The energy balance equation has served as an important tool for the study of bioenergetics. It is based on one of the most fundamental properties of thermodynamics and has been invaluable in understanding the interactions of energy intake, energy expenditure, and body composition. Recently, however, the obesity epidemic has extended the use of the equation to the creation of public health messages for preventing or even reversing secular trends in body mass index. This usage often fails to consider how changes in any one term of the equation can lead to accommodations in one or both of the other two terms. It is concluded that research and public health messages should not simply consider how interventions affect just energy expenditure or energy intake, but rather how they affect the balance or gap between energy intake and expenditure.