Scientists Discover Troubling Link Between Processed Foods and Preschool Behavior

Early childhood diets higher in ultra-processed foods were associated with more behavioral and emotional challenges two years later.

The preschool years are a critical period for both brain development and the formation of lifelong eating habits. New research led by the University of Toronto suggests that what children eat during this window may be associated with how they feel and behave later in early childhood.

The study found that higher consumption of ultra-processed foods was linked to greater behavioral and emotional difficulties, including anxiety, fearfulness, aggression, and hyperactivity.

“The preschool years are critical for child development, and it’s also when children begin to establish dietary habits,” said Kozeta Miliku, principal investigator on the study and an assistant professor of nutritional sciences in U of T’s Temerty Faculty of Medicine.

“Our findings underscore the need for early-life interventions such as professional advice for parents and caregivers, as well as public health campaigns, nutrition standards for child-care providers and reformulation of some packaged foods,” Miliku said.

Early diets shape behavior

Published in JAMA Network Open, the study is the first to use detailed, prospective data to examine ultra-processed food consumption alongside standardized behavioral assessments in young children. It is also among the largest studies to investigate behavior and mental health during early childhood.

Ultra-processed foods are industrial products made mostly from refined ingredients and additives that are not usually found in home kitchens. In Canada, these foods account for almost half of the calories consumed by preschoolers.

The researchers used data from the CHILD Cohort Study, a long-term, population-based study that enrolled pregnant women between 2009 and 2012 and has followed their children from before birth into adolescence at four sites across Canada.

The analysis included dietary information from more than 2,000 children at age three. When the children reached age five, the researchers evaluated their scores using the validated Child Behavior Checklist, a widely used tool for measuring emotional and behavioral well-being in children.

A cohort tracks childhood change

The research team, which included first authors Meaghan Kavanagh (a postdoctoral fellow) and Zheng Hao Chen (a PhD student in Miliku’s lab), found that every 10 percent increase in calories from ultra-processed foods was associated with higher scores for internalizing behaviors (such as anxiety and fearfulness), externalizing behaviors (such as aggression and hyperactivity), and overall behavioral difficulties.

Higher scores reflect more reported behavioral challenges.

Certain foods show stronger links

Some ultra-processed food categories had stronger associations than others. These included drinks sweetened with sugar, artificially sweetened drinks, and foods that are ready to eat or ready to heat, such as French fries or macaroni and cheese.

In statistical models that simulated dietary changes, replacing 10 percent of energy from ultra-processed foods with minimally processed foods, including fruits, vegetables, and other whole foods, was linked to lower behavioral scores.

Miliku, who is also a researcher at U of T’s Joannah & Brian Lawson Centre for Child Nutrition, said the findings suggest that even small dietary shifts may help support healthier development.

“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,” she said.

Small changes may matter

Miliku’s interest in the topic grew out of observations from her own life as a parent.

“As a parent of a toddler, I started noting how often convenience foods appear in children’s diets, sometimes even in places we consider healthy environments,” she said.

A growing body of research has connected ultra-processed foods with higher risks of obesity and cardiometabolic disease in both adults and children. Earlier studies have also suggested links between these foods and poorer behavior and mental health outcomes in adolescents and adults.

“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,” said Miliku.

“Ultra-processed foods are widely available, affordable, and convenient,” she added. “It is important to consider how we can gradually increase whole and minimally processed options when possible.”

Miliku said that small steps, such as offering a piece of fruit or replacing a sugary drink with water, may help support children’s emotional and behavioral development over time.

“The goal is to provide evidence that can help families make informed choices,” she said.

Reference: “Ultraprocessed Food Consumption and Behavioral Outcomes in Canadian Children” by Meaghan E. Kavanagh, Zheng Hao Chen, Sukhpreet K. Tamana, Theo J. Moraes, Elinor Simons, Stuart E. Turvey, Padmaja Subbarao, Piushkumar J. Mandhane and Kozeta Miliku, 3 March 2026, JAMA Network Open.
DOI: 10.1001/jamanetworkopen.2026.0434

This study was funded by the Canadian Institutes of Health Research and a Temerty Faculty of Medicine pathway grant.

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