Does diet affect clinical levels of depression?
At UniSA Psychology Clinic at Intake, we routinely assess whether clients adhere to national dietary guidelines. While it is clearly necessary to know whether a client is engaging in extreme caloric restriction or excess, I often wonder how much less-extreme forms of suboptimal diet matter to our clients’ mental health. Sure, I’m looking to save time whenever I can, but I’m also cognizant that healthy isn’t normal. According to the ABS in 2020-2021, 91% Australian adults self-report not adhering to recommended daily vegetable consumption and 55% don’t meet daily recommended fruit consumption. And although diet-mood links are often reported in the media, most of these studies draw from the general population with low levels of anxiety and depressive symptoms and weak causal designs. Another team of Australian researchers led by Djamila Eliby reviewed studies reporting on either diet quality or dietary interventions and depression and anxiety among those diagnosed with bona fide depressive or anxiety disorders.
There were 44 studies: 41 on diet quality, 12 of which were prospective, 7 mixed cross-sectional and prospective and 22 cross-sectional; and 3 RCTs of dietary interventions. They excluded studies where diagnosis of depressive or anxiety disorders was established solely via self-report measures or antidepressant use. All 44 studies assessed for depressive disorders but only 6 assessed for anxiety disorders. Although the authors intended to a meta-analysis, heterogeneity in methodology precluded this. Instead, a best evidence synthesis was conducted of the 25 studies whose mean quality ratings exceed the average of all 44 studies. This produced 9 cross-sectional findings, 12 prospective findings, and 4 combined cross-sectional and prospective.
There was strong prospective evidence that higher adherence to the Mediterranean diet was associated with reduced odds/risk for depression. By contrast, there was conflicting evidence as to whether adherence to national dietary guidelines affected prospective depression risk. Single prospective studies (constituting very limited evidence) suggested (in turn) that adherence to the Pro-vegetarian Dietary Pattern and adherence to the Alternative Healthy Index were associated with reduced odds of depression, and no association between adherence to Dietary Approaches to Stop Hypertension (DASH) diet or the Mediterranean-DASH diet Intervention for Neurodegenerative Delay (MIND) diet, and depression risk. There was one study that provided very limited evidence that adherence to the Dietary Inflammatory Index was prospectively associated with increased risk of depression. There was conflicting evidence of an association between depression and healthy or unhealthy eating patterns. Very limited evidence in one study showed no association between a mixed healthy and unhealthy dietary pattern, and depression. Regarding anxiety disorders, only one study provided very limited prospective evidence of no association between GAD and the Brazilian Healthy Eating Index. (These quirky ways of reporting findings are part of the methodology of best evidence synthesis, designed to minimise bias).
Of the RCTs, two studies showed that people with depression receiving a dietary support intervention encouraging adherence to a Mediterranean diet reduced their depressed symptoms compared to control groups (Befriending in one study; Social Support in the other). One of these also found a reduction in anxiety symptoms; in the same study, depression remission rates were 32% in the group that received dietary support compared to the control group (8%). The third study found that those in a dietary support group coaching participants to adhere to general nutrition guidelines – intended to be the control group, compared to problem-solving therapy – achieved equivalent reductions in depressive symptoms.
The authors speculated that there may be mechanisms through which a Mediterranean diet could be uniquely effective against depression. These include anti-inflammatory, antioxidant and endothelial effects, and via increasing brain-derived neurotrophic factor (BDNF) all of which might be neuroprotective. The Mediterranean diet has also been found to reduce inflammatory and pathogenic bacterial species in the gut microbiota, which differ between people with anxiety or depression, compared to healthy controls. However, the authors caution that longer-term studies are needed to be sure the Mediterranean diet has antidepressant effects and acknowledge that studies not meeting the present review’s inclusion criteria have failed to show effects of the diet on depression compared to control groups.
Despite the apparent ever-presence of articles on diet and mental health in my news feed, research into the effects of diet on mental health is relatively young and underdeveloped, with study quality below that of the best psychotherapy trials. Diet adherence is difficult to verify, and reliable diagnosis of mental health disorders is hard to achieve in large samples. Although therapists should be aware if clients are malnourished and routinely screen to ensure clients are neither underweight nor deprived of basic nutrients, the evidence for psychotherapists to routinely pay detailed attention to diet in anxiety and depressive disorders (without eating disorders and in the absence of client goals that focus on dietary goals, as with certain medical conditions) is not strong. An ethical case-by-case analysis is recommended.
Clinician implications
Most studies of diet and mental health focus on the general population and do not focus on people with clinically severe levels of anxiety and depressive disorders
There is little evidence that adhering to general nutritional guidelines affects one’s risk of a Major Depressive Disorder. There isn’t a compelling reason for therapists to monitor adherence to nutritional guidelines outside the context of eating disorders, obesity management or client goals.
Assuming the absence of eating disorders, how much psychotherapists attend to depressed clients’ diets should be made via ethical analysis, case-by-case. Assuming clients are taking in enough calories for sufficient energy and stability of mood, the evidence isn’t strong enough that diet be prioritised over other influences on mood (e.g., sleep, exercise). However, if it isn’t displacing more potent therapeutic activities, and dietary improvements fit with client goals, the client can, of course, choose to set dietary goals and may experience mood improvement via generic satisfaction of values and goals.
There is encouraging evidence that adherence to a Mediterranean diet may reduce risk of future episodes of depression and reduce depressive symptoms. If depressed clients are concerned about their diet, adherence to Mediterranean diet could be integrated into a behavioural activation intervention.
For the original article, go to: https://www.sciencedirect.com/science/article/pii/S2666915323001671?via%3Dihub
REFERENCES
Eliby, D., Simpson, C. A., Lawrence, A. S., Schwartz, O. S., Haslam, N., & Simmons, J. G. (2023). Associations between diet quality and anxiety and depressive disorders: A systematic review. Journal of Affective Disorders Reports, 14, 100629–. https://doi.org/10.1016/j.jadr.2023.100629