It is helpful to consider the major population questions around obesity in three categories. What is driving the rise in obesity prevalence, what are the moderating factors that result in a very wide range of obesity prevalence rates, and what are the most promising solutions to reverse the prevalence?

The increase in population body size experienced over the last few decades has been associated with an increase in both energy intake and energy expenditure. The latter is due to the higher resting metabolic rate associated with a larger body size. Thus, increased energy intake must be the major driver of weight gain and, indeed, studies which have estimated the impact of the increased food energy supply on increased body weight have concluded that the increased energy intake is more than sufficient to explain the increase in weight over the last 3 decades. This places a much greater emphasis on the need to reduce the obesogenic food environment we live in.

Despite these common global food pressures for overconsumption (especially in rich countries), there is an enormous range in obesity rates. For example, in women the prevalence of body mass index >30kg/m2 ranges from 0.7% in Bangladesh to 70% in Tonga. It is likely that the major differences in wealth, culture, and environments explain this variation. It is helpful to consider population wealth as an enabler of obesity, with relatively small amounts of national wealth allowing any predisposing or protective factors to become manifest. These socio-cultural and environmental factors are thus moderators which help to explain the relatively low trajectory of weight gain in countries with a protective cuisine (eg Japan and Korea) or active transport environment (eg Netherlands and Denmark) and the relatively high trajectory of countries, such as Pacific nations, where overprovision and consumption of food and large body sizes carry positive social meaning.

The solutions for the epidemic will need to be multiple but it is highly unlikely that changes in the physical environment, cultural norms or the economic drivers of obesity will occur in the absence of strong government policy. Currently, almost all governments are shying away from ‘hard’ policy options such as regulation and taxation, instead favouring the ‘soft’ options of education, social marketing, health promotion programs and industry self-regulation. The experience from the control of other difficult epidemics such as tobacco, alcohol, road deaths and occupational injuries suggests that the soft options will not be sufficient for an epidemic which is more difficult and more complex than any other we have addressed.

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