Our study, which aimed to evaluate the association between major depressive episodes and diet quality in adults and older adults from Brazil in 2013 and 2019, found that major depressive episodes were associated with poorer diet quality. Individuals who experienced major depressive episodes averaged higher diet quality scores, regardless of the criterion used to define the exposure and the potential confounders included in the analysis.
Studies focusing on the association between mental health and food consumption have mostly treated food consumption as the exposure and mental health as the outcome. However, some investigations have evaluated the association between mental health and food consumption in the same direction as the analysis carried out here 12,22,23. For example, Quehl et al., analyzing a sample of female university students in Canada, observed that depressive symptoms were associated with a diet of low nutritional quality 12. Similarly, a study conducted by Cebrino and Portero de la Cruz, involving adults in Spain across three phases (2006, 2011/2012 and 2017), found that depressive symptoms were a risk factor for poor or moderate diet quality 22. On the other hand, Elstgeest et al. suggested a possible reverse causality in the association between depression and diet. They noted that the presence and history of depressive symptoms are associated with a less healthy diet, especially in men. However, according to the authors, further studies are needed to understand the gender differences in this relationship 23.
To better understand the relationship between mental health and diet quality, we analyzed the association of major depressive episodes with the consumption of specific food items used to create the diet quality score. This score is composed of food items linked to unhealthy diets (red meat, sugar-sweetened beverages and sweets) and healthy diets (beans, fruits, vegetables and milk). Regarding the food items linked to an unhealthy diet, we observed that individuals with major depressive episodes had a higher prevalence of regular consumption of sugar-sweetened beverages and sweets. These foods can be classified as comfort foods, which are high-calorie foods that evoke a sense of nostalgia. This nostalgic feeling can be tied to an individual’s personal memories (for example, condensed milk pudding that reminds them of a family member or an emotional relationship with another person) or a broader cultural connection (for example, a Brazilian living abroad who seeks Brazilian foods to emotionally connect with their homeland) 24.
Emotions are directly related to eating behavior. According to Oliveira et al., “the emotional state is responsible for the process of choosing foods, as well as the frequency and quantity of food that is consumed”. Poor mental health influences food consumption since food can be seen as a form of reward or a source of affection. In the case of people with anxiety, for example, obsessively eating high-calorie foods can represent an escape from unpleasant situations and this practice can lead to the emergence of NCDs, such as obesity 24.
Another explanation for the association between major depressive episodes and regular consumption of sweets and sugar-sweetened beverages observed in our study may be linked to the release of serotonin, commonly known as the “happiness hormone”. The consumption of high-calorie foods, particularly those rich in carbohydrates, sugar, salt, and fat, triggers the release of this hormone, creating an immediate sense of comfort and pleasure, and reducing stress. However, this effect is short-lived, which increases the likelihood of individuals repeatedly consuming high-calorie foods 26. Additionally, our results showed a negative association between major depressive episodes and the consumption of food items linked to a healthy diet in both 2013 and 2019. According to Cebrino and Portero de la Cruz, the lack of energy or enthusiasm to prepare or enjoy food, as well as a loss of appetite, can negatively influence diet quality among individuals with depressive symptoms 22.
Our study showed other important results that go beyond the relationship between mental health and food consumption. One of them was the increase in the prevalence of major depressive episodes between 2013 and 2019, independent of the criteria used to define such condition, a fact that may indicate an increase in the presence of depressive symptoms in the general population. It is important to emphasize that the study analyzed a pre-pandemic context and future studies will be important to verify how much the scenario of the COVID-19 pandemic may have contributed to changing the magnitude of the relationship between major depressive episodes and diet quality.
The study has strengths, such as the use of data from the PNS, a population-based survey with national coverage, representative of the Brazilian population, whose data were collected by trained and standardized personnel. Furthermore, two different criteria were used to define major depressive episodes and, independent the way we used to define this condition, it remained associated with diet quality, indicating a certain robustness in the association analyzed here.
On the other hand, our study has limitations. One of them is the cross-sectional design, which does not allow establishing a cause-and-effect relationship. Another limitation is the presence of possible recall bias in the questionnaire responses, given that both exposure and outcome were self-reported. Finally, in the case of secondary data analyses, the association may be biased by residual confounding caused by some important variables possibly associated with major depressive episodes and diet quality, not available in the PNS database. One of these potential variables is food insecurity, associated with both depressive symptoms and diet quality, not available in both editions of the survey.
In conclusion, major depressive episodes was associated with worse diet quality, especially due to the increased consumption of unhealthy foods, such as sugar-sweetened beverages and sweets, and the decreased consumption of foods considered healthy, such as beans, vegetables, fruits and milk. Considering that poor diet quality is an important risk factor for NCDs and mortality, public health measures are needed to prevent and help reducing the prevalence of depressive symptoms and other mental health disorders in the Brazilian population. In addition, longitudinal studies are needed to better elucidate the association between mental health problems and food consumption.