The problem with pizza is that it's everything but nutritious. (Reuters/Mark Makela)

America has a pizza problem.

A team of researchers at the University of Illinois at Chicago found that too many kids are eating too much pizza, and all the excess calories are taking a toll on children's health.

"There are a bunch of takeaways from the study. But the biggest thing is that parents are serving their kids too much pizza," said Dr. William Dietz, one of the study's authors and the director of the Sumner Redstone Global Center for Prevention and Wellness at the Milken Institute School of Public Health at the George Washington University.

The researchers used data from the National Health and Nutrition Examination Survey, which tracked the diets of more than 11,000 children and teenagers. Researchers gauged how many children eat pizza in the United States, how often they eat it, and how much they eat when they do.

Pizza, pretty alarmingly, is the second leading source of calories in the diets of America's children, trailing only grain desserts, such as cookies and other carb-laden sweets. On any given day, roughly 20 percent of all children aged 2 to 11 and adolescents aged 12 to 19 eat pizza. And when they do, they eat a lot of it. On the days children eat pizza, they eat roughly 400 calories worth, according to the study. For teenagers, it's upwards of 600 calories.

All that is pretty problematic, according to Dietz, largely because kids don't tend to balance out the pizza slices with salads, vegetables, and other more nutritional foodstuffs. Days on which children and teenagers eat pizza are not only associated with considerably higher intakes of both saturated fat and sodium, but also, quite simply, with more food: on average, children consume 84 extra calories on the days they eat pizza, while adolescents consume an extra 230 calories.

"When you eat extra calories and don't compensate for it at another point of the day or week, it can lead to weight gain and even obesity," Dietz said.

There is a silver lining. Pizza consumption is still too high by nutrition standards, but it's lower than it used to be. Consumption fell by roughly 25 percent between 2003 and 2010, according to the study. Much of that has dip has come at dinner time, where it's fallen by 40 percent for children and about 33 percent for teenagers. It's unclear whether the decline has come on the heels of a growing concern over obesity, especially among the country's youth, health narratives which demonize carb intake, or an organic shift away from pizza.

But the drop in pizza consumption, while significant, hasn't been big enough. "It's a positive trend," Dietz said. "But we're not quite there yet."

It's easy to see the appeal of pizza. It's cheap. Parents can buy a lot of pizza for not a lot of money, and serve what's left over later, spreading pies out over more than a single meal. It's convenient. You can buy pizza from a chain, a mom and pop store, or a grocery freezer. And it's universally loved. The estimated 3 billion pizzas eaten each year in the United States is a testament to the food's unparalleled popularity.

Given how much the country loves pizza, what's to be done? Dietz suggests pizza with smaller serving sizes and healthier toppings.

"We're not suggesting that kids avoid pizza altogether," said Dietz. "But when parents serve it it's important that they understand it's extremely caloric. They should serve smaller pizzas, or at least smaller slices. They might also want to serve it with vegetables instead of sausage on top."