Television ads for junk food really do make children hungry for those treats, especially if they watch a lot of television, according to a study.

The findings, published in Pediatrics, come amid growing calls to ban junk food advertisements aimed at children in order to combat obesity – most recently from the American Academy of Pediatrics, which issued a policy statement on junk food ads this week.

In tests with 6- to 13-year olds, researchers led by Emma Boyland of the University of Liverpool in the UK found that a DVD featuring commercials for fast food and junk food seemed to whet children’s appetites for sweet and high-fat fare.

"Exposure to television food commercials enhanced high television viewers’ preferences for branded foods and increased reported preferences for all food items (branded and unbranded) relative to the low television viewers," she wrote.

The children involved in the research reported a greater desire for sweet and fatty foods after viewing the junk-food ads compared to days when they watched commercials for toys.

This was especially true for children who usually watched a lot of TV in their everyday lives, with "a lot" defined by the researchers as over 21 hours a week.

On average, kids wanted more high-carb, high-fat foods after watching food commercials.

But researchers said the effects of the food ads were modest, making only a small difference in the average number of food items the children said they wanted "right now."

In real life, as well, a lot of other factors would be at work, including parents’ willingness to buy those foods.

"It will never be possible to demonstrate in an experimental study that food advertising contributes to obesity. There are simply too many variables to take into account," Boyland wrote in an email to Reuters Health.

On the other hand, a number of studies have shown that children tend to want more, and eat more, tasty treats after seeing ads for them.

With older children, who often make their own food choices, that could translate into more French fries and chocolate bars. Even young children have "pester power," with studies suggesting they are more likely to use that power if they see a lot of food commercials.

"This study confirms the cumulative, sustained effect of food marketing on TV: the more children watch TV, the more susceptible they are to advertising," said Lori Dorfman, who directs the Berkeley Media Studies Group in California and has studied food marketing to children.

"This might not be so bad if food marketers put their best foods forward, but they don’t," Dorfman, who did not take part in the study, told Reuters Health by email.

Dorfman noted that children now watch TV on their computers and mobile gadgets as well as at home on TV, which can add up to a lot of hours.

Dorfman said that parents should limit TV time, but added that they need help.

"It’s simply not fair to expect parents alone to counter the $2 billion food companies spend each year targeting their kids with fun, irresistible ads for sugary, high-fat, salty foods," she added.