Teenagers who watch more than three hours of commercial TV a day are more likely to eat hundreds of extra junk food snacks, according to a report by Cancer Research UK.
Being bombarded by TV ads for unhealthy, high calorie food could lead teens to eat more than 500 extra snacks like crisps, biscuits and fizzy drinks throughout the course of a single year compared to those who watch less TV.
Energy and other fizzy drinks high in sugar, takeaways and chips were some of the foods which were more likely to be eaten by teens who watched a lot of TV with adverts.
The report, based on a YouGov survey, questioned 3,348 young people in the UK between the ages of 11-19 on their TV viewing habits and diet.
When teens watched TV without adverts researchers found no link between screen time and likelihood of eating more junk food. This suggests that the adverts on commercial TV may be driving youngsters to snack on more unhealthy food.
The report is also the biggest ever UK study to assess the association of TV streaming on diet.
It found that teens who said they regularly streamed TV shows with ads were more than twice as likely (139 per cent) to drink fizzy drinks compared to someone with low advert exposure from streaming TV, and 65 per cent more likely to eat more ready meals than those who streamed less TV.
Regularly eating high calorie food and drink - which usually has higher levels of fat and sugar - increases the risk of becoming overweight or obese.
Obesity is the second biggest preventable cause of cancer in the UK after smoking, and is linked to 13 types of cancer including bowel, breast, and pancreatic.
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. We're not claiming that every teenager who watches commercial TV will gorge on junk food but this research suggests there is a strong association between advertisements and eating habits.
"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10 years since the first, and only, TV junk food marketing regulations were introduced by Ofcom and they're seriously out of date.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."
The Obesity Health Alliance recently published a report which found that almost 60 per cent of food and drink adverts shown during programmes popular with adults and 4-16 year olds were for unhealthy foods which would be banned from children's TV channels.
Professor Linda Bauld, Cancer Research UK's prevention expert, said: "Obese children are five times more likely to remain obese as adults which can increase their risk of cancer later in life.
"The food industry will continue to push their products into the minds of teens if they're allowed to do so. The Government needs to work with Ofcom to protect the health of the next generation."