The obesity epidemic is an economic issue

Free-market forces have helped create a health crisis - and governments must take action to stop subsidising junk food

It is estimated that today's obesity epidemic costs the global economy about $2tn (1.6tn) or some 3% of GDP. For individuals, deciding what to eat is a jealously guarded privilege, but for economists obesity is not really about people exercising free-market choice. Instead it is a market failure.

The causes of the epidemic are complex, spanning the social sciences to biology and technology. Consider, for example, the shift towards urbanisation and car transport. By reducing many people's daily physical activity, these are estimated together to reduce individuals' need for food by 300 calories a day. So how much less food should the car driver eat to compensate? About one biscuit less a day - a trivial change that only goes to illustrate that few of us really understand the energy needs of our bodies.

Related: Sugar warnings have not reduced consumption in England, figures show