Friday March 14 2014
Fast food has become increasingly popular
"Encountering too many takeaway outlets near our homes, workplaces and even on the daily commute to work could be increasing our risk of obesity," The Independent reports.
The headline is based on a new study looking at whether the density of fast food outlets in some areas is contributing towards the obesity epidemic. Researchers looked at the availability of fast food outlets in the area around people's workplace and home, as well as along their commuting route.
The researchers then looked at how this related to how much fast food people said they ate and their body mass index (BMI). They found that increased exposure to fast food outlets was generally associated with increased fast food consumption and marginally increased BMI.
The work environment appeared to give the strongest results – people who had the most takeaways near their workplace ate an additional 5.3g of takeaway food per day and had a BMI score 0.92 higher than those least exposed.
It seems rational to expect that an increased prevalence of fast food outlets is linked to increased consumption, but the design of this fascinating study can't prove this is the case.
Nobody forces us to eat junk food. Most fast food outlets also have healthy alternatives. Read more about healthy eating out.
Where did the story come from?
The study was carried out by researchers from the University of Cambridge and was published in the peer-reviewed British Medical Journal. The article has been published on an open access basis, so it is freely available to access online.
The study was undertaken by the Centre for Diet and Activity Research, a UK Clinical Research Collaboration Public Health Research Centre of Excellence.
Additional funding was provided by the British Heart Foundation, Cancer Research UK, the Economic and Social Research Council, the Medical Research Council, the National Institute for Health Research and the Wellcome Trust under the UK Clinical Research Collaboration.
The media's reporting was generally good quality as it provided an accurate summary of the research. However, none mentioned the inherent limitations of the cross-sectional study design in that it cannot prove cause and effect, only highlight an association.
What kind of research was this?
This was a cross-sectional study that included a large population sample. Researchers looked at the takeaway food outlets available near to where the individuals in the sample lived and worked so they could look at whether this was associated with their body weight and eating habits.
The researchers say that the food environment of our neighbourhood – the so-called "foodscape" – has been considered as an influence on our health and diet.
Over the past 10 years, our consumption of food away from the home in the UK has increased by almost a third, and the number of takeaway outlets has increased dramatically. This could be creating what is known as an "obesogenic" environment (one that increases the risk of residents becoming obese).
It is thought that these social and environmental trends could be contributing to rising levels of people who are overweight or obese. It follows that modifying the availability of fast food outlets could be an element in influencing nutrition and health in the UK.
However, this cross-sectional study from one region in the UK can only demonstrate associations. It cannot prove that takeaway or fast food outlets contribute to the cause of the obesity problem, although many may think it is common sense that they would. As the Mail Online's headline put it, "Another study from the University of the Obvious: People who live or work near takeaways are twice as likely to be obese."
Still, there are likely to be a combination of several factors in our lifestyle, diet and activity that are contributing to the nation's growing waistlines – the foodscape may be an additional factor.
What did the research involve?
This research included a sample of 5,442 working adults (aged 29-62 years) who were participating in the Fenland study, an ongoing population cohort study based in Cambridgeshire in the UK.
It looked at whether there were fast food outlets near to where participants lived and worked, and compared this with their self-reported consumption of takeaway food and their BMI.
From the full sample of almost 10,500 people in the Fenland study, the researchers excluded those with incomplete data on their work and travel or who worked outside the county.
Participants' home and work addresses were mapped by postcode. Their home and work neighbourhoods were defined as circular regions with a one-mile straight line radius centred on the postcode.
Accurate data on food outlet locations was sourced from 10 local councils covering the study area, again mapped by postcode.
The participants also recorded their commuting route and distance, and the researchers looked at accessible takeaway food outlets along these routes. They used a 100-metre "buffer zone" if they were walking or cycling, and a 500-metre buffer if they were travelling by car.
Participants completed questionnaires relating to their general lifestyle and medical history, and were weighed and measured by trained researchers. They also completed food frequency questionnaires.
The researchers were mainly interested in how much energy-dense foods from takeaway outlets people reported eating. Using food frequency questionnaires, the researchers estimated people's daily intake (in grams) of:
- fried food (such as fried chicken)
Together, these foods gave an indication of the grams per day of takeaway-type food consumption.
The researchers also looked at the participants' body mass index (BMI). They then looked at the associations between these diet and BMI outcomes and the takeaway food environment around a person's home and work, as well as along travel routes.
Their models took into account various possible confounders, including:
- household income and educational level (a proxy for socioeconomic status)
- car ownership
- daily energy intake and physical activity
- smoking status
What were the basic results?
On average, the full sample was exposed to 9.3 takeaway food outlets at home, 13.8 at work and 9.3 along commuting routes. People were therefore exposed to 48% more takeaway food outlets at work than at home.
The researchers found that there was a positive association between exposure to takeaway food outlets and the consumption of takeaway food. The link was strongest in the work environment, where there was a dose-response relationship (exposure goes up, consumption goes up).
People most exposed to takeaway food outlets at work consumed an additional 5.3g per day of takeaway food (95% confidence interval (CI) 1.6 to 8.7g) compared with those least exposed.
At home, people in the most exposed areas ate 4.9g per day more than those least exposed, but there was less evidence for a dose-response relationship. There was also little evidence for an association between exposure across travel routes and consumption of fast food.
However, when combining exposure in all environments put together, those most exposed consumed 5.7g per day more fast food than those least exposed.
There was also a "dose-response relationship" between exposure to fast food at work and BMI (as you'd expect, those who said they ate most fast food had higher BMI). People most exposed had significantly higher BMI, with a difference of 0.92kg/m2 compared with those least exposed.
Again, when looking at all exposure environments put together, those with the highest exposure had BMI 1.21kg/m2 higher.
There was no difference by gender for either takeaway consumption or BMI.
How did the researchers interpret the results?
The researchers conclude that, "Exposure to takeaway food outlets in home, work, and commuting environments combined was associated with marginally higher consumption of takeaway food, greater body mass index, and greater odds of obesity.
"Government strategies to promote healthier diets through planning restrictions for takeaway food could be most effective if focused around the workplace."
Research has found that increased exposure to fast food outlets, particularly around work, is associated with increased fast food consumption and marginally increased BMI.
The research benefits from including a large population sample and from taking into account various possible confounders that could influence the association between fast food outlet exposure, consumption and BMI, including markers of socioeconomic status and diet and lifestyle in general.
The finding that people were exposed to almost 50% more takeaway food outlets around their work locations than their home is perhaps not surprising. Most people live in residential areas, while their work locations will often be in towns and city centres, where there are many more food outlets. It also may be expected that the more takeaway food outlets that people are exposed to, the more they are likely to eat.
However, this remains a cross-sectional study conducted in only one region of the UK, which can only demonstrate associations and cannot prove cause and effect. The availability of fast food outlets in our environment may certainly be a contributor, but it is likely to be a combination of several factors in our lifestyle, diet and activity that is contributing to the obesity epidemic.
While the study has attempted to adjust for several potential confounders, it possibly has not been able to account for all factors that may be having an influence.
When interpreting this study, it's important to note that it was only conducted in one very rural region of the UK, and different results may be found in other places. Also, despite the best efforts of the researchers, there may be some inaccuracies in how they determined people's exposure to fast food, as well as in the people's reporting of their food consumption.
It should also be pointed out that the study didn't look at consumption of soft drinks, which are commonly sold in fast food outlets and can contain a significant amount of calories.
Nevertheless, the researchers' suggestion that, "Policies designed to improve diets and body weight by restricting takeaway food access may work, and could be most successful if focused around the workplace" seems reasonable.
It is possible that promoting a voluntary scheme where employees are rewarded with small treats or prizes if they stay out of the local burger joint could work.
But ultimately, your risk of obesity comes down to the choices you make. You choose where and what you eat. The good news is that it is easy to make healthy food swaps and choose healthier options while eating out.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.