OBESITY

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Obesity is a chronic disease that is causally related to serious medical illnessesBody mass index (BMI) is calculated by dividing a person's weight (in kilograms) by height (in meters squared); alternatively, the weight (in pounds) multiplied by 704 and divided by height (in inches squared) may be used. There is a curvilinear relation between BMI and percent body fat mass.[3] However, the current practical definition of obesity is based on the relationship between BMI and health outcome rather than BMI and body composition.

Weight Classification Obesity Class BMI (kg/m2) Risk of Disease

Underweight   <18.5 Increased

Normal   18.5-24.9 Normal

Overweight   25.0-29.9 Increased

Obesity I 30.0-34.9 High

  II 35.0-39.9 Very high

Extreme Obesity III ≥40.0 Extremely high

•W e i g h t C l a s s i f i c a t i o n b y B o d y M a s s I n d e x ( B M I . )

Physiology of Energy Homeostasis

Energy homeostasis, which includes all processes that aim to maintain energy balance, requires complex molecular and physiologic processes and constant communication within and among adipose tissue, skeletal muscle, liver, pancreas, and the central nervous system The hypothalamus functions as the main cerebral center in which these

signals converge.[

1. balanced interaction between two sets of neurons

occurs within the arcuate nucleus of the hypothalamus.

Activation of neurons secreting neuropeptide Y (NPY)

and agouti-related protein (AgRP) promotes food intake,

whereas that of neurons secreting pro-opiomelanocortin

(POMC) and cocaine- and amphetamine-regulated

transcript (CART) has an anorexigenic effect

Orexigenicneuropeptide Y and agouti-related protein endocannabinoid system ghrelin,

Anorexicpro-opiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART) Glucagon-like peptide 1 (GLP1)

cholecystokinin (CCK). Leptin

Obesity is caused by an excessive intake of calories in relation to

energy expenditure over a long period of timeTotal daily energy expenditure (TEE) comprises resting energy expenditure (REE), which accounts for approximately 70% of TEE; energy expended in physical activity (approximately 20% of TEE); and the thermic effect of food (TEF), which accounts for approximately 10% of TEE. REE represents the energy expended for normal cellular and organ function under postabsorptive resting conditions. Energy expended in physical activity includes the energy costs of both volitional activity, such as exercise, and nonvolitional activity, such as spontaneous muscle contractions, maintaining posture, and fidgeting. The TEF represents the energy expended in digestion, absorption, and sympathetic nervous system activation after ingestion of a meal