The study, involving academics from Lausanne's federal institute of technology (EPFL), found that people living in the western, working-class areas of the city are more obese than their counterparts living in the more affluent neighbourhoods to the south and east.
Doctors and geographers pooled their expertise to develop a body-mass index (BMI) map of Lausanne after more than 6,000 city residents volunteered to hit the scales.
The results showed that the usual factors - education, income, age, health, ethnicity, gender and alcohol consumption - could not account for why residents in some parts of the city were heavier than those in others.
The data was analyzed by geographers from EPFL and epidemiologists from the university hospitals of Lausanne (CHUV) and Geneva (HUG).
A map uses red dots to identify high rates of obesity and blue dots for low BMI levels, clearly showing the east-west divide.
This remained even after obesity levels were weighted to account for factors that affect weight such as income, education level, age and other factors.
“It appears that the urban environment has a major impact, independent of income and other common factors,” Idris Guessous, a medical doctor from CHUV and HUG and co-author of the study is quoted as saying in a news release from EPFL.
Such factors as distance from green spaces, access to stores, fast-food restaurants and “geographical compartmentalization” could be responsible for the differences, although more research is needed, she indicated.
Contagious behaviour of residents in a neighbourhood could have an impact on human health, researchers believe.
If urban living does play an important role in obesity there may be ways to address the problem, Guessous said.
“You cannot change your age, it's not easy to act on your educational level, and equal income for all is the stuff of utopia,” she said. “But we can do something about city living,” she said.
“Once we've gained a better understanding of the role of urbanism, we'll be able to look at the more affluent suburbs and get ideas on how to improve disadvantaged neighbourhoods.”