Abstract

Consumption of ultra-processed foods (UPFs) has become ubiquitous across all age groups globally. Given their relatively recent introduction, the long-term health effects of UPF consumption remain largely unknown. There has been a marked increase in mental health disorders, suggesting a potential relationship warranting investigation. This review evaluates existing literature on the relationship between UPF consumption and depression and anxiety. The review focuses on depression and anxiety outcomes across populations, regardless of age, gender or geography. Peer-reviewed studies were identified through academic databases and synthesised to examine the state of the evidence.

Large-scale analyses consistently demonstrate a dose-response relationship between UPF consumption and depression and anxiety with increased consumption resulting in increased symptom severity. It is hypothesised that primary biological pathways involve the gut-brain axis (GBA), including gut microbiota composition. The GBA may impact blood-brain barrier function, neural reward circuitry activation and multiple immune pathways, modulating systemic inflammation. However, research is largely limited to animal studies and remains in its infancy.

Important limitations include potential discrepancies in epidemiological research due to self-reporting biases, inconsistent UPF definitions through the NOVA system and unmeasured confounders such as participants’ health history, social circumstances and lifestyle factors. Despite consistent associations between UPF consumption and depression and anxiety symptoms, further research is required to establish causality in relationships and further elucidate underlying mechanisms. Randomised controlled trials would significantly advance knowledge in this area. Current evidence suggests that limiting UPF consumption and following established dietary guidelines may reduce depression and anxiety.

Introduction

Ultra-Processed Foods

Ultra-processed foods (UPFs) comprise over half of dietary energy in high-income countries like the USA, UK and Canada, and up to one third in middle income countries (Marino et al., 2021; Monteiro et al., 2019). Rising UPF consumption is associated with increased depression and anxiety, though causal relationships remain unclear (Lane et al., 2022).

The NOVA classification system categorises foods by processing degree: Group 1 includes unprocessed foods like fruits and vegetables; Group 2 covers minimally processed culinary ingredients like oils and spices; Group 3 includes processed foods like bread and cheese; and Group 4 encompasses ultra-processed foods containing colours, flavours, emulsifiers and other additives to enhance appeal (Whelan et al., 2024; Monteiro et al., 2019). NOVA 4 foods include ready-to-eat meals, sodas, pizzas and chips, made with industrial ingredients where whole foods are minimal or absent, resulting in calorie-dense products.

The Rise of Ultra-Processed Foods

UPF consumption has increased dramatically since the 1930s, representing a fundamental shift in global dietary patterns. Data from nationwide household surveys demonstrate this transformation: in Canada, UPFs increased from 24.4% of total purchased calories in 1940 to 54.9% in 2001, while in Brazil, the proportion rose from 18.7% in 1987 to 26.1% in 2003 (Monteiro et al., 2013). These rises are in part due to increased urbanisation, dual-income households and growing demand for convenient ready-to-eat alternatives to homemade meals (Kearney, 2010). Markets have responded accordingly, with an increased prevalence of ready to eat ultra-processed food options.

Current consumption patterns reveal significant demographic variations. Children and adolescents show the highest UPF intake (40-68% of caloric intake), while older adults consume 15-30% of their daily caloric intake through UPFs (Marino et al., 2021). Internationally, the United States and United Kingdom lead consumption, with UPFs comprising 64.6% and 65.4% of total daily calories in children’s diets respectively, while Italy shows the lowest consumption at approximately 10% (Pereira de Araújo et al., 2024). These intake patterns represent unique concerns regarding childhood development and consequential effects on healthy aging or lack thereof.

The Global Mental Health Crisis

Depression and anxiety disorders affect over 580 million people globally, with depression causing 280 million cases and anxiety affecting 301 million (World Health Organization, 2023). Both conditions disproportionately impact women and increased 25% during COVID-19 (World Health Organization, 2022). Depression involves persistent sadness and loss of interest, while anxiety features excessive worry and physical symptoms interfering with daily life (Mayo Clinic, 2023; American Psychiatric Association, 2023). These conditions have substantial economic costs and quality of life impacts, with the most severe cases resulting in death (Centers for Disease Control and Prevention, 2024).

Despite growing treatment efficacy, several barriers remain. Only 25% of those with anxiety receive care (World Health Organization, 2023). Structural obstacles prevent 32.3% from seeking care, while stigma and discrimination cause 90.2% of those needing treatment to decline services (Coêlho et al., 2021; Thornicroft, 2008). Social stigmatisation towards pharmacotherapy and talking therapy remains. Waitlists vary around the world, though commonly fail to address acute episodes of depression/anxiety, average referrals take 6-18 weeks in the UK (NHS, 2024). Lastly, despite their efficacy pharmacotherapy and talking therapies struggle to maintain user adherence and relapse is a common concern, with 20-47% of patients dropping out from therapy prior to any form of recovery (Fernandez et al., 2015). These limitations have prompted exploration of dietary interventions as sole or adjuvant treatments. This shift toward nutrition is supported by emerging research suggesting whole food diets, such as the Mediterranean diet, may reduce depression and anxiety symptoms (Jacka et al., 2017; Parletta et al., 2019) further establishing nutritional psychiatry as a legitimate therapeutic approach.

The Emerging Field of Nutritional Psychiatry

Nutritional psychiatry studies how dietary factors impact psychiatric disorders, focusing on prevention and management (Sarris, 2019). Beginning in the 1970s with neurotransmitter research, this field explores diet’s effects on mental health through biological processes including inflammation, oxidative stress and the gut-brain axis (Jacka, 2017; Marx et al., 2017).

Research demonstrates protective effects: Mediterranean-style diets rich in fruits and vegetables may reduce depression rates (Adan et al., 2019), while meta-analyses of 117,229 participants show whole food consumption significantly lowers incidence of depression (Marx et al., 2017). Conversely, ultra-processed foods containing multiple artificial additives and preservatives have been associated with increased depression risk through proposed mechanisms involving gut microbiome disruption, oxidative stress and inflammation (Lane et al., 2022).

Why Food Processing Matters Beyond Nutritional Content

Ultra-processed foods create distinct metabolic and physiological effects beyond their nutritional profile. UPFs can cause rapid glucose fluctuations leading to metabolic instability and insulin resistance (Levine & Ubbink, 2023; Tristan Asensi et al., 2023), while disrupting the composition of the gut microbiota (Cuevas-Sierra et al., 2021). Added emulsifiers, flavourings and colourings may contribute to chronic inflammation and intestinal permeability (Monteiro et al., 2019). These hyperpalatable foods promote overconsumption (~800kcal daily increase) and are associated with rises in obesity rates (Hamano et al., 2024), creating a cycle where metabolic dysfunction and poor physical health outcomes may negatively impact mental health, specifically depression and anxiety, through both psychological and gut-brain axis pathways (Lane et al., 2024).

Review Rationale and Objectives

This review explores the relationship between UPF consumption and depression and anxiety risk. While UPFs’ adverse physical health outcomes are well documented (Lane et al., 2024), their impact on mental health and underlying biological mechanisms remain unclear. Given rising UPF consumption alongside increasing depression and anxiety rates globally (Lux et al., 2023), this review examines epidemiological evidence, investigates biological pathways including the gut-brain axis, identifies susceptible populations and evaluates evidence quality. Understanding these diet-mental health connections could inform clinical practice and public health policy amid the current mental health crisis.

Main Body

Cross-Sectional Research

Cross-sectional research has associated high consumption of UPFs with increased risk for depression and anxiety. Seminal studies such as analyses of the US NHANES data (National Health and Nutrition Examination Survey) show that adults with the highest intake of UPFs were 80% more likely to experience mild symptoms of depression compared to those with the lowest intake (Hecht et al., 2022). Similar patterns have been observed in different countries worldwide, where higher UPF intake is linked to increased risk of depressive symptoms (Lane et al., 2022). Data from the NutriNet-Santé cohort, which includes over 100,000 participants, also linked high UPF intake with greater levels of psychological distress, including symptoms of depression and anxiety (Adjibade et al., 2019).

Consistent associations have been observed across different populations and study sizes, suggesting that the link between UPF consumption and poor mental health may be universal. According to a systematic review and meta-analysis that combined data from multiple studies, effect sizes for depression and anxiety typically range from 1.3 to 1.9, indicating moderate but meaningful increases in risk (Lane et al., 2022).

Despite their large cohort sizes and consistent findings, cross-sectional research cannot establish causality and fails to investigate biological mechanisms of action and is largely reliant on self-reported information, thus reducing reliability and general application of findings. There is an urgent need for randomised controlled trials to build upon cross-sectional research.

Longitudinal Research

Unlike cross-sectional research, longitudinal studies are able to track participant data on multiple occasions, potentially over long periods of time. A longitudinal study of over 30,000 participants followed participants over an average of 12.6 years and found that those with high UPF intake exhibited increased risk of mental disorders, including depressive and anxiety disorders (Yuan et al., 2025).

The longitudinal approach is effective in demonstrating how the participants’ psychological well-being evolved over time to provide stronger evidence for the causal relationship between UPF consumption and mental health. Key prospective cohort studies have found that UPF consumption increases mental health risk (Mazloomi et.al., 2022). With data from over 26 studies and 260,000 participants, this systematic review was able to link the consumption of UPFs with an increased risk of depression. Additionally, it was found that for every 10% increase in UPF consumption per daily calorie intake, 11% higher risk of depression was observed among adults (Mazloomi et. al., 2022). This proportional correlation suggests UPF intake may be causally related to depressive symptoms. The strong association and deleterious health impacts of excessive UPF consumption warrants research into the potential mechanisms of action (Scheine Canhada et al., 2024).

Dose-Response

Establishing a dose-response relationship in UPF consumption is essential from a public health standpoint to inform policymakers of the nuances in consumption and to what degree UPF consumption may or may not be safe. Epidemiological research suggests that those with the highest UPF consumption (≥6 UPF products per day) have the greatest risk of mental health complaints. However, there is limited research establishing an exact dose-response relationship within UPF consumption. UPF consumption has been shown to impact biological responses within the body and evidence suggests that participants in the highest UPF consumption categories are at greatest risk for depression with less being understood about anxiety (Wiss & LaFata, 2024). However, due to a lack of precision in dietary intake and recall, research is yet to associate specific UPFs with health outcomes and establish exact doses at which deleterious health effects occur. Future research is required to establish which UPFs are detrimental to mental health and at which doses. Without such data, public health information will suffer a lack of nuance and may lead to blanket policies which do little to improve health.

Research Limitations

Current research investigating UPF consumption and mental health faces significant methodological limitations that constrain definitive conclusions. The primary weakness is reliance on self-reported dietary assessments, which are prone to recall bias and measurement errors, leading to unreliable UPF consumption data (Gibson et al., 2017).

Inconsistent UPF definitions and classifications create another major challenge. Variations in how researchers categorise UPFs generate inconsistent dietary data across studies, compromising the reliability of findings (Cainzos Archirica et al., 2018). Without standardised definitions and validated assessment tools, studies may reach conflicting conclusions about UPF-mental health relationships.

Mental health measurement limitations compound these issues. Standardised questionnaires may fail to capture the full range and volatility of psychological symptoms, potentially missing important variations. Additionally, the predominant use of cross-sectional designs makes establishing causality difficult, as these studies cannot determine whether UPF consumption leads to mental health problems or whether individuals with mental health issues are more likely to consume UPFs.

Publication and reporting biases further complicate the evidence base. Research has highlighted substantial outcome reporting issues, with 40-62% of studies having at least one primary outcome changed, added or removed compared to original protocols (Dwan et al., 2013). A systematic review of randomised controlled trials found that statistically significant outcomes were 2.2 to 4.7 times more likely to be fully reported, suggesting selective reporting that may overestimate UPF-mental health associations (Dwan et al., 2013).

Complex confounding factors present additional challenges. Socioeconomic status, overall dietary patterns, lifestyle factors and pre-existing health conditions can influence both UPF consumption and mental health outcomes. Lack of control for these variables may lead to spurious associations or mask true relationships.

These limitations collectively undermine confidence in establishing causal links between UPF consumption and mental health disorders, particularly depression and anxiety. While observational studies suggest associations, measurement errors, confounding variables and potential reverse causation complicate interpretation. It remains unclear whether UPF consumption leads to mental health problems or whether individuals with mental health conditions are more likely to consume UPFs. Future research must address these limitations through improved measurement methods, standardised definitions, longitudinal study designs and comprehensive confounding control to advance understanding of this important public health relationship.

Biological Pathways – Inflammation

When the body experiences mechanical injury or infection, an inflammatory response is triggered to clear and control harmful stimuli through mechanisms such as phagocytosis by immune cells and recruitment of white blood cells to destroy pathogens (Fernandes-Alnemri et al., 2009). Although inflammation is protective and beneficial, excessive or chronic inflammatory responses can lead to tissue damage and disease by affecting multiple areas throughout the body (Lyman et al., 2013). Chronic low-grade inflammation disrupts homeostasis, contributing to the development of various non-communicable diseases (Hotamisligil, 2017).

UPF consumption promotes inflammation through multiple pathways. Metabolic and nutrient overload can trigger immune cell infiltration and secretion of pro-inflammatory cytokines into body tissues, impairing glucose uptake and altering lipid metabolism. Moreover, high UPF consumption leads to displacement of anti-inflammatory foods such as fruits and vegetables, which contain beneficial phytochemical compounds (Bahrampour et al., 2022; Neale, Batterham & Tapsell, 2016). Additionally, UPF consumption can cause deficiencies in anti-inflammatory micronutrients including essential vitamins and minerals (Hébert et al., 2018; Asensi et al., 2023).

Specific UPF components may directly promote inflammation. Sweeteners and emulsifiers used in UPFs can disrupt gut bacteria composition and damage the intestinal lining, allowing bacterial components to enter circulation and trigger systemic inflammation and metabolic dysfunction (Van Hul et al., 2024).

Systemic inflammation can subsequently lead to neuroinflammation, where elevated pro-inflammatory cytokines in the brain affect specific brain regions. Cytokines such as interferon-γ, interleukin-1β and tumour necrosis factor-α can activate enzymes that convert tryptophan to kynurenine metabolites, some of which may influence neurotransmitter systems (Shang et al., 2014). However, the relationship between kynurenine pathway activation and depression appears more complex than initially thought, with recent studies showing variable pathway activity in depression. These inflammatory processes may contribute to alterations in brain circuits involving limbic and prefrontal structures, potentially affecting vulnerability to anxiety and mood disorders. Research has primarily focused on animal models with distinct barriers preventing such research in humans such as access to neurological structures. It is therefore difficult to determine the level of cytokines circulating within the brain. Research is currently limited to investigating proxy markers through blood and urinary excretion.

Biological pathways – Gut-Brain Axis

The gut-brain axis represents a complex bidirectional communication network connecting the brain’s emotional and cognitive centres with intestinal function through neural, hormonal and immune pathways (Carabotti et al., 2015; Mayer et al., 2022). Central to this system is the gut microbiome, a diverse ecosystem predominantly composed of Bacteroidetes and Firmicutes phyla that plays essential roles in digestion, immune function and intestinal barrier integrity (Jandhyala et al., 2015; Spencer et al., 2019).

UPFs may disrupt this microbial ecosystem, depleting beneficial bacteria and inhibiting production of health-promoting microbial metabolites such as short-chain fatty acids (SCFAs) (Rondinella et al., 2025). These beneficial bacteria, including Lactobacillus and Bifidobacterium species, contribute to human mental health by synthesising GABA and serotonin, which are key neurotransmitters in mood and anxiety regulation (Bertollo et al., 2025) while helping modulate cortisol levels and hypothalamic-pituitary-adrenal (HPA) axis activation (Suganya & Koo, 2020).

Gamma-aminobutyric acid (GABA) acts as an inhibitory neurotransmitter in the brain, helping to calm neural activity, while serotonin is essential for mood stability and emotional regulation. Additionally, SCFAs such as butyrate are known to influence brain function by reducing neuroinflammation, particularly through the suppression of microglial activation, enhancing blood-brain barrier integrity and engaging vagal and immune signalling pathways (Caetano-Silva et al., 2023). This suggests a potential epigenetic mechanism through which butyrate may exert neuroprotective effects. Although much of the evidence comes from animal and in vitro studies, there is growing support for the relevance of these mechanisms in humans (Dinan & Cryan, 2017).

A reduction in gut microbiota diversity may underlie the negative mental health effects associated with UPF consumption, though human randomised controlled trials are limited. It has been hypothesised that this microbial imbalance may contribute to depression and anxiety development through reduced mood-stabilising neurotransmitter production and impaired stress response mechanisms (Ross, 2023). The gut-brain axis, therefore, represents a critical pathway through which dietary choices, particularly UPF consumption, influence mental health outcomes via alterations in gut microbiome composition and function.

Nutrient displacement and metabolism

Ultra-processed food consumption is associated with increased risk of metabolic dysfunction, including weight gain, elevated blood pressure, insulin resistance and type 2 diabetes (Costa de Miranda et al., 2021). Research indicates that individuals consuming high UPF diets demonstrated a 10% increased risk of developing type 2 diabetes and elevated fasting glucose compared to those following minimally processed diets (Almarshad et al., 2022). These metabolic alterations may have important implications for mental health outcomes.

A significant concern with UPF consumption is nutrient displacement, where these foods crowd out nutrient-dense options from the diet. High UPF diets are characterised by reduced intake of essential micronutrients including vitamins A, C, D, E, B-complex vitamins and minerals such as iron, phosphorus, magnesium, selenium, chromium and potassium (García-Blanco et al., 2023). This occurs because UPFs typically contain low levels of antioxidants, anti-inflammatory compounds, prebiotics, fibre, vitamins and minerals, while being high in sugar, refined ingredients and additives (Lutz et al., 2025). These nutrient deficiencies have particular relevance for brain health. Many displaced micronutrients play crucial roles in neurological function and their deficiency can negatively impact the gut microbiome and gut-brain axis, potentially contributing to neuroinflammation, oxidative stress and neurodegeneration (García-Blanco et al., 2023). For instance, inadequate B-vitamin status in older adults is associated with a 3.5-fold higher risk of accelerated cognitive decline (Hughes et al., 2017).

Magnesium and selenium exemplify the importance of brain-essential nutrients in maintaining central nervous system homeostasis. Magnesium functions as an N-methyl-D-aspartate (NMDA) receptor antagonist, preventing receptor overactivation, while selenium helps neutralise oxidative stress and supports mood regulation. NMDA receptors are essential for information processing in the central nervous system, and alterations in these receptors have been observed in depression, linked with disrupted glutamate homeostasis and neurotransmission (Daw et al., 1993). Deficiencies in magnesium and selenium are associated with depressive symptoms, and NMDA receptors have been therapeutically targeted in depression treatment studies (Wang et al., 2018).

The cumulative effect of nutrient displacement demonstrates measurable cognitive consequences, with one study showing 28% faster global cognitive decline and 25% faster executive function decline among high UPF consumers (Gonçalves et al., 2023). This evidence suggests that UPF-mental health relationships may be mediated by both what these foods contain and the essential nutrients they displace, creating a dual mechanism of potential harm through harmful additives and absence of protective nutrients.

However, further human randomised controlled trials are required to establish the long-term effects of nutrient displacement in UPF-heavy diets and to confirm the mechanistic pathways linking nutrient deficiencies to mental health outcomes observed in preclinical studies.

Processing effects and addictive-like properties

Emerging research suggests potential parallels between UPF consumption patterns and addictive behaviours. A Delphi consensus study involving 40 specialists identified similarities in behavioural patterns and neurobiological mechanisms between problematic UPF consumption and substance use disorders, though this remains an area of ongoing scientific debate (Unwin et al., 2025). While not formally recognised by the World Health Organization (WHO), some researchers propose UPF addiction as a distinct clinical phenomenon characterised by compulsive eating, loss of control and intense cravings involving altered neural reward pathways (Unwin et al., 2025). Prevalence estimates suggest approximately 20% of the population may experience problematic UPF consumption patterns, rising to 55% among individuals with diagnosed binge eating disorders (Praxedes et al., 2022).

The proposed mechanisms involve the dopaminergic reward system, which regulates key brain functions related to reward seeking and decision making (Düzel et al., 2009). Regular consumption of high-glycaemic UPFs may cause repeated dopamine pathway stimulation, potentially leading to receptor desensitisation and requiring increased stimulation for similar reward responses. However, evidence for these mechanisms comes primarily from animal studies, with human research remaining largely observational and subject to confounding variables such as stress and medication effects. The combination of rapid blood sugar fluctuations and reduced satiety signals may contribute to overconsumption patterns as individuals seek maintained food satisfaction (Wiss and LaFata, 2024).

In restrictive eating disorders such as anorexia nervosa, neural responses to UPFs may become heightened, intensifying cravings. One study found UPFs comprised 100% of binge episodes in this population (Ayton et al., 2021), potentially creating restriction-overconsumption cycles accompanied by guilt and psychological distress.

Neuroimaging studies reveal that viewing high-calorie UPF images increases activity in brain regions associated with reward processing, craving and impulse control, with decreased response inhibition particularly in fasted states (Pursey et al., 2024). Epidemiologically, studies demonstrate correlations between UPF consumption and internalising symptoms including anxiety, depression and social withdrawal, with each 10% increase in UPF consumption associated with an 11% higher depression risk (Mazloomi et al., 2022).

While these findings suggest important relationships between UPF consumption and neurobiological responses, further research is needed to establish causality and develop clearer diagnostic criteria for problematic consumption patterns. The high societal reliance on UPFs and limited understanding of underlying biological mechanisms necessitate cautious implementation of interventions. Future research should focus on rigorous human studies to validate mechanisms observed in animal models and develop evidence-based approaches for addressing problematic UPF consumption patterns.

Conclusion

Epidemiological evidence consistently demonstrates significant associations between increased UPF consumption and mental health outcomes, particularly depression and anxiety. Cross-sectional studies across diverse populations, including analyses of US NHANES data and the NutriNet-Santé cohort involving over 100,000 participants, show that individuals with the highest UPF intake are 80% more likely to experience depressive symptoms compared to those with the lowest intake. Longitudinal studies provide stronger evidence for temporal relationships, with research following over 30,000 participants for an average of 12.6 years demonstrating increased risk of mental disorders among high UPF consumers. Meta-analyses combining data from 26 studies and 260,000 participants reveal effect sizes ranging from 1.3 to 1.9, indicating moderate but clinically meaningful increases in risk. The dose-response relationship is particularly compelling, with each 10% increase in UPF consumption associated with an 11% higher depression risk, suggesting a potentially causal relationship.

Four primary biological mechanisms explain the observed associations between UPF consumption and mental health disorders. First, inflammatory pathways show that UPF consumption promotes chronic low-grade inflammation through metabolic overload, nutrient displacement and direct effects of food additives like emulsifiers and sweeteners. This systemic inflammation can lead to neuroinflammation, affecting brain circuits involving limbic and prefrontal structures. Second, the gut-brain axis demonstrates that UPFs disrupt beneficial bacteria including Lactobacillus and Bifidobacterium species, which produce mood-regulating neurotransmitters like GABA and serotonin, while reducing production of neuroprotective short-chain fatty acids. Third, metabolic effects and nutrient displacement show that UPFs may crowd out essential micronutrients crucial for neurological function, with deficiencies in vitamins and minerals like magnesium and selenium affecting NMDA receptor function and neurotransmitter systems. Fourth, processing effects suggest potential addictive-like properties through dopaminergic reward system activation, though this mechanism requires further validation in human studies.

The associations between UPF consumption and mental health demonstrate clinical significance going beyond statistical significance. Effect sizes of 1.3 to 1.9 for depression and anxiety represent meaningful increases in risk that warrant clinical attention. The 10% increased risk of type 2 diabetes among high UPF consumers, combined with the established links between metabolic dysfunction and mental health, suggests substantial clinical implications. Studies showing 28% faster global cognitive decline and 25% faster executive function decline among high UPF consumers indicate measurable functional consequences that may spill over into mental health. With prevalence estimates suggesting 20% of the population may experience problematic UPF consumption patterns, rising to 55% among individuals with binge eating disorders, these findings represent a significant public health concern affecting millions of individuals globally.

Certain populations demonstrate heightened vulnerability to UPF-related mental health effects. Individuals with existing eating disorders show particular susceptibility, with UPFs comprising 100% of binge episodes in anorexia nervosa populations, creating destructive restriction-overconsumption cycles. Socioeconomic disparities in UPF access compound these effects as ultra-processed foods are often more affordable and accessible than nutrient-dense alternatives, disproportionately affecting low-income populations who already face higher rates of mental health disorders. Effects on the gut microbiota may be particularly pronounced in populations with pre-existing microbiome disruption, while the addictive-like properties may pose greater risks for individuals with substance use vulnerabilities. These disparities highlight important health equity implications requiring targeted interventions for high-risk groups.

Limitations

Several significant limitations constrain confidence in establishing definitive causal relationships. The primary weakness is reliance on self-reported dietary assessments prone to recall bias and measurement errors. Inconsistent UPF definitions and classifications across studies compromise finding reliability, while standardised questionnaires may fail to capture the full range of psychological symptoms. The predominant use of cross-sectional designs limits causal inference and publication bias analysis reveals that 40-62% of studies had primary outcomes changed compared to original protocols, with statistically significant results 2.2 to 4.7 times more likely to be fully reported. Complex confounding factors including socioeconomic status, lifestyle factors and pre-existing health conditions further complicate interpretation. The possibility of reverse causation that individuals with mental health conditions may be more likely to consume UPFs remains inadequately addressed in current research.

Public Health Implications

These findings have profound public health implications requiring comprehensive policy responses. Dietary guidelines should explicitly address UPF consumption levels, moving beyond traditional nutrient-focused recommendations to consider food processing as a key determinant of diet quality. Policy interventions might include front-of-package labelling identifying UPFs, taxation strategies similar to those implemented for sugar-sweetened beverages and restrictions on marketing ultra-processed products to vulnerable populations, particularly children. Food environment modifications are essential, including improving access to minimally processed foods in low-income areas and institutional settings. Population-level prevention strategies should focus on reducing UPF availability while simultaneously increasing access to affordable, nutritious whole foods. The dose-response relationship suggesting 11% increased depression risk per 10% increase in UPF consumption provides clear targets for public health interventions.

Healthcare providers should integrate dietary assessment into routine mental health care, specifically screening for UPF consumption patterns among patients with depression and anxiety. Clinical practice guidelines may consider incorporating evidence-based recommendations about UPF reduction as an adjunctive treatment approach. Mental health professionals require training to recognise the potential addictive-like properties of UPFs and their role in treatment-resistant cases. Multidisciplinary care models incorporating registered dietitians specialised in mental health nutrition could enhance treatment outcomes. Patient education should emphasise the dual mechanism of harm both the presence of harmful additives and the absence of protective nutrients while providing practical strategies for UPF reduction. The identification of vulnerable populations necessitates targeted screening and intervention approaches, particularly for individuals with eating disorders or those experiencing socioeconomic disadvantage.

Future Research

Critical research gaps require urgent attention to advance understanding and clinical applications. Randomised controlled trials investigating UPF reduction interventions for depression and anxiety treatment are essential to establish causality and therapeutic efficacy. Mechanistic research should focus on validating animal model findings in human populations, particularly regarding dopaminergic reward system alterations, gut-brain axis disruption and gut microbiota composition. Longitudinal studies with standardised UPF definitions and validated assessment tools are needed to address current methodological limitations. Dose-response research should identify specific UPF categories most harmful to mental health and establish safe consumption thresholds. Biomarker development for UPF-related neuroinflammation and microbiome disruption could provide objective outcome measures. Research addressing health equity implications and developing culturally appropriate interventions for diverse populations represents another critical priority. Finally, implementation research evaluating the effectiveness and feasibility of UPF-focused mental health interventions in real-world clinical settings is essential for translating evidence into practice.

The convergence of epidemiological evidence, plausible biological mechanisms and substantial public health implications establishes UPF consumption as an important modifiable risk factor for depression and anxiety. While methodological limitations require cautious interpretation, the consistency of findings across diverse populations and study designs, combined with clear dose-response relationships, provides compelling evidence for action. Addressing UPF consumption represents a promising avenue for both preventing and treating mental health disorders, while simultaneously addressing broader public health concerns including obesity, diabetes and cardiovascular disease. The dual mechanism of harm through harmful additives and nutrient displacement offers multiple intervention targets, making this a particularly attractive area for comprehensive public health action.

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The Impact of Ultra-Processed Foods on Depression and Anxiety: A Literature Review