Access is the biggest food cue of all

A study of hundreds of US primary school workers has found those whose daily commute passes through a corridor with more fast food restaurants have a higher body mass index (BMI), the measure used to gauge overweight and obesity. 

It’s the first ever study to link body weight and the availability of fast food on the journey to work.

The study’s author, biostatistician Adriana Dornelles, from the Department of Economics at Arizona State University, US, brought together three large databases to make her findings.

She took figures from the ACTION survey, including the age, weight and education level of 710 elementary school employees – 73% of whom were teachers – across 22 schools in Greater New Orleans.

Dornelles then used the Dun and Bradstreet commercial database to create maps of the food outlets located within one kilometre of each person’s home, the school they worked in, and their presumed commuting route while driving. 

Food outlets were classed as supermarkets, grocery stores, full-service restaurants and fast food restaurants, and the commute route was based on the shortest distance between home and work, which studies suggest is how most people navigate the trip. 

Finally, US Census data were tapped to measure income, used as a proxy for socioeconomic status.

The results show that for people trying to keep weight off, choosing which way they go to work is no small matter.

For every extra fast food restaurant within one kilometre of the commute corridor, the BMI of participants – their weight in kilos divided by height in metres squared – went up by 0.8 units. That represents a gain of around 2.4 kilograms for someone who is 1.74 metres tall.

The results held after controlling for the socioeconomic status of participants – socioeconomic disadvantage has been linked to higher BMI, although the relationship is not straightforward. {%recommended 7408%}

Dornelles also found the number of supermarkets and grocery stores along the commute were linked to higher BMI, but to a lesser extent.

The author offers some tentative explanations for her findings. Fast food consumption, she notes, has “increased substantially” in recent decades. Indeed, on one estimate, spending on fast food increased from 2% to 18% of the total US food spend in the half century to 2011.

“This situation along with fast-food portion sizes, results in the population’s overall higher consumption of fat, cholesterol, and carbohydrates and therefore increased weight and obesity,” she writes.

Dornelles has less to say about a causal link between fast food availability and BMI. There is, however, a literature suggesting the presence of food cues is a powerful driver of eating behaviour.

For example, studies of both chocolate and fruit and veg have found food that is visible and nearby is eaten in greater amounts. Moreover, as psychologist Alexandra Logue has noted, cues that simply get people to think about food, a billboard for example, can bump up insulin, drop blood sugar and make you hungry.

There is also evidence that food cues get linked to the reward of eating via a conditioning process, reinforcing eating behaviour still further.

It’s worth noting, however, that other results in Dornelles’ study weren’t so clear cut.

Having full-service restaurants near the commute seemed to be protective, with BMI actually dropping slightly for every such outlet within the one-kilometre buffer.  

And there was zero relationship between BMI and the number of fast food restaurants near workers’ homes. Dornelles does not account for these effects, but she is forthright on the main findings.

“The availability and variety of fast-food restaurants along our commute create endless opportunities for a quick, cheap, and unhealthy meal, which results, on average, in higher body mass index,” she says.

The upshot, it appears, is a lesson for those in a position to alter the built environment for the good of public health.

“Interventions that target… accessibility of fast-food restaurants should be considered,” Dornelles concludes.

The study appears in the journal PLOS One.