Study looking at the thousands of children in the south of England also found that children who love to eat foods that are vitamin has a pretty good intelligence in the future.
Head of research, Kate Northstone from Bristol University said that nutritious food provides a highly significant IQ differences from time to time.
Parents should begin thinking about the impact of healthy food for their children than merely a weight problem.
"Our message to parents to provide fresh food he could for their children," he said.
In this study found dietary changes after 3-year-old child there were no significant changes in IQ.
Research involving 14,000 people who were born in southern England between 1991 and 1992 whose health was monitored at age 3, 4, 7 and 8.
The study is published in the Journal of Epidemiology and Community Health.