Plenty of research has shown that the consumption of fast food is linked to childhood obesity and its associated ills, but the risks of junk food may go beyond the excess pounds it can bring.

The negative effect of fast food doesn't stop at children's waistlines. It goes on to affect their performance in school.

“There’s a lot of evidence that fast-food consumption is linked to childhood obesity, but the problems don’t end there,” said Kelly Purtell, the lead author of a new study and assistant professor of human sciences at Ohio State University, in a statement.

Children who reported daily fast food consumption experienced the slowest growth in their academic achievement across all three subjects.

Purtell and her research team looked at how well children were progressing academically as they moved through elementary and middle school. They found that kids who ate the most fast food progressed at a rate that was as much as 20 percent lower than kids who didn’t eat any fast food.

The results remained the same even when investigators considered many other factors that could explain lower test scores, including the level of physical activity, the amount of television watched, other foods eaten by the students, the family’s socioeconomic status, as well as the characteristics of the neighborhood they lived in and the school they attended.

The study used data on nearly 12,000 students who began kindergarten in the 1998-1999 school year. The students were tested in both the fifth and eighth grades in reading and literacy, math, and science. In fifth grade, they completed a questionnaire about their eating habits.

Fast food franchises know how to market their food to kids; and without a doubt, most kids love fast food — or maybe it’s the toys they get with their meal that they love, and the food is secondary.

So it's no surprise that over 70 percent of the students had had fast food in the week before they filled out the questionnaire. Ten percent reported eating it every day and another 10 percent ate fast food four to six times in a week. A little more than half of the students ate fast food one to three times during the previous week.

Children who reported daily fast food consumption experienced the slowest growth in their academic achievement across all three subjects. Children who ate fast food every day gained significantly fewer points in reading over the years from fifth to eighth grade than did children who reported consuming no fast food in the past week. Children who had fast food one to three times a week still had lower test scores in math when compared to those who ate no fast food.

While these findings don’t prove that eating fast food caused the lower test scores, the researchers believe a lack of certain nutrients that are notoriously missing in fast food, such as iron which is needed for proper cognitive development, may be a reason. Sugar and fat, which are plentiful in fast food, can also hinder memory and learning, according to the researchers.

If nothing else, the study underscores an often-overlooked perk of providing children with a nutritious diet full of fruits and vegetables, lean meats and fish, whole grains, and dairy — brain power.

It can be hard to counter the pull of brightly-colored fast food outlets and cartoon characters. Your children are more likely to eat a better diet if they eat at home.

The study is published in Clinical Pediatrics.