Obesity is a chronic disorder of energy balance: the amount of energy being spent must remain less than the amount of energy consumed for a long period of time for obesity to develop. The traditional paradigm for the development of obesity is that a process of 'creeping weight gain' occurs1, and that the rate or degree of positive energy balance is very small - in both adults and children - when considered over long periods (equivalent to perhaps as little as 50 kcal/day)1,2. This paradigm translates directly to public health messages aimed at persuading individuals to make small lifestyle changes in order to prevent obesity ("eat a little less, do a little more")1. The paradigm has been challenged by the finding that, in at least one population at high risk of obesity (Latino children, adolescents, and young adults in Houston Texas3), rates of positive energy balance are typically very much higher. In that study, the median positive energy balance was equivalent to greater than 200kcal/day for a year3.