We exploit the detail‐independence feature of thermodynamics to examine issues related to the development of obesity. We adopt a ‘global’ approach consistent with focus on the First Law – namely that the metabolic energy provided by dietary foodstuffs has only three possible fates: the performance of work (be it microscopic or macroscopic), the generation of heat, or storage ‐ primarily in the form of adipose tissue. Quantification of the energy expended, in the form of fat metabolised, during selected endurance events, reveals the inherent limitation of over‐reliance on exercise as a primary agent of weight‐loss. This result prompts examination of various (non‐exercise based) possibilities of increasing the rate of heat loss. Since these, too, give little cause for optimism, we are obliged to conclude that obesity can be prevented, or weight‐loss achieved, only if exercise is supplemented by reduction of food intake. This article is protected by copyright. All rights reserved.