Feeding toddlers processed foods may lower their future IQ, according to a U.K. study published Monday.
Researchers who monitored thousands of children in southwest England also found that a diet rich in vitamins could make young children more clever later in life.
Lead researcher Kate Northstone, of the University of Bristol, said a nutritious diet could produce a "reasonable difference" in IQ scores over time.
While pointing out that more study was needed to confirm the findings, she said parents needed to realize that healthy eating could have an impact on more than just a child's weight.
"Our message is to encourage parents to give fresh food as much as they can," she said.
The researchers found that changes to children's eating habits after the age of 3 made no difference to their later IQ.
"A possible explanation for this is that the brain grows at its fastest rate during the first three years of life," they said.
The study involved 14,000 people born in western England in 1991 and 1992 whose health and well-being were monitored at the ages of 3, 4, 7 and 8.
The research was published in the Journal of Epidemiology and Community Health.