For many scientists and clinicians, obesity has at last come of age. When the editors were going through medical school and even specialist training in diabetes and endocrinology, obesity was a nonentity that fell out of the mainstream of ‘real’ diseases and was notable for being dull and unrewarding to treat. Admittedly, this was in a previous century – although not quite, we hasten to point out, a whole century ago.

Over the last 20 years, obesity has moved steadily in from the wings to centre stage and is now acknowledged by a wide range of players – health-care professionals, governments, the media and even the general public – to be one of the most challenging threats to global health for the foreseeable future. We prefer to avoid using that cliched expression ‘an explosion of knowledge’, but this is a reasonable description of the rapid and accelerating growth in the scientifi c and medical literature on obesity during the last decade or so. At the same time, the mismatch between what we know and what we can usefully do with that knowledge has become ever more striking. In an age when many other diseases have been conquered, or at least beaten into submission, obesity stands out as a condition whose prevalence continues to rise, often at rates that exceed the most pessimistic predictions of a few years ago. Obesity is still waiting for a therapeutic breakthrough; although the focus is inevitably on novel drugs and surgical procedures, the most important advance will be in fi nding new, effective and affordable measures to make whole populations change the ways in which they have become accustomed to live. So obesity is here to stay, and an ever-increasing number of people will need to know about it.

Visit any good medical bookshop or its e-counterpart and you will fi nd a metre or so of shelf space occupied by books about obesity, some of which are very good. So why have we decided to invest the time and energy in bringing another textbook into an already crowded fi eld? Indeed, isn’t the relentless advance of electronic publishing pushing big medical books towards the brink of extinction?

Perhaps predictably, we don’t subscribe to the view that medical textbooks are about to join 35-mm fi lm and tape cassettes in the dustbin of defunct technologies. Also, we believe that there is room for a book on obesity with the qualities that we have aimed for here – namely, comprehensive but balanced coverage of the fi eld, with the scientifi c background, clinical practice and wider societal aspects all well integrated with each other. Any voyage of discovery should be enjoyable, and we also set out to produce an attractive book that will be a pleasure to read and to look at. A book of this size can never be as up to date as a speed-of-light electronic tour of the current literature, but it serves an entirely different purpose. A good textbook should provide expert guidance through the fi eld, building understanding while laying the ground for new knowledge; it should also highlight areas that remain uncertain, and explain why. In this book, we have attempted to capture not only the essential facts, but also to show how these fi t into the wider landscape of the science and clinical practice of obesity. Each chapter stands alone as a self-contained overview of the topic – with the key points summarised succinctly at the start – and can be read as such. Throughout the book, links and cross-references indicate the important portals of entry into other relevant areas. We have tried to make this book accessible and of interest to a wide readership, primarily doctors, dietitians, specialist nurses and other health-care professionals as well as scientists working in the many disciplines touched by obesity. We hope that it will also be valuable to those in public health and economics, and to policy makers at national and international level.

If we have succeeded in our aims, it is mainly because of the outstanding team of contributors that we have been fortunate to assemble. It will be immediately obvious from reading their chapters that they are world-class experts in their fi elds; we are also deeply grateful to them for having written for us – in an age when books command a lower priority than papers and reviews – and for their good nature and generous tolerance of editorial interference. It has been a great pleasure and a privilege to have worked with them on this book, and we hope that they are as happy with the end-product as we are.