Nudging customers to choose healthier options on takeaway delivery apps could cut their calorie intake by up to 15 per cent, research by Oxford University shows.
Small tweaks in design - such as promoting low calorie options and making small portions the default choice - saw consumers significantly reduce their food intake, the studies found.
Making healthier foods and restaurants more prominent on the app was the most effective change - leading to an average 15 per cent (209 calories) reduction per order.
The research involved three randomised trials involving over 23,000 UK adults examined the impact of 14 different changes.
Popular food delivery apps in the UK include UberEats, JustEat and Deliveroo, with around 25 million consumers a year making such purchases - up 55 per cent from 2015.
Researchers said small changes could have a powerful difference on people’s behaviour, helping them to slim down.
These included making lower calorie options and healthier restaurants prominent on menus, setting default options to smaller portions and displaying nutrition information.
Researchers said the findings, presented at this year’s European Congress on Obesity in Dublin showed the power of small changes combat.
Dr Filippo Bianchi, from the Behavioural Insights Team - known as the “nudge unit” - innovation agency Nesta and colleagues from the University of Oxford, carried out research using a simulated delivery app and compared the results to a control app.
Dr Bianchi said: “Our findings suggest that simple interventions could help people select lower-calorie options on delivery apps without the need to remove less healthy options.”
“This doesn’t mean that we always have to swap pizza for a green salad – even initiatives that make it easy to make small changes to what we eat could help to slowly reduce obesity, if delivered at scale.”
The randomised controlled trials included 23,783 adults who were users of food delivery apps.
In one trial looking at portion size, some 6,000 people were randomly assigned to a control group, meaning they ordered what they liked.
The rest were automatically given a small portion size as default, which was branded “regular” while “extra small” portions were offered.
The study found that those in the control group ordered a meal that contained, on average, 1,411 calories.
Those given the tweaked model ordered meals with significantly fewer calories. When all the changes were made, they consumed 177 fewer calories - a difference of 12.5 per cent.
A second trial then tested four interventions that repositioned foods and restaurants to make lower-calorie options more prominent on the app.
This study included 9,003 adults randomly allocated to either a control group, with restaurants and foods listed randomly, or other groups with lower-calorie food options listed at the top of menus, healthier restaurants at the top of the page, plus other combinations.
The study found that those in the control group ordered a meal that contained, on average, 1,382 calories. Making healthier foods and restaurants more prominent was the most effective change - leading to an average 15 per cent (209 calorie) reduction per order.
The final trial tested the impact of using seven different designs of calorie labels to encourage the selection of lower-calorie options in 8,780 adults.
Compared to the control app, with no calorie information provided, five out of seven labels significantly reduced the calorie content of orders ranging from an average of 2 per cent (33 calories per order) to 8 per cent (110 calories).
A further study on 20 adults then looked at how best to get people to accept the use of calorie labels in food delivery apps.
Measures included providing a filter that allows users to switch calorie labels on and off and setting out recommended energy intake per meal.
Dr Bianchi said: “These studies provide encouraging proof-of-concept evidence that small tweaks in delivery apps could help many people to identify and select healthier foods.
“Testing similar initiatives with real restaurants and delivery apps will be important to assess the long-term impact of these interventions in the real world.
“Further research should also explore the best way to balance desired health impacts while minimising effects on businesses and on cost-of-living concerns for consumers.”
Tam Fry, chairman of the National Obesity Forum, said: “This meticulous research ticks all the boxes. When the app allows the customer to avoid opting for unhealthy choices and directs them to lower calorie options, this is just what the doctor ordered.
“It is reasonable for the app to be able to hide calorie counts for people who find that they add to their eating disorders or, simply, annoy them.”
A Just Eat spokesperson said: "Just Eat works with over 60,000 restaurants across the UK, serving a diverse range of over 100 cuisines - from grilled chicken, vegan and vegetarian options to traditional curries, sushi or pizza. Many already offer healthier menu options and smaller portion sizes so customers can make the choices which are right for them and their families.
"One of the key aspects of our product development is ensuring customers can easily search and identify the dishes that they want including healthier options, and we have calorie labelling already in place so all partners have the ability to display this information on our app.
“We recognise that we are in a unique position to support the takeaway sector and continue to work with our partners to explore how they can grow their range to meet customer needs and preferences."