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Prevalence Data from the National Health and Nutrition Examination Surveys (NHANES) show that the percent of the American adult population with obesity (BMI 30) has increased from 14.5% (between 1976 and 1980) to 30.5% (between 1999 and 2000). As many as 64% of U.S. adults ≥20 years of age were overweight (defined as BMI 25) between the years of 1999 and 2000. Extreme obesity (BMI ≥40) has also increased and affects 4.7% of the population. The increasing prevalence of medically significant obesity raises great concern. Obesity is more common among women and in the poor; the prevalence. | Chapter 074. Biology of Obesity Part 2 Prevalence Data from the National Health and Nutrition Examination Surveys NHANES show that the percent of the American adult population with obesity BMI 30 has increased from 14.5 between 1976 and 1980 to 30.5 between 1999 and 2000 . As many as 64 of U.S. adults 20 years of age were overweight defined as BMI 25 between the years of 1999 and 2000. Extreme obesity BMI 40 has also increased and affects 4.7 of the population. The increasing prevalence of medically significant obesity raises great concern. Obesity is more common among women and in the poor the prevalence in children is also rising at a worrisome rate. Physiologic Regulation of Energy Balance Substantial evidence suggests that body weight is regulated by both endocrine and neural components that ultimately influence the effector arms of energy intake and expenditure. This complex regulatory system is necessary because even small imbalances between energy intake and expenditure will ultimately have large effects on body weight. For example a 0.3 positive imbalance over 30 years would result in a 9-kg 20-lb weight gain. This exquisite regulation of energy balance cannot be monitored easily by calorie-counting in relation to physical activity. Rather body weight regulation or dysregulation depends on a complex interplay of hormonal and neural signals. Alterations in stable weight by forced overfeeding or food deprivation induce physiologic changes that resist these perturbations with weight loss appetite increases and energy expenditure falls with overfeeding appetite falls and energy expenditure increases. This latter compensatory mechanism frequently fails however permitting obesity to develop when food is abundant and physical activity is limited. A major regulator of these adaptive responses is the adipocyte-derived hormone leptin which acts through brain circuits predominantly in the hypothalamus to influence appetite energy expenditure and neuroendocrine .
