Obesity and environments external to the body.

Studies of environment and obesity usually use epidemiologically tractable measures that are proxies for energy balance or macronutrient composition intake, mostly to identify individual behavioural changes for prevention or reduction of obesity, or inform policy. Of environments external to the body as they relate to obesity, the built environment and the food environment are considered among the most important. Incorporating human sociality into obesity and environments research enriches the field by offering possible ways for understanding obesity production via social stress, dietary preference, food consumption and physical activity. External environments are in flux, however, especially with changing urban form and social environmental hybridity since Web 2.0, with urban polycentricity and networked and online activity influencing obesity production in new ways. While the world's rural populations are experiencing the fastest increases in obesity, large urban populations benefit from scale in setting the physical conditions for physical activity and healthy food availability, with larger and polycentric cities having lower rates of obesity than smaller monocentric or dispersed cities. It is argued that built, food and social environments set the context for obesity production or its amelioration, with sociodemographic factors being more important than new phenomena such as digital and smart technologies. This article is part of a discussion meeting issue 'Causes of obesity: theories, conjectures and evidence (Part I)'.