A child's diet at just two years old may have lasting implications for how they think and learn years later, according to a new analysis.
Researchers found that toddlers who consumed more ultraprocessed foods at age two scored lower on intelligence tests at ages six and seven, even after accounting for a wide range of social, economic and family factors.
The analysis was based on data from the Pelotas Birth Cohort, which is following thousands of children born in southern Brazil from birth through childhood and beyond.
For this study, researchers from the University of Illinois and the Federal University of Pelotas collected detailed dietary data when children were two years old and later assessed their cognitive performance once they reached early school age.
Rather than examining individual foods or nutrients, the researchers focused on overall dietary patterns. Using a statistical technique called principal component analysis, they identified two dominant eating patterns among toddlers.
One pattern, described as "healthy," included foods such as beans, fruits, vegetables, baby foods and natural fruit juices. The other, labeled "unhealthy," was characterized by snacks, instant noodles, sweet biscuits, candies, soft drinks, sausages and processed meats -- many of which are considered ultraprocessed.
Children whose diets more closely matched the unhealthy pattern at age two had lower IQ scores at ages six to seven.
Importantly, the association held even after researchers adjusted for numerous factors that can influence cognitive development, including maternal education, socioeconomic status, family structure, breastfeeding duration, early childhood education and home stimulation.
Some commonly debated influences on cognition, such as parental IQ, were not included because they were not measured in the cohort. However, professor Thayna Flores, one of the study's authors, noted that the study used proxies for the home learning environment, including measures of stimulation and preschool attendance.
One unexpected finding was that the healthy dietary pattern was not associated with higher IQ scores. Flores said this likely reflects how widespread healthy foods already were in the sample, making differences harder to detect.
"Approximately 92 percent of children habitually consumed four or more of the foods that characterize the healthy pattern," she said.
The strongest effects were seen among children who were already biologically vulnerable. The link between unhealthy diets and lower IQ was more pronounced in children who had early deficits in weight, height or head circumference -- suggesting a cumulative disadvantage when poor nutrition compounds early growth challenges.
Although the study did not directly test biological mechanisms, Flores said existing research points to plausible explanations. Diets high in ultraprocessed foods may affect brain development through pathways involving inflammation, oxidative stress and changes in the gut-brain axis.
While the research is based in Brazil, the authors said the findings may have global relevance, given the widespread availability of ultraprocessed foods worldwide.
For Flores, the message is clear.
"We need to consider the rise in ultraprocessed foods," she said. "Stronger actions now can help prevent these foods, especially in early childhood."