A steady diet of fast food might hurt your child in the classroom, a new study finds.

Kids who frequently ate fast food in fifth grade lagged behind by eighth grade, said researchers who reviewed questionnaires and test scores of more than 8,500 U.S. students.

"The largest effects were found for the kids who reported daily consumption of fast food," said study leader Kelly Purtell, assistant professor of human sciences at Ohio State University. "On average they were scoring three or four points lower than the kids who did not report eating fast food at all in the past week." 

The researchers compared academic test scores in reading, math and science for fifth and eighth grade and looked at the students' responses to food questions on a national survey. 

On average, test scores increased 16 to 19 points, depending on the subject, Purtell said.

But kids who ate fast food the most had test-score gains of up to 20 percent less than those who never ate fast food, she found.

The study was published online this month in Clinical Pediatrics. 

More than two-thirds of the students surveyed reported some fast-food intake. And one in five had eaten at least four fast-food meals in the previous week, the survey found.

The amount of fast food consumed corresponded with eighth-grade scores, even after researchers took into account for physical activity, TV watching, income levels and school characteristics, Purtell said.

The proliferation of fast food is already a concern because of America's obesity epidemic.

However, the study can't prove the fast food caused the lower scores, only that the two were linked, Purtell noted. Still, other research has linked high-sugar and high-fat diets with an adverse effect on learning processes requiring attention, she said.

Although researchers can't explain the tie-in for sure, it's also possible that those with a fast-food habit may not get the nutrients needed for good learning, she suggested.

Experts aren't recommending you ban all fast foods on the basis of this one report, but they do advise moderation.

"It is premature to presume that frequent fast-food consumption will compromise one's later academic functioning," said Dr. Andrew Adesman, chief of developmental and behavioral pediatrics at the Steven & Alexandra Cohen Children's Medical Center of New York, who wasn't involved in the study.

"Although this study found an association between frequently eating fast food and weaker academic performance a year later, we cannot be certain that the observed differences were due to nutritional factors and not other variables," he said.

Still, it's advisable to "encourage kids to go slow when it comes to fast food" to preserve health and good nutrition, Adesman added.

More research is needed, he said, to determine what impact fast food has on students' learning potential.

In the meantime, Purtell said, "I don't think the occasional fast meal is anything to worry about." Once a week or less might be a good goal, she suggested.

Source: www.nlm.nih.gov