Parents already know giving children too much junk food can make them obese, but a new study says all that greasy, processed food may have a negative impact on their brains as well as their bodies.

Researchers from the United Kingdom and Canada found an association between foods high in fat and sugar and slightly reduced IQ. Using questionnaires that asked how often parents fed their children junk food, the researchers found that children whose dietary patterns consisted of fatty, sugary foods at age 3 had a lower IQ at age 8-1/2 than their peers who ate a lot more nutritious foods.

“This suggests that any cognitive/behavioural effects relating to eating habits early in childhood may well persist into later childhood, despite any subsequent changes (including improvements) to dietary intake,” the authors wrote. The work was led by Kate Northstone, a research fellow at the University of Bristol in England.

But that doesn’t mean that feeding kids a lot of pizza, hot dogs and potato chips will cause a lower IQ. The authors found an association, not a cause-and-effect relationship.

The researchers also say there could have been other factors, such as parenting style, that led to some children’s lower IQs.

Additionally, IQ was only lowered by a little more than one point — statistically significant but still small. There were nearly 4,000 children assessed, which is a large number and can lead to statistical significance.

“With a large enough sample size, you can show statistical significance with a small increment, but it may not mean anything clinically,” said Keith Ayoob, associate professor of pediatrics at the Albert Einstein College of Medicine in the Bronx, N.Y.

Diet Affects Us ‘From Head to Toe’

Despite the study’s limitations, nutritionists say the study reinforces the need to get children started on a proper diet early.

The authors said they took numerous factors into account that could have contributed to their findings, including stressful events the child experienced, parental education level and social class.

“I want to see more about parenting styles,” said Ayoob. “Do the parents interact with the children, do they eat dinner together — these are things that can also influence IQ.”

The authors found that dietary patterns between the ages of 4 and 7 did not have an impact on IQ.

“A possible explanation for this is that the brain grows at its fastest rate during the first three years of life. Studies have shown that head growth during this time is associated with cognitive outcome, and it is possible that good nutrition during this early period may encourage optimal brain growth,” the researchers wrote.

Junk Food and IQ

This study isn’t the first to look at the relationship between nutrition and IQ. A recent study found that children breastfed for six months did better on tests in school than their classmates who were formula-fed. The current research, however, is one of very few studies that look at the effects of overall diet on IQ development, the authors say.

Dieticians say the new study combines with others to send a very important message.

“It’s a reminder that our whole body, from head to toe, is impacted by what we eat,” said Connie Diekman, director of university nutrition at Washington University in St. Louis. “It’s a real eye-opener that the foods we feed our children lays the impact for not only their physical health, but also their mental health in terms of intelligence as well.”