It is hard to define the exact prevalence of people who are overweight or obese. However, in most Western nations, these conditions are generally accepted to be of widespread concern to health authorities and the general public. The physiological, psychological and social/environmental factors which may be implicated in the aetiology, maintenance and treatment of these conditions have been the subject of an extraordinary volume of research and technical and popular literature. One fact cannot be disputed: the conditions reflect positive energy balance, where consumption has consistently exceeded expenditure. This book focuses on the causes and nature of this overconsumption, and the role played by specific nutrients or perhaps even specific foods or groups of foods.