The average child views more than 40,000 commercials a year, and all that exposure may have contributed to America’s growing childhood obesity epidemic. After an in-depth look at the relationship between food advertisements and food consumption, a team of researchers from the University of Liverpool confirmed ads have a negative impact on children’s eating habits. Their findings, published in the American Journal of Clinical Nutrition, demonstrate how food advertisements go beyond influencing consumers what brand to choose, but also the amount they eat.

For the study, researchers scoured over 22 studies that were designed to examine the link between unhealthy food advertisements and food consumption. Participants were both children and adults. They measured the food consumption of those who were exposed to ads through the television or internet, and compared them to the food consumption of those who weren’t exposed to such ads. Children who were exposed to unhealthy food advertisements experienced a significant increase in their food consumption. When researchers looked at whether television ads had a greater effect than internet ads, they found no difference. Unhealthy food ads did not have the same impact on adults.

"Through our analysis of these published studies I have shown that food advertising doesn't just affect brand preference — it drives consumption,” said the study’s lead author Dr. Emma Boyland, a researcher at the University’s Institute of Psychology, Health & Society, in a press release. “Given that almost all children in Westernized societies are exposed to large amounts of unhealthy food advertising on a daily basis this is a real concern.”

In a recent study conducted by the National center for Education Statistics, researchers found if a child watched more than one hour of television a day, they were 39 percent more likely to become overweight and 86 percent more likely to become obese by the time they reached first grade.

"Small, but cumulative increases in energy intake have resulted in the current global childhood obesity epidemic and food marketing plays a critical role in this,” Boyland said. “We have also shown that the effects are not confined to TV advertising; online marketing by food and beverage brands is now well established and has a similar impact.”

Childhood obesity rates have more than doubled in children and quadrupled in adolescents in the last 30 years, according to the Centers for Disease Control and Prevention. Foods high in calories, sugars, salt, and fat, but low in nutrients are highly advertised and marketed to target children and adolescents, while healthy food advertisements are less prevalent. Boyland believes her team’s findings should serve as an impetus for change and hopes it will lead to strategies that’ll reduce children’s exposure to food advertising altogether.

Source: Boyland EJ, Nolan S, Kelly B, et al. Advertising as a cue to consume: a systematic review and meta-analysis of the effects of acute exposure to unhealthy food and nonalcoholic beverage advertising on intake in children and adults . American Journal of Clinical Nutrition . 2016.