Behavioural and environmental factors are primarily responsible for the dramatic increase in obesity in the past two decades, although genes play an important role in regulation of body weight.
Calculating body mass index (BMI) is the most widely accepted method of screening for obesity in children. Abnormal BMI cut-offs in children are determined by age- and sex-specific percentiles.
The dramatic increase in childhood obesity has led to a marked increase in the diagnosis of impaired glucose tolerance and type 2 diabetes mellitus in children.
Preventing excessive weight gain in children is of paramount importance in confronting the obesity epidemic, as obesity is difficult to treat at all ages, and obese children tend to become obese adults.
The mainstay of treatment is lifestyle modification to improve diet and increase physical activity. Pharmacotherapy and bariatric surgery may be considered as an adjunct to lifestyle modification in severely obese adolescents.
Obesity is a condition of excessive body fat or adiposity that exceeds healthy limits. The most widely accepted method to screen for excess adiposity is calculation of body mass index (BMI).  Abnormal BMI cut-offs in children are determined by age- and sex-specific percentiles based on growth charts, as the amount of body fat changes with age and differs between boys and girls.  Worldwide, the definition of overweight and obesity changes; however, a BMI >85th percentile is defined as overweight or at risk for overweight in the US and UK, a BMI ≥95th percentile is variably defined as obesity or overweight, and a BMI >99th percentile is defined as severe obesity.   For children under 2 years of age, BMI percentiles are not available; thus, obesity may be defined as a weight ≥95th percentile for height. 
Associate Professor of Pediatrics
Section of Adult and Pediatric Endocrinology
Pediatric Endocrinology Fellowship Program
University of Chicago
DD declares that she has no competing interests.
Chief of Pediatric Surgery
The Mother and Child Hospital
Associate Clinical Professor of Surgery
University of Colorado
SSR declares that he has no competing interests.
Assistant Professor of Pediatrics
SK declares that she has no competing interests.
Honorary Research Fellow
Department of Health Services Research
Institute of Psychology, Health and Society
University of Liverpool
PB declares that he has no competing interests.
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