Abstract:

This study aims to determine the association of adherence to the Mediterranean diet and its food groups with depressive symptoms in Chilean university students. The study design was cross-sectional. A total of 934 first-year students at a Chilean public university completed a self-report questionnaire. To assess adherence to Mediterranean diet, an index validated in Chile (Chilean-MDI) was used, and depression, anxiety, and stress symptoms were assessed using the Depression Anxiety and Stress Scale (DASS-21). Logistic regression models were used to analyze the association of adherence to Mediterranean diet and its food groups with depression, anxiety, and stress symptoms adjusted for the main confounders. Students with moderate and high adherence to Mediterranean diet showed lower odds of depression [DASS-21 > 5, odds ratio (OR) = 0.64; 95% confidence interval (95%CI): 0.47-0.88] than those with low adherence to Mediterranean diet. The consumption of 1-2 servings/day of vegetables (OR = 0.63; 95%CI: 0.43-0.92), > 2 servings/week of nuts (OR = 0.41; 95%CI: 0.21-0.80), 1-2 servings/day of fruits (OR = 0.60; 95%CI: 0.42-0.85), 1-2 servings/week of fish and seafood (OR = 0.67; 95%CI: 0.48-0.94), and 1/2-3 units/week of avocado (OR = 0.67; 95%CI: 0.48-0.93) showed low odds of depressive symptoms. The consumption of whole grains and cereals (> 2 servings/day) (OR = 1.63; 95%CI: 1.02-2.61) showed the opposite association. Adherence to Mediterranean diet and consumption of fruits, vegetables, nuts, avocado, fish, and seafood are associated with a lower likelihood of depression in Chilean university students. New policies and educational strategies are recommended to improve diet quality and the mental health of the entire university community.

Keywords:
Mediterranean Diet; Depression; Mental Health; Young Adults; Student Health

Resumen:

El objetivo de este estudio fue determinar la asociación entre la adherencia a la dieta mediterránea y sus grupos de alimentos y los síntomas depresivos en estudiantes universitarios chilenos. El diseño del estudio fue el transversal. Un total de 934 estudiantes de primer año de una universidad pública chilena completaron una encuesta de autoevaluación sobre la adherencia a la DM -utilizando un índice validado en Chile (IDM chileno)- y los síntomas de depresión, ansiedad y estrés, mediante el uso de la Escala de Depresión, Ansiedad y Estrés (DASS-21). Se utilizaron los modelos de regresión logística para analizar la asociación entre la adherencia a la dieta mediterránea y sus grupos alimenticios y los síntomas de depresión, ansiedad y estrés, ajustados por los principales factores de confusión. Los estudiantes con moderada o alta adherencia a la dieta mediterránea tenían menos probabilidades de presentar depresión [DASS-21 > 5, odds ratio (OR) = 0,64; intervalo de 95% de confianza (IC95%): 0,47-0,88] que aquellos con baja adherencia a la dieta mediterránea. Un consumo de 1-2 porciones por día de verduras (OR = 0,63; IC95%: 0,43-0,92), > 2 porciones por semana de nueces (OR = 0,41; IC95%: 0,21-0,80), 1-2 porciones por día de frutas (OR = 0,60; IC95%: 0,42-0,85), 1-2 porciones por semana de pescado y marisco (OR = 0,67; IC95%: 0,48-0,94) y 1/2-3 unidades por semana de aguacate (OR = 0,67; IC95%: 0,48-0,93) resultó en bajas probabilidades de síntomas depresivos. El consumo de cereales integrales (> 2 porciones por día) (OR = 1,63; IC95%: 1,02-2,61) tuvo una asociación opuesta. La adhesión a la dieta mediterránea y el consumo de frutas, verduras, nueces, aguacate, pescados y mariscos se asocian con una menor probabilidad de depresión en los estudiantes universitarios chilenos. Se sugiere la adopción de nuevas políticas y estrategias educativas para mejorar la calidad de la alimentación y promover la salud mental de toda la comunidad universitaria.

Palabras-clave:
Dieta Mediterránea; Depresión; Salud Mental; Adulto Joven; Salud del Estudiante

Resumo:

O objetivo do estudo foi determinar a associação da adesão à dieta mediterrânea e seus grupos alimentares com sintomas depressivos em estudantes universitários chilenos. O desenho do estudo foi transversal. Um total de 934 estudantes do primeiro ano de uma universidade pública chilena responderam a uma pesquisa de autoavaliação para analisar a adesão à dieta mediterrânea - por meio de um índice validado no Chile (IDM-chileno) - e sintomas de depressão, ansiedade e estresse, utilizando a Escala de Depressão, Ansiedade e Estresse (DASS-21). Modelos de regressão logística foram utilizados para examinar a associação entre a adesão à dieta mediterrânea e seus grupos alimentares com sintomas de depressão, ansiedade e estresse, ajustados para os principais fatores de confusão. Estudantes com adesão moderada ou alta à dieta mediterrânea apresentaram chances menores de ter depressão [DASS-21 > 5, odds ratio (OR) = 0,64; intervalo de 95% de confiança (IC95%): 0,47-0,88] do que aqueles com baixa adesão à dieta mediterrânea. Um consumo de 1-2 porções por dia de verduras (OR = 0,63; IC95%: 0,43-0,92), > 2 porções por semana de nozes (OR = 0,41; IC95%: 0,21-0,80), 1-2 porções por dia de frutas (OR = 0,60; IC95%: 0,42-0,85), 1-2 porções por semana de peixes e frutos do mar (OR = 0,67; IC95%: 0,48-0,94) e 1/2-3 unidades por semana de abacate (OR = 0,67; IC95%: 0,48-0,93) resultou em chances baixas de sintomas depressivos. O consumo de cereais integrais (> 2 porções por dia) (OR = 1,63; IC95%: 1,02-2,61) resultou na associação oposta. A adesão à dieta mediterrânea e o consumo de frutas, verduras, nozes, abacate, peixes e frutos do mar estão associados a uma menor probabilidade de depressão em estudantes universitários chilenos. Recomendamos a adoção de novas políticas e estratégias educacionais para melhorar a qualidade da alimentação e promover a saúde mental de toda a comunidade universitária.

Palavras-chave:
Dieta Mediterrânea; Depressão; Saúde Mental; Adulto Jovem; Saúde do Estudante

Introduction

Mental health disorders are among the leading causes of disability and the global health-related burden. The Global Burden of Diseases, Injuries, and Risk Factors (GBD) Study 2019 showed that the two most disabling mental disorders are depression and anxiety. A recent study conducted in 204 countries during the COVID-19 pandemic identified a global increase of 27.6% and 25.6% in cases of depressive and anxiety disorders, respectively, especially among women and younger populations ¹1. GBD 2019 Diseases and Injuries Collaborators. Global burden of 369 diseases and injuries in 204 countries and territories, 1990-2019: a systematic analysis for the Global Burden of Disease Study 2019. Lancet 2020; 396:1204-22..

The etiology of mental disorders includes biological, genetic, environmental, and lifestyle factors, such as diet ²2. Saveanu RV, Nemeroff CB. Etiology of depression: genetic and environmental factors. Psychiatr Clin North Am 2012; 35:51-71.. Many epidemiological studies have evaluated the association between individual food groups (i.e., fish, fruits, nuts, and vegetables) ³3. Yoshikawa E, Nishi D, Matsuoka Y. Fish consumption and resilience to depression in Japanese company workers: a cross-sectional study. Lipids Health Dis 2015; 14:51.^,44. Liu X, Yan Y, Li F, Zhang D. Fruit and vegetable consumption and the risk of depression: a meta-analysis. Nutrition 2016; 32:296-302.^,55. Fernández-Rodríguez R, Jiménez-López E, Garrido-Miguel M, Martínez-Ortega IA, Martínez-Vizcaíno V, Mesas AE. Does the evidence support a relationship between higher levels of nut consumption, lower risk of depression, and better mood state in the general population? A systematic review. Nutr Rev 2022; 80:2076-88.^,66. Cobo-Cuenca AI, Garrido-Miguel M, Soriano-Cano A, Ferri-Morales A, Martínez-Vizcaíno V, Martín-Espinosa NM. Adherence to the mediterranean diet and its association with body composition and physical fitness in Spanish university students. Nutrients 2019; 11:2830. and bioactive compounds (i.e., omega-3 fatty acids, folic acid, polyphenols, flavonoids, or B vitamins) ⁷7. Jia S, Hou Y, Wang D, Zhao X. Flavonoids for depression and anxiety: a systematic review and meta-analysis. Crit Rev Food Sci Nutr 2022; [Online ahead of print].^,88. Lin K, Li Y, Toit ED, Wendt L, Sun J. Effects of polyphenol supplementations on improving depression, anxiety, and quality of life in patients with depression. Front Psychiatry 2021; 12:765485. and mental health ⁹9. Dana-Alamdari L, Kheirouri S, Noorazar SG. Serum 25-hydroxyvitamin D in patients with major depressive disorder. Iran J Public Health 2015; 44:690-7.^,1010. Kim TH, Choi J-Y, Lee HH, Park Y. Associations between dietary pattern and depression in Korean adolescent girls. J Pediatr Adolesc Gynecol 2015; 28:533-7.^,1111. Sanhueza C, Ryan L, Foxcroft DR. Diet and the risk of unipolar depression in adults: systematic review of cohort studies. J Hum Nutr Diet 2013; 26:56-70.^,1212. Sánchez-Villegas A, Verberne L, De Irala J, Ruíz-Canela M, Toledo E, Serra-Majem L, et al. Dietary fat intake and the risk of depression: the SUN project. PLoS One 2011; 6:e16268.. However, diet is a multidimensional exposure that includes synergistic effects between different dietary components. Therefore, assessing dietary patterns is a more comprehensive approach to find diet-disease relationships and provide public health recommendations.

The Mediterranean diet is a dietary pattern based on the healthy traditional eating habits of the populations from the countries around the Mediterranean Sea, which includes a high consumption of plant-based foods (i.e., fruits, vegetables, whole grains, nuts, and seeds, and legumes and pulses), fish, and unsaturated fats (i.e., such as olive oil), a moderate consumption of dairy products and eggs, and a low consumption of red meat and processed meat products ¹³13. Willett EC, Sacks F, Trichopoulou A, Drescher G, Ferro-Luzzi A, Helsing E, et al. Mediterranean diet pyramid: a cultural model for healthy eating. Am J Clin Nutr 1995; 61(6 Suppl):1402S-6S.^,1414. Willett WC. The Mediterranean diet: science and practice. Public Health Nutr 2006; 9:105-10.. Some of its dietary components have been shown to play a key role in depression. Thus, the intake of n-3 polyunsaturated fatty acids (n-3 PUFAs) [docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and alpha-linoleic acid (ALA)], which are present in foods such as fish and vegetable oils, have a beneficial effect on depression. One hypothesis suggests that n-3 PUFAs affect depressive symptoms by several possible pathways, such as anti-inflammatory effects, neuroendocrine modulation, and neuroprotective/neurotrophic mechanisms ¹⁵15. Grosso G, Micek A, Marventano S, Castellano S, Mistretta A, Pajak A, et al. Dietary n-3 PUFA, fish consumption and depression: a systematic review and meta-analysis of observational studies. J Affect Disord 2016; 205:269-81.^,1616. Skarupski KA, Tangney C, Li H, Ouyang B, Evans DA, Morris MC. Longitudinal association of vitamin B-6, folate, and vitamin B-12 with depressive symptoms among older adults over time. Am J Clin Nutr 2010; 92:330-5.^,1717. Xu Y, Wang C, Klabnik JJ, O'Donnell JM. Novel therapeutic targets in depression and anxiety: antioxidants as a candidate treatment. Curr Neuropharmacol 2014; 12:108-19.. Some population-based studies have also reported an inverse association between adherence to Mediterranean diet and depressive disorder, but their results are contradictory ¹⁸18. Shafiei F, Salari-Moghaddam A, Larijani B, Esmaillzadeh A. Adherence to the mediterranean diet and risk of depression: a systematic review and updated meta-analysis of observational studies. Nutr Rev 2019; 77:230-9.^,1919. Sánchez-Villegas A, Martínez-González MA, Estruch R, Salas-Salvadó J, Corella D, Covas MI, et al. Mediterranean dietary pattern and depression: the PREDIMED randomized trial. BMC Med 2013; 11:208.^,2020. Yin W, Löf M, Chen R, Hultman CM, Fang F, Sandin S. Mediterranean diet and depression: a population-based cohort study. Int J Behav Nutr Phys Act 2021; 18:153.. Although a meta-analysis of cohort studies found a nonsignificant association between adherence to Mediterranean diet and risk of depression ¹⁸18. Shafiei F, Salari-Moghaddam A, Larijani B, Esmaillzadeh A. Adherence to the mediterranean diet and risk of depression: a systematic review and updated meta-analysis of observational studies. Nutr Rev 2019; 77:230-9., recent population-based prospective studies suggest lower odds of depression in individuals with high adherence to Mediterranean diet ²¹21. Oddo VM, Welke L, McLeod A, Pezley L, Xia Y, Maki P, et al. Adherence to a mediterranean diet is associated with lower depressive symptoms among U.S. adults. Nutrients 2022; 14:278.. Therefore, further studies are needed to clarify and strengthen the evidence regarding the association between this dietary pattern and mental health disorders.

The transition to university is a critical period for young adults, in which attending university can be a stressful time for most students. Besides academic pressure, some students have to handle several family and work responsibilities, while others face the stressful task of separating from their family and hometown. Thus, many students experience the onset of mental health disorders during the first years at university ²²22. Pedrelli P, Nyer M, Yeung A, Zulauf C, Wilens T. Buku panduan program ijazah dasar sesi akademik 2013/2014. Acad Psychiatry 2015; 39:503-11.. On the other hand, these first years are their first opportunity to make their own food choices ²³23. Deshpande S, Basil MD, Basil DZ. Factors influencing healthy eating habits among college students: an application of the health belief model. Health Mark Q 2009; 26:145-64.. Poor cooking skills, obesogenic environments with high availability of fast food, lack of time, and financial worries can lead to unhealthy eating habits and sedentary patterns, promoting weight gain, which may persist into adulthood ²⁴24. Payne-Sturges DC, Tjaden A, Caldeira KM, Vincent KB, Arria AM. Student hunger on campus: food insecurity among college students and implications for academic institutions. Am J Health Promot 2018; 32:349-54.^,2525. Vella-Zarb RA, Elgar FJ. The "freshman 5": a meta-analysis of weight gain in the freshman year of college. J Am Coll Health 2009; 58:161-6..

In Chile, no previous study has analyzed the relationship between adherence to Mediterranean diet and mental health disorders in this highly vulnerable population. Therefore, this study aimed to assess: (1) the association between adherence to Mediterranean diet and depression, anxiety, and stress symptoms; and (2) the relationship between the different Mediterranean diet food groups and depressive disorders in a sample of Chilean university students during their first year at the university.

Material and methods

Study design and participants

This cross-sectional online study recruited participants in March 2021. All first-year students at a Chilean university were considered eligible and invited to participate in the study. Of the 1,942 eligible students invited to participate, 1,243 (63.5%) agreed to answer an online questionnaire, of whom 934 (48.1%) provided complete data for the main variables of interest in the study (Figure 1).

Supplementary Material (Table S1. Supplementary Material https://cadernos.ensp.fiocruz.br/static//arquivo/supl-e00206722_8682.pdf) shows a comparison of the descriptive characteristics of the total number of university students initially selected and the final sample. Generally, no substantial differences were found, especially regarding the main variables of the study (i.e., depression, anxiety, and stress symptoms and adherence to Mediterranean diet).

Procedures

Participants were invited to voluntarily participate in an online health survey. After providing informed consent electronically, participants completed a 20-minute online questionnaire. All students who signed the informed consent form and completed the questionnaire were considered in the analyses.

Measurements

Assessment of adherence to the Mediterranean diet

A Mediterranean dietary index validated in Chile (Chilean-MDI) was applied. In total, 14 food groups were assessed [fruits, vegetables, legumes, nuts, fish and seafood, whole grains and cereals, fat-free or fermented dairy products, full-fat dairy products, lean meat, red meat and processed meat, wine, olive oil, other healthy fats (canola), and avocado and sugars]. The maximum score was 14 points. Higher scores represent greater adherence to Mediterranean diet. The following categories are considered: high (9-14 points), moderate (5-8.5 points), and low (< 5 points) adherence ²⁶26. Echeverría G Urquiaga I, Concha MJ, Dussaillant C, Villarroel L, Velasco N, et al. Validación de cuestionario autoaplicable para un índice de alimentación mediterránea en Chile. Rev Méd Chile 2016; 144:1531-43.. For this study, the high and moderate categories were grouped (> 5 points).

Assessment of depression, anxiety, and stress symptoms

Depression, anxiety, and stress symptoms were assessed using the Depression Anxiety and Stress Scale (DASS-21). This tool was validated in Chile ²⁷27. Mella FR, Vinet EV, Muñoz AMA. Escalas de Depresión, Ansiedad y Estrés (DASS-21): adaptación y propiedades psicométricas en estudiantes secundarios de Temuco. Rev Argent Clín Psicol 2014; 23:179-90. and has good reliability and validity in Hispano-American, British, and Australian adults.

Students rated 21 statements, seven for each construct assessed (depression, anxiety, and stress symptoms), answering to what extent the statement applied to them over the past week, on a four-point scale (0-3). The answers ranged from “did not apply to me at all” to “applied to me very much or most of the time” (lower scores corresponded to reduced symptoms). Thus, each construct has a total score ranging from 0 to 21 points. A score > 5 points was the cut-off point for depression and stress symptoms. A score > 4 points was the cut-off point for anxiety symptoms ²⁸28. Román F, Santibañez P, Vinet EV. Uso de Escalas de Depresión, Ansiedad, Estrés (DASS-21) como instrumento de tamizaje en jóvenes con problemas clínicos. Acta Investigación Psicol 2016; 6:2325-36..

Other covariables

This study considered other variables of interest:

(a) Sociodemographic data: age (years), sex (male, female), maternal schooling level (secondary education or lower, or higher education);

(b) Body mass index (BMI): estimated from self-reported weight and height. The cut-off points were < 18.5kg/m² for underweight, 18.5-24.9kg/m² for normal weight, 25-29.9kg/m² for overweight, and ≥ 30kg/m² for obesity;

(c) Sedentary lifestyle: according to the following question of the Physical Activity Questionnaire Short Form (IPAQ-SF): “During the last 7 days, how much time did you spend sitting on a week day?” ²⁹29. Lee PH, Macfarlane DJ, Lam T, Stewart SM. Validity of the International Physical Activity Questionnaire Short Form (IPAQ-SF): a systematic review. Int J Behav Nutr Phys Act 2011; 8:115.^,3030. Palma-Leal X, Costa-Rodríguez C, Barranco-Ruiz Y, Hernández-Jaña S, Rodríguez-Rodríguez F. Fiabilidad del Cuestionario Internacional de Actividad Física (IPAQ)-versión corta y del Cuestionario de Autoevaluación de la Condición Física (IFIS) en estudiantes universitarios chilenos. Journal of Movement & Health 2022; 19:1-12.. Students who spent ≥ 8 hours/day sitting were considered sedentary;

(d) Physical activity: assessed using the IPAQ-SF. Students were grouped into two categories (yes or no) according to their compliance with the recommendation of at least five days of moderate physical activity and walking ³¹31. Crespo-Salgado JJ, Delgado-Martín JL, Blanco-Iglesias O, Aldecoa-Landesa S. Guía básica de detección del sedentarismo y recomendaciones de actividad física en atención primaria. Aten Primaria 2015; 47:175-83.;

(e) Tobacco use: assessed by the Alcohol, Smoking and Substance Involvement Screening Test (ASSIST). “In the past three months, how often have you used tobacco products?” (never, once or twice, monthly, weekly, or daily or almost daily) ³²32. Group WAW. The Alcohol, Smoking and Substance Involvement Screening Test (ASSIST): development, reliability and feasibility. Addiction 2002; 97:1183-94.. The weekly and daily categories were grouped;

(f) Alcohol consumption was assessed using the same ASSIST question: “In the past three months, how often have you used alcoholic beverages?” (never, once or twice, monthly, weekly, or daily or almost daily) ³²32. Group WAW. The Alcohol, Smoking and Substance Involvement Screening Test (ASSIST): development, reliability and feasibility. Addiction 2002; 97:1183-94.. The weekly and daily categories were grouped.

Statistical analysis

Data are presented as mean and standard deviation (SD) for continuous variables and number and percentages for categorical variables. Student’s t-test and the Mann-Whitney test were used for variables with a normal or non-normal distribution, respectively. The chi-squared test was used for categorical variables. Logistic regression models were used to analyze the association between adherence to Mediterranean diet and depression, anxiety, and stress symptoms. Mediterranean diet food groups were also analyzed. In this analysis, consumption below recommended levels was divided into two or more categories for a better analysis of the isolated effects of each food group. Results are presented as odds ratios (ORs) and 95% confidence intervals (95%CIs). Models were adjusted for variables associated with Mediterranean diet and depressive symptoms ³³33. Zaragoza-Martí A, Cabañero-Martínez MJ, Hurtado-Sánchez JA, Laguna-Pérez A, Ferrer-Cascales R. Evaluation of Mediterranean diet adherence scores: a systematic review. BMJ Open 2018; 8:e019033.^,3434. Kang M, Park S-Y, Shvetsov YB, Wilkens LR, Marchand LL, Boushey CJ. Sex differences in sociodemographic and lifestyle factors associated with diet quality in a multiethnic population. Nutrition 2019; 66:147-52.^,3535. Koutsonida M, Kanellopoulou A, Markozannes G, Gousia S, Doumas MT, Sigounas DE, et al. Adherence to Mediterranean diet and cognitive abilities in the Greek Cohort of Epirus Health Study. Nutrients 2021; 13:3363.^,3636. Camilleri GM, Méjean C, Kesse-Guyot E, Andreeva VA, Bellisle F, Hercberg S, et al. The associations between emotional eating and consumption of energy-dense snack foods are modified by sex and depressive symptomatology. J Nutr 2014; 144:1264-73.^,3737. Gutiérrez-Rojas L, Porras-Segovia A, Dunne H, Andrade-González N, Cervilla JA. Prevalence and correlates of major depressive disorder: a systematic review. Braz J Psychiatry 2020; 42:657-72., such as sex (male, female), BMI (underweight, normal weight, overweight, or obesity), maternal schooling level (secondary education or lower, or higher education), tobacco use (never, occasionally, or weekly/daily), alcohol use (never, occasionally, or weekly/daily), sedentary lifestyle (yes or no), and physical activity (compliance with the recommendation: yes or no). Due to the evidence of interaction of the sex variable with depression and diet ³⁶36. Camilleri GM, Méjean C, Kesse-Guyot E, Andreeva VA, Bellisle F, Hercberg S, et al. The associations between emotional eating and consumption of energy-dense snack foods are modified by sex and depressive symptomatology. J Nutr 2014; 144:1264-73., the Mantel-Haenszel homogeneity test was used. Moreover, considering the low frequency of wine consumption, a sensibility analysis was performed for the total Chilean-MDI score and the score without “wine” (Supplementary Material. Table S2. Supplementary Material https://cadernos.ensp.fiocruz.br/static//arquivo/supl-e00206722_8682.pdf). All statistical analyses were performed using Stata version 15 (https://www.stata.com). The sample size for the a priori and post hoc analyses was determined using G*Power, version 3.1.9.6 (http://www.psycho.uni-duesseldorf.de/abteilungen/aap/gpower3). To estimate the a priori sample size, this study considered a medium effect size (1.3), a power of 80%, a two-tailed model, H0 = 0.20 for Pr(Y = 1 | X = 1), and α = 0.05. The estimated sample size was 721 participants. To estimate the post hoc power for each analysis, this study used the sample size, a two-tailed model, H0 = 0.20 for Pr(Y = 1 | X = 1), and α = 0.05 ³⁸38. Faul F, Erdfelder E, Buchner A, Lang AG. Statistical power analyses using G*Power 3.1: tests for correlation and regression analyses. Behav Res Methods 2009; 41:1149-60..

Ethical approval

This study was approved by the Research Ethics Committee of the La Frontera University (Chile; protocol n. 150/21).

Results

Of the 1,942 eligible students invited to participate, 1,243 (63.5%) agreed to answer an online questionnaire and 934 provided complete data for the main variables of interest of this study (Figure 1). Table 1 presents the main characteristics of the participants according to sex. A total of 494 (52.9%) were females, with a mean age of 19.2 years old (SD = 1.6), and 67% reported that their mother’s schooling level was secondary education or lower. More than half of students were of normal weight. Regarding lifestyle habits, most students practiced physical activity five or more times per week (70.1%), were not sedentary (72.1%), did not smoke (79.2%), and consumed alcohol occasionally (60.4%). Regarding mental disorders according to the DASS-21, all students reported a high prevalence of depression (23.9%), anxiety (29.4%), and stress (37.9%) symptoms, with a higher prevalence in women. Finally, adherence to Mediterranean diet was high (60.8%).

Compliance with Mediterranean diet recommendations was low, especially for the following food groups: wine (0.4%), fish and seafood (3.8%), olive oil (4.3%), avocado (4.6%), vegetables (6.8%), canola oil (6.9%), nuts (9.3%), fruits (12.9%), and whole grains (13.4%). Regarding both the healthy and unhealthy food groups (fats, processed meat, full-fat dairy products, and sweetened beverages), females complied with the recommendations to a greater extent than males (Table 2).

Table 3 presents the association between depressive symptoms and adherence to Mediterranean diet according to the index adjusted for the main confounders. The model shows that, compared with students with low adherence, students with moderate and high adherence to Mediterranean diet have a lower risk of depression (OR = 0.64; 95%CI: 0.47-0.88; power 99%). The results did not vary substantially between females and males. We conducted an interaction analysis for the sex variable using the Mantel-Haenszel homogeneity test and it was not significant (Pr > χ² = 0.9649). On the other hand, we found no association for anxiety or stress symptoms, which had a power of 86% and 56%, respectively (Table 3).

In the fully adjusted models, the OR (95%CI) for students with a high consumption of the recommended food groups showed a low risk of depressive symptoms: 0.63 (95%CI: 0.43-0.92) for 1-2 servings per day of vegetables, 0.41 (95%CI: 0.21-0.80) for > 2 servings per week of nuts, 0.60 (95%CI: 0.42-0.85) for 1-2 servings per day of fruits, 0.67 (95%CI: 0.48-0.94) for 1-2 servings per week of fish and seafood, and 0.67 (95%CI: 0.48-0.93) for 1/2-3 units per week of avocado. The consumption of whole grains and cereals showed the opposite association, since students who consumed more than two servings per day had a higher risk of depressive symptoms: 1.63 (1.02-2.61). The association was statistically significant for all food groups (Table 4).

Discussion

Our data showed that Chilean university students with greater adherence (high or moderate) to Mediterranean diet were 36% less likely to have depressive symptoms compared with students with low adherence in the fully adjusted models. Moreover, higher consumption of some food groups recommended for Mediterranean diet (vegetables, nuts, fruits, fish and seafood, and avocado) was associated with lower depressive symptoms.

Dietary intake and patterns change throughout life and are influenced by biological ³⁹39. Wakimoto P, Block G. Dietary intake, dietary patterns, and changes with age: an epidemiological perspective. J Gerontol A Biol Sci Med Sci 2001;56(Spec No 2):65-80. and social ⁴⁰40. Lee S, Cho E, Grodstein F, Kawachi I, Hu FB, Colditz GA. Effects of marital transitions on changes in dietary and other health behaviours in US women. Int J Epidemiol 2005; 34:69-78.^,4141. Nasuti G, Blanchard C, Naylor P-J, Levy-Milne R, Warburton DER, Benoit C, et al. Comparison of the dietary intakes of new parents, second-time parents, and nonparents: a longitudinal cohort study. J Acad Nutr Diet 2014; 114:450-6. issues and university entrance ⁴²42. Hilger J, Loerbroks A, Diehl K. Eating behaviour of university students in Germany: dietary intake, barriers to healthy eating and changes in eating behaviour since the time of matriculation. Appetite 2017; 109:100-7.^,4343. Bárbara R, Ferreira-Pêgo C. Changes in eating habits among displaced and non-displaced university students. Int J Environ Res Public Health 2020; 17:5369.. In this sense, sex seems to be an important feature, as males and females have different biological food consumption needs, which directly and indirectly promotes the adoption of different eating habits ⁴⁴44. Li K-K, Concepcion RY, Lee H, Cardinal BJ, Ebbeck V, Woekel E, et al. An examination of sex differences in relation to the eating habits and nutrient intakes of university students. J Nutr Educ Behav 2012; 44:246-50.. Moreover, sex can determine biological changes that increase the likelihood of mental disorders in females, with a possible increase in incidence during the COVID-19 pandemic ⁴⁵45. Xiong J, Lipsitz O, Nasri F, Lui LMW, Gill H, Phan L, et al. Impact of COVID-19 pandemic on mental health in the general population: a systematic review. J Affect Disord 2020; 277:55-64.. These mechanisms justify the greater adherence to Mediterranean diet and the frequency of depression in women, as shown in this study. However, in contrast to studies that found an association only in women ⁴⁶46. Saneei P, Hajishafiee M, Keshteli AH, Afshar H, Esmaillzadeh A, Adibi P. Adherence to Alternative Healthy Eating Index in relation to depression and anxiety in Iranian adults. Br J Nutr 2016; 116:335-42.^,4747. Rahmani J, Milajerdi A, Dorosty-Motlagh A. Association of the Alternative Healthy Eating Index (AHEI-2010) with depression, stress and anxiety among Iranian military personnel. J R Army Med Corps 2018; 164:87-91., in this study, the association was in the entire population (i.e., in males and females), and we observed no interaction between sex, greater adherence to Mediterranean diet, and lower depressive symptoms. Thus, sex was a control in the adjusted models, and this variable was not subjected to stratification analysis.

Regarding food consumption patterns, the frequency of adequate consumption of some foods was low compared with other studies involving university students, especially when in Mediterranean countries or countries closer to the culture, such as vegetables (6.8% versus 18.1% to 45,5%) ⁴⁸48. Rodrigues VM, Bray J, Fernandes AC, Bernardo GL, Hartwell H, Martinelli SS, et al. Vegetable consumption and factors associated with increased intake among college students: a scoping review of the last 10 years. Nutrients 2019; 11:1634.^,4949. Kyrkou C, Tsakoumaki F, Fotiou M, Dimitropoulou A, Symeonidou M, Menexes G, et al. Changing trends in nutritional behavior among university students in Greece, between 2006 and 2016. Nutrients 2018; 10:64., fruits (12.9% versus 23.9%) ⁴⁹49. Kyrkou C, Tsakoumaki F, Fotiou M, Dimitropoulou A, Symeonidou M, Menexes G, et al. Changing trends in nutritional behavior among university students in Greece, between 2006 and 2016. Nutrients 2018; 10:64., nuts (9.3% versus 66.9%) ⁴⁹49. Kyrkou C, Tsakoumaki F, Fotiou M, Dimitropoulou A, Symeonidou M, Menexes G, et al. Changing trends in nutritional behavior among university students in Greece, between 2006 and 2016. Nutrients 2018; 10:64., and fish and seafood (3.8% versus 41% to 77.3%) ⁴⁹49. Kyrkou C, Tsakoumaki F, Fotiou M, Dimitropoulou A, Symeonidou M, Menexes G, et al. Changing trends in nutritional behavior among university students in Greece, between 2006 and 2016. Nutrients 2018; 10:64.^,5050. El Ansari W, Suominen S, Samara A. Eating habits and dietary intake: is adherence to dietary guidelines associated with importance of healthy eating among undergraduate university students in Finland? Cent Eur J Public Health 2015; 23:306-13.. Adequate consumption of the following healthy food has been associated with a lower prevalence of depressive symptoms: fruits and vegetables ⁵¹51. Dharmayani PNA, Juergens M, Allman-Farinelli M, Mihrshahi S. Association between fruit and vegetable consumption and depression symptoms in young people and adults aged 15-45: a systematic review of cohort studies. Int J Environ Res Public Health 2021; 18:780., due to the presence of vitamins and folates that can act as antioxidants in the process of regeneration and production of neurotransmitters ⁵²52. Pano O, Martínez-Lapiscina EH, Sayón-Orea C, Martinez-Gonzalez MA, Martinez JA, Sanchez-Villegas A. Healthy diet, depression and quality of life: a narrative review of biological mechanisms and primary prevention opportunities. World J Psychiatry 2021; 11:997-1016.^,5353. Marx W, Lane M, Hockey M, Aslam H, Berk M, Walder K, et al. Diet and depression: exploring the biological mechanisms of action. Mol Psychiatry 2021; 26:134-50.; fish and seafood ⁵⁴54. Sánchez-Villegas A, Álvarez-Pérez J, Toledo E, Salas-Salvadó J, Ortega-Azorín C, Zomeño MD, et al. Seafood consumption, omega-3 fatty acids intake, and life-time prevalence of depression in the PREDIMED-plus trial. Nutrients 2018; 10:2000.^,5555. Berger M, Taylor S, Harriss L, Campbell S, Thompson F, Jones S, et al. Cross-sectional association of seafood consumption, polyunsaturated fatty acids and depressive symptoms in two Torres Strait communities. Nutr Neurosci 2020; 23:353-62. and avocado, due to their anti-inflammatory unsaturated fatty acids; and greater consumption of nuts ⁵5. Fernández-Rodríguez R, Jiménez-López E, Garrido-Miguel M, Martínez-Ortega IA, Martínez-Vizcaíno V, Mesas AE. Does the evidence support a relationship between higher levels of nut consumption, lower risk of depression, and better mood state in the general population? A systematic review. Nutr Rev 2022; 80:2076-88., due to the modulation of neuronal factors ⁵²52. Pano O, Martínez-Lapiscina EH, Sayón-Orea C, Martinez-Gonzalez MA, Martinez JA, Sanchez-Villegas A. Healthy diet, depression and quality of life: a narrative review of biological mechanisms and primary prevention opportunities. World J Psychiatry 2021; 11:997-1016.^,5353. Marx W, Lane M, Hockey M, Aslam H, Berk M, Walder K, et al. Diet and depression: exploring the biological mechanisms of action. Mol Psychiatry 2021; 26:134-50..

On the other hand, a higher consumption (> 2 servings per day) of whole grains and cereals showed a greater likelihood of depressive symptoms. Although the literature presents the consumption of whole grains and cereals as a protective factor for depression ⁵²52. Pano O, Martínez-Lapiscina EH, Sayón-Orea C, Martinez-Gonzalez MA, Martinez JA, Sanchez-Villegas A. Healthy diet, depression and quality of life: a narrative review of biological mechanisms and primary prevention opportunities. World J Psychiatry 2021; 11:997-1016.^,5353. Marx W, Lane M, Hockey M, Aslam H, Berk M, Walder K, et al. Diet and depression: exploring the biological mechanisms of action. Mol Psychiatry 2021; 26:134-50., the consumption of refined cereals may not be beneficial ⁵⁶56. Molendijk M, Molero P, Ortuño Sánchez-Pedreño F, Van der Does W, Angel Martínez-González M. Diet quality and depression risk: a systematic review and dose-response meta-analysis of prospective studies. J Affect Disord 2018; 226:346-54. and may also be associated with a higher frequency of depressive symptoms ⁵⁷57. Sadeghi O, Keshteli AH, Afshar H, Esmaillzadeh A, Adibi P. Adherence to Mediterranean dietary pattern is inversely associated with depression, anxiety and psychological distress. Nutr Neurosci 2021; 24:248-59.. We could hypothesize that students probably overreported whole grain consumption due to the inclusion of breakfast cereals in this group, which are mostly ultra-processed food and have a complex formulation, including ingredients such as glucose syrups, invert sugar, sweeteners, and additives, besides neo-formed contaminants harmful to health (e.g., acrylamide) ⁵⁸58. Morales FJ, Mesías M, Delgado-Andrade C. Association between heat-induced chemical markers and ultra-processed foods: a case study on breakfast cereals. Nutrients 2020; 12:1418.. These findings, along with the differences in the frequency of consumption of important food groups (vegetables, fruits, nuts, and fish and seafood), reinforce the importance of a broader dietary assessment for this population, recognizing cultural differences and the impossibility of comparing consumption frequencies, especially from different cultures ⁵⁹59. Martínez-González MA, Hershey MS, Zazpe I, Trichopoulou A. Transferability of the Mediterranean diet to non-Mediterranean countries. What is and what is not the Mediterranean diet. Nutrients 2017; 9:1226..

The consumption of fruits ⁵¹51. Dharmayani PNA, Juergens M, Allman-Farinelli M, Mihrshahi S. Association between fruit and vegetable consumption and depression symptoms in young people and adults aged 15-45: a systematic review of cohort studies. Int J Environ Res Public Health 2021; 18:780.^,5757. Sadeghi O, Keshteli AH, Afshar H, Esmaillzadeh A, Adibi P. Adherence to Mediterranean dietary pattern is inversely associated with depression, anxiety and psychological distress. Nutr Neurosci 2021; 24:248-59. and nuts ⁵5. Fernández-Rodríguez R, Jiménez-López E, Garrido-Miguel M, Martínez-Ortega IA, Martínez-Vizcaíno V, Mesas AE. Does the evidence support a relationship between higher levels of nut consumption, lower risk of depression, and better mood state in the general population? A systematic review. Nutr Rev 2022; 80:2076-88. is consistently associated with a reduction in depressive symptoms. However, the effect of consuming isolated foods has limitations of interpretation ⁵¹51. Dharmayani PNA, Juergens M, Allman-Farinelli M, Mihrshahi S. Association between fruit and vegetable consumption and depression symptoms in young people and adults aged 15-45: a systematic review of cohort studies. Int J Environ Res Public Health 2021; 18:780.^,5353. Marx W, Lane M, Hockey M, Aslam H, Berk M, Walder K, et al. Diet and depression: exploring the biological mechanisms of action. Mol Psychiatry 2021; 26:134-50.^,5757. Sadeghi O, Keshteli AH, Afshar H, Esmaillzadeh A, Adibi P. Adherence to Mediterranean dietary pattern is inversely associated with depression, anxiety and psychological distress. Nutr Neurosci 2021; 24:248-59.. This would justify the lack of association in our study for the consumption of fruits, vegetables, avocado, and fish and seafood. Similarly, different foods and nutrients have a synergistic effect on each other, which makes dietary pattern analysis recommended ⁶⁰60. Hu FB. Dietary pattern analysis: a new direction in nutritional epidemiology. Curr Opin Lipidol 2002; 13:3-9.. However, this reinforces the importance of a broader analysis of food consumption, such as the analysis of adherence to Mediterranean diet using Chilean-MDI.

This study found that high and moderate adherence to Mediterranean diet leads to a lower risk of depressive symptoms. This can be attributed to most micronutrients, including adequate B vitamins and folate and antioxidant compounds existing in Mediterranean diet, allowing simultaneous modulation between different body systems. On the other hand, different compounds have been associated with depressive symptoms, such as inflammatory cytokines, interleukin-6, tumor necrosis factor-α, and C-reactive protein. The main mechanisms attributed to Mediterranean diet can be explained by the modulation of glucocorticoids, promotion of neurogenesis, decrease in oxidative stress markers, reduction of inflammatory markers, and modulation of the microbiota and epigenetic state ⁵²52. Pano O, Martínez-Lapiscina EH, Sayón-Orea C, Martinez-Gonzalez MA, Martinez JA, Sanchez-Villegas A. Healthy diet, depression and quality of life: a narrative review of biological mechanisms and primary prevention opportunities. World J Psychiatry 2021; 11:997-1016.^,5353. Marx W, Lane M, Hockey M, Aslam H, Berk M, Walder K, et al. Diet and depression: exploring the biological mechanisms of action. Mol Psychiatry 2021; 26:134-50.. These mechanisms have a unidirectional character, starting from Mediterranean diet and resulting in depressive symptoms. Since longitudinal epidemiological studies corroborate this directionality ⁶¹61. Jacka FN, Cherbuin N, Anstey KJ, Butterworth P. Does reverse causality explain the relationship between diet and depression? J Affect Disord 2015; 175:248-50.^,6262. Lassale C, Batty GD, Baghdadli A, Jacka F, Sánchez-Villegas A, Kivimäki M, et al. Healthy dietary indices and risk of depressive outcomes: a systematic review and meta-analysis of observational studies. Mol Psychiatry 2019; 24:965-86.^,6363. Swainson J, Reeson M, Malik U, Stefanuk I, Cummins M, Sivapalan S. Diet and depression: a systematic review of whole dietary interventions as treatment in patients with depression. J Affect Disord 2023; 327:270-8. and the literature does not support the effect in the opposite direction ⁶⁴64. Adjibade M, Assmann KE, Andreeva VA, Lemogne C, Hercberg S, Galan P, et al. Prospective association between adherence to the Mediterranean diet and risk of depressive symptoms in the French SU.VI.MAX cohort. Eur J Nutr 2018; 57:1225-35., we reinforce the directionality identified in this study. Finally, another mechanism that may help understand this association is that greater adherence to Mediterranean diet is associated with lower consumption of ultra-processed foods ⁶⁵65. Dinu M, Asensi MT, Pagliai G, Lotti S, Martini D, Colombini B, et al. Consumption of ultra-processed foods is inversely associated with adherence to the mediterranean diet: a cross-sectional study. Nutrients 2022; 14:2073., which in turn are associated with a greater presence of depressive symptoms ⁶⁶66. Lane MM, Gamage E, Travica N, Dissanayaka T, Ashtree DN, Gauci S, et al. Ultra-processed food consumption and mental health: a systematic review and meta-analysis of observational studies. Nutrients 2022; 14:2568..

Greater adherence to Mediterranean diet was associated with lower odds of anxiety symptoms. This association has been reported in populations of adults and university students ⁵⁷57. Sadeghi O, Keshteli AH, Afshar H, Esmaillzadeh A, Adibi P. Adherence to Mediterranean dietary pattern is inversely associated with depression, anxiety and psychological distress. Nutr Neurosci 2021; 24:248-59.^,6767. Trigueros R, Padilla AM, Aguilar-Parra JM, Rocamora P, Morales-Gázquez MJ, López-Liria R. The influence of emotional intelligence on resilience, test anxiety, academic stress and the Mediterranean diet. A study with university students. Int J Environ Res Public Health 2020; 17:2071.. On the other hand, the association between Mediterranean diet and stress is not a consensus in the available evidence. Some studies show a lower risk of stress in students with moderate/high adherence to Mediterranean diet ⁵⁷57. Sadeghi O, Keshteli AH, Afshar H, Esmaillzadeh A, Adibi P. Adherence to Mediterranean dietary pattern is inversely associated with depression, anxiety and psychological distress. Nutr Neurosci 2021; 24:248-59.^,6868. Antonopoulou M, Mantzorou M, Serdari A, Bonotis K, Vasios G, Pavlidou E, et al. Evaluating Mediterranean diet adherence in university student populations: Does this dietary pattern affect students' academic performance and mental health? Int J Health Plann Manage 2020; 35:5-21., while another study found no association with general stress ⁶⁹69. Chacón-Cuberos R, Zurita-Ortega F, Olmedo-Moreno EM, Castro-Sánchez M. Relationship between academic stress, physical activity and diet in university students of education. Behav Sci (Basel) 2019; 9:59..

As a limitation of this study, we highlight the impossibility of assessing causality (directionality or bidirectionality) due to the cross-sectional design. Another limitation is that all data were self-reported, using an online questionnaire; thus, the answers may be affected by recall and social desirability bias. Although self-reported weight and height are a limitation of this study, the literature shows evidence of good agreement between self-reported and measured values in young adults, which minimizes the bias of the BMI variable ⁷⁰70. Davies A, Wellard-Cole L, Rangan A, Allman-Farinelli M. Validity of self-reported weight and height for BMI classification: a cross-sectional study among young adults. Nutrition 2020; 71:110622.^,7171. Moreira NF, Luz VG, Moreira CC, Pereira RA, Sichieri R, Ferreira MG, et al. Self-reported weight and height are valid measures to determine weight status: results from the Brazilian National Health Survey (PNS 2013). Cad Saúde Pública 2018; 34:e00063917.. Regarding sample size, we provided data for less than 50% of all eligible students, which may cause biases (since the participating students may be different from those who did not participate in terms of exposure and outcome variables). Thus, our results should be interpreted with caution. As strengths, we highlight the use of validated tools to assess Mediterranean diet and depression, anxiety, and stress symptoms, the use of models adjusted for confounders, and high power for most of the associations found.

Conclusion

Students who adhered to Mediterranean diet (highly or moderately) were 36% less likely to have depressive symptoms compared with students with lower adherence in the fully adjusted models. Moreover, higher consumption of vegetables, nuts, fruits, fish and seafood, and avocado was associated with lower depressive symptoms. Mediterranean diet was not associated with anxiety and stress symptoms.

New policies and educational strategies are recommended to improve diet quality and the mental health of the entire university community.

Acknowledgments

We thank all participants in the study. This research was funded by project DFP21-0029 of the La Frontera University (Temuco, Chile).

References

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