Teenagers are more than twice as likely to be obese if they can remember seeing a junk food advert every day compared to those who couldn't recall any over a month, according to a report by Cancer Research UK.
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This included ads on TV, billboards and social media, and is the largest survey of its kind to make a link between these forms of advertising and weight. Obese teenagers were more likely to recall social media adverts than the other mediums, so this platform had the greatest association with obesity.
The report was based on a YouGov survey which questioned 3,348 young people in the UK between 11-19 about their TV viewing habits, diet and their BMI.
Following statistical analysis the results also revealed that teens from the most deprived communities were 40% more likely to remember seeing junk food advertisements every day compared to teens from better-off families.
Previous research has shown that people from more deprived communities are also more at risk of being obese.
When teens watched shows on TV and streaming websites without adverts researchers found no link between screen time and likelihood of being obese. This suggests that the adverts may be prompting young people to eat more junk food.
Dr. Jyotsna Vohra, a lead author on the study from Cancer Research UK, 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."
Regularly eating junk food, which usually has high levels of fat and sugar, increases the risk of becoming overweight or obese.
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% 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.
"Young people from more deprived backgrounds have the most to gain from a 9pm ban on unhealthy TV adverts. Urgent action is needed from Ofcom to support efforts to reduce the health inequalities between the poorest and richest in our society."