The energy balance model (EBM) of obesity is defended as a biological model that integrates energy conservation with macronutrient partitioning. This article shows that the defense is self-defeating. If EBM is merely the principle of energy conservation, it is agnostic about obesity mechanisms and therefore explanatorily empty. If EBM is a biological model that specifies partitioning, it must satisfy mass balance for each macronutrient. But when its equations are made explicit, EBM entails sustained negative protein balance at stable body weight – a physiological impossibility. The only escape is to reduce EBM to the energy conservation principle, which its defenders explicitly disavow. EBM is therefore either trivial or false. The mass balance model (MBM), by contrast, satisfies energy conservation as a consequence of mass conservation, predicts weight and composition changes from first principles, and fits metabolic ward data without ad hoc tuning. The dispute is not symmetric: MBM is the coherent correction to an incoherent paradigm.