lipase in the stomach or small intestine, preventing dietary fat from being broken down, digested and absorbed, so it passes through undigested. No weight-loss drugs are registered for use in children and young people in New Zealand, and efficacy and safety below 18 years have not been established. Do not use weight-loss drugs under 12 years and generally avoid them in young people. Orlistat may be considered from age 12 if physical comorbidities (orthopaedic problems, sleep apnoea) or severe psychological comorbidities are present, started only in a specialist paediatric setting by a multidisciplinary team experienced in prescribing for this age group.
• Bariatric surgery promotes weight loss by changing the digestive system’s anatomy, limiting the amount of food that can be eaten and digested. Not recommended under 14 years. Criteria before considering a young person:
  • Minimum age 15, though surgery may be considered at 14 in exceptional circumstances.
  • Tanner stage 4 or 5 pubertal development.
  • Final or near-final adult height, that is bone age at least 13.5 in females and at least 15.5 in males.
  • Severe obesity: threshold BMI over 40 kg/m², or over 35 kg/m² in the presence of severe obesity-associated complications.
  • An associated severe comorbidity such as type 2 diabetes, hypertension, non-alcoholic steatohepatitis, benign intracranial hypertension or obstructive sleep apnoea.
  • Persistent obesity despite a formal multidisciplinary supervised programme of lifestyle modification and pharmacotherapy, with a minimum of six months of supervised multidisciplinary therapy beforehand.
  • Understanding by adolescent and family of the treatment, required lifestyle change and post-operative review, and motivation to engage.
  • Informed consent from the adolescent.
  • Not recommended for adolescents who are pregnant or breast-feeding, have significant cognitive disabilities, have an untreated or untreatable psychiatric or psychological disorder, or have Prader-Willi syndrome or other similar hyperphagic conditions.

Sleep, the forgotten lifestyle behaviour

• Sleep is the single largest slice of a child’s 24 hours, alongside physical activity, screen time and other sedentary time.
• Inadequate good-quality sleep has wide-ranging implications: weight status, school performance, driver safety, emotional and behavioural difficulties, risky behaviour and dietary intake. Children who sleep less than the recommended amount are twice as likely to be overweight or obese as those who meet the recommendation.
• Sleep problems are common: up to a third of parents of infants and toddlers report a sleep problem that negatively affects the family, and two-thirds of adolescents say their sleep needs are not being met.

Epidemiology: short sleep and incident obesity

Miller et al 2018, systematic review and meta-analysis of prospective studies, risk ratio for obesity with short sleep duration:

Age group	Participants (studies)	Risk ratio (95% CI)
Infant (under 3 years)	14,738 (7)	1.40 (1.19 to 1.65)
Early childhood (3 to under 9 years)	31,104 (8)	1.57 (1.40 to 1.76)
Middle childhood (9 to under 12 years)	3,005 (3)	2.23 (2.18 to 2.27)
Adolescents (12 to 18 years)	26,652 (3)	1.30 (1.11 to 1.53)

Risk is elevated across every age group, and highest in middle childhood.

Proposed mechanisms

Exactly how more sleep protects against weight gain is not clear, but sleep deprivation is thought to affect both sides of the energy balance equation. Being awake longer leaves more time to eat, and it also affects appetite regulation, leading to excess energy intake; too little sleep may also reduce physical activity and energy expenditure, though these effects may be weaker. The lecture’s flow diagram runs:

1. Short sleep branches into neuroendocrine changes, increased exposure to food, and increased fatigue.
2. Neuroendocrine changes lead to increased hunger, which leads to increased food intake.
3. Increased exposure to food leads directly to increased food intake.
4. Increased fatigue leads to both decreased physical activity and increased sedentary activity.
5. Decreased physical activity and increased sedentary activity feed into increased food intake and also directly into obesity.
6. Increased food intake leads to obesity.

Experimental evidence: the DREAM crossover trial

• Design: the only way to prove causality is to make children sleep deprived and see what happens to their diet and activity. 105 children aged 8 to 12 who were good sleepers. Randomised crossover over five weeks: week 1 baseline, then randomisation to either sleep restriction (week 2), washout (week 3), sleep extension (weeks 4 to 5), or the reverse order (extension first, then restriction).
• Result: they eat more, and it is mainly treat foods.

Intake (kJ)	Sleep extension	Sleep restriction	Mean difference (95% CI)
Total energy	8007	8369	361 (20, 702)
Core foods	4273	4194	-79 (-515, 358)
Non-core foods	4492	4996	504 (25, 984)
Ultraprocessed foods	5127	5649	523 (93, 952)
Sugary drinks	404	563	159 (15, 302)

Total energy, non-core foods, ultraprocessed foods and sugary drinks all increased significantly with sleep restriction (confidence intervals exclude zero); core foods did not change (CI crosses zero).

Important

An energy gap of just 200 to 300 kJ a day is enough to explain how young children who are a normal weight can become overweight over a few short years. The DREAM total energy difference of 361 kJ sits above that gap.

Recommended sleep durations

Age	Recommended hours per 24
Newborn (0 to 3 months)	14 to 17
Infant (4 to 11 months)	12 to 15
Toddler (1 to 2 years)	11 to 14
Preschooler (3 to 4 years)	10 to 13
School age (5 to 13 years)	9 to 11
Teenager (14 to 17 years)	8 to 10
Young people (18 to 25 years)	7 to 9

The National Sleep Foundation chart shown in the lecture presents the same idea as ranges that are recommended, may be appropriate, or not recommended, running from newborn to over-65s, with recommended ranges falling as age increases.

Sleep hygiene advice

Regular sleep and wake times including at weekends; a regular bedtime routine or ritual; a reasonable bedtime; a comfortable sleeping environment (quiet, warm, dark); no distractions including screens and portable electronic devices where children sleep, and limit electronic media in bed; avoid caffeine, especially caffeinated drinks; be active during the day; get natural light, particularly in the morning; make sure the child feels safe at night.

Note on the evidence base: the epidemiological link between short sleep and obesity risk is strong, but relatively few interventions have tested how feasible it is to change sleep behaviours, and most have been in clinical rather than public health settings. The sleep hygiene recommendations come from that behavioural and environmental literature.

Stage 4: Maintain

Long-term follow-up and monitoring of growth maintain positive changes and allow additional support. Steps:

• Maintain contact and support as necessary.
• Continue to monitor height, weight and BMI centile, ideally every three to six months, to check progress towards a healthy weight.
• Routinely review the suitability of the weight management approach and use relevant support services.
• Continue to offer advice on healthy eating, physical activity (including sedentary time and sleep), and behavioural strategies.
• Reassess and review management if progress is not sustained.

Good practice points: identify and promote local support services that encourage healthy lifestyles, and develop collaborative partnerships with Māori health providers, Whānau Ora providers, Pacific health providers and other community-based organisations. The lecturer’s challenge: do you have the resources to do this, and if not, how can you ensure they receive the care they need?

Your role as a doctor, and key takeaways

• To really address childhood obesity we need effective prevention strategies that make the environment a healthier place to live.
• We need population approaches promoting healthy lifestyles for everyone, regardless of current weight status.
• Continual monitoring of BMI is what gives the full picture of how a child’s weight is tracking; one-off measurements tell us little.
• Use empathetic language that steers away from blame and puts the person ahead of the obesity.
• Refer to a dietitian and/or other appropriate health care professional where available.
• Advocate for dietitians and other health professionals to be available to people who need help with weight and health behaviours:
  • For every $1spentfundingdietitiansinprimaryhealthcare,thecountryseesacost-savingbenefitof$99 over five years.
  • Up to 24% of GP visits are nutrition-related and could be covered by a dietitian, relieving pressure on the strained GP sector.
  • There are currently 16.1 dietitians per 100,000 population in New Zealand.
• Advocate for healthy environments in public spaces, and ask for more lecture content on nutrition and related behaviours.
• Resources to use: the Ministry of Health Clinical Guidelines for Weight Management in New Zealand Children and Young People; the Canadian Pediatric Obesity Clinical Practice Guideline, particularly for language and conversations with patients; the Heart Foundation; the Sleep Health Foundation; and Sit Less, Move More, Sleep Well: Active play guidelines for under-fives, plus other Ministry of Health guidelines.

Self-test

1. State the BMI centile cut-offs used on the NZ-WHO growth charts for overweight and for obesity, and explain why an age- and sex-specific centile is used rather than an absolute BMI value.
2. List the four stages of the Ministry of Health weight management pathway and give the aim of each in one clause.
3. Describe the recommended action for each of the four BMI bands in the monitoring stage.
4. Explain why waist circumference is not recommended for diagnosing obesity in children.
5. Quote the sensitivity and specificity of paediatric BMI cut-offs against DXA for obesity and for overweight, and explain what the discrepancy between sensitivity and specificity means clinically.
6. Describe the pathways in the complications wheel that link childhood obesity to type 2 diabetes, to cardiovascular disease, and to impaired fertility.
7. Explain why the lecturer argues that focusing only on childhood obesity is insufficient, and what follows from that for public health strategy.
8. List the ethnic and deprivation gradients in obesity prevalence among New Zealand children aged 2 to 14.
9. What does the INFORMAS food environment assessment report for fast food outlet density and convenience store density in the most versus the least deprived areas?
10. Explain what the takeaway versus supermarket price comparison in the lecture was designed to demonstrate.
11. Expand the BEARS mnemonic and give the screening question that goes with each letter.
12. List the endocrine and the genetic or congenital causes of obesity that assessment should exclude, and name the clinical signs typically associated with the genetic conditions.
13. A 13-year-old with a BMI over the 98th centile has velvety dark markings in the axillae and neck, striae, and poor linear growth. Explain what each of these findings should make you consider.
14. Which three laboratory or specialist investigations does the guideline list, and what does each measure?
15. Explain what FAB stands for and state the overall aim of management in a growing child.
16. Describe the physical activity recommendation for a previously inactive 10-year-old, including how to start, the eventual target, and the strengthening component.
17. State the screen time limits recommended for under-twos, for two to five year olds, and for 5 to 18 year olds.
18. Name the five behavioural tools and give a one-line description of each.
19. Describe the mechanism of action of orlistat and state the circumstances in which it may be considered in a young person.
20. List the criteria a young person should meet before bariatric surgery is considered.
21. Describe the design and the main dietary result of the DREAM sleep crossover trial, and explain why a 361 kJ difference matters.
22. Explain, using the lecture’s mechanism diagram, the routes by which short sleep could lead to obesity.
23. State the recommended sleep durations for school age children and for teenagers, and the risk ratio for obesity with short sleep in middle childhood.
24. Distinguish person-first from stigmatising language with an example, and list two other communication rules the lecturer gives about discussing weight.

Answers

Reveal answers

1. Overweight is over the 91st centile and obesity is over the 98th centile. An age- and sex-specific centile is used because body composition changes with normal growth and maturation and varies by sex, so children’s cut-offs differ at each age and are not the adult cut-offs.
2. Monitor: measure and plot growth regularly, ideally every 12 months, to enable brief intervention early. Assess: full history and examination in those over the 98th centile to identify comorbidities, underlying causes and contributing factors. Manage: slow the rate of weight gain so the child grows into their weight, using Food, Activity and Behavioural strategies. Maintain: long-term follow-up and monitoring of growth to hold onto positive changes and give additional support.
3. Under the 91st centile and stable, monitor opportunistically, ideally annually or per the Well Child schedule. Under but trending towards the 91st centile, give brief food and activity advice and monitor ideally six monthly. Between the 91st and 98th centiles, discuss current and long-term health risks with the family and give brief food and activity advice, monitoring ideally six monthly. Over the 98th centile, discuss health risks and proceed to Stage 2, Assess.
4. Because there is no clear threshold for waist circumference associated with morbidity outcome in children and young people. The lecture adds that it can be a confronting measurement, particularly for teenagers.
5. Against DXA in more than 25,000 children: obesity, sensitivity 90% and specificity 94%; overweight, sensitivity 77% and specificity 92%. The guideline meta-analysis gives specificity 93% and sensitivity 73% for obesity cut-offs. High specificity with lower sensitivity means a high BMI is fairly trustworthy but a normal BMI does not exclude high body fat, so BMI is a screening tool rather than a diagnosis and should be interpreted alongside family history and other health indices.
6. Childhood obesity leads to insulin resistance, which leads to type 2 diabetes. It leads to hypertension and dyslipidaemia, which lead to cardiovascular disease. It influences puberty, which leads to impaired fertility.
7. Because not everyone living with obesity in adulthood had obesity as a child, so targeting children alone will miss much of the adult burden; and health behaviours matter for wellbeing regardless of weight. It follows that individual guidance must be combined with population approaches promoting healthy lifestyles for all, which is also more strengths-based and reduces stigma.
8. Obesity: Pacific about 38%, Māori about 15%, European/Other about 9%, Asian about 5%. By deprivation, obesity rises from about 5% in the least deprived to about 22% in the most deprived, and children in the most deprived areas are three times as likely to be obese as those in the least deprived. Combined overweight and obesity shows the same ordering: Pacific about 58%, Māori about 39%, European/Other about 26%, Asian about 23%, and about 24% in the least deprived rising to about 42% in the most deprived.
9. 13.7 fast food and takeaway outlets per 10,000 people in the most deprived areas versus 3.7 in the least deprived, and 12.7 convenience stores per 10,000 people in the most deprived versus 4.5 in the least deprived.
10. That the takeaway option is cheaper: a fast-food meal deal for two at $29againstasupermarketbasketofingredientstotalling$40.38, illustrating cost as an environmental driver of food choice.
11. B, bedtime issues, “Does your child have any difficulty going to bed or falling asleep?”; E, excessive daytime sleepiness or disruptive symptoms, “Is your child difficult to wake in the morning? Do they act sleepy, or are they overactive, inattentive or easily frustrated?”; A, awakenings at night, “Does your child have trouble with waking up at night?”; R, regularity and duration of sleep, “What time does your child go to bed and get up on schooldays? And on weekends?”; S, snoring or sleep-disordered breathing, “Does your child have noisy breathing, or snore on most nights?”.
12. Endocrine: hypothyroidism and Cushing’s syndrome. Genetic or congenital: Prader-Willi syndrome, Trisomy 21 (Down’s syndrome), and rare syndromes such as Alström, Carpenter and Cohen. These are typically associated with short stature, delayed growth and sexual maturation, and cognitive impairment.
13. Acanthosis nigricans suggests insulin resistance. Striae can be due to Cushing syndrome. Poor linear growth can be due to hypothyroidism, Cushing syndrome or Prader-Willi syndrome.
14. A fasting lipid profile, measuring total cholesterol, triglycerides, HDL cholesterol and calculated LDL cholesterol; HbA1c, measuring average blood glucose over the previous 8 to 12 weeks and so longer-term glucose control; and an overnight sleep study using pulse oximetry, a non-invasive method of monitoring blood oxygen levels.
15. Food and drink, Activity (including reducing sedentary time and supporting sufficient sleep), and Behavioural strategies. The aim is to decrease the rate of weight gain so the child or young person grows into their weight, not to lose weight.
16. Start with 5 to 10 minutes of aerobic activity a day and increase the time each week, or split activity into smaller bouts totalling at least 60 minutes per day. Progressively increase intensity to at least 60 minutes of moderate to vigorous activity each day. Include muscle-strengthening and bone-strengthening activities such as trampolining, skipping, climbing and gymnastics on at least three days a week, avoiding power lifting, body building and maximal lifts until skeletal maturity.
17. Discourage screen time altogether for under-twos; limit it to less than one hour per day from age two; and aim for less than two hours of recreational screen time per day for 5 to 18 year olds.
18. Self-monitoring, recording food intake and physical activity to build awareness of patterns. Stimulus control, limiting exposure to high-risk situations so the triggering stimulus is absent. Problem solving, identifying the problem, brainstorming and choosing a solution, implementing it and evaluating the outcome. Contingency management or contracting, planned use of intrinsically valuable non-monetary rewards for specific beneficial activities. Cognitive restructuring, actively changing unrealistic goals and inaccurate beliefs and replacing self-defeating thoughts with rational responses.
19. Orlistat is a gastrointestinal lipase inhibitor: it binds lipase in the stomach or small intestine and blocks the breakdown, digestion and absorption of dietary fat, which then passes through undigested. It may be considered from age 12 if physical comorbidities such as orthopaedic problems or sleep apnoea, or severe psychological comorbidities, are present, and only started in a specialist paediatric setting by an experienced multidisciplinary team. No weight-loss drug is registered for children and young people in New Zealand.
20. Minimum age 15, or 14 in exceptional circumstances; Tanner stage 4 or 5; final or near-final adult height (bone age at least 13.5 in females, 15.5 in males); severe obesity with BMI over 40 kg/m², or over 35 kg/m² with severe obesity-associated complications; an associated severe comorbidity such as type 2 diabetes, hypertension, non-alcoholic steatohepatitis, benign intracranial hypertension or obstructive sleep apnoea; persistent obesity despite a formal supervised multidisciplinary lifestyle and pharmacotherapy programme, with at least six months of such therapy beforehand; understanding by adolescent and family of the treatment, lifestyle change and follow-up, with motivation to engage; and informed consent from the adolescent.
21. 105 good-sleeping children aged 8 to 12 in a randomised crossover: baseline week, then sleep restriction or sleep extension, a washout week, then the opposite condition. Under restriction total energy intake rose by 361 kJ (95% CI 20 to 702), with significant increases in non-core foods (504 kJ), ultraprocessed foods (523 kJ) and sugary drinks (159 kJ), while core foods did not change. It matters because an energy gap of just 200 to 300 kJ a day is enough to explain how a normal-weight young child becomes overweight over a few years, and 361 kJ exceeds that.
22. Short sleep produces neuroendocrine changes that increase hunger and so increase food intake; it increases exposure to food, which increases intake directly; and it increases fatigue, which both decreases physical activity and increases sedentary activity. Reduced activity and increased sedentary time feed into increased food intake and also lead to obesity directly, and increased food intake leads to obesity.
23. School age children (5 to 13 years) need 9 to 11 hours per 24 and teenagers (14 to 17 years) need 8 to 10 hours. The risk ratio for obesity with short sleep in middle childhood (9 to under 12 years) is 2.23 (95% CI 2.18 to 2.27).
24. Person-first language names the person before the condition, for example “child with obesity” rather than “obese child”. Other rules: ask permission before measuring anyone’s weight or height and before discussing weight with a family; avoid any language that blames the child or parent or implies fault; and if you measure BMI and raise weight, follow up with actual help rather than just telling them to lose weight or eat better and exercise more.