ABSTRACT
It is generally accepted that the cause of obesity is multifactorial, brought about by an interaction between predisposing genetic and metabolic factors and a rapidly changing environment. Among the cultural and societal factors, unhealthy diets and sedentary behaviors have been identified as the primary causes. This makes sense since by simple definition, obesity is a disorder of energy imbalance, where energy in exceeds energy out. The resulting weight gain is a function of time (months or years) × surplus energy (kcal). Energy balance is critical as daily calorie mismatch of only +1% would theoretically lead to a gain of approximately two pounds of fat per year (1). Data from the National Health and Nutrition Examination Surveys (NHANES) shows that during 1971 to 2000, a significant increase in average energy intake occurred—for men, average intake increased from 2450 to 2618 kcal, and for women, from 1542 to 1877 kcal (2). In contrast, trends in physical activity have remained stable with only about one-quarter of Americans engaging in recommended levels of activity between 1990 and 1998 (3). Due to this increasing “calorie gap” between intake and expenditure, the prevalence of obesity in the United States over the past 30 years has doubled, increasing from 14.5% to 30.9%. These two principal factors, overconsumption of calories and lack of engagement in physical activity, overwhelm an individual’s innate physiological adjustment to maintain 218normal energy balance. Attention to these two behavioral factors forms the cornerstone for obesity treatment.
