Ultra Processed Food and Mental Health: What Research Says
An evidence-based review of current research examining associations between ultra-processed food consumption and mental health outcomes including depression and anxiety. This guide presents both the findings and their significant limitations.
Important Medical Disclaimer
This guide is for educational purposes only and is not mental health advice. Depression, anxiety, and other mental health conditions are complex disorders with genetic, neurological, psychological, and environmental components. Diet is not a primary cause of mental illness and dietary changes are not a substitute for professional mental health treatment. Always consult a psychiatrist, psychologist, or licensed therapist for mental health concerns.
If you or someone you know is in crisis, contact the 988 Suicide and Crisis Lifeline by calling or texting 988, available 24/7.
Introduction
Nutritional psychiatry is an emerging field examining how diet quality relates to mental health outcomes. Within this broader field, a smaller body of research has begun to investigate whether ultra-processed foods specifically may be associated with conditions such as depression and anxiety. This research is newer, less established, and more methodologically limited than the research linking UPFs to physical health outcomes such as cardiovascular disease or type 2 diabetes.
This guide presents what the current evidence shows and -- equally important -- what it does not show. Mental health is influenced by a vast array of factors including genetics, neurobiology, life experiences, trauma, social support, socioeconomic conditions, and access to care. Diet is, at most, one piece of a much larger picture.
For broader context on UPF research and physical health outcomes, see our comprehensive health effects guide.
A note on sensitivity: Mental health conditions carry significant stigma, and people experiencing depression or anxiety should never be made to feel that their condition is caused by their food choices. This guide is careful to present research findings without assigning blame or oversimplifying the complex causes of mental illness.
The Emerging Field of Nutritional Psychiatry
Nutritional psychiatry emerged as a recognized research discipline in the 2010s, driven largely by the work of researchers such as Felice Jacka at Deakin University in Australia. The field examines how overall dietary patterns -- not individual nutrients or foods -- relate to mental health outcomes. This is an important distinction: the research that has gained the most scientific credibility studies whole-diet quality, not specific food categories or additives.
The SMILES Trial (Jacka et al., BMC Medicine, 2017)
Design: Randomized controlled trial, 67 participants with moderate-to-severe depression
Intervention: 12 weeks of dietary counseling toward a Mediterranean-style diet versus social support control
Result: The dietary intervention group showed significantly greater improvement in depression symptoms; 32% achieved remission versus 8% in the control group
Critical context: This trial studied overall diet quality improvement, not UPF reduction specifically. The sample was small (n=67), the intervention was short-term (12 weeks), and all participants continued their existing mental health treatment throughout
The SMILES trial is significant because it was one of the first randomized controlled trials to demonstrate that dietary improvement could benefit depression symptoms when added to standard treatment. However, it does not tell us whether ultra-processed foods specifically played a role -- the intervention focused on increasing fruits, vegetables, whole grains, legumes, fish, and olive oil, rather than on reducing or eliminating any particular food category.
The Gut-Brain Axis
A key area of investigation in nutritional psychiatry is the gut-brain axis: the bidirectional communication system between the gastrointestinal tract and the central nervous system. The gut microbiome produces neurotransmitters including approximately 90-95% of the body's serotonin and significant quantities of gamma-aminobutyric acid (GABA), both of which play roles in mood regulation.
Research on the gut-brain axis provides a plausible biological pathway through which diet could influence mental health. However, the specific chain from UPF consumption to gut microbiome disruption to altered neurotransmitter production to clinical depression has not been demonstrated in human studies. Most evidence for additive-driven microbiome disruption comes from animal models. For more on how UPFs may affect gut health, see our gut health guide.
Key takeaway: Nutritional psychiatry has established that overall diet quality is associated with mental health outcomes, and the SMILES trial provided preliminary randomized evidence for dietary intervention in depression. But the leap from “diet quality matters” to “ultra-processed foods harm mental health” involves assumptions that have not yet been validated by rigorous research.
UPF-Specific Mental Health Research
A growing number of observational studies have specifically examined associations between ultra-processed food consumption and mental health outcomes. The following are among the most cited. Each is presented with its methodology and its limitations, because understanding the limitations is as important as understanding the findings.
Adjibade et al. (European Journal of Nutrition, 2019)
Cohort: 26,730 French adults from the NutriNet-Santé study
Finding: Higher UPF consumption was associated with increased risk of depressive symptoms
Limitations: Cross-sectional design makes it impossible to determine temporal direction; self-reported dietary data; French population may not generalize globally
Gomez-Donoso et al. (European Journal of Nutrition, 2020)
Cohort: 14,907 Spanish university graduates from the SUN cohort, followed for a median of 10.3 years
Finding: Participants in the highest quartile of UPF consumption had a higher risk of developing depression compared to those in the lowest quartile
Limitations: Observational design; participants were predominantly young, educated, and health-conscious, limiting generalizability; self-reported depression diagnosis
Lane et al. (BMJ, 2024)
Design: Umbrella review of 45 meta-analyses covering nearly 10 million participants across multiple health outcomes
Mental health finding: Higher UPF exposure was associated with adverse mental health outcomes including depression and anxiety, rated as “highly suggestive” evidence
Limitations: An umbrella review inherits the limitations of the underlying studies, nearly all of which were observational; “highly suggestive” is not equivalent to “convincing” or “causal”
Zheng et al. (Journal of Affective Disorders, 2020)
Design: Meta-analysis of observational studies examining dietary patterns and depression risk
Finding: Dietary patterns characterized by high consumption of processed foods, refined grains, and sweets were associated with increased depression risk, while fruit- and vegetable-rich patterns were associated with lower risk
Limitations: This studied dietary patterns broadly, not NOVA-classified UPFs specifically; heterogeneity across studies was high; self-reported dietary and depression data
Samuthpongtorn et al. (JAMA Network Open, 2023)
Cohort: 31,712 women from the Nurses' Health Study II, followed from 2003 to 2017
Finding: Higher UPF intake was associated with increased risk of depression; artificially sweetened beverages and artificial sweeteners specifically showed associations
Limitations: Women-only population of health professionals; observational design; dietary assessment at limited time points may not capture changing consumption patterns
Research Summary
The following table summarizes key studies examining UPF consumption and mental health outcomes. Evidence levels reflect the strength of the study design and findings, not the certainty of a causal relationship.
| Study | Year | Participants | Mental Health Outcome | Finding | Evidence Level |
|---|---|---|---|---|---|
| Adjibade et al. | 2019 | 26,730 | Depressive symptoms | Association between higher UPF intake and depressive symptoms | Moderate |
| Gomez-Donoso et al. | 2020 | 14,907 | Depression risk | Higher UPF quartile associated with higher depression risk over 10 years | Moderate |
| Zheng et al. | 2020 | Multiple cohorts | Depression | Processed food dietary patterns associated with increased depression risk | Preliminary |
| Samuthpongtorn et al. | 2023 | 31,712 | Depression risk | Higher UPF intake associated with increased depression risk; artificial sweeteners implicated | Moderate |
| Lane et al. (BMJ) | 2024 | ~10 million (pooled) | Depression and anxiety | Dose-response relationship; “highly suggestive” evidence grade for mental health outcomes | Strong |
| Jacka et al. (SMILES) | 2017 | 67 | Depression (RCT) | Dietary improvement improved depression symptoms; studied diet quality, not UPFs specifically | Moderate |
Reading this table: “Strong” evidence reflects methodological rigor and consistency across multiple studies, not proof of causation. Even the strongest observational evidence cannot establish that UPFs cause mental health disorders. “Moderate” indicates well-conducted studies with meaningful limitations. “Preliminary” indicates early-stage findings requiring substantial replication.
Potential Mechanisms Under Investigation
Researchers have proposed several pathways through which ultra-processed food consumption could theoretically influence mental health. Each of these mechanisms is supported by varying degrees of evidence, and none has been conclusively demonstrated in humans as a pathway from UPF consumption to clinical mental health disorders.
1. Gut-Brain Axis Disruption
Some food additives commonly found in ultra-processed foods -- particularly emulsifiers such as polysorbate 80 and carboxymethylcellulose -- have been shown to alter gut microbiome composition in animal models. Because the gut microbiome produces neurotransmitters including serotonin and GABA, which are involved in mood regulation, disruption of gut bacteria could theoretically affect brain chemistry. However, the evidence for this specific chain in humans remains limited and largely extrapolated from animal research.
Evidence level: Plausible biological pathway; strong animal model evidence; limited direct human evidence linking UPF additives to gut-brain-mediated mood changes.
2. Systemic Inflammation
Several studies have found associations between high UPF consumption and elevated markers of systemic inflammation, including C-reactive protein (CRP) and interleukin-6 (IL-6). Separately, a body of research has linked chronic low-grade inflammation to depression -- sometimes called the “inflammatory hypothesis of depression.” The proposed connection is that UPFs may promote inflammation, which in turn may contribute to depressive symptoms. However, these are two separate bodies of research that have not been directly connected in a single causal chain.
Evidence level: Each link in the chain (UPF-inflammation and inflammation-depression) has moderate evidence; the full chain from UPF to depression via inflammation has not been demonstrated.
3. Blood Sugar Fluctuations
Many ultra-processed foods have high glycemic indices, causing rapid blood sugar spikes followed by crashes. These fluctuations can acutely affect mood, energy, and cognitive function. Some research has found associations between high glycemic diets and increased risk of depression, though the relationship is not straightforward. Blood sugar effects are also highly individual and depend on factors including insulin sensitivity, meal composition, and timing.
Evidence level: Well-established that blood sugar affects short-term mood; less established as a pathway to clinical depression.
4. Nutrient Displacement
Diets high in ultra-processed foods tend to be lower in nutrients that are important for brain health, including omega-3 fatty acids, folate, zinc, magnesium, and B vitamins. These nutrients play documented roles in neurotransmitter synthesis and brain function. A diet dominated by UPFs may leave less room for nutrient-dense whole foods that provide these compounds. This displacement mechanism does not require UPFs to be directly harmful -- the issue is what nutrients are missing rather than what additives are present.
Evidence level: Well-supported by nutritional analysis; individual nutrient deficiencies have established links to mental health; less clear whether UPF-driven displacement specifically accounts for observed associations.
5. Reverse Causation
This is not a mechanism by which UPFs affect mental health -- it is a confounding factor that may explain the observed associations. People experiencing depression may eat more ultra-processed foods due to reduced motivation to cook, seeking comfort in palatable foods, or having less energy for food preparation. This means the association could run in the opposite direction: depression leads to higher UPF consumption, rather than UPF consumption leading to depression. This possibility is so significant that it warrants its own section below.
Evidence level: Well-established that depression changes eating behavior; this alternative explanation has not been adequately ruled out in most UPF-mental health studies.
The Reverse Causation Problem
Why this section matters: Reverse causation is the single most important limitation in research on UPFs and mental health. Without understanding this issue, it is easy to misinterpret the research as showing that ultra-processed foods cause depression, which is not what the current evidence supports.
Depression and anxiety fundamentally change how people eat. These changes are well-documented in clinical literature and include:
How Depression Affects Eating
- Reduced motivation and energy to shop for groceries and prepare meals
- Seeking comfort in highly palatable foods (often ultra-processed)
- Loss of interest in cooking or meal planning
- Changes in appetite -- both increased and decreased eating
- Disrupted daily routines that support regular, balanced meals
How Anxiety Affects Eating
- Stress eating and reaching for convenient, palatable foods
- Disrupted meal patterns and irregular eating
- Difficulty concentrating on meal preparation
- Gastrointestinal distress that limits food choices
- Using food as a coping mechanism for emotional regulation
When an observational study finds that people who eat more ultra-processed foods have higher rates of depression, there are at least three possible explanations:
UPF consumption contributes to depression (the commonly assumed direction)
Depression leads to increased UPF consumption (reverse causation)
Both directions operate simultaneously, creating a reinforcing cycle
Observational studies -- no matter how large or well-conducted -- cannot distinguish between these explanations. Only randomized controlled trials, which assign participants to specific dietary conditions before mental health outcomes develop, can address the direction of causation.
The SMILES trial (discussed above) is the closest available evidence, and it tested overall diet quality improvement in people already experiencing depression -- not UPF reduction in a general population. Its sample size was small (n=67), the intervention was short (12 weeks), and it cannot tell us whether UPFs specifically contributed to depression onset. No randomized controlled trial has specifically tested whether reducing ultra-processed food consumption prevents or improves depression or anxiety.
Bottom line: Until randomized controlled trials specifically test UPF reduction and mental health outcomes, the direction of the observed association remains genuinely uncertain. It would be irresponsible to tell someone that ultra-processed foods caused their depression when the evidence does not support that conclusion.
What Current Evidence Does Not Support
Given the sensitive nature of mental health and the significant limitations of current research, it is important to be explicit about claims that are not supported by the evidence, even if such claims appear in media coverage or popular discussion.
That diet causes depression or anxiety
Depression and anxiety are complex conditions with genetic, neurobiological, psychological, and social causes. No credible research claims that diet is a primary cause of clinical depression or anxiety disorders.
That changing diet alone can treat clinical depression
Evidence-based treatments for depression include psychotherapy (such as cognitive behavioral therapy and interpersonal therapy), medication, and structured interventions. Even the SMILES trial -- which showed dietary benefits -- was conducted alongside continued standard treatment, not as a replacement for it.
That UPFs are a primary driver of the mental health crisis
Rising rates of mental health conditions are driven by many factors including social isolation, economic stress, social media, reduced access to mental health care, and the lasting effects of the COVID-19 pandemic. Attributing the mental health crisis to food choices oversimplifies a complex societal issue.
That everyone who eats UPFs will develop mental health problems
The majority of people consume ultra-processed foods regularly without developing depression or anxiety. Population-level statistical associations do not predict individual outcomes. Many factors contribute to mental health resilience and vulnerability.
That dietary changes should replace medication or therapy
Stopping prescribed psychiatric medication or discontinuing therapy in favor of dietary changes could be dangerous. Any changes to mental health treatment should only be made under the guidance of a qualified mental health professional.
Practical Perspective
Given the significant limitations of the current research, what practical conclusions can be drawn? The answer requires holding two things in balance: the research shows consistent associations that should not be dismissed, but the evidence does not justify making mental health claims about food choices.
Evidence-Based Approaches to Mental Health
The following interventions have the strongest evidence base for improving mental health outcomes. Diet quality may complement these approaches but should not replace them:
Psychotherapy
Cognitive behavioral therapy (CBT), interpersonal therapy (IPT), and other evidence-based psychotherapies have strong research support for treating depression and anxiety.
Medication
Antidepressants and anti-anxiety medications prescribed by a psychiatrist or other qualified provider have demonstrated efficacy in large clinical trials.
Physical Activity
Regular exercise has consistent evidence for reducing symptoms of depression and anxiety, with effect sizes comparable to medication in some studies.
Social Connection
Strong social relationships and community involvement are consistently associated with better mental health outcomes across populations.
Where Diet Fits In
Diet quality may function as a complementary factor in mental health -- one that supports overall well-being alongside primary interventions. If you are interested in exploring how dietary changes might support your mental health, consider the following:
Work with your mental health provider first. Discuss any interest in dietary approaches with your psychiatrist, psychologist, or therapist before making changes.
Consider consulting a registered dietitian who can work alongside your mental health provider to develop a dietary approach tailored to your needs and circumstances.
Mediterranean-style dietary patterns have the most evidence for mental health benefits. This means emphasizing fruits, vegetables, whole grains, legumes, fish, and olive oil -- not obsessing over eliminating specific foods.
Reducing UPFs may improve overall diet quality, which could have secondary benefits for well-being. Our guides on reducing ultra-processed food, food swaps, and meal planning offer practical strategies.
No specific food or additive has been identified as a primary mental health risk factor. Avoid any claim that a single ingredient or product type is responsible for mental health problems.
If you are struggling with your mental health: Please reach out to a qualified professional. Evidence-based treatment works, and you deserve support that goes far beyond dietary changes.
988 Suicide and Crisis Lifeline: Call or text 988, available 24/7.
Frequently Asked Questions
Can ultra-processed food cause depression?
Current research cannot establish that ultra-processed food causes depression. Several observational studies have found statistical associations between higher UPF consumption and increased risk of depressive symptoms, but observational studies cannot prove causation. Depression is a complex condition influenced by genetics, neurobiology, life events, social factors, and many other variables. The reverse causation problem -- where people experiencing depression may eat more UPFs rather than UPFs causing the depression -- has not been adequately resolved. No scientific body has stated that UPFs cause depression.
Should I change my diet to help with depression or anxiety?
Dietary changes should never replace evidence-based mental health treatment such as psychotherapy or medication prescribed by a qualified professional. If you are interested in how diet might complement your existing mental health treatment, discuss this with both your mental health provider and a registered dietitian. The SMILES trial (2017) showed that dietary improvement alongside standard treatment was associated with better depression outcomes, but this studied overall diet quality -- not UPF reduction specifically -- and involved professional dietary support.
What is the strongest evidence linking UPFs to mental health?
The BMJ umbrella review by Lane et al. (2024) rated the evidence linking UPF consumption to common mental health disorders (depression and anxiety) as "highly suggestive" -- the second-highest evidence grade. This was based on consistent associations across multiple large observational studies. However, "highly suggestive" still falls short of "convincing" and does not establish causation. No randomized controlled trial has specifically tested whether reducing UPF consumption improves mental health outcomes.
Does the gut-brain axis explain how food affects mental health?
The gut-brain axis is a real and well-documented bidirectional communication system between the gut and brain. Research has shown that gut bacteria produce neurotransmitters including serotonin and GABA, and that gut health can influence brain function. Some studies suggest that certain food additives may alter gut microbiome composition. However, the specific pathway from UPF consumption to gut microbiome changes to mental health outcomes has not been established in human studies. Most evidence for this pathway comes from animal models and in-vitro research. It remains a plausible hypothesis under active investigation.
Are there foods that are proven to improve mental health?
No single food has been proven to treat or prevent mental health conditions. However, several dietary patterns have been associated with lower rates of depression in observational studies, most notably the Mediterranean diet, which emphasizes fruits, vegetables, whole grains, legumes, fish, and olive oil. The SMILES trial (2017) provided randomized controlled trial evidence that a Mediterranean-style dietary intervention improved depression symptoms compared to social support alone. These findings relate to overall dietary patterns rather than individual foods, and dietary approaches should complement -- never replace -- professional mental health care.
Continue Learning
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UPF and Gut Health →
How ultra-processed food may affect your gut microbiome and what research says about the gut-brain connection
Reducing UPF →
Practical strategies for gradually reducing ultra-processed food in your diet with category-by-category swaps
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