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Systematic Review

Impact of Dietary Interventions on Depression in Adolescents and Young Adults: A Systematic Review and Meta-Analysis

by
Hanhwa Koo
1,
Kodai Ishihara
2,3,4,
Yuji Kanejima
2,3,5,
Miki Nakatani
1 and
Kazuhiro P. Izawa
2,3,*
1
Department of Health Science, Faculty of Medicine, Kobe University, Kobe 654-0142, Japan
2
Department of Public Health, Graduate School of Health Sciences, Kobe University, Kobe 654-0142, Japan
3
Cardiovascular Stroke Renal Project (CRP), Kobe 654-0142, Japan
4
Department of Physical Therapy, Faculty of Nursing and Rehabilitation, Konan Women’s University, Kobe 658-0001, Japan
5
Department of Rehabilitation, Kobe City Medical Center General Hospital, Kobe 650-0047, Japan
*
Author to whom correspondence should be addressed.
Psychiatry Int. 2025, 6(2), 62; https://doi.org/10.3390/psychiatryint6020062
Submission received: 12 April 2025 / Revised: 9 May 2025 / Accepted: 21 May 2025 / Published: 27 May 2025
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Abstract

:
This review aimed to evaluate the effects of dietary interventions on depressive symptoms, quality of life (QOL), and daily functioning in adolescents and young adults with depression. We searched PubMed, Web of Science, and CENTRAL on 17 August 2024. Participants aged 13–40 years with depression, receiving dietary interventions, and enrolled in randomised controlled trials published in English after 2000 were included. For the meta-analysis of depressive symptoms, pooled Hedges’ g was calculated. Five studies involving 288 participants were included in this review, with three showing significant improvements in depressive symptoms favouring the intervention group. Three studies were included in the meta-analysis, which demonstrated a nonsignificant effect (Hedges’ g = −0.45; 95% CI: −1.29, 0.39; p = 0.2946) and high heterogeneity (I2 = 88%). One study reported significant improvements in QOL, and another showed enhancements in executive function, both favouring the intervention group. All included studies reported high adherence to the intervention or low dropout rates. Dietary interventions are highly acceptable to adolescents and young adults with depression and might help improve their depressive symptoms and QOL. However, the results should be interpreted cautiously due to high heterogeneity and the limited number of included trials.

1. Introduction

According to a report by the World Health Organization, approximately 280 million people in the world have depression [1]. In the United States, the prevalence of depression in adolescence and young adulthood is high: 16.9% in 12- to 17-year-olds and 17.2% for 18- to 25-year-olds [2].
Depression during these life stages is often explained in terms of developmental concepts. Emerging adulthood (18 to 29 years) is characterized by instability in love relationships, work, and habitation, as well as a high prevalence of psychiatric disorders [3]. Erikson’s stages of psychosocial development define adolescence as 12 to 18 years and young adulthood as 18 to 40 years [4]. Adolescence is a life stage of discovering and often being confused about one’s identity [4], and identity confusion is both a cause and a consequence of social-emotional disorders [5]. Young adults begin to share themselves more intimately with others, but avoiding intimacy can sometimes lead to depression [4]. Thus, adolescents and young adults are psychologically vulnerable.
Furthermore, depression during these life stages can significantly impact academic, occupational, and social functioning. Previous studies have reported associations between depression and academic achievement [6,7], friendships [6], work absenteeism, and reduced productivity [8].
Pharmacotherapy is the standard treatment for depression [9], but there are several problems with this method. First, about 30% of depressed patients do not respond adequately to antidepressants [10]. Second, half of patients with major depressive disorder (MDD) do not follow their prescribed medication [11]. A major factor contributing to poor adherence to antidepressants is the severe side effects [11,12], and another contributing factor is being a young adult [11,13]. Third, it has been reported that taking antidepressants during pregnancy may have a negative impact on the foetus and mother [14]. This can be a serious problem for continuing medication during pregnancy. Therefore, it is necessary to consider alternative or supplementary treatments for depression other than pharmacotherapy.
Dietary intervention is superior to pharmacotherapy in several aspects. First, the low dropout rate observed in the study of dietary intervention suggests its high acceptability [15]. Second, dietary interventions have few side effects [16]. However, consuming high amounts of specific nutrients through supplements can be harmful [12]. Therefore, in this review, we focussed on dietary interventions that do not involve the intake of dietary supplements or fortified foods.
The effects of dietary interventions on depression have been investigated in many studies. A meta-analysis in children and adolescents aged 6 to 19 years reported a nonsignificant effect of dietary interventions on reducing depressive symptoms (Hedges’ g = 0.05; 95% confidence interval [CI]: −0.25, 0.35; p = 0.70) [17]. Of the two systematic reviews in adults aged 18 years and over, one study found that all included studies showed a reduction in depression measures from baseline to conclusion [18], while the other suggested some positive effect on mood across all included studies [19]. However, there is limited evidence focusing on depressed adolescents and young adults, particularly those aged 18 to 40 years. To our knowledge, no systematic reviews to date have focused specifically on this population. In addition, the effectiveness of dietary interventions alone in treating depression has not been well established, and previous reviews have not considered their impact on quality of life (QOL) and daily life, such as study, work, and relationships.
We hypothesised that dietary interventions would improve depressive symptoms and QOL in adolescents and young adults with depression compared to no dietary intervention or dietary interventions designed to minimize the effects of specific nutrients.
We also hypothesised that dietary interventions would have a positive impact on daily life. The purpose of this review was to clarify the impact of dietary interventions on depressive symptoms, QOL, and daily life in adolescents and young adults with depression.

2. Materials and Methods

The design of the present study was based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement [20]. The study was registered in the OSF registries (https://doi.org/10.17605/OSF.IO/GKH36, accessed on 12 February 2025).

2.1. Eligibility Criteria

Inclusion criteria for this review were as follows: (1) participants were 13 to 40 years old, were medically diagnosed as having MDD or showed depressive symptoms as indicated by a depression measurement scale, and were on the same treatment (including no treatment) for a certain period before the trial; (2) a dietary intervention was conducted; (3) outcomes of the study included depressive symptoms and/or QOL; (4) randomised controlled trial (RCT); (5) articles were written in English; and (6) articles were published after 2000.
Exclusion criteria were as follows: (1) the study included participants not 13 to 40 years old, with mental disorders except for MDD (e.g., postpartum depression, seasonal affective disorder, bipolar disorder, post-traumatic stress disorder, schizophrenia, substance abuse disorder, alcoholism, personality disorder), with symptoms that are barriers to dietary intervention (e.g., gastrointestinal disorders, food allergies, intolerances, aversions), with diseases associated with depression (e.g., cerebral vascular disease, cancer, Cushing’s syndrome, hyperthyroidism, hypothyroidism), or with no depressive disorders; (2) the intervention was for losing weight, for treating other diseases, only supplement intake, or combined with other intervention; and (3) measures that cannot evaluate depressive symptoms independently were used.
The age range was defined based on Erikson’s stages of psychosocial development [4]. While Erikson’s stages define adolescence as 12–18 years and young adulthood as 18–40 years, we included boundary ages in the earlier stage and thus defined the study population as 13–40 years.
We defined dietary intervention based on the previous systematic reviews on whole-diet interventions [17,18,19]. We included factors such as a change in meal content, diet and drink rich or limited in certain nutrients, and counselling on diet-related issues in the dietary intervention and excluded supplement intake. To verify the impact of dietary interventions alone, we excluded studies where the intervention was combined with other types of intervention. However, if participants had been undergoing pharmacotherapy or psychotherapy prior to the trial and continued these treatments during the intervention period, the study was included in this review. The year of publication was defined in the inclusion criteria according to the description in a previous systematic review on a similar topic [18]. Additionally, we did not set inclusion/exclusion criteria for comparisons.

2.2. Search Strategy

One researcher (H.K.) searched studies in three databases: PubMed, Web of Science Core Collection, and Cochrane Central Register of Controlled Trials through Evidence-Based Medicine Reviews. We built search strategies using the following search terms: ‘depressive disorder’, ‘depression’, ‘adolescent’, ‘young adult’, ‘diet’, and ‘nutrition therapy’ (Supplemental Tables S1–S3). We used the filter for year of publication in all databases, and the RCT filter provided in the Cochrane Handbook in the PubMed search strategy [21]. The search strategies were reviewed by a librarian. The study search was conducted on 17 August 2024, and Rayyan was used for literature management after searching [22].

2.3. Selection Process

Two researchers (H.K. and M.N.) independently conducted the title and abstract screening and the full text screening based on the eligibility criteria. The screening results of these two researchers were compared, and the opinion of a third researcher (K.I.) was incorporated to resolve any conflicts in each screening.

2.4. Data Collection Process

We extracted the following information from the included studies: author, year of publication, country, participants (sample size, age, and sex), recruitment, intervention (duration, contents, and frequency), comparisons, outcome measures, and summary of findings.

2.5. Study Risk of Bias Assessment

Two researchers (H.K. and M.N.) independently assessed the risk of bias of the included studies in a blinded manner using the Revised Cochrane risk-of-bias tool for randomized trials (RoB 2) [23]. The assessment results of the two researchers were compared, and the opinion of a third researcher (Y.K.) was incorporated to resolve any conflicts.
RoB 2 is the tool used to assess the risk of bias in a single estimate of an intervention effect reported from a randomised trial [23]. Assessment using RoB 2 was conducted for each outcome. We evaluated each of five domains (the randomisation process, deviations from the intended interventions, missing outcome data, measurement of the outcome, and selection of the reported result) as having ‘low risk’, ‘some concerns’, or ‘high risk’ according to signalling questions. We integrated the domain-level judgments and categorized the overall judgments as ‘low risk’, ‘some concerns’, or ‘high risk’.

2.6. Synthesis Methods

We conducted meta-analysis of depressive symptoms using EZR analysis software (R version 4.4.1) [24]. We used Hedges’ g as an effect size to standardise the results of the studies to a uniform scale because the depression scales used in each study were different. Hedges’ g value was calculated based on mean change, standard deviation (SD), and sample size. The effect size was classified using the following cut off values: trivial (≤0.2), small (>0.2), moderate (>0.5), large (>0.8), and very large (>1.3) [25]. The mean change was calculated by subtracting the mean baseline score from the mean score after the intervention, with a negative value indicating an effect favouring the intervention group.
The overall effect size was calculated by a random effects model. If SDs were not provided, we calculated them based on the 95% CI or participants’ data provided in additional data files [26]. If sufficient data for calculating SDs were unavailable, the study was excluded from the meta-analysis. Statistical heterogeneity was assessed by calculating I2 and τ2. We used the following cutoffs for the assessment of heterogeneity based on I2: 25%, 50%, and 75% indicating low, moderate, and high heterogeneity, respectively [27]. The complete PRISMA checklist is provided in Supplemental Table S4 for further reference.

3. Results

3.1. Study Selection (See Figure 1)

The study selection process is shown in Figure 1. We identified 3090 studies from the three databases: 1664 studies from PubMed, 827 studies from the Web of Science Core Collection, and 599 studies from the Cochrane Central Register of Controlled Trials through Evidence-Based Medicine Reviews. Before the screenings, 576 duplicate studies were removed, and 2455 studies were excluded based on eligibility criteria after the title and abstract screening. Two studies were excluded before the full text screening because it was impossible to obtain the full text, and 52 studies were excluded after the full text screening. Finally, 5 studies were included in the present review, and 3 studies were included in the meta-analysis.
Psychiatryint 06 00062 g001
Figure 1. Flow diagram of the study.
Figure 1. Flow diagram of the study.
Psychiatryint 06 00062 g001

3.2. Study Characteristics

3.2.1. Overview

A summary of the included studies is shown in Table 1. Two studies [28,29] were conducted in Australia, two [30,31] in Korea, and one [32] in the United Kingdom, highlighting a potential geographical bias. The number of participants ranged from 40 to 76, and their mean age ranged from 19.53 to 24.70 years old. One study included only males [29], and the others included both sexes [28,30,31,32]. Participants were recruited from the university community in two studies [28,32] and from the community in three studies [29,30,31]. In all included studies, participants were screened for depressive symptoms at the time of recruitment [28,29,30,31,32]. In two studies [28,29], participants receiving medication and/or psychotherapy were included if they had continued the same treatment for at least two weeks prior to enrolment or study participation. In the remaining three studies [30,31,32], people with a history of psychiatric disorders or who had received pharmacotherapy for psychiatric disorders or psychotherapy were excluded.

3.2.2. Dietary Intervention

The included studies ranged in length from 3 to 12 weeks. In two studies [28,29], participants were recommended to follow the Mediterranean diet as a daily diet. This diet is high in fruits, vegetables, legumes, nuts, seafood, wholegrains, and olive oil while being low in sugar-sweetened beverages, red and processed meats, milk, butter, and sweets [33]. In these two studies [28,29], counselling by a nutritionist, provision of a Mediterranean food hamper, and a handout with information about meals were also included in the intervention. The control group received no intervention in one study [28] and befriending support instead of dietary intervention in the other [29]. Befriending involves the researcher talking to the participant about neutral topics that interested the client, including music, sport, books, cooking, and pets [34]. These two studies of a Mediterranean diet intervention investigated diet quality using several questionnaires and spectrophotometry. All of these measures showed significant improvements in diet quality in the intervention group, indicating high adherence to the Mediterranean diet intervention. The dropout rates in these studies were lower (25.4% and 5.3%, respectively) than those reported in the previous study on medication adherence [11].
In two studies [30,31], the intervention was the consumption of a flavonoid-rich orange juice twice or three times a day before meals while the control group consumed a flavonoid-low orange cordial drink. There were no dropouts in these two studies.
In the remaining study [32], the intervention was the consumption of a blueberry drink every morning, whereas the control group consumed a placebo drink. This study showed a low dropout rate of 6.25% that was not related to dietary intervention.

3.2.3. Depressive Symptoms

Depressive symptoms were assessed in all included studies [27,28,29,30,31]. Measurement tools used in the studies were the Center for Epidemiological Studies Depression Scale (CES-D) [28,30,31], Beck Depression Inventory II (BDI-II) [29,31,32], Hamilton Depression Rating Scale (HAMD-17) [31], the 9-item Patient Health Questionnaire (PHQ-9) [32], and subscales on depression such as the Depression Anxiety Stress Scale-21 (DASS-21)-Depression [28] and Profile of Mood States (POMS)-Depression [28].
In three studies [28,29,30], the decrease in symptom scores of the intervention group was significantly greater than that of the control group. In one study [31], the decrease in symptom scores of the intervention group was numerically greater than that of the control group, but there was no significant between-group difference. In the other study [32], the decrease in symptom scores of the control group was significantly greater than that of the intervention group. In addition, this study by Velichkov et al. [32] also analysed the interactions of ‘treatment fruit and vegetable (FV) intake (low: <4 servings/day vs. high: >4 servings/day)’, and the results showed that depression score decreased more in the control group among low FV consumers compared to high consumers.

3.2.4. Quality of Life

The study by Bayes et al. [29] assessed QOL using the World Health Organization Quality of Life Assessment-brief version (WHOQOL-BREF). The WHOQOL-BREF assessment consists of answering 26 questions, from which the total and four domain scores (physical health, psychological health, social relationships, and environment) can be derived [35]. At the conclusion of the study, significant increases in scores were observed in the intervention group compared to the control group for total, domain 1: physical health, and domain 2: psychological health. There were no significant differences between groups at the conclusion of the intervention for scores of domain 3: social relationships and domain 4: environment.

3.2.5. Outcomes Potentially Impacting Daily Life

We also examined outcomes evaluated in the included studies that could impact daily life. The study by Francis et al. [28] assessed self-efficacy using the New General Self-Efficacy Scale (GSES) and memory using Hopkins Verbal Learning Test Revised (HVLT-R). There were no significant differences between groups for GSES and HVLT-R results after the intervention.
The study by Velichkov et al. [32] evaluated both acute effects (2 h after the first consumption of the drink) and chronic effects (after 6 weeks of consumption) on executive function. Outcome measures included accuracy and reaction time using a modified task-switching paradigm. For acute effects, accuracy on switching trials significantly improved in the intervention group compared to the control group, while reaction time significantly improved in the control group compared to the intervention group. As for chronic effects, no significant differences were observed between the groups in either accuracy or reaction time on switching trials at the conclusion of the intervention. The findings are summarised in Table 2.

3.3. Risk of Bias in Studies

The results of the assessment of risk of bias are shown in Figure 2. For overall judgements, three studies [28,29,32] had a high risk of bias, and the other two studies [30,31] had some concerns in measuring depressive symptoms. The study that measured QOL [29] also had some concerns. The study that measured self-efficacy and memory [28] had a high risk of bias for each outcome, whereas the study that measured executive function [32] showed a low risk of bias.
For domain-level judgements, all studies [28,29,30,31,32] had a low risk of bias in regard to deviations from the intended interventions. In terms of missing outcome data, the study by Francis et al. [28] showed a high risk of bias in measuring depressive symptoms, self-efficacy, and memory, and the study by Velichkov et al. [32] showed a high risk in measuring depressive symptoms. The study by Francis et al. [28] showed a high risk in terms of the measurement of the outcome in measuring depressive symptoms and self-efficacy, whereas the study by Bayes et al. [29] had a high risk in the selection of the reported result in measuring depressive symptoms.

3.4. Meta-Analysis of Depressive Symptoms

The results of the meta-analysis of depressive symptoms are shown in Figure 3. Of the five studies included in the review, two studies [30,31] were excluded from the meta-analysis because sufficient data for calculating SDs were unavailable; thus, meta-analysis was conducted on only three studies [28,29,32]. The pooled Hedges’ g was −0.45 (95% CI: −1.29, 0.39; p = 0.2946), indicating a small but nonsignificant effect favouring dietary interventions for reducing depressive symptoms. There was high between-study heterogeneity (I2 = 88%, τ2 = 0.4921). Considering Hedges’ g in each study, the study of the Mediterranean diet intervention for three weeks [28] showed a moderate effect favouring intervention, that for 12 weeks [28] showed a large effect favouring intervention, and the study of the blueberry drink intake for six weeks [32] showed a small effect favouring the control group.
All three studies included in the meta-analysis had a high risk of bias: due to missing outcome data and measurement of the outcome in the study by Francis et al. [28]; due to selection of the reported result in the study by Bayes et al. [29]; and due to missing outcome data in the study by Velichkov et al. [32]. Because of the very small number of included studies, tests of symmetry for the funnel plot were not performed.

4. Discussion

4.1. Summary of Main Findings

To our knowledge, this is the first systematic review to examine the impact of dietary interventions in adolescents and young adults with depression. In three of the five included studies, depression scores significantly improved in the intervention group compared to the control group. The results of the three studies included in the meta-analysis showed a statistically nonsignificant effect of dietary interventions on depressive symptoms and high between-study heterogeneity. One study each measured QOL and outcomes that could impact daily life (self-efficacy, memory, executive function). Significant improvements in QOL (total and domains 1 and 2) and executive function over the short term, favouring the intervention group, were reported.

4.2. Effect on Depressive Symptoms

Interventions demonstrating a significant between-group difference favouring the intervention group included a recommendation for a Mediterranean diet and the intake of orange juice. Adherence to a Mediterranean diet is associated with reduced depressive symptoms, as demonstrated in numerous interventional and observational studies [36,37,38].

4.2.1. Possible Mechanisms Behind Symptom Improvement

Depression is believed to result from an interaction of biological, psychological, and social factors [39]. Biologically, the Mediterranean diet is rich in fruits, vegetables, nuts, seafood, and whole grains, while oranges are high in flavonoids, a type of polyphenol. Omega-3 fatty acids found in fish and nuts possess anti-inflammatory properties, which can counteract inflammation-induced reductions in neurogenesis [40]. Additionally, fibre and polyphenols in fruits and vegetables are thought to promote brain health by influencing the gut microbiota [40]. In the study on orange juice intake [30], changes in the gut microbiota and a significant increase in levels of brain-derived neurotrophic factor (BDNF)—a neurotrophin with protective action against the pathogenesis of depressive disorders [40]—were observed in the intervention group.
Psychological factors include the presence of strong, repetitive stressors in certain circumstances [39], while social factors involve having a fragile social support network [39]. As reported in an RCT of a Mediterranean diet intervention for adults [37], mental health improvements may be linked to the social component, where peer support, such as cooking workshops, was effective in addressing depression. In the present review, the two studies recommending a Mediterranean diet [28,29] provided counselling and phone calls by nutritionists, assisting participants in navigating challenges related to the dietary intervention. Furthermore, in the study by Bayes et al. [29], 86% of participants resided in shared housing, student accommodations, or their parents’ homes, suggesting that housemates may have facilitated dietary changes. These biological mechanisms and social support factors likely contributed to the observed improvements in depressive symptoms through dietary interventions.

4.2.2. Potential Reasons Limiting Improvement in Depressive Symptoms

Contrary to our hypothesis, the study by Choi et al. [31] demonstrated a nonsignificant between-group difference in reducing depressive symptoms. Additionally, in the study by Velichkov et al. [32], the control group experienced a significantly greater reduction in depression scores compared to the intervention group. Velichkov et al. [32] hypothesized that individuals with lower fruit and vegetable (FV) consumption were more responsive to effects on depressive symptoms in the control group, stating: “It is possible that a high FV intake results in greater exposure to phytochemicals, which renders individuals less responsive to FV-based dietary interventions via habituation”.
Furthermore, both studies that did not show an effect from dietary interventions [31,32] lacked screening for participants’ diet quality, suggesting that habitual diet quality may have influenced the therapeutic effectiveness of the dietary interventions. Measuring diet quality at baseline could be a critical consideration for future research. Both studies [31,32] also shared a commonality where participants in the control group consumed a placebo drink, potentially introducing expectation bias into the results.

4.2.3. Interpretation of Meta-Analysis Results

The meta-analysis revealed a nonsignificant effect of dietary interventions on depressive symptoms and high between-study heterogeneity. Multiple factors could explain this heterogeneity. First, the duration and contents of the interventions varied across studies. Second, baseline levels of depression among participants differed, with one study reporting severe depression [28] and two studies reporting moderate depression [28,32]. Third, in two studies [28,29], participants continued pharmacotherapy and/or psychotherapy during the intervention, which may have confounded results.
To better estimate the effect size of dietary interventions in the adolescent and young adult population, future analyses should consider more controlled interventions and homogeneous participant groups. A comparison of effect sizes across studies indicated that longer interventions produced greater effects compared to shorter ones. However, even a three-week intervention showed a moderate effect size, suggesting that relatively short-term interventions may also be effective.

4.3. Effect on QOL

In the study by Bayes et al. [29], total score, domain 1: physical health score, and domain 2: psychological health score of the WHOQOL-BREF significantly improved in the intervention group compared to the control group, with no significant between-group differences found for the other two domain scores. In a previous RCT of a Mediterranean diet intervention for adults [37], health-related QOL was assessed, and it showed that dietary changes were associated with better QOL, along with significant improvement in the intervention group only in the dimension of mental health after 3 months [37]. The study by Bayes et al. [29] showed results similar to those of this previous RCT.
For the domains showing improvements, in domain 1, physical health includes physical pain, dependence on medical treatment, energy, activities in daily life, sleep, performance ability in daily living activities, and work capacity [35]. In domain 2, psychological health includes enjoyment in life, concentration, acceptance of appearance, self-esteem, and negative feelings [35]. Some of these factors are included in the symptoms of MDD defined by the DSM-5 [41]. Therefore, it is thought that the improvements in QOL were accompanied by improvements in depressive symptoms.

4.4. Impact on Daily Life

We also examined outcomes evaluated in the included studies that could impact daily life in adolescents and young adults. Self-efficacy is associated with high academic performance and career decisions and has an interactive effect on friendships [42,43,44]. In addition, we considered memory and executive function (accuracy and reaction time) to affect performance in study and work.
The study of the Mediterranean diet by Francis et al. [28] measured self-efficacy and memory and found no significant difference between groups for either of these outcomes. The study of a blueberry drink by Velichkov et al. [32] measured executive function (accuracy and reaction time) and showed an acute but no chronic effect.
Previous research on non-depressed older adults has reported that blueberries and the Mediterranean diet have improved cognitive function, such as memory and executive function, after intervention [45,46]. The results of the study by Velichkov et al. [32] contrast with previous studies in terms of chronic effects. One possible reason for this is that most research on the effects of dietary interventions on cognitive function has been conducted on older people. Addressing the differences from previous research, Velichkov et al. considered that ‘emerging adults, who are at the peak of their cognitive functioning age-wise, might be less susceptible to the effects of blueberries compared to older adults, whose cognitive capacities are in decline’ [32].
Acute improvements in executive function suggested that performance in study, work, and other activities can improve for a short time after dietary intervention, but the long-term impact on daily life was not clear. There was insufficient data to examine the impact on study, work, and relationships, and further research is needed.

4.5. Implications for Future Research or Clinical Practice

This review showed that further research is needed on the topic of this study, and at the same time it provided several suggestions to examine dietary interventions as a treatment for depression.
Previous studies of dietary interventions for depressed individuals have mainly focussed on biological mechanisms for improvement of depression, but little attention has been paid to other aspects. The present study suggests that support from others in changing diet is also an important factor. As adolescence and young adulthood are characterised by challenges in forming and maintaining relationships, dietary interventions that include social support components, such as cooking workshops, may play a significant role in alleviating depression during this life stage.
Diet quality is generally poorer during adolescence and young adulthood compared to other stages of life [47,48]. In fact, one included study suggested that the quality of the participants’ usual diet may have influenced the effectiveness of the dietary interventions. Therefore, adolescents and young adults with usual diets of poor quality may be more likely to benefit from dietary interventions.
All of the included studies showed significant improvements in diet quality in the intervention group or low dropout rates due to adherence to the dietary interventions. This supports the high acceptability of dietary intervention suggested by a previous study [15]. Young adults are considered to have low adherence to antidepressants [13], so dietary intervention is expected to be a highly acceptable treatment for depression.
The calculation of effect sizes in each study showed that even a relatively short-term dietary intervention may improve depressive symptoms. Furthermore, in a comparison of effect sizes of the two studies of a Mediterranean diet intervention, the longer intervention had a greater effect. Future research is needed to clarify the optimal duration of intervention to achieve significant benefits and maintain high adherence.

4.6. Limitations

The present study has several interpretative limitations. First, studies including participants with psychiatric disorders other than depression or comorbidities associated with depression were excluded from this review. Second, a bias was evident in the countries where the included studies were conducted: the two studies recommending a Mediterranean diet were both in Australia, and the two studies on orange juice intake were both from Korea. Third, outcomes other than depressive symptoms were each measured in only one study, preventing data synthesis. Due to these factors, it is difficult to determine whether the findings of this review are generalizable to adolescents and young adults with depression worldwide. Additionally, only one of the included studies reported a biological marker associated with depression, such as BDNF, limiting our ability to draw conclusions about the physiological mechanisms underlying symptom improvement.
This study has several methodological limitations. First, the meta-analysis results showed high between-study heterogeneity and a high risk of bias across all included studies, severely limiting the reliability of the findings. Second, the study was constrained by the overall small number of eligible studies (five in the systematic review, three in the meta-analysis), reflecting the relatively nascent state of research on dietary interventions for depression in adolescents and young adults. Additionally, the small sample sizes and variability in study designs among the included references further restrict the robustness and generalizability of the findings. While methodological rigor was upheld, these constraints highlight the need for further research to expand and strengthen the evidence base.
Additionally, in this review, the strict inclusion of only RCTs, while enhancing internal validity, may have limited the number of eligible studies and the breadth of available evidence. In research areas where RCTs are scarce, well-designed observational studies (e.g., cohort or case-control studies) can provide valuable insights. We strongly suggest that future reviews consider expanding the inclusion criteria to incorporate high-quality observational studies to enhance the comprehensiveness and generalisability of findings.

5. Conclusions

This review demonstrated that dietary interventions are highly acceptable to adolescents and young adults with depression and might help improve depressive symptoms and QOL. However, current evidence remains inconclusive due to high heterogeneity, high risk of bias, and limited data. The limited number of studies included in this review reflects the early stage of this research area. Thus, these findings should be considered preliminary and interpreted with caution.
Further research is needed to verify the therapeutic effects and challenges associated with dietary interventions for adolescents and young adults with depression. Future studies should consider investigating their impact on QOL and daily life as well as exploring more effective content and duration of interventions. Expanding the evidence base through larger, higher-quality studies will be crucial to strengthen the reliability and generalizability of conclusions in this emerging field.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/psychiatryint6020062/s1, Table S1: Search strategy for PubMed; Table S2: Search strategy for the Web of Science Core Collection; Table S3: Search strategy for the Cochrane Central Register of Controlled Trials through Evidence-Based Medicine Reviews; Table S4: The PRISMA Checklist.

Author Contributions

Conceptualization, H.K., K.I., Y.K., M.N. and K.P.I.; methodology, H.K., K.I., Y.K., M.N. and K.P.I.; validation, H.K., K.I., Y.K., M.N. and K.P.I.; formal analysis, H.K. and M.N.; investigation, H.K., K.I., Y.K., M.N. and K.P.I.; resources, H.K., K.I., Y.K., M.N. and K.P.I.; writing—original draft preparation, H.K. and M.N.; writing—review and editing, K.I., Y.K. and K.P.I.; visualization, H.K.; supervision, K.P.I.; funding acquisition, K.P.I. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The authors confirm that the data supporting the findings of this study are available within the article or its Supplementary Materials. The data that support the findings of this study are available from the corresponding author, K.P.I, upon reasonable request.

Acknowledgments

We express our gratitude to the members of the Department of Public Health, Graduate School of Health Sciences, Kobe University, for their support and encouragement throughout this study. Additionally, we appreciate the assistance provided by Kobe University Library in reviewing the search strategies.

Conflicts of Interest

The authors report there are no competing interests to declare.

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Psychiatryint 06 00062 g002
Figure 2. The risk of bias summary for the included studies [28,29,30,31,32].
Figure 2. The risk of bias summary for the included studies [28,29,30,31,32].
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Psychiatryint 06 00062 g003
Figure 3. Forest plot of the meta-analysis of depressive symptoms [28,29,32].
Figure 3. Forest plot of the meta-analysis of depressive symptoms [28,29,32].
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Table 1. Summary of the included studies.
Table 1. Summary of the included studies.
Author (Year),
Country		Sample Size (% Female), Mean Age ± SD or SE Marked with *RecruitmentDurationInterventionComparisonMeasure of Depressive Symptoms, Mean Score (Baseline → After Intervention)Other Outcomes [Measure]Summary of Findings
Francis et al. (2019), Australia [28]I: n = 38 (63.2), 19.53 ± 2.1
C: n = 38 (63.2), 19.67 ± 2.8		University community3 weeks
  • Recommendation of Mediterranean dietInstructions from a registered dietician via a 13 min video
  • Provision of a Mediterranean food hamper and a handout with information about meals
  • 5 min phone call from a registered dietician on Days 7 and 14
No intervention
  • [CESD-R]
    I: 20.56 → 14.62
    C: 20.28 → 20.81
  • [DASS-21-Depression]
    I: 7.18 → 4.37
    C: 7.03 → 6.59
  • [POMS-Depression]
    I: 2.26 → 1.76
    C: 3.41 → 2.97
  • Self-efficacy
    [GSES]
  • Memory
    [HVLT-R (linear, quadratic,
    % recall)]
  • The Intervention group had significantly lower CESD-R (p = 0.007) and DASS-21-Depression (p = 0.002) scores compared to the control group after intervention.
  • There were no significant differences between groups for POMS-Depression (p = 0.459), GSES (p = 0.077), and HVLT-R (linear: p = 0.097, quadratic: p = 0.532, % recall: p = 0.491) after intervention.
Bayes et al. (2022), Australia [29]I: n = 36 (0), 21.5 ± 2.9
C: n = 36 (0), 22.5 ± 2.5		Community12 weeks
  • Recommendation of Mediterranean diet
  • 60 min nutritional counselling by a clinical nutritionist at 0, 6, and 12 weeks
  • Provision of a Mediterranean food hamper and booklet with information about meals
Befriending support on the same visit schedule and duration as the dietary intervention group
  • [BDI-II]
    I: 34.8 → 14.1
    C: 33.5 → 27.3
  • QOL
    [WHOQOL-BREF]
  • The mean change in BDI-II score between groups before and after the intervention was significant, favouring the intervention group (p < 0.001).
  • For QOL, there were significant increases in scores in the intervention group at study conclusion for total (p < 0.001), domain 1: physical health (p < 0.001), and domain 2: psychological health (p < 0.001) compared to the control group.
  • There were no significant between-group differences at the conclusion of study for domain 3: social relationships score (p = 0.676) and domain 4: environment score (p = 0.512).
Park et al. (2020), Korea [30]I: n = 20 (60.0), 22.20 ± 2.6 *
C: n = 20 (60.0), 21.45 ± 2.3 *		Community8 weeks
  • Intake of a flavonoid-rich fresh orange juice (190 mL each) twice a day (30–60 min before breakfast and dinner)
Intake of a flavonoid-low orange cordial (190 mL each) twice a day (30–60 min before breakfast and dinner)
  • [CES-D]
    I: 30.4 → 15.15
    C: 28.35 → 17.85
—
  • The p-values of the CES-D score in the intervention group decreased significantly (p < 0.0001) after the intervention compared to that of the control group (p < 0.001).
Choi et al. (2022), Korea [31]I: n = 20 (70.0), 24.70 ± 2.8
C: n = 20 (70.0), 23.10 ± 2.6		Community8 weeks
  • Intake of a flavonoid-rich orange fresh juice (190 mL each) three times a day (30–60 min before breakfast, lunch, and dinner)
Intake of a flavonoid-low orange cordial (190 mL each) three times a day (30–60 min before breakfast, lunch, and dinner)
  • [BDI-II]
    I: 26.05 → 14.10
    C: 26.55 → 17.05
  • [CES-D]
    I: 34.25 →15.90
    C: 30.30 → 18.15
  • [HAMD-17]
    I: 21.30 → 8.30
    C: 21.80 → 12.40
—
  • The decrease in BDI-II, CES-D, and HAMD-17 scores of the intervention group from baseline to the end of intervention was numerically greater than that of the control group, but there were no significant between-group differences in all scales.
Velichkov et al. (2024), United Kingdom [32]I: n = 30 (66.7), 19.9 ± 1.3
C: n = 30 (70.0), 20.1 ± 1.5		University community6 weeks
  • Intake of a drink prepared by mixing 250 mL water with 22 g freeze-dried wild lowbush blueberries every morning
Intake of a blueberry-flavoured placebo drink every morning
  • [BDI-II]
    I: 26.6 → 18.0
    C: 27.0 → 14.9
  • [PHQ-9]
    I: 14.5 → 9.9
    C: 14.4 → 7.9
  • Executive function
    [A modified version of a task-switching paradigm (accuracy, reaction time)]
Acute effects (2 h)
  • Accuracy on switching trials significantly improved, favouring the intervention group (p = 0.025), whereas reaction time significantly improved, favouring the control group (p = 0.033).

Chronic effects (6 weeks)
  • There were significant improvements in BDI-II scores (p = 0.023) and PHQ-9 scores (p = 0.040), favouring the control group.
  • There were no significant differences between groups in accuracy (p = 0.99) and reaction time (p = 0.11).
BDI-II: Beck Depression Inventory II; C: control group; CES-D: Center for Epidemiological Studies Depression Scale; CESD-R: Center for Epidemiological Studies Depression Scale-Revised; DASS-21: Depression Anxiety Stress Scale-21; GSES: General Self-Efficacy Scale; HAMD-17: Hamilton Depression Rating Scale; HVLT-R: Hopkins Verbal Learning Test Revised; I: intervention group; PHQ-9: 9-item Patient Health Questionnaire; POMS: Profile of Mood States; QOL: quality of life; SD: standard deviation; SE: standard error; WHOQOL-BREF: World Health Organization Quality of Life Assessment-brief version.
Table 2. Summary of the results for executive function.
Table 2. Summary of the results for executive function.
AccuracyReaction Time
Acute effectSignificant difference favouring the intervention groupSignificant difference favouring the control group
Chronic effectNo significant difference between groupsNo significant difference between groups
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Koo, H.; Ishihara, K.; Kanejima, Y.; Nakatani, M.; Izawa, K.P. Impact of Dietary Interventions on Depression in Adolescents and Young Adults: A Systematic Review and Meta-Analysis. Psychiatry Int. 2025, 6, 62. https://doi.org/10.3390/psychiatryint6020062

AMA Style

Koo H, Ishihara K, Kanejima Y, Nakatani M, Izawa KP. Impact of Dietary Interventions on Depression in Adolescents and Young Adults: A Systematic Review and Meta-Analysis. Psychiatry International. 2025; 6(2):62. https://doi.org/10.3390/psychiatryint6020062

Chicago/Turabian Style

Koo, Hanhwa, Kodai Ishihara, Yuji Kanejima, Miki Nakatani, and Kazuhiro P. Izawa. 2025. "Impact of Dietary Interventions on Depression in Adolescents and Young Adults: A Systematic Review and Meta-Analysis" Psychiatry International 6, no. 2: 62. https://doi.org/10.3390/psychiatryint6020062

APA Style

Koo, H., Ishihara, K., Kanejima, Y., Nakatani, M., & Izawa, K. P. (2025). Impact of Dietary Interventions on Depression in Adolescents and Young Adults: A Systematic Review and Meta-Analysis. Psychiatry International, 6(2), 62. https://doi.org/10.3390/psychiatryint6020062

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