Energy Balance: Through the Looking Glass

Human metabolic energy balance has been an area of intrigue and confusion for decades. An imbalance between energy intake and energy expenditure is considered the primary etiology for weight changes. Behavioral interventions, however, have generally resulted in a smaller than expected weight loss, which in part has been attributed to compensatory adaptations in other components contributing to energy balance [1,2]. Conversely, physically active individuals can exhibit negative energy balance without weight loss [3-5].