It is the first time a study has shown how viewing habits could be used as a predictor of future diet.
Scientists have long observed a link between a sedentary "couch potato" lifestyle and failing to eat healthily, but the researchers from the University of Minnesota concluded that fast food advertising was also playing a significant role.
"To our knowledge, this is the first study to examine the association between television viewing and diet over the transition from adolescence into young adulthood," said Dr Daheia Barr-Anderson, who led the team."We have shown that TV viewing during adolescence predicts poorer dietary intake patterns five years later."
The scientists found that those who had been watching most television five years before had significantly higher intakes of fried food, sugary drinks and snacks but much lower consumption of vegetables, fruit and fibre.
On average, young adults who watched more than five hours a day of television as teenagers had a 10 per cent higher calorie intake than those who had spent less than two hours a day in front of the box.
Their average fast food intake was 15 per cent higher and their consumption of sugary drinks was 17 per cent higher than those who watched least television as teenagers, the study published in the International Journal of Behavioral (corr) Nutrition and Physical Activity, shows.
Meanwhile those who watched under two hours of television a day as high school children consumed 36 per cent more fruit and 33 per cent more vegetables five years later than those who spent most time in front of the small screen.
"These less than healthy foodstuffs are commonly advertised on television while healthy foods rarely receive the same publicity.
"Although young people may be aware that many foods advertised on television are not healthy, they may chose to ignore or do not fully realize the consequences, because the actors they see advertising and eating the foods in the commercials are usually not overweight."