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. Conversely, physically active individuals can exhibit negative energy balance without weight loss.
Change in energy stores=energy intake–energy expenditure. Despite its use as the prevalent equation for energy, it lacks consideration regarding additional factors. Hence, simplistic notions based on “energy in and energy out” are largely ineffective. Human energy homeostasis is complex and there are many unanswered questions. This commentary reviews assumptions related to energy balance, especially emphasizing weight maintenance in exercising individuals. Additionally, paths for further studies are presented that may address some of the discrepancies in the current research literature.