The Science of Ultra-Processed Foods and Mental Health

By Dr. Chinta SidharthanReviewed by Lily Ramsey, LLM

What are ultra-processed foods?
Recent evidence linking UPFs to mental health
Potential mechanisms linking UPFs to mental health
Global trends and industry implications
Critiques and limitations of current research

What we eat does not just shape our bodies — it also shapes our minds. Ultra-processed foods (UPFs) have become a staple of modern diets, but beneath their convenience lies a growing body of evidence linking them to rising rates of depression, anxiety, and cognitive decline.

UPFs have become a dominant part of modern diets, constituting a significant proportion of daily caloric intake in many countries.¹ Produced through extensive industrial processing, UPFs include packaged snacks, sugary drinks, instant meals, and fast food — products that are often high in refined sugars, unhealthy fats, additives, and preservatives.

While the physical health risks of UPFs, such as obesity and cardiovascular disease, are well-documented, emerging research suggests that these foods may also negatively affect mental health and contribute to conditions such as depression and anxiety.²

The growing concern about the potential mental health effects of UPFs has led researchers to explore the underlying biological and psychological mechanisms.

This article examines recent evidence linking UPFs to mental health conditions, potential mechanisms of action, global trends and industry responses to this growing concern, and the limitations of current research.

Image Credit: Prostock-studio/Shutterstock.com

What are ultra-processed foods?

UPFs are classified according to the NOVA food classification system, which categorizes foods based on the extent and purpose of their processing rather than solely on their nutrient content.¹ The NOVA system defines four groups:

1. Unprocessed or minimally processed foods — whole foods such as fruits, vegetables, grains, and meats with no or minimal alterations;
2. Processed culinary ingredients — substances extracted from foods, such as oils, sugars, and salt, used for cooking;
3. Processed foods — foods that undergo some processing, including canned vegetables, cheese, and fresh bread, typically containing a few added ingredients; and
4. Ultra-processed foods — industrial formulations containing little or no whole foods, often with artificial flavors, preservatives, emulsifiers, and other additives to enhance shelf life and palatability.

Examples of UPFs include soft drinks, instant noodles, processed meats, packaged baked goods, and sugary breakfast cereals.

These foods are engineered for convenience and long shelf life but often contain high levels of added sugars, refined carbohydrates, unhealthy fats, and synthetic additives that may contribute to poor health outcomes.¹

The NOVA Method of Food Classification

Recent evidence linking UPFs to mental health

An increasing number of studies suggest a correlation between UPF consumption and poor mental health, particularly depression and anxiety. Large-scale epidemiological studies have identified associations between diets high in UPFs and increased risk of depressive symptoms.

For example, a 2020 study that examined dietary patterns in over 10,000 adults in the United States found that individuals consuming the highest amounts of UPFs had a 35% greater likelihood of experiencing depressive symptoms compared to those with the lowest intake.³

Similarly, another study by Harvard Medical School researchers found that higher UPF consumption was associated with a 50%  risk of developing depression, particularly among individuals consuming high quantities of artificially sweetened beverages and processed snacks.⁴

Longitudinal studies have also indicated that habitual consumption of UPFs is linked to deteriorating mental well-being over time.

A large cohort study following over 25,000 individuals for more than five years reported that increased UPF intake was associated with higher rates of depressive episodes, independent of other lifestyle factors such as exercise and socioeconomic status.⁵

Potential mechanisms linking UPFs to mental health

Several biological and physiological mechanisms have been proposed to explain the link between UPFs and mental health disorders, with particular focus on the gut-brain axis, inflammation, blood sugar regulation, and artificial additives.

Gut-brain axis dysfunction

The gut microbiome plays a crucial role in mental health by regulating neurotransmitter production, immune responses, and inflammation. Diets high in UPFs often lack dietary fiber and essential nutrients, leading to an imbalance in gut microbiota.⁶

Studies also indicate that alterations in the gut microbiome can negatively impact the production of serotonin and gamma-aminobutyric acid (GABA), which are neurotransmitters essential for mood regulation.⁷

Chronic inflammation

UPFs are known to promote systemic inflammation due to their high content of refined carbohydrates, unhealthy fats, and artificial additives. Chronic low-grade inflammation has been strongly linked to depressive and anxiety disorders.

Furthermore, markers of inflammation, such as C-reactive protein (CRP) and interleukin-6 (IL-6), are often elevated in individuals consuming diets high in UPFs.⁸

Blood sugar fluctuations

The high glycemic index of many UPFs can cause rapid spikes and crashes in blood glucose levels, potentially affecting mood stability and increasing the risk of depression.

Frequent blood sugar fluctuations are also thought to contribute to irritability, fatigue, and cognitive impairment, further exacerbating mental health conditions.⁴

Artificial additives and neurotoxicity

Ultra-processed foods frequently contain artificial sweeteners, emulsifiers, and preservatives that may negatively impact brain function.

Some studies suggest that artificial sweeteners such as aspartame can alter neurotransmitter activity and exacerbate symptoms of depression and anxiety.

Additionally, emulsifiers used in processed foods have been shown to disrupt gut microbiota composition, potentially influencing neuroinflammatory pathways linked to mood disorders.⁵

Global trends and industry implications

The food industry continues to expand the availability of highly processed, shelf-stable products due to their cost-effectiveness and consumer demand for convenience.

In response to growing health concerns, some food companies are reformulating products by reducing added sugars, artificial ingredients, and unhealthy fats.¹ However, the extent to which these modifications improve mental health outcomes remains uncertain.

Nonetheless, public health initiatives promoting whole-food diets, such as the Mediterranean and Dietary Approaches to Stop Hypertension (DASH) diets, are being increasingly advocated as potential interventions for mental health improvement.⁹

Critiques and limitations of current research

Despite the growing body of evidence linking UPFs to mental health issues, there have been some limitations to the current research in the area. Many studies have been observational, making it difficult to establish causality.

While the associations between UPFs and mental health concerns are evident, it is unclear whether UPF consumption directly causes mental health disorders or if individuals with pre-existing depression and anxiety are more likely to consume these foods as a coping mechanism.⁹

Additionally, dietary studies often rely on self-reported food intake, which may be subject to recall bias.⁹

Other confounding factors, such as socioeconomic status, lifestyle habits, and genetic predisposition, may also influence mental health outcomes, indicating that more randomized controlled trials are needed to establish causal relationships between UPF consumption and mental health.^5,9

The Role of Fiber in Preventing Chronic Disease

Future directions

Emerging evidence strongly suggests a link between ultra-processed food consumption and mental health disorders such as depression and anxiety. Potential mechanisms, including gut-brain axis disruption, inflammation, blood sugar dysregulation, and artificial additives, provide plausible explanations for this association.

The current evidence indicates that future research should focus on elucidating the precise mechanisms by which UPFs impact mental health, incorporating advanced methodologies such as microbiome analysis, neuroimaging, and biomarker assessments.

Moreover, longitudinal studies with diverse populations will be essential in determining the long-term effects of UPF consumption on mental well-being, as well as establishing causality.

Public health policies aimed at reducing UPF consumption and promoting whole-food-based diets may play a critical role in improving mental health outcomes on a population level.

Increased education on nutrition and mental health, along with regulatory efforts to limit harmful food additives, could also contribute significantly to healthier dietary patterns and improved psychological well-being.

As global consumption of UPFs continues to rise, addressing their potential risks will be crucial for both public health and future research initiatives.

References

1. Monteiro, C. A., Cannon, G., Moubarac, J. C., Levy, R. B., Louzada, M. L. C., & Jaime, P. C. (2018). The UN Decade of Nutrition, the NOVA food classification and the trouble with ultra-processing. Public health nutrition, 21(1), 5–17. https://doi.org/10.1017/S1368980017000234
2. Lane, M. M., Gamage, E., Travica, N., Dissanayaka, T., Ashtree, D. N., Gauci, S., Lotfaliany, M., O'Neil, A., Jacka, F. N., & Marx, W. (2022). Ultra-Processed Food Consumption and Mental Health: A Systematic Review and Meta-Analysis of Observational Studies. Nutrients, 14(13), 2568. https://doi.org/10.3390/nu14132568
3. Zheng, L., Sun, J., Yu, X., & Zhang, D. (2020). Ultra-Processed Food Is Positively Associated With Depressive Symptoms Among United States Adults. Frontiers in nutrition, 7, 600449. https://doi.org/10.3389/fnut.2020.600449
4. Samuthpongtorn, C., Nguyen, L. H., Okereke, O. I., Wang, D. D., Song, M., Chan, A. T., & Mehta, R. S. (2023). Consumption of Ultraprocessed Food and Risk of Depression. JAMA network open, 6(9), e2334770. https://doi.org/10.1001/jamanetworkopen.2023.34770
5. Adjibade, M., Julia, C., Allès, B., Touvier, M., Lemogne, C., Srour, B., Hercberg, S., Galan, P., Assmann, K. E., & Kesse-Guyot, E. (2019). Prospective association between ultra-processed food consumption and incident depressive symptoms in the French NutriNet-Santé cohort. BMC Medicine, 17, 78. https://doi.org/10.1186/s12916-019-1312-y
6. Clapp, M., Aurora, N., Herrera, L., Bhatia, M., Wilen, E., & Wakefield, S. (2017). Gut Microbiota’s Effect on Mental Health: The Gut-Brain Axis. Clinics and Practice, 7(4), 987. https://doi.org/10.4081/cp.2017.987
7. Chen, Y., Xu, J., & Chen, Y. (2021). Regulation of Neurotransmitters by the Gut Microbiota and Effects on Cognition in Neurological Disorders. Nutrients, 13(6), 2099. https://doi.org/10.3390/nu13062099
8. Kiecolt-Glaser, J. K., Derry, H. M., & Fagundes, C. P. (2018). Inflammation: Depression Fans the Flames and Feasts on the Heat. American journal of psychiatry, 172(11), 1075–1091. https://doi.org/10.1176/appi.ajp.2015.15020152
9. Lassale, C., Batty, G. D., Baghdadli, A., Jacka, F., Sánchez-Villegas, A., Kivimäki, M., & Akbaraly, T. (2019). Healthy dietary indices and risk of depressive outcomes: a systematic review and meta-analysis of observational studies. Molecular psychiatry, 24(7), 965–986. https://doi.org/10.1038/s41380-018-0237-8

Further Reading

• All Nutrition Content
• The Role of Nutrition in Health
• What Are the Positive Health Effects of Eating Meat?
• What Are the Negative Health Effects of Eating Meat?
• Macrominerals and Trace Minerals in the Diet