Understanding How and Why Does Junk Food Affect IQ?

October 8, 2025 •

4 min read

A 2011 study published in the Journal of Epidemiology and Community Health found that children with a processed food diet at age three had a slightly lower IQ at age eight and a half, suggesting that nutrition during early brain development can have a long-term impact on intelligence. This raises a critical question: does junk food affect IQ in measurable ways, and if so, how does it happen? (ABC News report on study).

Quick Summary

Higher consumption of ultra-processed, high-sugar, and high-fat foods is linked to faster cognitive decline and impaired brain function, impacting memory, focus, and reward pathways across all ages.

Key Points

Early Diet Matters: A diet high in processed foods during early childhood is linked to slightly lower IQ scores later in life, regardless of later dietary improvements.
Adolescence is Vulnerable: The developing adolescent brain, particularly the prefrontal cortex, is highly susceptible to the negative effects of junk food, impacting memory, learning, and decision-making.
Inflammation and Oxidative Stress: Junk food consumption contributes to chronic inflammation and oxidative stress in the brain, damaging neurons and impairing cognitive function.
Dopamine System Hijack: Processed foods manipulate the brain's reward system by triggering dopamine release, potentially leading to addiction-like eating behaviors and reduced sensitivity to healthier rewards.
Reversal is Possible: In some cases, improving your diet, exercising, and restoring glucose availability can help reverse or mitigate some of the negative cognitive effects of a poor diet.
Gut-Brain Connection: The gut microbiome's balance is disrupted by ultra-processed foods, which can negatively affect mood, cognition, and overall brain health via the gut-brain axis.
Lifelong Impact: The cumulative effects of poor nutrition on the brain, from early development through adulthood, can increase the risk of cognitive decline and neurodegenerative diseases.

The Critical Window of Childhood Development

Scientific evidence has increasingly pointed to a significant link between a child's diet and their cognitive development. The brain undergoes its most rapid growth during the first three years of life, making this period particularly sensitive to nutritional deficiencies or imbalances. A study conducted by the University of Bristol on nearly 4,000 children tracked dietary patterns from age three to eight and a half. The researchers categorized diets as 'processed' (high in fats and sugar), 'traditional' (meat and vegetables), and 'health-conscious' (fruits, vegetables, and fish). The findings showed that a higher processed food intake at age three was associated with a lower IQ score at eight and a half, even if the child's diet improved later on. Conversely, a health-conscious diet was linked to a higher IQ. While the measured IQ differences were modest, they were statistically significant, highlighting the importance of early-life nutrition for optimal brain development.

Adolescent Brain Vulnerability

Adolescence is another key period of rapid brain maturation, particularly in regions responsible for executive functions, like the prefrontal cortex, which governs impulse control and decision-making. During this time, the brain's reward center becomes highly sensitive, and studies show that junk food can exploit this, creating a cycle of craving and poor eating habits. A diet high in saturated fats and sugar during adolescence has been shown to impair learning, memory, and cognitive flexibility. Some of these diet-induced effects in adolescents may not be completely reversible with a change to a healthier diet in adulthood, reinforcing the idea of a particularly vulnerable period for brain development.

The Mechanisms Behind Cognitive Impairment

Several biological pathways explain how junk food can damage brain function and, potentially, affect IQ:

Neuroinflammation: Processed and high-sugar diets can trigger chronic, low-grade inflammation throughout the body, including the brain. This inflammation can harm neurons and interfere with synaptic function, impairing learning and memory.
Oxidative Stress: Junk foods, often lacking in antioxidants, can lead to increased oxidative stress in the brain. This damages brain cells and accelerates brain aging, contributing to cognitive decline.
Dopamine System Dysregulation: Highly palatable junk foods are engineered to activate the brain's reward system by releasing dopamine, similar to addictive substances. Over time, this constant stimulation can desensitize dopamine receptors, making healthier foods less rewarding and perpetuating a cycle of cravings and overconsumption.
Reduced Neurogenesis: High-fat and high-sugar diets have been shown to reduce levels of brain-derived neurotrophic factor (BDNF), a protein crucial for the survival, growth, and formation of new neurons. Low BDNF is associated with impaired memory and learning.
Disruption of the Gut-Brain Axis: The gut microbiome, a community of microorganisms in the digestive tract, plays a critical role in brain health via the gut-brain axis. A diet high in processed foods and low in fiber disrupts this delicate balance, affecting mood, cognition, and neurotransmitter production.

Can the Effects Be Reversed?

Fortunately, for some, the damage may not be permanent. Recent studies indicate that restoring glucose availability to the brain, either through dietary changes, fasting, or pharmacological intervention, can calm overactive neurons and improve memory performance. Switching from a high-fat and sugar diet to a standard, healthy diet can also restore behavioral flexibility and brain metabolism in animal models, though the reversibility depends on the timing and duration of the poor diet. Combining a healthy diet rich in nutrients like omega-3 fatty acids with regular exercise has a synergistic effect, providing added benefits for brain health and plasticity.

The Impact of Diet on Cognitive Performance: A Comparison


Feature	Nutrient-Rich Diet	Junk Food-Centric Diet
Energy Source	Provides sustained energy from complex carbohydrates and healthy fats.	Causes blood sugar spikes and crashes from simple sugars, leading to energy slumps.
Nutrient Density	High in essential nutrients like omega-3 fatty acids, antioxidants, vitamins, and minerals.	Low in crucial micronutrients needed for brain function and development.
Inflammation	Anti-inflammatory due to high levels of antioxidants and healthy fats.	Promotes chronic, low-grade inflammation in the brain.
Neurotransmitter Function	Supports balanced production of key neurotransmitters like serotonin and dopamine.	Disrupts dopamine signaling, affecting reward processing and impulse control.
Brain Plasticity	Enhances neuroplasticity and the production of BDNF.	Reduces neuroplasticity markers and BDNF levels.
Gut Health	Promotes a diverse and healthy gut microbiome through high fiber intake.	Disrupts gut microbiome balance, impacting the gut-brain axis.

A Lifelong Choice for Brain Health

The impact of junk food on cognitive abilities is a multifaceted issue influenced by factors like age, duration of poor eating, and individual genetics. While the direct impact on IQ scores may seem modest in some studies, the broader picture points to significant and cumulative harm. From impairing memory and focus to altering brain development and mood regulation, a diet high in ultra-processed foods, saturated fats, and sugar can have lasting consequences. By prioritizing a diet rich in whole foods, fruits, vegetables, nuts, and fish, individuals can support lifelong cognitive vitality and build resilience against age-related decline. Ultimately, nutrition is a foundational component of brain health, and the choices we make can have a profound impact on our intellectual and mental well-being throughout our lives.

Outbound Link

For more in-depth information on the scientific research into this topic, you can explore the extensive research on how diet affects brain function published on the National Institutes of Health website.

Frequently Asked Questions

Yes, research suggests that switching to a healthy diet and lifestyle, including regular exercise, can help reverse some of the negative effects of junk food on brain function. The degree of reversal often depends on the timing and duration of the poor diet.

Studies in animal models have shown that a high-fat diet can disrupt memory circuits in the brain and impair memory function almost immediately, with changes occurring in as little as four days.

The prefrontal cortex is the brain region responsible for executive functions like decision-making, planning, and impulse control. It is one of the last areas of the brain to fully mature, making it vulnerable to the negative effects of a junk food diet during adolescence.

The gut microbiome, or gut bacteria, communicates with the brain via the gut-brain axis. A diet high in junk food and low in fiber disrupts this balance, which can lead to increased inflammation and negatively impact mood, cognition, and neurotransmitter production.

While not all processed foods are equally harmful, ultra-processed foods (UPFs) are particularly concerning. UPFs are engineered to be hyper-palatable, often contain unhealthful fats, refined sugars, and additives, and lack essential nutrients, making them particularly detrimental to brain health.

Yes, studies on children and adolescents have linked poor dietary habits, including higher consumption of junk food and sugary beverages, with reduced attention spans, lower cognitive control, and poorer academic achievement.

For optimal brain health, key nutrients include omega-3 fatty acids (found in fish, nuts, and seeds), antioxidants (in berries and vegetables), B-vitamins (in eggs and whole grains), and minerals like zinc, magnesium, and iron.