Ultra-processed foods in early childhood linked to lower IQ scores

Toddlers who consume a diet high in processed meats, sugary snacks, and soft drinks may have lower intelligence scores by the time they reach early school age. A new study published in the British Journal of Nutrition suggests that this negative association is even stronger for children who faced physical growth delays in infancy. These findings add to the growing body of evidence linking early childhood nutrition to long-term brain development.

The first few years of human life represent a biological window of rapid change. The brain grows quickly during this time and builds the neural connections necessary for learning and memory. This process requires a steady supply of specific nutrients to work correctly. Without enough iron, zinc, or healthy fats, the brain might not develop to its full capacity.

Recent trends in global nutrition show that families are increasingly relying on ultra-processed foods. These are industrial products that often contain high levels of sugar, fat, and artificial additives but very few essential vitamins. Researchers are concerned that these foods might displace nutrient-rich options. They also worry that the additives or high sugar content could directly harm biological systems.

Researchers from the Federal University of Pelotas in Brazil and the University of Illinois Urbana-Champaign investigated this issue. The lead author is Glaucia Treichel Heller, a researcher in the Postgraduate Program in Epidemiology in Pelotas. She worked alongside colleagues including Thaynã Ramos Flores and Pedro Hallal to analyze data from thousands of children. The team wanted to determine if eating habits established at age two could predict cognitive abilities years later.

The researchers used data from the 2015 Pelotas Birth Cohort. This is a large, long-term project that tracks the health of children born in the city of Pelotas, Brazil. The team analyzed information from more than 3,400 children. When the children were two years old, their parents answered questions about what the toddlers usually ate.

The scientists did not just look at single foods like apples or candy. Instead, they used a statistical method called principal component analysis. This technique allows researchers to find general dietary patterns based on which foods are typically eaten together. They identified two main types of eating habits in this population.

One pattern was labeled “healthy” by the researchers. This diet included regular consumption of beans, fruits, vegetables, and natural fruit juices. The other pattern was labeled “unhealthy.” This diet featured instant noodles, sausages, soft drinks, packaged snacks, and sweets.

When the children reached six or seven years of age, trained psychologists assessed their intelligence. They used a standard test called the Wechsler Intelligence Scale for Children. This test measures different mental skills to generate an IQ score. The researchers then looked for a statistical link between the diet at age two and the test results four years later.

The analysis showed a clear connection between the unhealthy dietary pattern and lower cognitive scores. Children who frequently ate processed and sugary foods at age two tended to have lower IQ scores at school age. This link remained even when the researchers accounted for other factors that influence intelligence. They adjusted the data for the mother’s education, family income, and how much mental stimulation the child received at home.

The researchers faced a challenge in isolating the effect of diet. Many factors can shape a child’s development. For example, a family with more money might buy healthier food and also buy more books. To manage this, the team identified potential confounding factors. Thaynã Ramos Flores, one of the study authors, noted, “The covariates were identified as potential confounding factors based on a literature review and the construction of a directed acyclic graph.”

The team used these adjustments to ensure the results were not simply reflecting the family’s socioeconomic status. Even with these controls, the negative association between processed foods and IQ persisted. The findings suggest that diet quality itself plays a specific role.

The negative impact appeared to be worse for children who were already biologically vulnerable. The study looked at children who had early-life deficits. These were defined as having low weight, height, or head circumference for their age during their first two years.

For these children, a diet high in processed foods was linked to a drop of nearly 5 points in IQ. This is a substantial difference that could affect school performance. For children without these early physical growth problems, the decline was smaller but still present. In those cases, the reduction was about 2 points.

This finding points to a concept known as cumulative disadvantage. It appears that biological vulnerability and environmental exposures like poor diet interact with each other. A child who is already struggling physically may be less resilient to the harms of a poor diet.

The researchers also looked at the impact of the healthy dietary pattern. They did not find a statistical link between eating healthy foods and higher IQ scores. This result might seem counterintuitive, as fruits and vegetables are known to be good for the brain. However, the authors explain that this result is likely due to the specific population studied.

Most children in the Pelotas cohort ate beans, fruits, and vegetables regularly. Because almost everyone ate the healthy foods, there was not enough difference between the children to show a statistical effect. Flores explained, “The lack of association observed for the healthy dietary pattern can be largely explained by its lower variability.” She added that “approximately 92% of children habitually consumed four or more of the foods that characterize the healthy pattern.”

The study suggests potential biological mechanisms for why the unhealthy diet lowers IQ. One theory involves the gut-brain axis. The human gut contains trillions of bacteria that communicate with the brain. Diets high in sugar and processed additives can alter this bacterial community. These changes might lead to systemic inflammation that affects brain function.

Another possibility involves oxidative stress. Ultra-processed foods often lack the antioxidants found in fresh produce. Without these protective compounds, brain cells might be more susceptible to damage during development. The rapid growth of the brain in early childhood makes it highly sensitive to these physiological stressors.

There are limitations to this type of research. The study is observational, which means it cannot prove that the food directly caused the lower scores. Other factors that the researchers could not measure might explain the difference. For example, the study relied on parents to report what their children ate. Parents might not always remember or report this accurately.

Additionally, the study did not measure the parents’ IQ scores. Parental intelligence is a strong predictor of a child’s intelligence. However, the researchers used maternal education and home stimulation scores as proxies. These measures help account for the intellectual environment of the home.

The findings have implications for public health policy. The results suggest that officials need to focus on reducing the intake of processed foods in early childhood. Merely encouraging fruit and vegetable intake may not be enough if children are still consuming high amounts of processed items. This is particularly important for children who have already shown signs of growth delays.

Future studies could look at how these dietary habits change as children become teenagers. It would also be helpful to see if these results are similar in countries with different food cultures. The team notes that early nutrition is a specific window of opportunity for supporting brain health.

The study, “Dietary patterns at age 2 and cognitive performance at ages 6-7: an analysis of the 2015 Pelotas Birth Cohort (Brazil),” was authored by Glaucia Treichel Heller, Thaynã Ramos Flores, Marina Xavier Carpena, Pedro Curi Hallal, Marlos Rodrigues Domingues, and Andréa Dâmaso Bertoldi.