A new study suggests the amount of fast food a child eats could influence their grades in school.

Researchers found the more fast food fifth graders reported eating, the lower their test scores in reading and math tended to be by eight grade, Ohio State University reported. Students who ate the most fast food had test scores that were about 20 percent lower than those who did not eat any at all.

"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, lead author of the study and assistant professor of human sciences at The Ohio State University. "Relying too much on fast food could hurt how well children do in the classroom."

The results remained the same even after the researchers factored in possible influences such as socioeconomic status and characteristics of the participants' 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.

To make their findings the researchers looked at about 11,740 students who completed a food consumption questionnaire and reported their scores in reading, science and mathematics.

About 10 percent of the participants reported having fast food every day and an additional 10 percent had it four to six times per week; more than half of the children ate fast food about three times per week. The children who ate fast food four to six times per week were found to have lower academic growth in all three categories than those who did not eat any fast food, children who ate fast food about three times per week only showed learning deficits in 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," Purtell said.

The study did not determine why fast food consumption is linked to lower grades, but past studies have shown these foods lack nutrients crucial to cognitive development.

The findings were published in a recent edition of the journal Clinical Pediatrics.