Energy expenditure.

Although human energy expenditure has been studied for over 100 years, many unanswered questions remain regarding the role that individual components of energy expenditure have in the etiology of obesity. Most techniques for measuring physical activity, the most variable component of TDEE, are less than adequate, and differences in energy metabolism are difficult to detect in a static comparison. When energy expenditure is examined in obese and lean subjects at one point in time, there frequently are no differences in energy expenditure when appropriately normalized. However, when subjects are studied longitudinally or when the system is perturbed (such as overfeeding or exercising), differences can be observed. Using a combination of the techniques available today, each component can be reliably studied, and the role that each has in the development of obesity can be ascertained.