Obesity is a global phenomenon, a disease which is spread by increasing urbanization and which causes major morbidity and mortality. Over the last two decades it has reached unprecedented and dramatic levels in industrially developed countries but the rise in prevalence affects almost every part of the world. It is already placing huge burdens on the health systems of many countries. Its potential to cause disability amongst working-age populations worldwide, particularly as a result of complications of diabetes, makes it imperative to work towards both preventative and curative solutions.

Yet, despite the fact that obesity has become such a widespread disease, there remains within the medical community a tradition of stigmatizing individual sufferers. Doctors and other health professionals have tended to provide what is seen as self-evident advice, namely, to consume less food and to expend more energy through physical activity. The subsequent failure of patients to lose weight, despite good advice, and in the face of complications of their condition, is then viewed as evidence of an inability to control lifestyles and to resist urges. At the root of this view lies an historical absence of knowledge of the hugely complex and fascinating innate homeostatic mechanism which controls satiety and energy balance: a mechanism that has evolved over millions of years, has seen humankind through feast and famine, and has run into trouble only since the advent of mechanization.