The study consisted of 11,740 students that were tested in mathematics, science and reading/literacy for fifth and eighth grades and completed a fifth grade food consumption questionnaire. The study was conducted by Kelly Purtell, lead author and assistant professor of human sciences at the Ohio State University, and Elizabeth Gershoff, associate professor of human ecology at the University of Texas at Austin. Data from the study came from the Early Childhood Longitudinal Study Kindergarten Cohort and was collected by the National Center for Educational Statistics.
Results of the study published online in the journal Clinical Pediatrics - 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. Other factors included how much they exercised, how much television they watched, what other food they ate, their familys socioeconomic status, and characteristics of their school and neighborhood.
Theres a lot of evidence that fast-food consumption is linked to childhood obesity, but the problems dont end there, Purtell said. Relying too much on fast food could hurt how well children do in the classroom. 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.
- Less than a third of the children did not have any fast food during the week before they completed the questionnaire
- 10 percent reported having fast food every day while another 10 percent ate it four to six times a week.
- Slightly more than half of the children ate fast food one to three times in the previous week.
- 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.
- 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.
While this study cant prove that fast food consumption caused the lower academic growth observed in the study, by controlling for other possible explanations for this link such as family background and what other foods 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. Because the study examined only changes in test scores between fifth and eighth grade it controls for all the early childhood factors that may affect test grades.
This study cant say why fast-food consumption is linked to lower grades. But other studies have shown that fast food lacks certain nutrients, especially iron, that help cognitive development. In addition, diets high in fat and sugar similar to fast-food meals have been shown to hurt immediate memory and learning processes. Were 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 added.