COLUMBUS, Ohio – The amount of fast food children eat may be linked to how well they do in school, a new study suggests.

Researchers at The Ohio State University found that the more frequently children reported eating fast food in the 5th grade, the lower their growth in reading, math and science test scores by the time they reached the 8th grade.

Students who ate the most fast food had test score gains that were as much as 20% lower than those who didn’t eat any fast food, said Kelly Purtell, lead author of the study and assistant professor of human sciences at The Ohio State University.

“There’s a lot of evidence that fast-food consumption is linked to childhood obesity, but the problems don’t end there,” Purtell said. “Relying too much on fast food could hurt how well children do in the classroom.”

The results remained even after the researchers took into account a wide variety of other factors that may have explained why those with high fast-food consumption might have lower test scores, including how much they exercised, how much television they watched, what other food they ate, their family’s socioeconomic status and characteristics of their neighborhood and school.

“We went as far as we could to control for and take into account all the known factors that could be involved in how well children did on these tests,” Purtell said.

Data from the study came from the Early Childhood Longitudinal Study–Kindergarten Cohort, a study of about 11,740 students in kindergarten during the 1998-1999 school year. They were tested in reading/literacy, mathematics and science in both the 5th and 8th grades and they also completed a food consumption questionnaire in 5th grade.

Children who ate fast food four to six times per week, or daily, showed significantly lower gains in all three achievement areas compared to children who did not eat any fast food the week before the survey. However, children who ate fast food just one to three times a week had lower academic growth compared to non-eaters in only one subject, math.

“We’re not saying that parents should never feed their children fast food, but these results suggest fast-food consumption should be limited as much as possible,” said Purtell.

Purtell emphasized that this study cannot prove that fast-food consumption caused the lower academic growth. However, by controlling for other possible explanations for this link, such as family background and what other food they ate, and by looking at change in achievement scores, the authors are confident fast food is explaining some of the difference in achievement gains over time.

She also said that the study can’t say why fast-food consumption is linked to lower grades, but noted that other studies have shown that fast food lacks certain nutrients, such as iron, that help cognitive development.