Depression is currently a leading cause of health and economic burden, internationally
]. Increased investment in recognition and treatment has failed to improve depression outcomes substantially in recent years, suggesting that other factors may be influencing the burden of this condition
]. Traditionally, treatment of depression has primarily focused on targeting biological and psychological pathways
]. Accumulating evidence now suggests that lifestyle factors such as diet quality contribute to a number of mental illnesses
] and play an important role in the risk and genesis of depression specifically
]. Dietary modification is widely recognised and promoted for the primary prevention of non-communicable disorders, such as cardiovascular disease (CVD), obesity and diabetes, yet has not been considered for the management of mental illness. To date, there are virtually no data regarding the therapeutic impact of dietary changes on depression.
This impact of habitual diet on the common mental disorders, is garnering significant scientific and public interest worldwide. There are many published studies providing consistent support for an association between habitual diet quality and depression
]. For example, in a population based sample of 1046 Australian women aged 20–94 years, a ‘healthy’ dietary pattern was associated with a reduced likelihood of clinically diagnosed depressive disorders, whereas a dietary pattern comprising processed and ‘unhealthy’ foods was associated with an increased likelihood of psychological symptoms and depression
]. Higher diet quality scores were also associated with reduced psychological symptoms
]. The associations between diet quality and mental illness have also been shown in the Hordaland Health Study of 5731 adults in Norway where participants with better quality diets were less likely to be depressed or anxious
]. This association was further investigated in a cross sectional study of more than 7000 Australian adolescents that found dose–response relationships between two measures of diet quality: healthy (negative) and unhealthy (positive) and the likelihood of adolescent depression, after adjustment for confounders
]. A population based study has also demonstrated a cross sectional and longitudinal relationship between diet quality and mental health in approximately 3000 Australian adolescents
]. Importantly, improvements in diet quality were mirrored by improvements in mental health, while reductions in diet quality were associated with declining psychological functioning over the two year follow up period
Similarly, recent prospective data from the SUN Cohort study in Spain demonstrated an inverse association between the level of adherence to a Mediterranean dietary pattern and the risk for incident depression in more than 10,000 adults
]. The Whitehall II cohort study of 3486 participants found an increased risk of self-reported depression after five years for those adhering more strongly to a ‘western’ style diet pattern, and a reduced risk for those following a ‘whole foods’ diet pattern
]. Interestingly, these studies have identified that when ‘unhealthy’ dietary patterns were assessed in relation to depression, they showed positive associations with depression
], indicating that what is excluded from the diet may be as important as what is included.
These recent data consistently support a role for diet quality in depressive illness
]. However, there are currently no available data regarding the therapeutic impact of dietary changes on existing mental illness. Studies involving dietary interventions, in non-psychiatric conditions, have demonstrated that diet can be successfully modified, leading to physiological changes that have implications for improved mental health
]. Taken together with previous data indicating success with individualised nutrition education counselling in those with mental illness
], an intervention targeting dietary improvement may also be feasible for individuals with depression. If found efficacious, such a treatment strategy has the advantage of being of population wide public health importance, and of substantial additional benefit across many disease states
This paper presents the study protocol for the SMILES trial: “Supporting the Modification of lifestyle In Lowered Emotional States.” This is a randomised controlled trial that aims to investigate the efficacy and cost-efficacy of dietary improvement in the treatment of Major Depressive Episodes (MDE). We hypothesise that a structured dietary intervention, focusing on dietary improvement, will be superior to a control condition (befriending) in the treatment of MDE.