Fast food has been shows to be linked to lower test scores in kids, according to a new study.

At least for fifth graders, the more frequently they reported eating fast food, the lower their growth in reading, math, and science test scores by the time they reached eighth grade. What's more, those that consumed the most fast food had test score gains that were up to about 20 percent lower than students who didn't eat any fast food.

"There's a lot of evidence that fast-food consumption is linked to childhood obesity, but the problems don't end there," lead author Kelly Purtell at The Ohio State University said in a statement. "Relying too much on fast food could hurt how well children do in the classroom."

Even taking into consideration other factors like exercise, socioeconomic status, how much television they watched, and what other food they ate, fast food was still found to be associated with how well students do in school.

Described in the journal Clinical Pediatrics, researchers surveyed 11,740 kids in grades five and eight, testing them in three subjects: reading/literacy, mathematics and science. Children who ate fast food four to six times per week or every day 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," Purtell said.

Purtell and her colleagues are quick to note that their study does not imply a cause-and-effect relationship, but they do say that fast food plays an important part in test scores in school.

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