WHAT CAUSES OBESITY? At its most simplistic, this is easy to answer – an individual piles on the pounds because there is a mismatch between energy intake and expenditure. That balance is most commonly affected by alterations in food intake and energy expended during exercise, but may also be influenced by the efficiency of substrate utilisation, factors that alter metabolic rate, and/or nutrient partitioning (storage of excess calories). The veterinary literature has mainly focussed on how owners manage their dogs and has identified many predictable food and exercise related risk factors. But breed, age and gender also consistently identified as risk factors for obesity and remain there even when management factors are evened out in mathematical modelling, meaning their effect is physiological and independent of owners. So, while the physics of the energy balance equation between intake and expenditure is true, and owners should be able to control their dogs’ food an exercise to keep them lean, it is disingenuous to dismiss the role of physiology in obesity development.