Teenagers who are bombarded with junk food adverts could be eating hundreds more packets of crisps, chocolate bars and fizzy drinks each year then those who are not, new research has found.
Cancer Research UK said teenagers who watch more than three hours of commercial TV a day are more likely to eat hundreds of extra junk food snacks each year.
The charity said junk food marketing is a "clear, consistent and cumulative risk factor" for high junk food consumption.
It questioned more than 3,300 British youngsters aged 11 to 19 on their television habits and food consumption.
Researchers found that those with high TV exposure were 1.9 times more likely to consume two or more sugary drinks per week and 1.8 times more likely to have a weekly takeaway.
Overall, young people with high levels of advert exposure were more likely to be high consumers of junk food.
When teenagers watched TV without adverts, researchers found no link between screen time and likelihood of eating more junk food.
The difference between being a high consumer and a low consumer was at least 520 junk food products per year, the researchers found.
"This means advert exposure may have a substantial impact on a population level," according to CRUK's new report.
The authors found that youngsters exposed to adverts during on-demand streaming services were also at risk.
Those exposed to high levels of marketing were 1.5 times more likely to have two to four fizzy drinks each week.
Dr Jyotsna Vohra, a lead author on the study from Cancer Research UK, said: "This is the strongest evidence yet that junk food adverts could increase how much teens choose to eat.
"It's been 10 years since the first, and only, TV junk food marketing regulations were introduced by Ofcom and they're seriously out of date.
"Ofcom must stop junk food adverts being shown during programmes that are popular with young people, such as talent shows and football matches, where there's currently no regulation.
"Our report suggests that reducing junk food TV marketing could help to halt the obesity crisis."
Commenting on the study, Caroline Cerny, Obesity Health Alliance lead, said: "Now is the time for action, with restrictions on junk food advertising before the 9pm watershed to protect children from exposure to junk food marketing."