The energy balance theory is an inconsistent paradigm.

Metabolic physiology asserts that body weight stability is achieved when over time the average absorbed energy intake equals the average expended energy. This principle, known as energy balance, justifies the design of numerous investigations that aim to elucidate the biology of obesity. The present work provides a mathematical analysis that demonstrates, nonetheless, that weight stability must coexist with a constant energy imbalance, i.e., the average absorbed energy intake and the average expended energy are significantly different during steady weight periods. This analytical finding is not in contradiction with the First Law of Thermodynamics since open systems can manifest a stable mass in the absence of energy equilibrium. The effect of caloric imbalance on weight fluctuations is thus the result of its underlying net mass flux. The energy balance theory is, consequently, an inconsistent paradigm; and as such, the data analysis and interpretation that follows from its postulates is expected to be erroneous.