Your body mass index (better known as your BMI, weight (kg) / height² (m²)) is measure to express your weight normalized to your height. A high BMI is linked to an increased risk for non-communicable diseases like diabetes, heart disease, stroke, or cancer.
In 2016, 39% of the world’s population had a BMI over 25 and was classified as being overweight. Globally, overweight, obesity, and the associated burden of disease are on the rise and are now being linked to more deaths than underweight.
High BMI is a result of an imbalance between energy intake and energy consumption. While our diet has become fattier and more energy-dense, our lives have become more sedentary. There has been an increase in physical inactivity due to the increasingly sedentary nature of many forms of occupational and domestic activities. A form of physical activity that would benefit our cities and the people living there, is the use of active transport modes. Historically, many cities in Europe and around the globe were flooded with walkers and cyclists as a fast and cheap mode of transport, but with the invention of the automobile, walkers and cyclists disappeared from the streets.
What if I don’t like the gym?
Not all of us are professional sportsmen; you may not like the gym, or you might not have time to work on your physical condition. However, you may like to be sufficiently active (at least 150 minutes of moderate-intensity physical activity per week, according to the World Health Organization) and maybe even lose weight. Active mobility, defined as walking or cycling to go to places, may be the next best thing for you.
Your BMI changes over time. In adults, BMI increases with age at rates of approximately 0.1 kg/m² per year. In a sample of urban dwellers in Europe, it was investigated whether a change in BMI over time could be explained by a change in transportation habits. Information on height, weight, and frequency of use of different transport modes was collected through an online questionnaire. 2316 adults completed the questionnaire twice with on average 492 days in between. About half of the sample was male, and the average participant was 41 years old with a healthy BMI of 23.87 kg/m².
A person switching from regular car use to regular bike use for his trips was found to lose up to one kilogram over a period of 1.5 years. People who cycle at least occasionally to go to work or to run errands maintained their weight. In this way, cycling prevents overweight people from gaining additional weight and it prevents those who are of normal weight from becoming overweight or obese. Unfortunately, when frequent cyclists stopped cycling they increased their weight again. These changes were independent of changes in other factors like changes in recreational cycling, walking or jogging, sports, or being physically active at work.
It’s unclear what the impact is of electric-assisted bikes on BMI. Our results suggest that switching to an electric-assisted bike may not be as beneficial. At least in part of our sample, we see that a trip with an electric-assisted bike replaces a trip with a regular bike, resulting in an increase of BMI. However, only in Antwerp and Zurich, there was a fair number of e-bikes, and therefore the total number of e-bikers in our sample was too small to make firm conclusions. Future research should further investigate this.
This study followed urban dwellers over time, complementing our previous analysis that found cyclists to be 3 kilograms slimmer than car drivers. However, by only measuring at one point in time, results are skewed by only considering people who are already cyclists, as someone of a lower weight is more likely to cycle in the first place. By surveying the same people as they change their transportation habits, the researchers could measure the true effect on people’s health and BMI.
Healthy cities
In the past, physical inactivity has received little emphasis in public health programs compared to, for example, healthy diet, alcohol or tobacco, but times are changing. Rapid urbanization, awareness of environmental pollution, and the high burden of non-communicable diseases are all drivers of a new vision for active and healthy cities.
Urban planners, transport planners, and public health professionals should work together in order to develop policies that promote the use of active transport modes. Actions such as building new cycle lanes or promoting the combination of active modes with public transport are transforming a city into a better environment for walkers, cyclists, and citizen as a whole.
These findings are described in the article entitled Transport mode choice and body mass index: Cross-sectional and longitudinal evidence from European-wide study, recently published in the journal Environment International. This work was conducted by Evi Dons, David Rojas-Rueda, Esther Anaya-Boig, Ione Avila-Palencia, Christian Brand, Tom Cole-Hunter, Audrey de Nazelle, Ulf Eriksson, Mailin Gaupp-Berghausen, Regine Gerike, Sonja Kahlmeier, Michelle Laeremans, Natalie Mueller, Tim Nawrot, Mark J. Nieuwenhuijsen, Juan Pablo Orjuela, Francesca Racioppi, Elisabeth Raser, Arnout Standaert, Luc Int Panis, and Thomas Götschi from Hasselt University, the Flemish Institute for Technological Research (VITO), ISGlobal, Universitat Pompeu Fabra (UPF), CIBER Epidemiología y Salud Pública (CIBERESP), Imperial College London, the University of Oxford, Colorado State University, Trivector Traffic, the University of Natural Resources and Life Sciences Vienna, the Dresden University of Technology, the University of Zurich, the University of Leuven, and the World Health Organization Regional Office for Europe.