Researchers have long known that junk food advertising can prompt children to eat more. But a new study, presented this week at the European Congress on Obesity in Málaga, Spain, goes further — showing how even fleeting exposure to such marketing can alter a child’s daily calorie intake.

After watching just five minutes of ads for foods high in sugar, salt, or saturated fats, children consumed an average of 130 extra calories over the course of the day. That’s about the energy in two slices of white bread, or an extra 6-7% of the daily calorie intake of an adult.

More ads? More food

Your brain loves junk food. It’s loaded with ingredients that tap into the pleasure centers in our brain, the so-called dopamine reward pathway. Your brain also loves advertising. The visual and emotional appeal of ads are tailored for this purpose. Put them together, and it’s not hard to see why junk food advertising is so efficient.

For children, it’s even worse. Adults are (presumably, hopefully) more aware that ads are meant to sell and involve a healthy amount of manipulation. But children and teenagers are vulnerable.

“Even short exposure to marketing of foods high in fat, salt, and sugar can drive excess calorie consumption and potentially weight gain, particularly in young people who are more susceptible to advertising and whose eating patterns influence their lifelong health,” says lead author Professor Emma Boyland from the University of Liverpool in the UK.

Boyland and colleagues conducted a randomized crossover trial that involved 240 children aged 7 to 15 from some schools in Liverpool, UK. The researchers varied not only the content (some were product-focused, others just showed branding) but also the medium: TV-like audiovisuals, social media-style visuals, audio only (as in podcasts), or static images such as posters.

After the ads, children were offered snacks like grapes or chocolate buttons and later a varied lunch. Without knowing it, they revealed the study’s most striking result: children exposed to junk food ads consumed more food at both stages. They ate 58.4 more calories in snacks and 72.5 more at lunch, compared to when they had watched non-food ads.

“Our findings offer crucial novel information on the extent, nature, and impact of unhealthy food marketing via different types of media on young people’s eating behaviour,” added the researcher.

And it didn’t matter whether the ad showed actual food or just a logo. Brand-only advertisements were just as effective at triggering increased intake.

“The foods that we served them weren’t the same foods that were shown in the advertisements and were presented with no branding information. So, it wasn’t that they were driven to buy the particular food or go and consume fast food, it was just a prompt to consume what was available,” Boyland told The Guardian.

Why this matters

This study lands at a critical time. Childhood obesity rates are high and rising in much of the world. We’re also reaching a bizarre point where malnourished children are also becoming obese. This phenomenon known as the “double burden of malnutrition,” occurs when children eat energy-dense but nutrient-poor foods.

That’s exactly what fast-food is; a lot of calories with not enough useful nutrients.

A lot of causes tie into this. Junk food tends to be cheap and fills you up; environment and biology also play a role. But increasingly, advertising is coming under fire.

Children are being targeted more and more with food advertising. And it works.

But food marketing plays a potent, modifiable role. Previous studies had already shown that audiovisual ads could boost kids’ immediate eating. This study shows that it doesn’t matter whether it’s brand-only ads or general ads; both get children to eat more.

“Our results show that unhealthy food marketing leads to sustained increases in caloric intake in young people at a level sufficient to drive weight gain over time. This study is the first to demonstrate that brand-only food ads, for which there is currently no restrictive advertising policy globally, increase children’s food intake. This new knowledge will help in the design of urgent restrictive food marketing policies that can protect children’s health.”

Should we treat junk food ads like cigarette ads?

Both studies and real-life data have shown that banning tobacco ads works and can get people to smoke less. Researchers and doctors are increasingly calling for a ban on junk food ads.

The UK government has pledged action. From October, unhealthy food ads will be restricted on TV before 9 p.m. and banned online altogether. But experts say this study reveals glaring loopholes.

“But loopholes remain. Brands will still be able to advertise to young people even without showing specific products, on billboards and at bus stops, and children living with overweight or obesity are especially vulnerable,” says Katharine Jenner, the director of the Obesity Health Alliance.

Around the world, a growing number of countries are moving to restrict junk food advertising to children, though approaches vary widely. In Chile, landmark legislation introduced in 2016 banned marketing of high-sugar, high-salt, and high-fat products to children under 14 across all media. Mexico has implemented similar restrictions during children’s viewing hours, while South Korea banned junk food ads on TV channels targeting young audiences during prime time.

Still, it can take years or even decades before we start seeing changes in obesity rates.

But for many scientists and health advocates, the path forward is clear. Just as public health campaigns took aim at tobacco marketing to protect the next generation, a similar reckoning with junk food advertising may now be overdue. The evidence is mounting that even fleeting exposure to cleverly crafted ads — whether flashing a logo or showing a sizzling burger — can shift children’s eating habits in ways that linger long after the screen goes dark.

This is about creating an environment where the healthy choice is the easy choice. And that may start not in the kitchen or the classroom, but on the billboards, bus stops, and screens where young minds are quietly, steadily shaped.