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INTRODUCTION

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The last 50 years have seen a marked increase in the prevalence of overweight and obesity in the pediatric population. This deviation from historical norms has been so great that agencies such as the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC) have opted to ignore the most recent weight data from their reference populations when generating their newest growth curves for the clinical follow-up of height, weight, and body mass index (BMI) by health professionals.

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Faced with this dramatic change in growth patterns, general practitioners and pediatricians commonly refer overweight and obese children to the pediatric endocrinologist for evaluation, weight management, and treatment of metabolic complications. This is due first to the widely held—but inaccurate—belief that endocrine conditions are a frequent cause of excessive weight gain and second, to the correct assumption that weight excess has metabolic consequences that are relevant to the practice of pediatric endocrinology.

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From the dietician to the psychologist, from the public health physician to the clinician, and from the family doctor to the subspecialist, obesity is one of the few medical conditions that is relevant to virtually all health professionals. This chapter presents our most recent understanding of the causes and consequences of the “obesity epidemic” in youth, focusing on the hormonal and genetic aspects that are of particular interest to the pediatric endocrinologist.

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We are aware of the controversy surrounding the use of the word “obesity,” as it may lead to stigmatization and discrimination. For the sake of clarity and for the purpose of this chapter, we define childhood obesity as “a condition where excess body fat may negatively affect a child’s quality of life and his/her physical or mental health.”

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EPIDEMIOLOGY

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Methodological Aspects

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Epidemiology, defined as the distribution and determinants of health-related states or events (including disease) and the application of this study to the control of diseases and other health problems, relies on the accurate measurement of variables of interest at the population level. The establishment of the burden of child and adolescent obesity raises a number of issues related to the tools and methodologies used to measure obesity.

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Body Mass Index and Waist Circumference

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There is much discussion about the appropriateness of using BMI as a marker of obesity. Despite being easily derived from weight and height in a clinical setting, health professionals do not always measure and plot BMI data.1 At the population level, BMI correlates well with total, subcutaneous, and visceral adiposity in both children (coefficient of correlation ~ 0.8)2 and adults.3 In adults, BMI relates well to morbidity and mortality. At the individual level, however, BMI is limited by its inability to differentiate adiposity from lean body mass. A muscular, athletic adolescent may have the same BMI as an overweight youth with poor muscle ...

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