"Banning sweets at supermarket checkouts 'works'," reports BBC News.
Arrays of sweets, chocolate and crisps at supermarket checkouts has long been blamed for prompting impulse buys, and for children pestering parents while they wait in the queue.
In recent years, some supermarkets have introduced policies to remove these unhealthy snacks from the checkout area. However, there's been little research into the effect.
Researchers used information from 30,000 UK households to monitor their purchases of typical checkout goods – small packs of crisps, sugary sweets and small bars of chocolate – before and after 6 of 9 UK supermarkets changed their policies. They also compared purchases of these goods for consumption "on the go" (before reaching home) between supermarkets with and without checkout food policies.
The study showed average purchases of these unhealthy goods dropped by about 17% immediately after the introduction of new policies. And people were 75% less likely to buy and eat these goods before getting home when visiting supermarkets with checkout food policies.
The study suggests that how and where supermarkets display food may have an impact on how much of this type of food we eat. However, we don't know if people shifted their purchases to other shops, or bought bulk packs of crisps and chocolates instead.
Evidence suggests that when children are encouraged to have healthy eating habits, they're more likely to continue these habits as adults. Read more advice about healthy eating for children.
The researchers who carried out the study were from the University of Cambridge, University of Stirling and Newcastle University in the UK. The study was funded by the Public Health Research Consortium and the Centre for Diet and Activity Research and published in the peer-reviewed journal PLOS Medicine. This is an open-access journal, so the study is free to read online.
Both BBC and ITV News gave a reasonable overview but didn't go into detail about the study methods.
Studies over time are more robust because you can see and account for natural variations in purchase patterns, rather than just a snapshot of one point in time.
Researchers used data from a commercial company, Kantar Worldpanel, which pays households to take part in mass surveys.
For the time series study, the researchers used data from a survey of 30,000 UK households, who recorded purchased food goods by scanning them when they got home.
For the cross-sectional study, they used data from a smaller survey of 7,500 people who used a mobile phone app to record the food they bought and ate before reaching home.
The time series study used data from 2013 to 2017, at 4-weekly intervals. The data showed what food people had bought, from which supermarket, and at what time.
Researchers focused on small packs of sweets, crisps and chocolate bars. They compared the results from 13 4-week periods before and after supermarkets introduced checkout food policies.
The researchers used 3 categories to describe checkout policies:
They used results from supermarkets that did not change their policies during the same period, as comparison stores. They compared the predicted levels of purchases had the policies not changed, with the actual levels of purchases.
For the cross-sectional study, survey data was not available for periods before and after changes in policies, as the survey only started in 2015. Instead, the researchers compared purchases at supermarkets with and without checkout food policies.
For all results, researchers used the figures of number of packs purchased per percentage of market share of each supermarket. As this figure is not immediately easy to understand (or particularly relevant in terms of public health), we're reporting only percentage changes.
Stores that introduced a checkout food policy during the study sold on average 17.3% fewer small packs of sweets, crisps and chocolates in the 4 weeks after implementing the policy.
By 12 months after implementing the policy, they sold 15.5% fewer packs than the average before the policy was introduced.
But after adjusting for sensitivity to time of year and market share, the 12-month figures were no longer statistically significant.
This suggests that the beneficial effects of the policy may drop off over time.
Stores that had checkout food policies sold on average 75.3% (95% confidence interval (CI) 45.4% to 88.8%) fewer small packs of sweets, crisps and chocolates than those without such policies. Stores with "clear and consistent" policies sold on average 79.5% (95% CI 44.7 to 92.4) fewer packs.
The researchers said their study showed "the implementation of supermarket checkout food policies was associated with an immediate reduction in take-home purchase of sugary confectionery, chocolate and crisps". They say this suggests that "voluntary supermarket-led activities have the potential to promote healthier food purchasing".
The study suggests that removing temptation, in the form of small packs of sweets and crisps, while we are waiting in a queue, can make a big difference to how likely we are to buy these foods.
That's perhaps not surprising, as people may be more likely to pick up snack food on impulse, rather than plan to buy it, especially if bored and restless children are asking for it. The study shows encouraging results, especially for the reduction of buying "eat on the go" snacks.
However, the study has limitations that mean we can't be sure how effective the policies are. We don't know whether the policies themselves are directly responsible for the change in shopping habits – other outside influences could be partly responsible.
It's unclear whether the change in shopping habits lasts over time – there was a drop-off by 12 months, which suggests people might, for example, get used to finding small snack products elsewhere in the store. Also, we don't know whether the reduction in buying small snack items in the supermarket was offset by people buying bigger packs, or buying small packs elsewhere.
With the "eat and go" cross-sectional study, we can't see changes over time, which makes it harder to attribute cause and effect to the results. It could be, for example, that people shopping in the types of supermarkets with checkout policies are simply less likely to buy snacks to eat "on the go".
While there are questions over the reliability of all the results, the study is an interesting insight into how changes made by supermarkets may be affecting our behaviour – and even our health.