There is no doubt that, in the developed world, people, by various measures, are healthier than they have ever been. Mortality and morbidity rates have fallen over the past century or more, notwithstanding occasional blips when crises such as war or economic depression have halted or temporarily reversed gains. The crude death rate in the US, for example, has fallen from around 1 per cent to about 0.8 per cent since the 1940s, but the age-adjusted rate has fallen much more quickly. People on average live longer, since fewer people die young.

This trend is a global phenomenon; and the biggest falls in death rates have occurred in countries with the fastest economic growth rates. We know that mortality and morbidity rates are correlated with per capita gross domestic product (GDP), although the quite large variation across countries shows that other factors are also important. We know, too, that mortality and morbidity rates vary across social classes, with the rich living longer and, on average, having better health than poorer people. We can further note that, while this increase in the health of the world's population is enhanced by better health care (that is, the provision of medical services), the major cause is healthier lifestyles due to better food, water and living conditions.

Despite this good news for people's health, there is growing concern in the developed world about increasing obesity among the population. This was first brought to public attention by health professionals – the World Health Organization was a major player in publicizing the issue – but it is increasingly discussed by politicians, commentators and the public.

The issue has been described as a crisis, and obesity as an epidemic. These rhetorical flourishes are to be expected when an issue is first brought to public attention. In themselves, they are not very helpful descriptions. The scale of the obesity crisis is highly contested, with some people suggesting we should not concern ourselves with body shape. The manner in which it is discussed also varies cross-nationally. In the UK, for example, the costs to the taxpayer-funded NHS are a concern. Obesity therefore becomes a public issue, since those not suffering health problems due to excess weight subsidize the health costs of those who are.