People who drive cars as their main form of transport are on average heavier than those who cycle, according to an ongoing Europe-wide study.
Researchers have so far monitored 11,000 volunteers in seven European cities, asking them how they move around the city, which mode of transport they use and how much time they spend travelling.
The project also asks volunteers to record their height and weight, and to provide information about their attitudes towards walking and bicycling.
An analysis of the data so far shows that those people who drive cars as their main form of transport are on average four kilograms (8.8 lbs) heavier than those who cycle.
The EU-funded Physical Activity through Sustainable Transport Approaches (PASTA) project - led by an international group of experts, including Imperial College London and the World Health Organization - is studying how different forms of transport relate to levels of physical activity, and consequently people's health.
While the researchers cannot yet draw a causal link between the type of transport people choose and their weight, they said the initial results are intriguing, and hope that by following more people they can draw some firmer conclusions.
PASTA researchers are still looking for volunteers, and plan to follow 14,000 volunteers in seven cities around Europe: Antwerp, Barcelona, London, Orebro in Sweden, Rome, Vienna and Zurich.
Imperial's project lead Dr Audrey de Nazelle from the Centre for Environmental policy, said: "We don't have cause and effect yet, but we hope this first finding will encourage more people to take part in the survey so that we can get more data over time and make a link between transport decisions and health."
Dr Adrian Davis, a UK transport and health expert and member of PASTA's advisory board, said: "People who are physically inactive are at higher risk of developing chronic diseases, such as cancer, stroke and heart attacks, as well as becoming overweight.
"Our research shows that factors like urban design, how we move in cities, and the use of cars, bikes or walking could all play an important role in determining the level of people's daily physical activity."
Dr de Nazelle added: "If people can integrate this into their daily lives, such as going to work or going shopping, then it means you don't have to make special time commitments and it's more affordable for everybody.
"Getting people to walk and bike as part of their daily transport modes is really an ideal solution to try to tackle this epidemic of physical inactivity."
The survey also aims to determine how people make transport decisions, and what measures cities can take to encourage walking and cycling.
Dr de Nazelle said: "Cycling is at low levels in the UK - when you compare that to places like northern Europe you can see there's really huge potential to increase the levels."