Children exposed to just a few minutes of unhealthy food and beverage marketing ate more during and after the ads.

In spite of all your efforts to steer your children toward fresh fruits and vegetables, junk food ads may still have a strong hand in driving your kids toward overeating.

Of course, you could keep your kids from watching ad-filled TV shows or movies. But junk food ads also show up all over the internet and even in video games.

Sometimes food marketing is subtler — like logos on packaging or special food deals. But it’s just as effective

“‘Free popcorn Monday’ at our movie theater has conditioned my 9-year-old to ask for popcorn each time we go to the movies,” Angela Cardello Pattison, a mother from Pennsylvania, told Healthline. “When we don’t go on those days we don’t buy anything. My daughter still asks, though.”

Read more: Get the facts on childhood obesity »

A new study, published online this week in Obesity Reviews, raised even more red flags about the power of junk food marketing aimed at children.

“Our meta-analysis showed that in children exposed to unhealthy dietary marketing, dietary intake significantly increased during, or shortly after, exposure to advertisements,” study author Bradley Johnston, Ph.D., a scientist at The Hospital for Sick Children in Toronto, and assistant professor at McMaster University in Ontario, told Healthline in an email.

Researchers analyzed 29 previous randomized trials that together included almost 6,000 children ages 2 to 18 years old.

These studies looked at many types of food and beverage marketing, including ads in TV shows, movies, video games, magazines, and packaging with licensed characters.

On average, children in the studies were exposed to food or beverage ads for about 4 minutes. As a result, they ate 30 kilocalories more during the 17 minutes after seeing the ad, compared to kids who saw nonfood ads or no ads at all.

This is about the same number of kilocalories found in one-tenth of a chocolate bar. It may not seem like a lot, but all those extra — and empty — junk food calories can add up.

Plus, children watch at least 10 food-related ads each day. And the bulk of these ads are for products that are high in fat, sugar, and sodium.

So the opportunity for ads to shape children’s eating behaviors is high.

The results of the study also suggest that children 8 years of age and younger may be more susceptible to marketing of unhealthy foods and beverages. The researchers write that younger children may imitate the unhealthy behaviors they see in the ads.

Read more: Getting rid of junk food in the checkout aisle »

Advertising of unhealthy foods and beverages is only one factor that can contribute to children becoming overweight and obese, alongside activity levels, availability of healthy foods, and family eating habits.

But as much as parents would like to have the final say on what their kids eat, children’s eating habits are also shaped outside the home.

“We only have Netflix, we don’t see ads on TV,” said one mother in response to a post on Facebook, “[but my son] asks for junk food because that’s apparently the snack I pay for at aftercare/before care at school.”

Children spend a great deal of time at school, but some school officials have found it challenging to convince children to choose carrot sticks over burgers and fries. One approach to changing this may be to use the power of marketing for “good.”

A recent study in Pediatrics by researchers from The Ohio State University found that turning vegetables into superheroes — Miki Mushroom, Zach Zucchini, and Suzie Sweet Pea — increased the number of kids choosing healthy foods from the salad bar.

“Marketing can have both positive and negative effects,” study author Andrew Hanks, Ph.D., a professor of human sciences at The Ohio State University, said in a press release. “But instead of avoiding it completely, we can harness the power of marketing to help us.”

Other groups, including the World Health Organization (WHO), have called for restrictions on the marketing of high-density, low-nutrition foods and beverages to children. There is some research to back this up.

“Results of a recent study suggested that a ban on television advertising of unhealthy foods (e.g., trans fats, high sugar, and salt) could reduce overweight and obesity in childhood by 18 percent and 2.5 percent, respectively,” Behnam Sadeghirad, a Ph.D. student in clinical epidemiology and biostatistics at McMaster University, and lead author of the Obesity Reviews study, told Healthline in an email.

To see the extent of food ads targeting kids, you only have to visit the places where they hang out, such as schools, playgrounds, pediatric doctor’s offices, and sporting and cultural events.

It’s here where you’ll often see the most aggressive — and creative — marketing.

“One of the major soft drink manufacturers now has a vending machine where the entire front has been transformed into a video game,” said Johnston. “Our study shows that this type of marketing influences children’s caloric intake and preferences for junk food, and the placement of such vending machines should be restricted.”

Read more: What foods should be considered ‘healthy?’ »