A groundbreaking study shows that children will eat more calories in the day after watching only five minutes of junk food ads.

The study found that young people who saw or heard advertisements for products with high saturated fats, sugars and salt consumed an average of 130 extra calories, equivalent to two slices of bread.

The study involved children aged 240 to 15 from Merseyside Schools. In two different cases, they were displayed or played for five minutes of junk food ads, followed by non-food ads.

They then get snacks like grapes or chocolate buttons, and then serve lunch for a range of savory, sweet and healthy items.

The authors calculated that after the ad, the kids consumed 58 calories in snacks, while lunch had 73 more calories than they had exposed to non-food ads.

The study, which will be presented at the European Obesity Conference in Malaga, Spain, also found that the impact on calorie intake is the same whether the ad is targeting specific foods or a universal ad for fast food brands.

It is not affected by the types of ads, such as videos with sounds, social media posts, podcast ads, and posters or billboards.

Emma Boyland, lead author of the study at the University of Liverpool and professor of food marketing and child health, said: “This is the first study that only branded food advertising affects what children eat.

“We also show that not only did the kids eat more immediately after the food ad, but actually also eat more at lunch meals, hours after watching the ad.

"The food we serve them is not the same as the food displayed in the ad, and does not provide brand information. So it's not because they are forced to buy specific foods or go to fast food, but to consume what is available in a timely manner."

Experts warn that the findings reveal loopholes in the government's proposal to ban junk food TV ads, which will take effect in October.

Katharine Jenner, director of the Obesity Health Alliance, said the study must “send a clear message to policy makers: Food advertising is driving children’s excessive calorie intake.”

She added: “From October, the new restrictions will limit unhealthy food advertising on TV by 9pm and be online at any time, which will protect children from the worst offenders.

“But the loopholes remain. Even without displaying specific products, billboards and bus stops, brands can still advertise to young people, and children with overweight or obesity are particularly vulnerable.

“If the government takes the end of junk food ads to children, they have to close the loopholes so that companies can continue bombarding them.”

"Child obesity is stubbornly high, and children in the poorest areas face more than twice the rate of their peers. Pediatricians recognize that this crisis cannot be resolved without regulations such as the food industry."

A spokesperson for the Ministry of Health and Social Care said: “The government has taken bold moves to end junk food advertising targeting children on TV and online, which will reduce the number of obesity by 20,000 and bring health benefits to the £20 billion economy.

“We encourage the industry to focus on healthier options by allowing companies to promote healthier alternatives in identified categories.”