Children who order a combination meal at fast-food restaurants are more likely to get a sugary drink that ups the meal’s total calories, according to a new study.

Researchers found those beverages such as soft drinks, sweet tea and flavored milk add about 179 more calories to meals.

“Sugar-sweetened beverages are increasingly linked to health problems such as diabetes,” said senior study author Brian Elbel of the New York University School of Medicine.

“Any information we can find about why this high-risk group of kids is purchasing these drinks is important,” he said. “We haven’t had a great sense of who these kids are, especially at fast food restaurants.”

The research team analyzed nearly 500 receipts and surveys collected in fast-food restaurants in New York City and in nearby Newark and Jersey City, New Jersy during 2013 and 2014. They found that 60 percent of the drinks bought for children were sugar-sweetened, and combination meals were more likely to include a sugary drink.

“It’s always tough to get data on kids that represents the real world, and this was based on what kids are actually purchasing, not some experimental setting,” Elbel told Reuters Health. “We were surprised by the broad variety of purchase predictors we saw.”

In addition to ordering a combination meal, male children and those above age 12 were more likely to get a sugar-sweetened beverage and consume a higher number of calories and grams of sugar. Caregivers and parents who had a high school degree or less, bought the meal during dinner hours, and ate at the restaurant were also more likely to purchase sugary drinks for their kids.

“We know that families frequent fast-food restaurants often, and these places have highly caloric meals,” Elbel said. “A preponderance of healthy food is not being purchased.”

About 17 percent of children under age 19 in the U.S. are classified as obese by the Centers for Disease Control and Prevention. A major contributor to the recent growth in obesity has been increased calories, the study authors write in the American Journal of Public Health. The Dietary Guidelines for Americans recommend that children limit sugar intake to 10 percent of total calories, or about 120-180 calories.

“We’re no longer fighting about whether children need to drink fewer sugary drinks. That’s accepted,” said Marlene Schwartz, director of the Rudd Center for Food Policy and Obesity at the University of Connecticut in Hartford, who was not involved with the study.

“The question now is finding the best way to do that,” she told Reuters Health. “Based on this study, if parents substitute milk or water for the sugary drink, that eliminates almost 200 calories right there.”

One limitation of the study is that the researchers didn’t account for drink refills, and they couldn’t observe how much of each drink was consumed, only what was purchased. In addition, the study only surveyed walk-in customers, not drive-through customers, who make up a significant portion of fast-food restaurant traffic across the country.

“The New York City context makes this a little less generalizable to other areas,” Elbel said. The results also may not apply to fast casual dining, sit-down restaurants or full-service restaurants.

The new study’s findings support an ordinance passed in Stockton, California, in June that decouples sugar-sweetened beverages from combination meals, making water or milk the default choice for kids’ meals rather than soda. The “healthy-by-default” rule was passed unanimously by the Stockton City Council, following on a similar ordinance passed in Davis, California.

“We have to put the pressure on restaurants to see a change,” Schwartz said. “If more consumers speak up, more restaurants will listen.”