Huge study links ultra-processed foods to heightened depression risk

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Recent research published in the journal Clinical Nutrition reveals a significant link between high consumption of ultra-processed foods and an increased risk of developing depression. This study, conducted in Brazil, indicates that individuals adhering to diets rich in ultra-processed foods are more likely to experience depressive symptoms over time. These findings underscore the potential mental health risks associated with dietary patterns characterized by processed and convenience foods.

Depression, also known as major depressive disorder, is a common and serious mental health condition characterized by persistent feelings of sadness, hopelessness, and a lack of interest or pleasure in activities once enjoyed. It can also manifest through physical symptoms such as changes in sleep, appetite, energy levels, and concentration.

Depression affects millions of people worldwide and is a leading cause of disability. Its impact extends beyond the individual, affecting families and communities. Despite being a common condition, depression is complex and can result from a combination of genetic, biological, environmental, and psychological factors.

Ultra-processed foods are products that have been significantly altered from their original form through various industrial processes. These foods typically include ingredients like preservatives, sweeteners, artificial flavors, and colorants that are not found in the average kitchen. Examples of ultra-processed foods include sugary snacks, ready-to-eat meals, instant noodles, and sodas.

These products are designed to be convenient, affordable, and highly palatable, often making them an attractive option for busy consumers. However, their high content of added sugars, unhealthy fats, and sodium, combined with low nutritional value, has raised concerns about their impact on health.

Previous studies have shown that healthy, nutrient-dense diets are associated with a lower risk of depression. However, there was a lack of large-scale, prospective studies examining the impact of ultra-processed food consumption on depression, particularly in low- and middle-income countries like Brazil. By addressing this gap, the researchers aimed to provide more comprehensive evidence on how dietary patterns are related to mental health and to inform public health policies and dietary guidelines.

“I have been interested in exploring the relationship between health-related behaviors, particularly movement behaviors such as physical activity and sedentary behavior, and mental health-related outcomes since my undergraduate studies,” said study author André de Oliveira Werneck, a PhD candidate at the Center for Epidemiological Research in Nutrition and Health at the University of Sao Paulo.

Consequently, I have also been interested in understanding the link between diet and health-related behaviors. While there are various studies linking specific aspects of diet, such as higher sugar consumption or increased intake of healthy foods, as well as certain dietary patterns such as the Mediterranean diet or the inflammatory potential, the classification of foods based on their processing level and purpose (Nova classification) has introduced a new paradigm in the field.”

“Certainly, several characteristics of ultra-processed foods could be associated with the onset of depressive symptoms. Therefore, I became interested in investigating whether there is an association between ultra-processed foods and the incidence of depressive symptoms.”

The study utilized data from the NutriNet Brasil cohort, a large-scale research project designed to investigate dietary patterns and chronic diseases in Brazil. Participants were adults aged 18 and over from all Brazilian regions who agreed to complete periodic online questionnaires about their diet and health. Recruitment began in January 2020, utilizing various media channels and public spaces to attract participants.

Participants completed a series of baseline questionnaires that collected detailed information on sociodemographic characteristics, lifestyle factors (such as tobacco and alcohol use and physical activity), dietary habits, and self-reported health conditions. The dietary intake of participants was assessed using the Nova24h tool, a validated web-based dietary recall system that classifies foods according to the Nova food classification system.

This classification distinguishes between unprocessed or minimally processed foods, processed culinary ingredients, processed foods, and ultra-processed foods. Each participant’s dietary intake was measured twice, at the 6th and 12th month follow-ups, to establish a baseline for their consumption of ultra-processed foods.

Depressive symptoms were evaluated using the two-item Patient Health Questionnaire (PHQ-2) at the 14th-month follow-up. Participants without a prior diagnosis of depression who scored less than three points on the PHQ-2 were further assessed using the more detailed nine-item PHQ-9 every six months. This approach allowed the researchers to track the onset of depressive symptoms over time.

For their analysis, the researchers included participants who were free of depressive symptoms at baseline, had completed the dietary recalls, and had at least one follow-up assessment using the PHQ-9. The final sample consisted of 15,960 participants. The data were then analyzed to examine the relationship between the proportion of ultra-processed foods in the diet and the development of depressive symptoms.

The researchers found a clear association between high consumption of ultra-processed foods and the onset of depressive symptoms. Participants with the highest intake of ultra-processed foods had a greater risk of developing depressive symptoms compared to those with the lowest intake, even after adjusting for various potential confounders such as sociodemographic factors, lifestyle behaviors, and overall diet quality.

“The main findings were that the group of participants who most consumed ultra-processed foods had a 42% higher risk of developing depressive symptoms over time compared to the group with the lowest consumption,” Werneck told PsyPost.” Additionally, a 10% increase in the consumption of ultra-processed foods was associated with a 10% increase in the risk of developing depressive symptoms.”

In addition to analyzing data from the NutriNet Brasil cohort, the researchers conducted a systematic review and meta-analysis to provide a broader context for their findings. They systematically searched seven scientific databases for prospective cohort studies that examined the relationship between ultra-processed food consumption and the incidence of depressive symptoms or major depressive disorders among adults.

After screening the literature, they included six studies (including their own) that met their criteria. These studies varied in follow-up length and methods for assessing diet and depression but consistently found that higher consumption of ultra-processed foods was linked to an increased risk of depression.

By pooling data from these studies using a random-effects meta-analysis, the researchers were able to estimate a 32% higher risk of developing depressive symptoms for individuals with the highest intake of ultra-processed foods compared to those with the lowest intake. This meta-analysis reinforced the findings from the NutriNet Brasil cohort and highlighted the consistent association across different populations and study designs.

“It is worth noting that in additional analyses, we found that the association persisted (although reduced) even after adjusting for the nutritional profile of the diet and healthy foods (e.g., fiber content, saturated fat, added sugar, fruits, and vegetables), indicating that the higher risk associated with ultra-processed foods does not solely stem from their poorer nutritional composition,” Werneck explained.

“Considering the recent longitudinal studies, we were already expecting an association between ultra-processed food consumption and depressive symptoms, even though Brazil has a lower average consumption of ultra-processed foods compared to other countries such as the United States and the United Kingdom.”

“However, the fact that ultra-processed foods are associated even after adjustments for nutritional composition, as well as the consistency of all studies included in the systematic review showing an association between ultra-processed food consumption and depressive outcomes, highlights the importance of strategies focused on reducing the consumption of these foods.”

Despite its significant findings, the study has some limitations. The sample was non-probabilistic and predominantly included participants with higher socioeconomic status and internet access, potentially limiting the generalizability of the results. Additionally, dietary data were collected using self-reported recalls, which might be subject to recall bias and social desirability bias, where participants might underreport unhealthy food consumption.

“There are inherent limitations to any population-based study of this nature,” Werneck noted. “For instance, although we used two 24-hour dietary recalls to estimate ultra-processed food consumption, there may still be variation in actual consumption, as well as potential biases related to memory and social desirability.”

“Additionally, considering that this study and the studies included in the systematic review are observational, there may be a level of residual confounding, and causal inference needs to be made with caution. However, several factors such as consistency, plausibility, etc., suggest that the association could be causal.”

“The next step in the near future is to explore how movement behaviors (i.e. physical activity and sedentary behavior) could interact with the consumption of ultra-processed foods in the association with depressive symptoms, considering that they may share mechanisms. Additionally, we intend to investigate how increased consumption of ultra-processed foods could be associated with a higher risk for physical health in people with depressive disorders.”

“I would like to emphasize that I have a PhD scholarship from the São Paulo Research Foundation, which was crucial for the development of this research,” Werneck added. “Additionally, the NutriNet Brazil cohort receives funding from various organizations, including the Brazilian National Council for Scientific and Technological Development, the São Paulo Research Foundation, and UMANE.”

The study, “Adherence to the ultra-processed dietary pattern and risk of depressive outcomes: Findings from the NutriNet Brasil cohort study and an updated systematic review and meta-analysis,” was authored by André O. Werneck, Euridice M. Steele, Felipe M. Delpino, Melissa M. Lane, Wolfgang Marx, Felice N. Jacka, Brendon Stubbs, Mathilde Touvier, Bernard Srour, Maria LC. Louzada, Renata B. Levy, and Carlos A. Monteiro.

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