Dr. Kozeta Miliku, an assistant professor at the University of Toronto, in June, 2025.Claire Dam/The Globe and Mail
Picture an average Canadian child’s lunchbox, and what do you see? Perhaps a Thermos of boxed mac and cheese, or an English muffin sandwich, thrown in with some goldfish crackers and granola bars.
Whatever the mix, chances are a significant portion is ultraprocessed, a food category that’s rapidly taking over children’s diets and considered “one of the most urgent yet inadequately addressed threats to human health in the 21st century,” according to a recent commentary in The Lancet medical journal.
Researchers are now studying whether ultraprocessed foods might be contributing to a range of health issues, from obesity and diabetes to anxiety and depression. And this week, Canadian researchers published a new study investigating their possible role in another growing health concern: childhood behavioural disorders.
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Published in JAMA Network Open, the new study analyzed data collected from 2,077 children across Canada, including detailed information about their diets at age 3 and their behaviour at age 5.
The Globe and Mail spoke with senior author Kozeta Miliku, an assistant professor at the University of Toronto, to learn more about what the researchers found.
Everyone’s heard of ultraprocessed foods, but many people aren’t sure how to define them. What exactly is an ultraprocessed food?
That’s a really excellent question because sometimes even we researchers struggle to define what an ultraprocessed food is. In simple terms, ultraprocessed foods are industrially formulated foods, made mostly from refined ingredients and additives that we typically wouldn’t use in home cooking. For example: sugary drinks, packaged snack foods, instant noodles, sweetened cereals and many ready-to-eat meals.
What are examples of ultraprocessed foods that might surprise people?
The packaged bread that we buy in the supermarket. Flavoured yogurt. The majority of granola bars.
You’ve basically just described my kid’s entire lunch box.
Sometimes mine as well.
Do we know how much ultraprocessed food Canadian children are eating?
Among preschoolers – so three-year-olds – ultraprocessed foods make up almost half of the calories they consume. We also have an upcoming study showing that for some children, this percentage goes up to 80 per cent. So that is alarming.
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There’s been a lot of research into the possible health effects of ultraprocessed foods. But what does the literature tell us about connections with behavioural issues?
That’s actually what triggered us to study this question; we’ve already seen so much in the literature linking ultraprocessed foods with many physical and metabolic health outcomes. But we didn’t know much about behaviour in children. This is one of the first studies to look this early in life at behavioural outcomes.
So what did your study find?
Children who consumed more ultraprocessed foods tended to have slightly higher scores for behavioural and emotional difficulties. This included internalizing behaviours, such as anxiety or withdrawal, and externalizing behaviours, such as hyperactivity or aggression.
What was also important in our findings is that we tried to estimate what might happen if a portion of ultraprocessed foods was replaced with minimally processed foods. What we observed were lower behavioural difficulty scores, meaning better behavioural outcomes.
While these effects are modest, and this study is just observational, it suggests that early childhood diet may play a role in children’s behavioural development.
Were you surprised by any of these findings?
I was surprised that even the smallest shift in diet can improve behavioural outcomes – substituting just 150 kilocalories, which is equal to maybe a granola bar, with whole fruits, vegetables, etc. That’s a very important message because it tells us that even small changes in children’s diets may support better behavioural development.
Were certain foods more tightly associated with behavioural issues?
Yes. We found that sugary, sweetened beverages were primarily linked to behavioural outcomes. And then we also found that breads and cereal and ready-to-eat or ready-to-heat dishes were also related more strongly with adverse health outcomes.
I know your study doesn’t prove causation, but it suggests something here. Why do you think we might be seeing these associations?
There might be several potential biological pathways. Firstly, ultraprocessed foods tend to be low in fibre and low in key nutrients that are important for brain function. Secondly, they may affect the gut microbiome, which communicates with the brain through the gut-brain axis. And thirdly, there is a huge movement to look into the additives found in ultraprocessed foods, which may promote inflammation or metabolic changes that could influence brain function. But these mechanisms still need further study.
I’m imagining an exhausted parent out there, reading this article and feeling completely crushed by the extra pressure to ensure their kids eat home-cooked meals and snacks. What would you say to this parent?
Parents are doing their best. The goal isn’t perfection. We should focus on the overall pattern and not try to eliminate ultraprocessed foods completely, because it’s almost impossible.
What we should focus on is increasing whole or minimally processed foods, and reducing reliance on packaged snack-type foods. Our research showed that even substituting just 10 per cent was associated with better behavioural outcomes. Maybe we can start with the drinks, making water the default. Or swap one daily snack for a whole-food option.
The preschool years are a sensitive developmental window for brain development, and it’s when dietary habits are established. What children eat during this period can shape their long-term patterns that may influence their health later in life.
You have a four-year-old of your own. You’re also one of the foremost experts on ultraprocessed foods and their potential health consequences. Do you struggle with all of this yourself?
Absolutely I struggle. And absolutely I give that granola bar to my child.
I have the education, I have the income, I have everything – but I don’t have the time. I’m really struggling with getting away from all these ultraprocessed foods, even though I know the research. It’s the environment and society around us that pushes us to the limits and makes it so hard to make healthy choices.
This interview has been edited and condensed.
Editor’s note: A previous version of this article incorrectly stated that animal-based products were related more strongly with adverse health outcomes. Breads and cereal, along with the other foods listed in the article, were related more strongly with adverse health outcomes.