Summary: The food on a two-year-old’s plate may cast a long shadow over their future academic performance. A longitudinal study following thousands of children in Brazil has found that toddlers who habitually consume “unhealthy” diets—characterized by ultraprocessed foods like instant noodles, candies, and processed meats—score significantly lower on IQ tests by ages six and seven.
Interestingly, the study found that while unhealthy foods actively hindered cognitive development, a “healthy” diet of fruits and vegetables didn’t necessarily boost IQ above average, largely because these foods are already so common in early childhood. This research highlights a “cumulative disadvantage,” where poor nutrition combined with early biological vulnerabilities (like low birth weight) creates a permanent gap in a child’s cognitive potential before they even start school.
Key Facts
- The Two-Year Pivot: Dietary patterns at age two are strong predictors of cognitive performance and IQ four to five years later.
- Ultraprocessed Impact: The “unhealthy” pattern—snacks, soft drinks, candies, and sausages—was consistently linked to lower IQ scores, even after adjusting for socioeconomic status and maternal education.
- Cumulative Disadvantage: The negative impact of poor diet was significantly stronger in children who already faced early-life deficits in height, weight, or head circumference.
- Biological Mechanisms: Researchers suggest that ultraprocessed diets may interfere with brain development through systemic inflammation, oxidative stress, and disruptions to the gut-brain axis.
- The “Healthy” Baseline: 92% of children in the study consumed a “healthy” pattern (beans, fruits, vegetables), making it a baseline rather than a performance booster in this specific population.
Source: University of Illinois
A new analysis from the 2015 Pelotas Birth Cohort suggests that dietary patterns at just two years of age are associated with cognitive performance at ages six and seven.
The findings add to growing global evidence that early childhood nutrition—particularly exposure to ultraprocessed foods—may play a meaningful role in shaping brain development.
The Pelotas Birth Cohort is one of the most comprehensive long-running population studies in Latin America, following thousands of children from birth. Researchers from the University of Illinois and the Federal University of Pelotas collected detailed information on what children were eating at age two and later assessed their cognitive performance once they reached early school age.
Rather than focusing on individual foods or nutrients, the research team examined overall dietary patterns.
Using principal component analysis, a statistical method that identifies common combinations of foods, they identified two dominant patterns among toddlers in the cohort. One, labeled “healthy,” included 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.
Children who more closely adhered to the unhealthy dietary pattern at age two scored lower on IQ tests at ages six to seven. The association remained even after accounting for a wide range of social, economic, and family factors that could influence cognitive development.
“The covariates were identified as potential confounding factors based on a literature review and the construction of a directed acyclic graph,” said Thayna Flores, an assistant professor in the Department of Health and Kinesiology in the College of Applied Health Sciences at the University of Illinois and one of the study’s authors.
“The analyses were adjusted for child’s sex, maternal age, maternal schooling, maternal work, maternal depression, family structure, parental relationship, socioeconomic status, number of people in the household, number of older siblings, preschool, score of stimulation, duration of exclusive breastfeeding and food introduction before 6 months.”
Some factors often raised in debates about child cognition—such as parental IQ—were not included, largely because they were not measured in the cohort. However, Flores noted that the study did incorporate proxies for the home learning environment.
“We didn’t measure the parental IQ, but home stimulation and early childhood education were both used in our adjustments,” she said.
One of the study’s more surprising findings was what it did not show. The healthy dietary pattern was not associated with higher IQ scores. Rather than undermining the importance of fruits and vegetables, Flores said the result reflects how common these foods already were in the sample.
“The lack of association observed for the healthy dietary pattern can be largely explained by its lower variability,” she said.
“Approximately 92% of children habitually consumed four or more of the foods that characterize the healthy pattern.” When nearly everyone is eating similarly, statistical differences become harder to detect, she said.
Where the results became especially concerning was among children who were already biologically vulnerable. The negative association between unhealthy diets and cognitive performance was stronger in children who had early-life deficits in weight, height, or head circumference.
“According to the literature, children with a deficit in height and head circumference from birth to the first year of life were more likely to be classified as having a low IQ,” Flores said. “Other studies suggest that insufficient growth before age two is related to impaired cognitive development.”
This pattern points to what researchers call cumulative disadvantage: when biological vulnerability and environmental exposures—like poor diet quality—interact to produce worse outcomes than either would alone.
The study did not directly test biological mechanisms, but Flores said existing research offers plausible explanations. “Diets of poor nutritional quality, particularly those high in ultraprocessed foods, may interfere with neurodevelopmental processes through mechanisms involving systemic inflammation, oxidative stress and alterations in the gut–brain axis,” she said.
The researchers, who also included study co-author HK Professor Pedro Hallal—who came to the University of Illinois after a long stint at Pelotas—also examined whether breastfeeding and the timing of complementary feeding influenced the results. Both were included as confounders, and exploratory analyses looked for interactions.
“We identified that the association between adherence to unhealthy dietary patterns and IQ scores was significantly modified by the presence of early-life deficits,” Flores said.
“No evidence of effect modification by sex, birth weight, gestational age, or duration of exclusive breastfeeding was found.”
Although the study is based in southern Brazil, its implications may extend far beyond Pelotas. Ultraprocessed foods are now common in early childhood diets worldwide, including in high-income countries.
“The longitudinal design, high follow-up rates and the large sample size strengthen the study,” Flores said.
“While direct comparison should be made with caution, our findings are informative and can generate hypotheses for studies conducted in high-income countries,” such as the United States.
Whether similar effects would be seen in countries with greater food fortification or different health systems remains an open question. Still, Flores believes the core message is broadly relevant.
“Considering the worldwide dissemination and higher prevalence of ultraprocessed foods, I think so,” she said when asked whether similar patterns might emerge elsewhere.
For policymakers, the findings carry clear implications. In Brazil, infant and young child feeding guidance is already part of primary health care, but Flores said the study highlights a gap between recommendations and reality.
“Our results reinforce the importance of strengthening counseling during routine child health visits, emphasizing the need to limit the habitual offer of ultraprocessed and unhealthy foods,” she said.
“Despite established guidelines, consumption of ultraprocessed foods is already common at this age.”
Flores said public health efforts should focus on promoting healthy foods and reducing the emphasis on unhealth ones, but timing matters.
“We need to consider the rise in ultraprocessed foods,” she said. “Stronger actions now can help prevent these foods, especially in early childhood.”
The Pelotas study is not the final word on diet and cognition. Researchers are now collecting more detailed dietary data as cohort members reach adolescence, opening the door to stronger causal analyses and a better understanding of long-term effects. Still, the takeaway is difficult to ignore.
Long before report cards and standardized tests, children may already be accumulating advantages—or disadvantages—based on what is offered to them at the age of two. In a world where ultraprocessed foods are cheap, convenient and heavily marketed, the study suggests that early dietary choices may quietly shape how children learn, think and thrive years later.
Key Questions Answered:
A: No. The study looked at habitual dietary patterns. It’s the consistent, daily reliance on ultraprocessed foods like instant noodles and soft drinks at age two that was linked to lower cognitive scores years later.
A: In this specific study, nearly all children were eating healthy foods (like beans and fruit). Because there wasn’t much variety—almost everyone had a healthy baseline—the researchers couldn’t statistically “see” a boost. The real difference was made by the addition of unhealthy foods.
A: While the brain is plastic, the study suggests that age two is a critical window. Children who start with a disadvantage (like being small at birth) are the most vulnerable to the negative effects of a poor early diet, making early intervention vital.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this diet, IQ, and brain development research news
Author: Vince Lara-Cinisomo
Source: University of Illinois
Contact: Vince Lara-Cinisomo – University of Illinois
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Dietary patterns at age 2 and cognitive performance at ages 6–7: an analysis of the 2015 Pelotas Birth Cohort (Brazil)” by Heller GT, Flores TR, Carpena MX, Hallal PC, Domingues MR, Bertoldi AD. British Journal of Nutrition
DOI:10.1017/S000711452610628X
Abstract
Dietary patterns at age 2 and cognitive performance at ages 6–7: an analysis of the 2015 Pelotas Birth Cohort (Brazil)
The early years of life are crucial for developing cognitive abilities, such as intelligence. This period is marked by rapid brain development, in which nutrition is essential. This study aimed to characterise dietary patterns at age 2 and investigate their association with cognitive performance at ages 6–7.
The study used data from the 2015 Pelotas Birth Cohort, Brazil (n 4275). Dietary intake was assessed using a habitual consumption questionnaire, and patterns were derived using principal component analysis.
Cognitive performance was assessed using the Wechsler Intelligence Scale for Children (4th edition), providing intelligence quotient (IQ) scores. Associations were tested using linear regression models.
The unhealthy dietary pattern (characterised by packaged snacks, instant noodles, sweet biscuits, sweets and candies, soft drinks, sausages and processed meats) was negatively associated with IQ (P < 0·001).
Exploratory analyses suggest that early-life deficits (low weight, height or head circumference for age) may amplify the negative effect of unhealthy dietary pattern on IQ (interaction P = 0·020).
Children with high adherence to this pattern and early-life deficits showed a 4·78-point IQ reduction (95 % CI: −7·06, −2·49), while those without deficits had a 2·24-point reduction (95 % CI: −3·35, −1·13), compared with those with low adherence, even after adjustments.
No significant associations were found between the healthy dietary pattern (characterised by beans, baby foods, fruits, vegetables and natural fruit juices) and IQ scores.
These findings suggest that an unhealthy diet in early childhood may impair cognitive performance, particularly among children with early-life deficits.
