The Relationship between Diet Quality, Measured by the Recommended Food Score, and Depression, Assessed Using the Patient Health Questionnaire-9: An Observational Study in Korea
Article information
Abstract
Background
Depression is a prevalent mental health disorder that presents substantial public health challenges. Emerging evidence underscores the role of dietary patterns in mitigating depressive symptoms. This study investigated the association between diet quality, assessed using the Recommended Food Score (RFS), and depressive symptoms, evaluated with the Patient Health Questionnaire-9 (PHQ-9), in a sample of Korean adults.
Methods
This cross-sectional study analyzed data from 19,786 participants recruited from a general hospital in Korea, all of whom completed the RFS and PHQ-9 assessments. General characteristics and anthropometric indices were recorded. Statistical analyses included chi-square tests and binary logistic regression to calculate odds ratios (ORs) and 95% confidence intervals for depressive symptoms according to RFS scores, adjusting for potential confounders.
Results
Higher RFS scores were associated with reduced odds of depression in univariate (OR, 0.59; P<0.001) and multivariate (OR, 0.72; P<0.001) analyses. Sociodemographic factors, including older age, higher education, marital status, higher income, professional occupation, and regular exercise, were linked to decreased odds of depression. Conversely, female sex, current smoking, and alcohol consumption were associated with increased odds.
Conclusion
The findings reveal an inverse relationship between diet quality and depressive symptoms among Korean adults, emphasizing the potential of dietary improvements in mental health promotion. Sociodemographic factors significantly influence depression risk. Future studies should adopt longitudinal designs incorporating a wider range of variables to elucidate these complex interactions.
INTRODUCTION
Depression is a widespread mental health disorder that presents significant public health challenges, affecting over 280 million people globally [1]. Despite advancements in treatment, approximately one-third of patients fail to respond to standard medications, underscoring the need for effective healthcare strategies to promote mental health [2].
Recent research has increasingly focused on the relationship between diet and mental health, with studies highlighting the influence of dietary patterns on psychological well-being. Evidence indicates that a traditional Western diet, characterized by processed or fried foods and sugary products, is associated with a heightened risk of mental disorders, including anxiety and depression [3]. In contrast, a systematic review and meta-analysis revealed that the Mediterranean diet, which prioritizes vegetables, fruits, olive oil, dairy products, nuts, and fresh seafood while limiting processed and red meats, is inversely associated with depression risk [4]. These findings suggest that nutritional interventions may significantly affect mental health, emphasizing the role of diet in managing mental health conditions.
In South Korea, depression is a critical public health issue with distinct epidemiological features. Although the country reports a lower prevalence of major depressive disorder compared to other nations, it has one of the highest suicide rates among Organization for Economic Cooperation and Development countries [5]. This disparity highlights the urgent need for targeted mental health interventions in South Korea.
Rapid urbanization and globalization have led to considerable changes in the traditional Korean diet, with increased consumption of processed and high-calorie foods [6]. This dietary shift necessitates further investigation into the association between modern dietary patterns and depression in the Korean population. Previous research has explored the relationship between diet quality and mental health in Korean adults [7-9]. However, these studies are limited, both in number and scope, particularly concerning the Korean diet. Notably, while various methods have been employed to assess diet quality and depressive symptoms, this study is the first in South Korea to specifically examine the association between diet quality, measured using the Recommended Food Score (RFS), and depressive symptoms, assessed using the Patient Health Questionnaire-9 (PHQ-9)—both established screening tools.
This study aims to investigate the relationship between diet quality, as assessed by the RFS, and depressive symptoms, measured by the PHQ-9, in a sample of Korean adults. The findings are expected to contribute to the growing body of evidence on the impact of diet on mental health and provide valuable insights into potential dietary interventions for depression prevention in South Korea.
METHODS
1. Study Design and Participants
This cross-sectional study examined the association between diet quality and the presence of depressive symptoms in participants who visited Seoul Metropolitan Government-Seoul National University (SMG-SNU) Boramae Medical Center’s health examination center in Korea between October 13, 2014, and March 12, 2020. Of 23,042 participants, 19,786 completed both the RFS and PHQ-9 questionnaires. A total of 7,204 individuals who did not complete either the PHQ-9 or RFS questionnaires or had missing data were excluded from the analysis (Figure 1). This study was approved by the Institutional Review Board (IRB) of SMG-SNU Boramae Medical Center (IRB no., 20-2023-56). The requirement for obtaining informed consent was waived due to the retrospective nature of the study.
Flowchart of study participants. RFS, Recommended Food Score; PHQ-9, Patient Health Questionnaire-9.
2. General Characteristics and Anthropometric Indexes
Participants completed a self-reported questionnaire prior to health examinations. The questionnaire included information on education, marital status, income, occupation, depressive symptom screening using the PHQ-9, and dietary habits assessed via the RFS. It also covered personal medical history, medication use, smoking habits, alcohol consumption, exercise, and the presence of metabolic syndrome. Components of metabolic syndrome include abdominal obesity (waist circumference ≥90 cm in men, ≥85 cm in women), impaired fasting glucose (fasting plasma glucose ≥100 mg/dL), elevated triglycerides (fasting triglyceride levels ≥150 mg/dL), reduced high-density lipoprotein (HDL) cholesterol (HDL-cholesterol <40 mg/dL in men, <50 mg/dL in women), and elevated blood pressure (systolic blood pressure ≥130 mm Hg or diastolic blood pressure ≥85 mm Hg).
Participants’ age and sex were recorded. Age was categorized as follows: under 40 years (≤39 years), 40 to 49 years, 50 to 59 years, and 60 years and above (≥60 years). The subdivision of older age groups was based on evidence from a systematic review and meta-analysis that reported an increased prevalence of depression in the older population [10]. Body mass index was calculated using an automatic height/weight meter. Waist circumference was measured in the standing position at the midpoint between the lowest rib and the top of the hip bone during light breathing. Resting systolic and diastolic blood pressures were also recorded. Blood samples were collected for laboratory analysis, and fasting blood glucose, glycated hemoglobin, total cholesterol, triglycerides, and high-density lipoprotein cholesterol levels were assessed after at least an 8-hour overnight fast.
3. Diet Quality Assessment and Outcomes
Diet quality was measured using the RFS, a food-based metric developed to assess adherence to dietary guidelines [11]. To better align with the Korean diet, a modified version of the RFS was used, which included food items such as beans, mixed grains, vegetables, fruits, seafood, dairy products, and nuts [12].
The RFS assigns points to food items as follows: daily meal frequency (1), legumes (4), grains (1), vegetables (17), fruits (12), seaweeds (2), fish (5), dairy products (3), nuts (1), and tea (1). In total, 46 food items or groups consistent with dietary recommendations were included. Participants received one point for each food or regular eating habit (three meals per day) consumed at least once per week. The total possible score ranges from 0 to 47 points, with higher scores indicating better dietary quality. To simplify the analysis, the RFS scores were categorized into two groups: scores below 23 and scores of 23 or higher. This cutoff was based on a median score of 23; those scoring 23 or higher were categorized as having good overall meal quality, whereas those scoring below 23 were classified as having poor meal quality.
4. Depressive Symptoms Assessment and Outcomes
The severity of depressive symptoms was assessed using the PHQ-9, a tool intended for the criteria-based diagnosis of depression and related mental disorders [13]. The questionnaire required participants to report the frequency of nine symptoms over the past 2 weeks, in accordance with the criteria outlined in the Diagnostic and Statistical Manual of Mental Disorders, 4th edition. Each item was rated from 0 to 3, resulting in a total score between 0 and 27. In this study, scores of 5 or higher indicated mild, moderate, or severe depressive symptoms, categorizing participants into the positive PHQ-9 group. As outlined by a study validating the Korean adaptation of the PHQ-9, a total score of 5 or higher serves as a reliable cut-off value for screening depressive disorders [14].
5. Statistical Analysis
The general characteristics of men and women were compared using the chi-square test to identify significant differences. Participant characteristics are presented as numbers and percentages of categorical variables.
Binary logistic regression, employing the backward stepwise method, was used to estimate the odds ratios (OR) and 95% confidence intervals (CI) for the likelihood of depression based on RFS. Univariate and multivariate analyses were performed. Univariate analysis provided crude ORs without adjustment, while multivariate analysis adjusted for potential confounders.
Statistical significance was set at P<0.05. Statistical software R ver. 4.2.2 (R Foundation for Statistical Computing, Vienna, Austria) was used for all analyses.
RESULTS
1. Demographic Characteristics of Study Participants
Table 1 presents the demographic characteristics of the study participants by sex. Among the 12,582 participants, 6,955 were men and 5,627 were women. Statistically significant sex differences were observed across all listed characteristics. Women were more likely to be in the positive PHQ-9 group and had lower RFS scores (both P<0.001) compared to men. Regarding age distribution, women were more frequently represented in the younger age group (under 40 years) compared to men. Women were also more likely to have lower education levels, be single, have lower income, be unemployed, and be nonsmokers and non-drinkers. Additionally, they had less exercise and a lower prevalence of metabolic syndrome (all P<0.001).
Demographic characteristics of study participants by sex
2. Association between Depression and Demographic Characteristics among Study Participants
Depressive symptoms were assessed using the PHQ-9. Participants were categorized into two groups based on their PHQ-9 scores: those with scores below 4 were placed in the negative PHQ-9 group, while those with scores of 5 or higher were placed in the positive PHQ-9 group. Table 2 shows the association between various demographic, socioeconomic, and lifestyle factors and the likelihood of participants being in the positive PHQ-9 group compared with the negative PHQ-9 group.
Association between sociodemographic factors and depression (PHQ-9)
Univariate and multivariate analyses revealed that older age, higher education level, marital status, higher income, professional occupation, and exercise were significantly associated with a reduced likelihood of being in the positive PHQ-9 group. Conversely, female sex, current smoking status, and increased alcohol consumption were significantly associated with a higher likelihood of having positive PHQ-9 scores. Metabolic syndrome did not show a significant correlation with PHQ-9 groups in the univariate analysis, but it was significantly associated with positive PHQ-9 scores in the multivariate analysis. The forest plot in Figure 2 illustrates the association between various demographic variables and the PHQ-9 groups, showing ORs and 95% CIs derived from the multivariable analysis.
Forest plot showing the multivariable analysis of variables associated with depression (Patient Health Questionnaire-9, PHQ-9). OR, odds ratio; CI, confidence interval; RFS, Recommended Food Score.
3. Association between Diet Quality and Depression
Higher RFS was associated with lower odds of being in the positive PHQ-9 group in both univariate (OR, 0.59; P<0.001) and multivariate (OR, 0.72; P<0.001) analyses.
4. Association between Diet Quality and Depression by Item
The forest plot in Figure 3 illustrates the association between various RFS items and the PHQ-9 groups, showing ORs and 95% CIs derived from the multivariable analysis. The results were adjusted for sex, age, education, marital status, income, occupation, smoking, drinking, exercise, and metabolic syndrome.
Forest plot showing the subgroup analysis of nutrient intake and its association with depression (Patient Health Questionnaire-9, PHQ-9). OR, odds ratio; CI, confidence interval.
Consuming three meals per day was associated with lower odds of being in the positive PHQ-9 group (OR, 0.68; P<0.001). Furthermore, the consumption of soybean paste, beans, spinach, nuts, tangerines, tomatoes, and yogurt was significantly associated with lower odds of being in the positive PHQ-9 group. In contrast, exposure to pollution was associated with higher odds of being in the positive PHQ-9 group (OR, 1.19; P=0.001).
DISCUSSION
This study examined the relationship between diet quality, as measured by the RFS, and depressive symptoms, assessed using the PHQ-9, in a sample of Korean adults. The results demonstrated that a high RFS was associated with low PHQ-9 scores, indicating that overall diet quality is inversely related to depressive symptoms.
Previous studies have investigated the association between diet quality and depression in the Korean population. The 2014–2015 National Fitness Award Project explored this relationship by using the RFS to assess diet quality and the Beck Depression Inventory to measure depressive symptoms [7]. These findings suggest that higher diet quality correlates with fewer depressive symptoms. A study by Hwang et al. [8] employed the modified Mediterranean diet score to evaluate diet quality, revealing that adherence to the Mediterranean diet was inversely associated with depression in both male and female Korean adults. Kim et al. [9] used the Korean Health Eating Index to assess diet quality and concluded that a higher-quality diet is associated with a reduced risk of depression and an improved quality of life. Overall, previous studies emphasize that adopting healthy eating behaviors may enhance mental health.
Moreover, previous research has proposed a mechanism underlying the association between high diet quality and a lower risk of depression. High-quality diets that include fruits, vegetables, whole grains, and lean proteins provide essential nutrients such as vitamins B and D, zinc, magnesium, and omega-3 fatty acids, which have been shown to protect against depression [15]. In contrast, high glycemic index foods and calorie-dense foods may have detrimental effects on psychological well-being [16].
In this study, we examined the association between depressive symptoms and dietary patterns through a subgroup analysis of each item, as shown in Figure 3. Consumption of soybean paste, beans, spinach, nuts, tangerines, tomatoes, and yogurt was linked to a lower risk of depressive symptoms, consistent with previous studies. In contrast, our study found a positive association between pollack consumption and an increased risk of depressive symptoms, which diverges from earlier research. A specific association between depression and pollack consumption has not been reported previously. However, this relationship may be attributed to the fact that fish contains animal proteins that have been linked to an increased risk of depression [17]. Animal proteins can promote inflammation, disrupting neurotransmitter metabolism and negatively affecting brain function. However, previous meta-analyses have demonstrated that high fish consumption is associated with a reduced risk of depression [18]. The observed inconsistency between fish consumption and depression underscores the importance of considering other nutritional factors, such as omega-3 fatty acids, to fully understand this association and highlights the need for further investigation.
We also explored the association between depressive symptoms and various sociodemographic factors, as assessed using the PHQ-9. Consistent with previous research, our study found higher odds of developing depressive symptoms in women, current smokers, and individuals with higher alcohol consumption [19-21]. In contrast, higher education levels, marital status, higher income, professional occupation, and regular exercise were associated with reduced odds of depressive symptoms [22-24]. Participants with metabolic syndrome had significantly higher odds of developing depressive symptoms than those without metabolic syndrome [25]. Contrary to expectations, participants in their 50s and 60s had lower odds of experiencing depressive symptoms, as measured by the PHQ-9, compared to those in their 40s. Previous studies have suggested that aging is associated with poor health, which may increase the risk of depression [26]. However, other studies have indicated that aging can reduce stress after retirement [27]. These findings underscore the complex interplay between various sociodemographic and lifestyle factors that influence the risk of depression.
The multifactorial nature of depression requires recognition that its relationship with various sociodemographic and lifestyle factors, such as alcohol consumption and smoking, may be bidirectional rather than strictly causal. Previous research has highlighted the complexity of these interactions, with each condition potentially exacerbating the other. Alcohol consumption can contribute to depression through legal issues, social consequences, and physical health decline, whereas depression may increase alcohol use as a form of self-medication and encourage social isolation [28]. Similarly, smoking can exacerbate depression through chronic health issues and a reduced quality of life, while depression may promote smoking as a means of self-medication or for temporary symptom relief through nicotine exposure [29]. These bidirectional relationships underscore the need for mental health strategies that address these dynamic interactions.
Although this study provides insights into the association between diet quality, as measured by the RFS, and depressive symptoms, as assessed by the PHQ-9, several limitations must be considered. First, the cross-sectional design precluded causal inferences regarding the relationship between diet quality and depressive symptoms. Future longitudinal studies are necessary to clarify the direction of this relationship. Second, both the RFS and the PHQ-9 rely on self-reported data, which may be subject to recall bias and inaccuracies. Self-reported dietary assessments, such as the RFS, are common in epidemiological studies but may not fully capture all aspects of dietary intake, including meat consumption or nutrient quantities, which could lead to measurement errors. Third, this study did not account for prior diagnoses of depression or the use of related medications, both of which could have served as confounding factors. Nonetheless, the findings remain relevant, as dietary interventions are often used alongside medication as preventive or adjunctive treatments, making the results applicable to both medicated and non-medicated individuals. Fourth, the study did not assess exercise intensity. Previous research suggests that moderate-intensity exercise is effective in reducing depressive symptoms, emphasizing the importance of incorporating exercise of varied intensity into mental health strategies [30]. Fifth, this study used a single tool to assess depressive symptoms. Future studies should consider using multiple tools to assess depressive symptoms, as this would increase the validity and robustness of the findings. Sixth, the study population consisted of individuals who visited a single general hospital, which limits the generalizability of the results to the broader Korean adult population. Finally, although adjustments were made for various sociodemographic and health-related variables, residual confounding factors may not have been fully accounted for. Future research should include a broader range of variables to gain a more comprehensive understanding of these associations.
In conclusion, our study demonstrated that higher diet quality was inversely associated with depressive symptoms in a sample of Korean adults. This suggests that dietary improvements play a crucial role in promoting mental health and preventing depression in diverse populations. Furthermore, our findings indicated significant associations between various sociodemographic factors and depression risk. Future research should employ longitudinal designs that consider a broader range of variables to further elucidate these complex interactions.
Notes
CONFLICT OF INTEREST
No potential conflict of interest relevant to this article was reported.