Large study links ultra-processed foods to increased risk of depression

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 who eat a diet high in ultra-processed foods are more likely to experience depressive symptoms over time. These findings highlight the potential mental health risks associated with diets characterized by processed and convenience foods.

Depression, also known as major depressive disorder, is a common and serious mental health problem characterized by persistent feelings of sadness, hopelessness, and a lack of interest or pleasure in activities once enjoyed. It can also manifest as 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 and touches families and communities. Although a common illness, depression is complex and can result from a combination of genetic, biological, environmental and psychological factors.

Ultra-processed foods are products whose original form has been significantly altered by various industrial processes. These foods usually contain ingredients such as preservatives, sweeteners, artificial flavors and colors 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 very tasty, often making them an attractive option for busy consumers. However, their high content of added sugars, unhealthy fats and sodium, combined with their low nutritional value, has raised concerns about their impact on health.

Previous studies have shown that a healthy, nutrient-rich diet is 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 filling this gap, researchers sought to provide more comprehensive evidence on how dietary habits are linked 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 cycle,” said study author André de Oliveira Werneck, a doctoral student at the Center for Epidemiological Research in Nutrition and Health at the University of Sao Paulo.

Therefore, I was also interested in understanding the connection between diet and health-related behaviors. Although there are various studies linking specific aspects of diet, such as higher sugar intake or increased consumption of healthy foods, as well as certain dietary patterns like the Mediterranean diet or inflammatory potential, food classification depending on their level of transformation and their destination (Nova Classification) introduced a new paradigm in the field.

“Certainly, several characteristics of ultra-processed foods could be associated with the appearance of depressive symptoms. Therefore, I was interested in determining whether there was an association between ultra-processed foods and the incidence of depressive symptoms.

The study used data from the NutriNet Brasil cohort, a large-scale research project designed to study dietary habits and chronic diseases in Brazil. Participants were adults aged 18 and over from all regions of Brazil who agreed to periodically complete online questionnaires about their diet and health. Recruitment began in January 2020, using 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 consumption and physical activity), dietary habits and self-reported health problems. Participants’ dietary intake 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 assessed using the two-item Patient Health Questionnaire (PHQ-2) at 14-month follow-up. Participants without a prior diagnosis of depression and scoring 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 researchers to track the onset of depressive symptoms over time.

For their analysis, the researchers included participants who had no depressive symptoms at baseline, who completed the dietary recalls, and who 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.

Researchers found a clear association between high consumption of ultra-processed foods and the onset of depressive symptoms. Participants with the highest consumption of ultra-processed foods had a higher risk of developing depressive symptoms than those with the lowest consumption, even after adjusting for various potential confounders such as sociodemographic factors, behavioral linked to lifestyle and overall diet quality.

“The main findings were that the group of participants who consumed the most ultra-processed foods had a 42% higher risk of developing depressive symptoms over time compared to the group with the lowest consumption,” said Werneck at PsyPost. Additionally, a 10% increase in 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 broader context for their findings. They systematically searched seven scientific databases for prospective cohort studies examining the relationship between consumption of ultra-processed foods and the incidence of depressive symptoms or major depressive disorder in adults.

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

By pooling the 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 consuming the most ultra-processed foods per compared to those who consumed the least. This meta-analysis reinforced the results of the NutriNet Brasil cohort and highlighted the consistent association between different populations and study designs.

“Of note, in additional analyzes 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 come solely from their lower nutritional composition,” Werneck explained.

“Given recent longitudinal studies, we already expected an association between consumption of ultra-processed foods and depressive symptoms, even though Brazil has a lower average consumption of ultra-processed foods than other countries like 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 consumption of ultra-processed foods and depressive effects, highlight the importance of strategies focused on reducing the consumption of these foods.

Despite its important results, the study has some limitations. The sample was non-probability and included primarily 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 could be subject to recall bias and social desirability bias, as participants may underestimate their intake of unhealthy foods.

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

“Additionally, because this study and the studies included in the systematic review are observational, there may be a level of residual confounding, and causal inference should 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 will be to explore how movement behaviors (i.e. physical activity and sedentary behavior) might interact with consumption of ultra-processed foods in association with depressive symptoms , considering that they can share mechanisms. In addition,…