Does urban living make us gain (or lose) weight?

The citizens of Lausanne may provide some insight into the causes of obesity. The extra weight carried by people living in the working-class neighborhoods of the western side of the city defies the usual explanations, and urbanism may have something to do with it. We are not all equal when it comes to obesity. While genetics plays a role, the main causes of excess weight relate to the social environment. In the United States, researchers have long been aware that obesity levels in low-income groups are above average. The same is true in Europe and in the Swiss cities of Geneva and Lausanne, according to researchers in western Switzerland. Doctors and geographers have pooled their expertise to create a body-mass index (BMI) map for the city of Lausanne. The map shows a clear correlation between low income and obesity: the working-class neighborhoods are overwhelmingly red (above-average BMI), while the middle-class suburbs are covered in blue (below-average BMI). But this mapping exercise did not just confirm what was expected. In western Lausanne, the usual factors - education, income, age, health, ethnicity, gender and alcohol consumption - could not account for the residents' extra weight. Something is missing, and the researchers have hypothesized that urban living itself could play a role. Their conclusions have been published in the British Medical Journal Open. Thousands of residents hit the scales