People who commute to work by foot, bicycle or public transport tend to have significantly lower body weight and body fat than people who drive a car or motorcycle to work, suggests a large British study published last week in the journal BMJ.
“The use of public transport and walking and cycling in the journey to and from work should be considered as part of strategies to reduce the burden of obesity and related health conditions,” write the study’s authors, who are from the London School of Hygiene and Tropical Medicine and University College London.
Three-quarters drive to work
Unlike most past research on this topic, this new study relied not on people’s own reports of their weight (which are very unreliable), but on objective body-mass-index (BMI) and body-fat measurements taken by nurses. The data were collected from more than 7,500 people participating in an ongoing, nationally represented study in the U.K. (The body-fat measurements were taken with a digital body-fat floor scale, a device that is somewhat controversial because it is less accurate for certain groups of people, such as older people and athletes. In addition, the scale tends to overestimate body fat in people who are heavy and underestimate it in people who are lean.)
Among those 7,500-plus participants, 76 percent of the men and 72 percent of the women commuted to work by private motorized transport (mostly cars, but some motorcycles), 10 percent of the men and 11 percent of the women said they used public transport (buses, trains and subways), while 14 percent of the men and 17 percent of the women walked or cycled to work.
By contrast, in 1971 only 42 percent of workers in the U.K.’s most populous country, England, traveled to work by car or motorcycle, the study’s authors point out.
Bigger impact than dieting
The overall BMI scores were 28 for the men and 27 for the women. An analysis of the data revealed, however, that British men who took public transport or walked or cycled to work had, on average, a BMI one point lower than those who used a car or motorcycle. That’s the equivalent of 6.6 pounds in weight for the average man.
For British women, the effect was only slightly less: just under one BMI point lower, or 5.5 pounds in weight for the average woman.
The body-fat findings corroborated those for BMI. Furthermore, the association between mode of travel to work and body composition held even after adjusting for such as factors as age, illness or disability, income, social class, diet, participation in sports and level of physical activity in the workplace.
“These differences are larger than the effect sizes seen in most individually focused interventions based on diet and physical activity to prevent overweight and obesity,” the study’s authors point out.
Most robust data to date
This was an observational study, and therefore can’t prove cause and effect. Other factors, not identified and adjusted for in the study, might explain why people who don’t use a car to get to work have healthier body compositions than their walking, cycling and public-transport riding peers.
Still, because this study used objective measures and involved a large number of people, its findings appear to be the most impressive to date on this topic.
The findings are also important because they show that commuting to work by public transport — not just by foot or by bike — reduces body fat.
Leave your car at home
The public needs to be persuaded to leave their cars at home — for both health and environmental reasons — and that means politicians and other policymakers must implement laws and policies that give pedestrians, bicyclists and users of public transportation highest priority, say the authors of a commentary that accompanies the study.
Nor is the public’s reliance on the automobile to get to work a problem only of developed countries like the U.K. and the U.S. “Active commuting” is also rapidly declining in many low- and middle-income countries, “where governments and donors have priortised investments in road infrastructure and levels of motor vehicles ownership have soared,” write (with British spellings) the commentary’s authors, Anthony Laverty and Christopher Millet, both public health researchers at Imperial College London.
Increasing car ownership has been linked to an increase in obesity in China, they point out.
“Given the political sensitivity around policy measures that discourage use of cars,” Laverty and Millet conclude, “it is crucial that the public health community, including healthcare professionals, provide strong and consistent messages to politicians and the public which frame these measures as positive public health actions.”
You can read the study in full on the BMJ website.