Fast food restaurants on commuter routes 'contributing' to obesity8 August 2019

"Fast-food outlets on commuter routes may fuel obesity crisis," reports The Guardian.

A researcher in the US has linked the number of fast food restaurants along the route to work for 710 women who worked in New Orleans primary schools, to their chances of being overweight or obese. The study also looked at grocery stores, supermarkets and "full service" restaurants, along commuter routes and near people's homes and workplaces.

The researcher did find a link between having a high number of fast food restaurants around a person's home with a trend towards having a higher body mass index (BMI).

The researcher speculated that this could be down to the fact that the workers were too tired or busy to cook when they got home, so ate at fast food outlets on the way home instead.

Fast food restaurants tend to offer higher calorie food in large portions. However, because of the nature of the study, we do not know if this was the case. The participants were not asked about their food and lifestyle habits, so we do not know the cause for higher BMI.

The study made a number of assumptions, including that all the workers drove to and from work, and used the same route each day. The results may not apply to places where more people commute by public transport, or by walking or cycling. Neither can we assume that a study of school workers from one US region can be applied to wider populations.

It can be tempting to pick up an unhealthy snack or takeaway after a hard day's work. The good news is that these days, most shops or takeaways now offer healthier options.

Read more advice about making healthier choices when eating out.

Where did the story come from?

The research was carried out by a researcher from Arizona State University in the US. The research received no specific funding. It was published in the peer-reviewed journal PLOS One on an open access basis, meaning it is free to read online

The Guardian carried a balanced and accurate account of the research, making it clear that this was study by 1 US researcher looking at a specific population sample.

What kind of research was this?

This was a cross-sectional cohort study that analysed information about female employees of 22 schools in the New Orleans area. The researchers wanted to see how food availability near the home, workplace and along the journey to and from work was linked to the women's body mass index (BMI).

Cross-sectional studies just take a snapshot of 1 point in time, in this case the women's BMI and the food exposures in their environment, such as fast food outlets. They cannot prove that 1 has directly caused the other, as many unmeasured factors may be involved.

What did the research involve?

The researcher used data from a previous study of eating habits in women who worked in school in New Orleans. She took information about 710 women, including their BMI (measured by trained examiners), salary range, education, type of work, activity levels measured by accelerometer, and home address.

The researcher then mapped the shortest route between the women's home and workplace. She counted the number of different food outlets within a 1km radius of the home and workplace, and along the commuting route. Types of outlet were supermarkets, grocery stores, fast food restaurants and "full service" or traditional restaurants.

She then used statistical models to look for links between women's BMI and the number of different types of food outlets in the 3 environments – home, work and commuting route. She adjusted figures to take account of other factors such as income and education, and then combined data from all 3 environments into 1 model, so that results for each took account of the other 2 environments.

What were the basic results?

The study found:

Most of the women in the study had a BMI that fell into the overweight (29.3%) or obese (41.7%) categories. The majority were white (72.9%) and the biggest age group represented was 40 to 59 years (63.8%).

How did the researchers interpret the results?

The researcher said that "the results indicate that the density of fast food restaurants within 1km of participants' routes was positively associated with BMI" and that the study shows "the importance of multiple environmental factors with regard to BMI". She suggested that: "Interventions that target reducing fast food meal frequency and accessibility of fast food restaurants should be considered.”

Conclusion

Eating often at fast food restaurants and choosing high-fat, high-sugar, high-calorie food is likely to lead to an increase in weight. It would seem to make sense that time-pressed people might make more use of fast food restaurants if they were conveniently situated on their way home from work.

However, the study does not tell us whether that's what was happening here. We do not know how often the women in the study ate at fast food restaurants, or even whether they took the route home from work that the researcher assumed they did.

There are also unexplained findings in the study. For example, you might expect that having supermarkets or grocery stores near to home would increase the chances of people buying healthy food to prepare at home, but in this study having more access to supermarkets increased the chances that people would have a higher BMI. Meanwhile having more full service restaurants nearby was linked to lower BMI.

The study did find that women with higher incomes tended to have lower BMIs. One explanation for the link between traditional restaurants and lower BMI, or between fast food restaurants and higher BMI, could be if traditional restaurants tend to be sited in richer areas and fast food restaurants in poorer areas.

But this is guesswork. What the findings demonstrate is how difficult it is to try to take a generalised observational view of a person's environment – while having no direct interaction with the people or their habits and lifestyle at all – and try to link this with their BMI. It suggests that, as expected, the availability of food outlets is not the only thing affecting people's weight. Their individual dietary habits, health and lifestyle, will have the biggest influence.

It's also worth remembering that the study looked at a very specific group of workers in a specific geographical location of the US. It may not be relevant to people living in different environments with different lifestyles.

Analysis by Bazian
Edited by NHS Choices