Mental health disorders are increasingly recognized as leading causes of disease burden with a lifetime prevalence of around 30 % (WHO Team, 2017). Depression and anxiety are labelled common mental disorders because of their high prevalence worldwide, with 6 % and 10 % affecting the Brazilian population, respectively (WHO Team, 2017) and contribute to greater disability-adjusted life years (DALYs) as compared to other mental disorders (GBD Mental Disorders Collaborators, 2022). Women and adults are the most affected by these common disorders. The Lancet Commission on Global Mental Health and Sustainable Development (GBD Mental Disorders Collaborators, 2022) emphasizes mental health as an essential right and crucial to all countries' development. Thus, the Commission called for more investment in mental health studies for the development of successful strategies to prevent these disorders and better integration of these strategies as part of the universal health priorities (GBD Mental Disorders Collaborators, 2022). Dietary behaviours play a major role in the prevention of these common disorders.

The International Society for Nutrition Psychiatry Research recommended dietary factors as promising modifiable targets for the prevention and treatment of common mental disorders (Sarris et al., 2015). Anti-inflammatory dietary patterns have been perceived to have benefits in multiple aspects of mental health (Sofi et al., 2010; Willett et al., 1995). This dietary pattern is rich in key nutrients, such as monounsaturated fatty acids (olive oil), polyunsaturated fatty acids (fish, nuts), dietary fibre (grains, vegetables, fruits, legumes), polyphenols (wine, extra virgin oil, fruit, vegetables), vitamins (A, D, E, folic acid, vitamin B12), and minerals (potassium, calcium, phosphorus, magnesium), which could explain the mental health benefits (Estruch and Camafort, 2015).

Meta-analyses of cross-sectional and longitudinal observational studies have shown that a pro-inflammatory diet (e.g., red and processed meats, white bread and rice, and sweets and desserts) was associated with mental health disorders (Tolkien et al., 2019). Similarly, another review showed that a higher diet quality, known as a healthy/prudent diet (i.e., fruits and vegetables, fish, and whole grains), was associated with reduced risk for having these common mental disorders (Molendijk et al., 2018). There are benefits to analyzing dietary patterns to verify the potential synergistic effect of different food groups. Nevertheless, there are some limitations to analyzing dietary patterns. The main disadvantages are (i) if the total effect of the diet quality on these mental disorders is because of a specific food group, then this effect would be attenuated, and (ii) although individuals may have similar values of diet quality, it does not necessarily mean that the combination and amounts of food groups consumed are the same. Thus, it is not known if this association between diet quality and mental disorders results from all components or if it is driven by one or a few key food groups within the total value (Gibson-Smith et al., 2020). Previous studies on isolated food groups have shown mixed results. For instance, high fish, fruit/vegetables, and fibre intake were associated with positive effects on mental health disorders. However, analyzing individual food groups has limitations as the effect of these individual components is investigated without considering the complexity of a whole diet pattern (McNaughton, 2020). Certain food group consumption is frequently correlated. Therefore, should be of interest to understand which component(s) of the diet, if any, has the largest association with common mental health disorders both individual and in combination with other dietary components.

Although previous studies were mostly performed in high-income countries, no research has yet been carried out in low-middle-income countries, such as Brazil. Therefore, this study aimed to examine whether there is a relationship between examining the association between individual food groups with depression and other mental health issues. This study described these differences using a screening questionnaire that was developed to be used in the National Health Survey (Lopes et al., 2022) – which evaluates depression and other common mental health disorders, including schizophrenia, bipolar disorder, obsessive-compulsive disorder, and others. Moreover, participants reported their daily limitations, use of medications, and chronicity of mental disorders. All of these were evaluated as potential influences on dietary patterns. Food groups were analyzed in isolation and in combination with each other to establish which dietary components are independently related to these diagnosed disorders and/or symptom severity. Finally, the individual clinical symptoms encompassing features of depressive disorder were evaluated and crossed with dietary patterns.