Cancer Research UK found the obesity risk doubled for teens who could recall seeing such campaigns on any advertising platform every day compared with those who could not remember seeing any in the last month.
The charity said its survey, which took into account campaigns on television, billboards and social media, was the largest of its kind to make a link between advertising and weight.
It found obese teenagers were more likely to recall social media adverts than the other mediums, concluding that this platform had the greatest association with obesity.
The YouGov survey questioned 3,348 11 to 19-year-olds in the UK about their television viewing habits, diet and their BMI.
The results also revealed that teenagers from the most deprived communities were 4 per cent more likely to remember seeing junk food adverts every day compared with those from better-off families.
Dr Jyotsna Vohra, from Cancer Research UK and a lead author on the study, said: “It’s particularly worrying that the poorest teens had the best recall of junk food ads.
“We can’t allow the industry free rein to target young people, especially as we know that eating habits adopted in childhood are more likely to remain into adulthood.
“Since this data was collected new restrictions on junk food adverts on social media aimed at children have come into force. But it’s been 10 years since we’ve seen any update to the rules on TV adverts.
“Curbing exposure to junk food ads would help reduce obesity rates among young people, particularly as their passion for social media shows no signs of waning.”
Obesity is the biggest preventable cause of cancer in the UK after smoking and is linked to 13 types of cancer including bowel, breast, and pancreatic.
Professor Linda Bauld, Cancer Research UK’s prevention expert, said: “This study found a strong link between exposure to junk food ads and an increase in teens’ risk of being obese, and suggests that the poorest are hit hardest.
“Although being overweight is the biggest preventable cause of cancer after smoking, only 15 per cent of people recognise that obesity is a proven cancer risk.
“Right now, we hope to see a 9pm ban on junk food ads in the Government’s upcoming obesity strategy which requires a simple change of rules from Ofcom.
“Cancer Research UK is also funding more research into the potential impact of social media on obesity so we can start to investigate this area more.”
