The preschool years are a time of remarkable growth. Children are learning to regulate emotions, interact with others and develop habits that may last a lifetime — including what they eat.

The results of a large Canadian study suggest that when children eat diets high in ultra-processed foods during early childhood, they are more likely to experience behavioral and emotional difficulties just a few years later.

The research followed over 2,000 children from the Canadian Healthy Infant Longitudinal Development (CHILD) Cohort Study. Investigators examined how much ultra-proceed food children ate at age three and then looked to see whether that diet was associated with certain behavior patterns by age five.

Children who ate more ultra-processed foods at age three tended to have slightly higher behavioral symptom scores by age five.

Ultra-processed foods are foods made in factories largely from refined ingredients and additives rarely found in home kitchens. They are an appealing mix of fat, sugar, carbohydrates and sodium designed to encourage craving. Examples include sugary beverages, snack foods like chips and cheese puffs, ready-to-heat meals and packaged baked goods like cookies and cupcakes.

In Canada, these products often make up a striking share of children's diets. Previous research suggests these “hyperpalatable” foods account for nearly half of the daily calories consumed by preschoolers.

The long-running population-based CHILD project recruited pregnant women between 2009 and 2012 and has followed their children from before birth through adolescence at study sites in Vancouver, Manitoba, Toronto and Edmonton.

The researchers, led by Kozeta Miliku, PhD, assistant professor of nutritional sciences at the University of Toronto's Temerty Faculty of Medicine and an investigator at the Joannah & Brian Lawson Centre for Child Nutrition, first assessed children's diets at age three using a detailed 112-item food-frequency questionnaire, which captured what children were eating and how often.

Foods were categorized using the NOVA classification system, a widely used method for identifying ultra-processed products.

After adjusting for a wide range of factors that could affect the results — such as maternal education, prenatal stress, breastfeeding, household income, childcare exposure, physical activity and body mass index — the researchers found a consistent pattern.

Children who ate more ultra-processed foods at age three tended to have slightly higher behavioral symptom scores by age five. For every ten percent increase in calories from ultra-processed foods, scores for internalizing behaviors (such as anxiety and fearfulness), externalizing behaviors (such as aggression or hyperactivity) and total behavioral symptoms increased modestly, typically by less than one point on the standardized scale.

However, certain foods appeared to show stronger links. Higher consumption of sugar-sweetened beverages, artificially sweetened drinks, ready-to-eat meals and some packaged breads were associated with higher scores for internalizing behaviors.

Swapping out sugary drinks for water, adding fresh fruit to snacks or choosing simpler, minimally-processed foods more often could potentially support children's emotional, as well as physical health.

The researchers also ran statistical models simulating what might happen if children replaced ultra-processed foods with minimally processed options such as vegetables and other whole foods. Those results were encouraging: When 10 percent of calories from ultra-processed foods were replaced with minimally processed foods, children showed modestly lower behavioral symptom scores across all categories.

“The preschool years are critical for child development, and it's also when children begin to establish dietary habits,” Miliku said in a press release. “Our findings suggest that even modest shifts toward minimally processed foods like whole fruits and vegetables, in early childhood may support healthier behavioral and emotional development.”

The researchers emphasize that the effects observed in the study were modest, and the findings do not prove that ultra-processed foods directly cause behavioral problems. Still, the results add to a growing body of research linking these foods in a variety of health concerns, including obesity and cardiometabolic disease.

Swapping out sugary drinks for water, adding fresh fruit to snacks or choosing simpler, minimally-processed foods more often could potentially support children's emotional, as well as physical health.

The goal is not to place blame on families navigating busy lives and limited resources. “Parents are doing their best and not all families have access to single-ingredient foods, or the tools and time needed to incorporate them into their families' diets,” Miliku said.

But it may be worth the effort. The study suggests that helping children eat more minimally processed foods can be a small step with potentially meaningful benefits for their well- being.

The study is published in JAMA Network Open.