An American-wide study published in the journal Clinical Pediatrics found that the more frequently children ate fast food in fifth grade, the lower their test scores when they reached 8th grade in reading, mathematics and science. Though children who ate fast food four to six times a week scored lower than those who didn't eat any fast food the week before the survey in all three subjects, kids who ate fast food one to three times a week showed lower growth only in mathematics. Even after accounting for possible contributing factors like family background and what other food the kids ate, the researchers were confident the changes were linked to fast food.
How much did it affect the kids' scores, exactly? Those who ate the most fast food had scores 20 percent lower than those who ate the least amount. More research needs to be done to prove causation; since the study started following children in fifth grade, it doesn't account for developmental differences in early childhood. But the results do underscore the difference small changes in your family's fast food consumption can make. Skipping the drive-thru just once a week can boost everyone's health—mental and physical.