In recent decades obesity has become an increasing concern for governments and health organisations around the world. Changes in diet in modern conditions have led to our food environment being labelled "toxic" and "obesogenic", and are portrayed in marked contrast to the types of food environment in which humans evolved and are adapted to biologically. In this article I question whether the modern food environment is genuinely so different from those that humans evolved in, and whether domesticated animals, like humans, tend to become obese in conditions where food is plentiful. I continue by offering a model of eating behaviour based on the marginal value theorem. The model implies that many parents and public policy unwittingly encourage unhealthy diets by controlling or over-regulating children's diet: although it may feel counterintuitive to respond to the risk of obesity by allowing individuals to make choices rather than restricting their choices, a more relaxed and less regulated approach to food intake should allow appropriate modulation of food intake in conditions where food is plentiful. (C) 2009 Elsevier Ltd. All rights reserved.