One-in-10 pupils from poor, inner-city backgrounds eats or drinks at fast-food outlets at least once a day, according to today’s Metro. The newspaper claimed that “medical experts” are calling for a ban on junk food outlets near schools because “many of the children are already overweight or obese and will likely become obese as adults”.
This news story is based on a survey of just under 200 schoolchildren aged 11 to 14, all from Tower Hamlets in central London. Contrary to the newspaper’s alarmist tone, the survey actually found no link between fast-food consumption and the children’s body mass indices (BMI) after taking into account their age and gender. However, as it looked at both fast-food consumption and BMI at the same point in time, it can't tell us how one factor might influence the other. It also can't tell us how the rates of fast-food consumption in these children differ from those in other areas with different levels of deprivation or fast-food availability. It certainly can’t tell us whether banning fast-food outlets would lead to a reduction in the children's BMI.
Despite its limitations, the study does provide us with some useful information about some schoolchildren’s eating habits, and highlights areas where their diets could be improved. It is important that children have a healthy, balanced diet and maintain a healthy weight.
Where did the story come from?
The study was carried out by a freelance researcher and researchers from Newcastle University and Central London Community Healthcare NHS Trust. It was funded by NHS Tower Hamlets. The study was published in the peer-reviewed open access online medical journal BMJ Open.
The Metro focused on the call to ban fast-food outlets in deprived areas, which was a minor point in the authors’ conclusions. The freesheet did not report the important point that the study found no link between BMI and fast-food consumption.
The “medical experts” cited in the Metro’s headline were in fact the people who carried out the study. To find out more about why this matters, see How to read the health news. However, the researchers did not directly call for a ban on junk food outlets near schools. Instead they said: “Clearly, actions need to be taken either to limit the ability of these children to access fast-food outlets [the schools operated “open-gate” policies at lunchtimes] or to change the foods they purchased at these outlets (such as opting for less calorie-dense lunches, with more fruit and vegetables and less fat and salt).” They also called for a ban on the sale of sweetened soft drinks at fast-food outlets located near schools.
What kind of research was this?
This was a cross-sectional study looking at whether there is an association between schoolchildren’s weights and their consumption of food and drink from fast-food and takeaway outlets in a deprived inner London borough. The authors said that increasing consumption of takeaway and fast food has previously been held responsible for the “obesity epidemic” but that evidence on this has had mixed findings. The authors also commented that there is little UK data on the availability of fast-food and takeaway outlets and its association with childhood obesity. The borough selected for this study, Tower Hamlets, has a high concentration of fast-food outlets and a higher level of childhood obesity than national levels.
This type of study can provide us with descriptive information about the characteristics of groups of people (in this case, their BMI) and about whether these characteristics show patterns of association with other factors (in this case, frequency of purchasing at fast-food and takeaway outlets). However, as all of the characteristics and factors are assessed at the same time, they cannot tell us whether any associated factors have caused the characteristics seen.
What did the research involve?
The researchers assessed 193 schoolchildren, aged between 11 and 14, attending school in the London Borough of Tower Hamlets. They measured the children’s BMIs and asked them about their consumption of fast food and preferred foods and drinks. They then assessed whether there was any relationship between the children’s BMI and their fast-food eating habits.
The children in the study came from two state schools and were assessed in early 2010. They were asked to complete questionnaires, including information on their age, date of birth, gender and receipt of free school meals (as a measure of deprivation). They were also asked:
- how often they purchased food or drinks from fast-food takeaway outlets over a week
- what portion-size of chips they would usually purchase
- the three drinks they would most frequently purchase
- why they purchased fast food
- what their average physical activity levels were in the week and on weekends (under two hours, two-to-five hours or five or more hours daily)
Trained researchers measured the children’s heights and weights. Their BMIs were calculated and compared with standard growth charts calculated in 1990. Children who were in the top 5% of the BMI charts for their age and gender were considered obese, and those in the next highest 10% were considered overweight. Data on BMI, age and gender were available for 121 children.
What were the basic results?
The ethnic background of the study population was mainly Asian (48.3%, excluding Chinese), with 21.1% white and 19.4% black African-Caribbean. More than half of the children (61%) were entitled to free school meals, which is often used an indicator of deprivation. Almost a third (30.6%) were classified as being overweight or obese.
The researchers found that:
- More than half of the children surveyed (54%) purchased food or drinks from fast-food or takeaway outlets twice or more times a week.
- About 10% consumed fast food or drinks from these outlets every day.
- About 70% of children from black ethnic groups and 54% of Asian children purchased fast food more than twice a week, compared with 39.5% of white children.
- Almost three-quarters (71%) of children reported that a better choice of products would motivate them to choose more healthy options.
- Most children (70%) reported that fizzy sweetened drinks were their first choice of beverage to buy.
- There was no relationship between gender, age or deprivation and fast-food consumption.
Perhaps surprisingly, children with lower levels of fast-food consumption were found to have significantly higher BMIs on average, while those with higher levels of fast-food consumption had significantly lower BMIs on average. However, once the researchers took into account age and gender this relationship was no longer significant.
How did the researchers interpret the results?
The researchers concluded that there was a high frequency of fast-food consumption among the schoolchildren. They said that the children are exposed to an environment that is likely to cause obesity, and many of these children are already overweight and will likely become obese as adults. The researchers recommended that:
- The sale of sweetened soft drinks at fast-food outlets near schools should be banned, and the children’s access to fast-food outlets should be limited.
- Measures should be taken to change the foods the children purchase at these outlets so that their current levels of salt, fat and calories are reduced and more fruit and vegetables are provided.
This survey has assessed fast-food consumption and BMI in children aged 11 to 14 in a deprived London borough. Although the news coverage focused on the reported call to ban fast-food outlets in deprived areas, the study did not actually find a relationship between fast-food outlets and children’s BMI after taking into account their age and gender. There are several limitations to this study:
Small, limited sample
The survey includes a relatively small number of children, all from one deprived inner London borough. Larger studies covering wider geographical areas would be needed to confirm the findings and to determine how the children’s habits compare in areas with different levels of deprivation.
Self-reporting of eating habits
Children reported their own fast-food consumption, which may not be an accurate reflection of their true consumption.
As the study is cross-sectional, it can't tell us whether one factor could have directly caused another.
It is not possible to say from this study whether banning fast-food outlets would lead to a reduction in children’s BMI. Furthermore, this was not the direct conclusion that the researchers came to.
Despite its limitations, the study does provide us with some useful information about some schoolchildren’s eating habits, and highlights some areas where their diets could be improved. It is important that children have a healthy, balanced diet and maintain a healthy weight.
Analysis by Bazian. Edited by NHS Choices.