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Obesity: Causes, Consequences and Treatment

Prevalence and related conditions 

In Canada, child and adolescent obesity is increasing dramatically and currently represents one of the most common conditions affecting children and youth. The Canadian Community Health Survey reported a tripling of obesity rates in 12 to 17 year olds, from  three per cent in 1978/79 to nine per cent in 2004.1 The combined overweight/obesity rate for this group increased from 14 per cent to 26 per cent. Prevalence data on younger children are highly variable, demonstrating the need for directed surveillance.2 Nevertheless, the prevalence of obesity in youth is rising faster than in adults.3 Obesity that develops during childhood generally continues into adulthood in approximately 75 per cent of individuals, and this is associated with a greater clustering of metabolic and cardiovascular risk factors and accelerated atherosclerosis.4 An epidemic of premature cardiovascular disease looms in the near future.5

Complications of Childhood Obesity

With the rapid increase in prevalence of childhood obesity, there has been a coincident rise in the incidence of conditions associated with excess body fat.6 Complications of childhood obesity are multiple and include insulin resistance, type 2 diabetes, hypertension, dyslipidemia, nonalcoholic fatty liver disease (NAFLD), orthopedic abnormalities, obstructive sleep apnea, low self-esteem, increased rates of depression and increased risk of cancer.6 Morbid obesity, increasingly seen at our pediatric institution, can be viewed as obesity associated with life threatening complications,6 the most immediately threatening of which is obesity hypo-ventilation syndrome,7-9 without treatment this leads to cardiopulmonary failure and death.

Determinants of childhood obesity 

The increase in rates of childhood obesity is believed to be due to environmental changes promoting over-consumption of calorie-dense food and increased sedentary behavior in susceptible individuals. Children are particularly vulnerable to these behaviours; however, the interaction between the biological, psychosocial, environmental and socioeconomic factors contributing to these changes are complex and remain poorly understood. 10-13Food and its components play a role in the regulation of food intake. Humans consume excess energy when provided with highly palatable energy dense foods or a high fat diet, 14, 15 suggesting that the effect on food intake cannot be predicted simply from their energy content. Energy balance is achieved through a complex interaction between the hormones involved in the regulation of food intake and the central nervous system. Satiety (hunger satisfying) and regulatory hormones from the gastrointestinal tract are relatively short-term signals that, by themselves, do not produce sustained alterations in calorie intake and body fatness, but interact with long-term regulators (the hormones: insulin, leptin) to maintain energy balance.16 The effects insulin resistance (a state associated with excess body fatness) to modulate hormones related to satiety and food intake has rarely been evaluated in children, although a recent study demonstrated good correlation between ghrelin, a satiety hormone, suppression following food intake and degree of insulin resistance.17  Since this is not seen in all obese individuals, it is apparent the underlying mechanisms of obesity are complex and ‘heterogeneous’; determinants include genetic and epigenetic (environmental factors that cause a individuals genes to behave differently) influences on physiologic pathways of metabolism and appetite regulation as well as environmental influences on behavior. Environmental factors (low maternal education, maternal smoking during pregnancy, birth weight, and parental obesity), sedentary behaviors (television watching, playing video games, and computer use, collectively known as screen time),18,19 combined with poor eating habits contribute to the prevalence.  

Determinants of metabolic risk 

Factors contributing to obesity

The ‘metabolic syndrome’ (MetS) is a clustering of risk factors and markers that, in adults, predict heart disease and diabetes, and includes excess visceral adipose tissue (VAT), insulin resistance/ elevated glucose levels, hypertension and dyslipidemia.20, 21 In children, these features may also be present, and increase with severity of obesity. As many as six different definitions have been proposed for defining MetS in childhood, but no universal standardized accepted definition exists because single cut-off points are not useful in children who are growing, and z-score (age corrected body measurements) cut-off points have not been well-established. Nevertheless, simple clinical criteria to identify those at greatest risk for complications such as heart disease and diabetes would be invaluable. Inactivity appears to be a primary causative factor in the progression of obesity and MetS. Fat accumulation, centrally and in muscle cells, may explain how positive energy balance (consuming more energy than one burns) mediates the faulty metabolic regulation in obesity. Two possible, perhaps not mutually exclusive, events may lead to fat accumulation in muscle cells and muscle cell mitochondrial (cell structure which creates useable energy for the cell) dysfunction in patients with obesity.22 High intake-associated fat accumulation in muscle may interfere with mitochondrial function through generation of reactive oxygen species (dangerous byproducts of energy conversion in mitochodria) leading to mitochondrial membrane injury and disruption of mitochondrial membrane enzymes (the enzymes responsible for this energy conversion; this in turn leads to impaired mitochondrial energy production. This primary defect in mitochondrial energy production may be responsible for a reduction in fatty acid break down leading to subsequent muscle cell lipid accumulation.  Little is known about the metabolic consequences of childhood obesity, with controversy regarding the disease mechanisms and definitions of MetS specific to children. 23, 24

The role of the health care system 

A recent publication provides evidence-based practice guidelines for the identification, prevention, and management of obesity in adults and children.25  Due to a lack of available ‘best evidence’, many of the paediatric recommendations are derived from lower quality studies or professional opinion. There is a small amount of literature on the selection of treatment strategies for youth with differing degrees of obesity, or for those with existing related conditions, and the role and effectiveness of health care providers and medical management is poorly defined.26-28 Although it is the impression of clinicians that the ‘intensity’ of intervention should be tailored to the needs of the individual, there is a critical need for the implementation and evaluation of evidence-based effective strategies to further research to support this approach.29, 30 While health care providers routinely monitor growth and provide some counseling, engagement around issues of obesity has not yet occurred. Health care providers can be effective agents of change around prevention, assessment and recognition, and management of childhood obesity.31, 32 Efforts to address obesity in paediatric practice may be greatly enhanced by systems that encourage providers to adopt standardized approaches to diagnosis and treatment of overweight, increasing their acceptance.31, 33 Childhood obesity is already having an important impact on health care resources, and practitioners require a greater understanding of the mechanisms of morbid obesity and related complications and their effective identification and management.34-36

Primary care setting

Providing anticipatory guidance during health supervision visits in early childhood is a defining component of paediatric primary care practice.37  Physicians are amongst the only professionals who see nearly all preschool children, and they remain in a unique position to address the questions and concerns of parents.31, 32, 37 Evidence regarding the effectiveness of anticipatory guidance in paediatric care has recently been reviewed38-40 and age appropriate guidelines have been developed by the American Academy of Pediatrics (AAP) Guidelines for Health Supervision and the Maternal and Child Health Bureau’s Bright Futures.41, 42  In a survey of parents of US children four to 35 months of age, 95 per cent reported receiving a health supervision visit in the last 12 months but a recent study showed that children received only 41per cent of indicated preventive care.43   It has been proposed that failure to deliver preventive services could be more detrimental to children than any other age group given the potential for early investments to establish optimal, lifelong habits for health and well-being.44 A recent review proposed compelling evidence that: overweight begins at a young age and persists;45 parents have control over feeding and activity at young age;46, 47 BMI at young ages tracks well into older ages;48 and problematic adiposity rebound may occur as early as three years of life and is associated with metabolic diseases,49 and that obesity prevention should be focused on preschool aged children. The placement of priority on these topics is uniquely responsive to the personal intervention of the physician.50 While awaiting scientific evidence regarding effective prevention strategies in the primary care setting, it has been recommended that paediatricians target the following behaviors: limiting television, encouraging outdoor play, encouraging breast feeding, and limiting sugar sweetened soft drinks.51 Finally, sensitive and effective communication with children and families, with a focus on healthy nutrition and healthy activity habits, rather than weight, has been strongly advocated.51, 52 Examples include counseling at regular checkups to promote consumption of fibre, fruit and vegetables, limiting sugar-sweetened beverages, and limiting television time.

Measurement tools for preschool aged children are emerging but an absence of valid and reliable preschool nutrition screening exists.53 Nutrition Screening Tool for Every Preschooler (NutriSTEPTM) is a community-based, parent administered nutrition screening tool for children three to five years that includes constructs of nutrition risk as defined as: physical growth, food and fluid intake, physical activity and sedentary behavior and factors affecting food intake for this age group.53  An increased score indicates an increased nutrition risk. Interventions in the school setting have been shown to be effective at reducing screen time, and lowering BMI (Body Mass Index) - an indirect measure of body fatness that has been shown to correlate with more direct measures of body fatness) in school aged children.54 Dwyer et al have recently reported the development of the Preschool Physical Activity Questionnaire (Pre-PAQ).55 The instrument is currently undergoing assessment of utility, validity and reliability.  

A recent survey asked US paediatric primary care providers to identify important yet inadequately addressed research questions; these included evaluating effective counseling methods or techniques to use in anticipatory guidance, strategies to prevent and treat obesity, and understanding the effectiveness of services provided as part of well-child care.56  There is no comparable body of literature regarding anticipatory guidance and health supervision in Canada. Barriers to physician implementation of such guidelines include: lack of time, resources, knowledge and low self-efficacy in counseling skills.57 There is a lack of evidence as to why physicians are not participating in interventions aimed at implementing these guidelines and it has been suggested that focus groups could provide that information.58   

Specialty care

Behavioral strategies such as motivational interviewing (a patient-centered, directive method for enhancing personalized motivation to change by exploring and resolving ambivalence) 59, 60, peer enhanced strategies, cognitive behavior therapy, parental modeling and/or inclusion of family in treatment, and separation of youth from parents for psycho-educational groups are essential components for successful treatment.61, 62 Comprehensive weight management programs that integrate dietary prescription/ education,  physical activity instructions, and a behavioral intervention, are much more successful than those that focus on only one element (e.g. calorie intake) of weight management.63-65  Such programs have been modestly successful with young children (six to 12 years of age) 64, 66 but have not been successful with adolescents.67  Likewise, although it as been concluded that bariatric surgery can be performed safely and successfully (results in mean weight loss of 63 to 66 per cent of excess body weight) in adolescents, concerns have been raised regarding the extent that adolescents are able to adhere to highly structured dietary regimens, vitamin/mineral supplement prescriptions, and physical activity changes necessary to achieve and maintain appropriate weight loss. Therefore, paediatric practitioners continue to search for alternative approaches to enhance the success of the behavioral components of their obesity programs.68

Originally developed by Miller, motivational interviewing has been used extensively and effectively in the addiction field and is also being applied to diabetes, pain management, eating disorders, HIV, and recently, obesity.69-74 It has been suggested as a promising new approach.59, 60  Although very few studies report on actual changes in BMI and/or weight, motivational interviewing has been successful at modifying diet and physical activity behaviors in adults 75 with evidence base for youth beginning to emerge. Receiving more or less motivational interviewing sessions did not affect changes in BMI in one study. Several studies have shown motivational interviewing to be successful with youth with other chronic conditions such as diabetes and a review of MI for pediatric obesity has suggested that the essential question may not be whether motivational interviewing is effective for control of paediatric obesity but how effective, in what populations, at what dose, and what cost.75 Additional issues for investigation are inclusion of parents and peers72, 74 and type of health care provider needed to deliver motivational interviewing sessions effectively.72

For further information on childhood overweight and obesity, please read Causes and consequences of childhood obesity by co-lead investigator Dr. Jill Hamilton.

References

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