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A study at Ohio State University found that those who at fast food every day saw test scores improve 20 percent less than those who didn't over three years. The test started when children were 10 years old, and compared test scores in reading, math and science.

Even when researchers took other variables into account, the fast food seemed to have a significant effect.

Read The Washington Post's full breakdown, or check out the original study (Note: Most of the study is behind a paywall.)