Ultra-Processed Brains: The business of trading brain efficiency for eating efficiency

25. March 2025 by Maria Eduarda Barbosa

Introduction

There are two main strategies in nature regarding eating behaviors: big guts or big brains. The first is exemplified by the koala, which has a cecum that allows it to digest eucalyptus leaves and extract all necessary nutrients. Koalas, therefore, do not need to think about what they eat, as there is only one option. The second strategy is best represented by humans, whose bodies and minds are not only capable of, but also dependent on, a diverse diet. Humans may be the ultimate omnivores. Our relatively small gastrointestinal tract allows us to digest both elastin—a protein found exclusively in meat—and starch, a carbohydrate present in plants.^[1]

Moreover, our brains are equipped with numerous mechanisms that drive us to seek nutritious food. For instance, our "sweet tooth," shared by virtually all other mammals, instinctively guides us toward high-energy foods. Animals that adopt the “big brain” strategy also develop natural aversions to certain flavors, such as bitterness. However, in humans—more than in any other omnivores—culture plays a crucial role in overcoming these natural aversions.^[2] Through shared knowledge, we learn about the safety and potential benefits of consuming species that might not initially taste appealing.

In modern life, however, the necessity to think about what we eat has diminished, obscured by the rise of ultra-processed foods—ready-to-eat or ready-to-heat products composed of substances extracted from food, along with artificial additives.^[3] But as we increasingly abandon the “big brain” strategy, it seems that our brains abandon us in return. High consumption of ultra-processed food has been linked to various psychiatric disorders, from neurodevelopmental issues in the womb to food addiction in childhood and adolescence, as well as adult depression, cognitive decline, and dementia.^[4][5][6]

Ultra-processed foods contribute to psychiatric disorders, likely by impairing brain metabolism throughout the human lifespan. As modern society prioritizes convenience over cognitive well-being, we risk trading long-term mental health for short-term dietary efficiency.

To understand the extent of ultra-processed food's impact, we must first grasp why it has become so ubiquitous in modern diets.

Why we overeat Highly Processed Food

The first reason why humans overeat highly processed food is that it tastes exceptionally good. These products exploit our natural taste for fat or sweet flavor to an extreme making them hyper-palatable.^[7]

The second reason why humans overeat highly processed food is that it is cheap. It is inexpensive, in large part, because since the Nixon administration, the U.S. government has subsidized corn production, incentivizing farmers to flood the market with surplus corn. Add to that technological advancements that enable extensive corn processing—such as the use of glucose and xylose isomerases to convert corn into large quantities of fructose, an especially sweet sugar—and you have a perfect formula for supersized hyper-palatable soft drinks.^[1] Soft drinks are supersized because, as it turns out, offering a larger portion for just a few extra cents is a more effective marketing strategy than simply lowering prices.^[8]

The third and final reason humans overeat ultra-processed food is that it is, by nature, fast food. In fact, ultra-processed foods are primarily consumed in fast-food restaurants, whereas eating at home is associated with lower consumption.^[9]

While the palatability and affordability of ultra-processed food explain its widespread consumption, its long-term consequences on brain health are particularly alarming.

What is the Impact of Ultra-Processed Food through the Human Lifecycle

The impact of ultra-processed food (UPF), especially soft drinks, begins early in life. Children of mothers who consume high quantities of UPF are more likely to have lower verbal IQs and exhibit executive function deficits.^[8] (Executive functions refer to higher-order cognitive processes essential for goal-oriented behavior, such as planning complex tasks, organizing information, and inhibiting impulsive actions.)^[10] This alone makes it more difficult for children to succeed academically. However, if the same environment (saturated with ultra-processed foods) that shaped the mother’s eating habits is also the child’s, the situation can become even worse.

Children who regularly consume soft drinks—engineered to be particularly palatable—are at risk of dysregulating their reward pathways. In other words, they become addicted.^[11] To understand the impact of a dysregulated reward system, it is crucial to first grasp its intended function: when working properly, reward pathways motivate individuals to engage in challenging activities that lead to meaningful rewards. In addiction, however, the brain fixates on a single stimulus—the drug or behavior of choice—at the expense of all other motivators.^[12] Adding insult to injury, food addiction is a frequent comorbidity in children and adolescents with clinically diagnosed psychiatric disorders.^[13]

A child with a mental illness often grows into an adult with a mental illness.^[14] This is especially true when the environmental factors that contribute to childhood disorders persist into adulthood. In this case, dietary habits formed in childhood tend to shape adult food preferences^[15]—an important consideration given that ultra-processed food consumption increases the risk of developing adult depression by more than 50%.^[16] The issue continues to affect individuals in the final stage of life, as both depression and ultra-processed food consumption are independent risk factors for cognitive decline and dementia.^[17][18]

This scenario heavily burdens communities, since depression is one of the leading causes of disability.^[19] It impairs occupational functioning, disrupts social life, and significantly increases mortality risk.^[20] Moreover, healthcare costs for dementia patients are estimated at one trillion dollars annually, in addition to the frequent reliance on at least one unpaid caregiver.^[21] At the individual level, both depression and dementia pose major threats to lifespan and healthspan, meaning they not only shorten life expectancy but also reduce the number of years lived free from debilitating diseases.^[22]

How could Ultra-Processed Food lead to Mental Illness

Ultra-processed diets contribute to excess calorie intake and weight gain.^[23] This finding aligns with the hypothesis that psychiatric illnesses are primarily metabolic dysfunctions of the brain.^[24]

Metabolism is the process by which the body converts food into usable energy or structural components. This process is disrupted in diabetes mellitus, a condition in which the body cannot properly use glucose, either due to a lack of insulin—the hormone that allows glucose to enter most cells—or due to insulin resistance, where cells fail to respond effectively to insulin.^[25] In diabetic patients, the metabolic irregularities have been shown to also induce depression.^[26]

Metabolic dysfunction also plays a role in cancer, where cells become excessively dependent on glucose. In normal conditions, mitochondria regulate energy metabolism and promote cell death when necessary. However, in cancer, the mitochondria fail to eliminate malfunctioning cells before they multiply uncontrollably.^[27] In this context, depressive symptoms often precede cancer diagnosis and such symptoms predict higher mortality rates.^[28]

Notably, high consumption of ultra-processed food is independently associated with cancer, diabetes and depression.^[29][30][31] Knowing that the same eating pattern leads to excessive caloric intake, it is plausible that all the cited hazards from these foods stem from their influence on energy metabolism.

Conclusion

While natural taste preferences once guided humans toward nutrient-rich foods, ultra-processed alternatives now hijack these instincts, providing only the illusion of nourishment. This process harms the human brain at all stages of development.

This correlation supports the hypothesis that psychiatric disorders, in their various forms, stem from metabolic dysfunctions in the brain. In short, modern society appears to be trading cognitive efficiency for the convenience of highly processed foods—an exchange that comes at a great cost.

If we continue prioritizing dietary convenience, the evidence suggests that we risk a future in which mental illness and cognitive decline become the norm rather than the exception. In fact, that scenario is already in the horizon, with the rates of psychiatric conditions rising continually over the last decades.^[32][33]

It is extremely likely, therefore, that it is time to recognize the cost of ultra-processed food and prioritize real nourishment—for both body and mind.