Chapter 20. Obesity

• α-MSH α-Melanocyte–stimulating hormone
• ACTH Adrenocorticotropic hormone
• AGRP Agouti-related peptide
• ARC Arcuate nucleus of the hypothalamus
• BDNF Brain-derived neurotrophic factor
• BMI Body mass index
• CCK Cholecystokinin
• CCK-1R CCK 1 receptor
• CSF Colony-stimulating factor
• FFA Free fatty acid
• FTO Fat mass- and obesity-associated gene
• GI Gastrointestinal
• GLP1 Glucagon-like peptide 1
• IL-6 Interleukin 6
• LepR Leptin receptor
• LHA Lateral hypothalamic area
• MC4R Melanocortin-4 receptor
• MCP-1 Monocyte-chemoattractant protein-1
• NAFLD Nonalcoholic fatty liver disease
• NCEP National Cholesterol Education Program
• NEGR1 Neuronal growth regulator 1
• NHANES National Health and Nutrition Examination Survey
• NHLBI National Heart, Lung, and Blood Institute
• NTRK2 Neurotrophic tyrosine kinase, receptor, type 2
• NPY Neuropeptide Y
• OSA Obstructive sleep apnea
• PAI-1 Plasminogen-activated inhibitor
• PC-1 Proconvertase 1
• PCOS Polycystic ovarian syndrome
• POMC Pro-opiomelanocortin
• PVN Paraventricular nucleus
• PYY Peptide YY
• RYGB Roux-en-Y gastric bypass
• SH2B1 Adapter protein 1
• SOS Swedish Obese Subjects
• SIM1 Single minded 1
• STAT Signal transducer and activator of transcription
• T2DM Type 2 diabetes mellitus
• TMEM18 Transmembrane protein 18
• TNF Tumor necrosis factor-α
• WHO World Health Organization

Definition

Obesity and overweight categories have been defined by examining longitudinal study data that associate a given weight with future adverse health effects. The currently accepted surrogate measure of body fatness is body mass index (BMI) which is measured as weight in kilograms divided by height in meters squared. For adults, a BMI <18.5 kg/m2 is underweight, 18.5 to 24.9 kg/m2 is healthy weight, 25.0 to 29.9 kg/m2 is overweight, and ≥30 kg/m2 is obese. For children and adolescents, a BMI between the 85th and 95th percentile for age and sex is considered at risk of overweight, and BMI at or above the 95th percentile is considered overweight or obese.

However, BMI does not account for ethnic differences in skeletal structure or musculature. Body frame size varies dramatically by race/ethnicity from small-framed East Asian adults to larger framed Pacific Islanders. Moreover, conventional cut-points for adult overweight (BMI ≥25 kg/m2) and obesity (BMI ≥30 kg/m2) do not correspond to similar absolute or relative metabolic risk in all ethnic group. As a result, the World Health Organization (WHO) and International Obesity Task Force proposed a lower BMI cut-point to define obesity in South and East Asian adults: 23 kg/m2 for overweight and 25 kg/m2 for obesity.

Prevalence and Projections

National surveys performed by the Centers for Disease Control and Prevention in the United States have found a significant increase in the prevalence of overweight and obesity over the past 30 years. In 2003 to 2004, according to data from the National Health and Nutrition Examination Survey (NHANES), 32.2% of adults were obese. Trends among adults have been tracked by repeat NHANES surveys, showing that the percent of overweight or obese have climbed from 47.0% in 1976 to 1980 to 66.2% in 2003 to 2004, and the prevalence of obesity alone has more than doubled from 15.0% to ...