Friday October 17 2014
Fizzy drinks have a high calorie count due to their sugar content
“Signs warning shoppers how much exercise they need to do to burn off calories in sugary drinks can encourage healthier choices,” BBC News reports. Signs in shops in an area of Baltimore seemed to have led to a change in shopping habits amongst Afro-American teenagers.
Researchers first studied beverage purchases by black teens at six corner stores in Baltimore.
They then tested the effect on purchasing habits of displaying different types of calorie information, such as the number of calories in a sugary drink, or how much walking or running you’d need to do to burn off the calories.
Overall, they found that displaying the information changed beverage purchases, with fewer sugary drinks purchased and fewer large drinks purchased, leading to fewer overall calories.
Environmental interventions, including product information and advertising, are known to have some effect on purchasing intentions, so may be a way to target the obesity epidemic. However, it would be premature to generalise these results to other environments and populations at this stage.
There has been a significant amount of research suggesting that that people habitually underestimate the amount of calories they eat, as well as the amount of exercise required to burn off these calories. Therefore, a case could be made that manufacturers could consider adding information such as exercise data to their products.
Where did the story come from?
The study was carried out by researchers from Johns Hopkins Bloomberg School of Public Health, Baltimore, in the US, and was funded by the Robert Wood Johnson Foundation through its Healthy Eating Research programme.
The study was published in the peer-reviewed American Journal of Public Health.
Both the BBC News and the Mail Online's reporting of the study was accurate.
What kind of research was this?
This was a type of case-crossover study, which aimed to look at the effect that displaying calorific information in different ways in a small sample of corner stores in the US had on the purchase of sugar sweetened beverages (SSBs) by US teenagers from black minority ethnic groups.
SSBs that were assessed by the study included “soda”, fruit drinks, sport drinks, vitamin water and “Hug” (a US product similar to Fruit Shoot).
A traditional case-crossover study is one where each individual is being used as their own control. In one circumstance, they will be exposed to the risk exposure (the “case”), and in another they will be exposed to the “control” exposure. In this study, the exposure being altered is calorie information. Though described by the researchers as a case-crossover study, this wasn’t a traditional example of this study type, as they weren’t ensuring that it was the same individuals being exposed to each scenario. Rather, they were looking at the same environment (an area of inner-city Baltimore) after an exposure.
It could also be considered to be a type of “before and after” study, where they are just looking at the differences before and after an intervention.
The researchers say that consumption of SSBs is believed to be an important contributor to adolescent obesity, particularly among minority ethnic groups. The researchers report that SSB consumption makes up 15% of the daily calorie intake of minority adolescents, with black adolescents drinking at least twice the daily maximum of SSBs advised by American guidelines (eight to 12 ounces a day). Understanding the potential for environmental interventions is said to be essential for curbing the obesity epidemic.
What did the research involve?
This study was conducted in six corner stores in low-income black neighborhoods in Baltimore over a 10-month period, between 2012 and 2013. The target population was black adolescents aged between 12 and 18.
They investigated the effect of displaying four different types of calorific information on SSBs:
- absolute number of calories in the drink
- number of teaspoons of sugar
- minutes of running required to burn off the calories
- miles of walking required to burn off the calories
Each of these different pieces of information was displayed on a brightly coloured sign in a prominent location on the fridge containing drinks saying, respectively:
- “Did you know that a bottle of soda or fruit juice has about 250 calories?”
- “Did you know that a bottle of soda or fruit juice has about 16 teaspoons of sugar?”
- “Did you know that working off a bottle of soda or fruit juice takes about 50 minutes of running?”
- “Did you know that working off a bottle of soda or fruit juice takes about 5 miles of walking?”
The signs were based on the estimate that the average 15-year-old would weigh around 50kg (110lbs).
Information was collected of purchases by black adolescents who appeared to be aged 12 to 18 years. A random sample of 35 adolescent purchases per store per week was collected, with information recorded on whether or not the adolescent purchased a beverage and, if so, what type and size of drink.
Over a four-week period, they collected baseline information of SSB purchases when no calorie information was available. Then the six stores displayed each of the different types of information for two weeks, during which time the information on adolescent purchases continued. There was a one week “washout” period between the different signs, where no sign was displayed. For a final six-week post-interventional period, all calorie information was removed.
They also conducted a sample of interviews, where adolescents were stopped and asked whether they had noticed the signs, understood the information, and whether this had influenced their purchases.
The main outcomes described in the study were:
- whether an SSB was purchased
- total number of calories
- whether a large volume was purchased (above 16 ounces, as there had been recent local efforts to ban these sizes in food establishments)
What were the basic results?
Over the course of the study, information was collected on 4,516 purchases by black adolescents, 3,098 of which were for beverages of any type. This included 601 beverage purchases during the baseline weeks, 2,311 beverage purchases spread across all four calorie information interventions, and 186 beverage purchases in the post-intervention period.
During the baseline week, just under three-quarters of purchases included a beverage, 97% of which were for SSBs, just over half of which were large volume SSBs, and mean calories of all beverages was 207kcal (206 for SSB beverages).
During each of the interventions there was a change in beverage purchases, with fewer SSBs purchased, fewer large volume SSBs and fewer beverage calories. For example, across all four interventions, the calorie content of any beverage fell from 207 to 184kcal (206 to 196 for SSBs). The proportion of all beverage purchases that included an SSB fell to 89% and the proportion of SSB purchases that were large volume fell from 55% to 37%.
Even in the post-intervention period, after removing the signs, SSB purchases, volume and total calories remained lower than at baseline.
In the interviews, just over a third of adolescents reported seeing the calorie information displayed, 95% of whom reported understanding them, and 40% said they changed their purchase as a result.
How did the researchers interpret the results?
The researchers conclude that, “Providing caloric information was associated with purchasing a smaller SSB, switching to a beverage with no calories, or opting to not purchase a beverage; there was a persistent effect on reducing SSB purchases after signs were removed”.
This is an interesting study exploring how displaying different types of calorie information in corner stores may change SSB purchases among minority ethnic groups in the US.
Environmental interventions, including product information and advertising, are known to have some effect on purchasing intentions, so may be a way to target the obesity epidemic.
Many experts argue that we are now living in an "obesogenic environment", where the everyday world around us encourages unhealthy food. For example, a study we covered in March 2014 found an association between the number of fast food outlets in a given area and body mass index.
However, little can be firmly concluded from this study. It has focused on studying only black adolescents in one specific region of the US, and has only looked at the effect of the interventions in six corner stores. We don’t know the effect of displaying such information in the wider population, or in different locations (for example fast food outlets, rather than just corner stores).
It is also difficult in such a study to definitely know how much the intervention is having a direct impact on people’s purchasing habits. In this study, the sample of interviews helped to inform this, which suggested that around a third had noticed the signs, and it had influenced the subsequent purchases of 40% of people.
The overall changes in beverage calories during and after the interventions was also fairly small (around 10-20kcal) so it is difficult to say whether or not this would have any meaningful effect on targeting overweight and obesity.
Though environmental interventions are likely to be of some effect in targeting the obesity epidemic, the overall change needs to be towards a healthier, balanced diet in general, combined with regular exercise, rather than change in just one specific area, such as whether or not you purchase an SSB.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.