Depression and Nutrition. The Role of Nutrients in Supporting Mental Health, and Contributing to and Combating Depression
This article includes significant excerpts from The Role of Nutrition in Mental Health: Depression, written by Jesse A Solomon, Ziv Zukier, and Mazen J. Hamadeh from the School of Kinesiology and Health Science, Faculty of Health, York University, Toronto, Ontario. (http://www.mindingourbodies.ca/about_the_project/literature_reviews/depression_and_nutrition)
Depression and Nutrition – A Link
Currently, depression is often treated with a combination of therapy and medication, the latter with an inherent risk of unwanted side effects. For this article, an online literature search to review published peer-reviewed articles investigating a connection between dietary habits and risk of depression, as well as nutritional interventions used to treat symptoms of depression, was conducted.
The literature suggests a link between dietary habits and the risk of depression. Studies have implicated a relatively low intake of fish, omega 3 fatty acids, and fruits and vegetables as risk factors for depression. In addition, relatively high amounts of refined sugar and processed foods have been shown to increase the risk of depression. Although promising, more nutrition-based intervention studies are required to firmly establish effective diet-based treatments for people diagnosed with depression.
Depression is a disorder that compromises an individual’s ability to perform day-to-day tasks due to feelings of sadness, leading to chronic symptoms affecting everyday functioning . Depression is an umbrella term that includes psychotic depression, postpartum depression, seasonal affective disorder, and the most commonly diagnosed forms of depression: major depressive disorder and dysthymic disorder. The major depressive disorder presents symptoms of decreased mood, increased sadness and anxiety, loss of appetite, loss of interest in pleasurable activities, and more .
Depression, Medication, and Nutrition
Depression is often treated with antidepressants and other prescription medication. This often leads to severe side effects and the termination of continued medication [2, 5]. Recently, nutritional status has been linked to depression, and several epidemiological studies have assessed its relationship with micro-and macro-nutrient consumption. Micronutrient deficiencies in folic acid [6, 7], thiamine , magnesium , and omega 3 fatty acids [2, 9] have been linked to the prevalence of depression. Some have attributed these deficiencies to an American  or Westernized diet  which is low in fiber, fruits and vegetables, and fish intake, and high in processed foods.
Depression and Diet Patterns
In a 2009 study , 3,486 adult men and women (age 33-55) were categorized as having either a “whole food” (rich in fish, fruits, and vegetables) or “processed food” (rich in processed meat, chocolates, sweet desserts, pies, condiments, fried food, refined cereals, and high-fat dairy products) dietary pattern.
After adjusting for covariates (among them gender, age, marital status, education, physical activity, smoking habits, hypertension, diabetes, cardiovascular disease, use of antidepressant drugs, cognitive functioning and others), participants of the highest-matching ‘whole food’ dietary pattern were the least likely to be depressed compared to the lowest-matching based on the Center for Epidemiologic Studies-Depression Scale (CES-D scale). Dietary pattern factor scores revealed that participants in the highest-matching of the ‘processed food’ dietary pattern were at greater risk for depression compared to those in the lowest-matching group.
These results were based on respondents, some self-identified as having depression and some not. Therefore, a diet rich in processed foods may increase the risk of depression; or those already at greater risk of depression may tend to consume more processed foods. To address this issue, the authors removed those who self-identified as having significant depression.
The re-analyzed data revealed that those in the highest-matching group of the ‘whole food’ dietary pattern were least likely to be at risk for depression, compared to those in the lowest-matching group of the ‘whole food’ dietary pattern. In addition, those in the highest-matching group of the ‘processed food’ dietary pattern were found to be at greater risk of depression compared to the lowest-matching group of the ‘processed food’ dietary pattern.
Although the authors concluded that the results confirm that the lower the quality of the diet, the higher the risk of depression, cause and effect cannot be established because this was an epidemiological study. The role of each individual food item in the risk of depression was not assessed.
A 2008 study (11) involving elderly men and women, aged 65 y and older, found that “healthy” eaters, men who consumed higher amounts of fish and women who consumed higher amounts of fruits and vegetables, had better cognitive performance and self-related health in both sexes, as well as less depressive symptoms in women. In men, “healthy” eaters had significantly lower scores of depression (lower CES-D scores) compared to those identified as “pasta eaters”. In women, “healthy” eaters had significantly lower CES-D scores compared to the “biscuits and snacking” group. .
Moreover, the Sarlio-Lähteenkorva study  showed that 6,243 middle-aged men and women with poor mental health were less likely to eat fruits and berries; this finding was independent of socioeconomic status and health behaviors. The results from the two studies above possibly demonstrate a cyclical pattern of poor eating habits leading to depression and then depression exacerbating poor eating habits.
Other studies have found that higher servings of fish and Omega-3 fatty acids have also been associated with positive effects on depression [17, 18]. The Edwards Study et al  found that a small sample of ten men and women (depressed patients aged 29-49) who were diagnosed with a major depressive episode according to the DSM-IV criteria, consumed 27% less Omega-3 fatty acids in their diet compared to healthy controls, however, this difference was not statistically significant. In addition, depressed individuals had 29% less n-3 fatty acids in red blood cell (RBC) membranes compared to healthy controls.
An epidemiological study  of 3,204 Finnish men and women (age 25-64) revealed that mild to severe depressive symptoms were found to be more prevalent among women who consumed fish less than once per week, compared to women who consumed fish more than once per week (34.2 % vs. 27.0 %). A similar trend was found among men, however, the relationship was not as statistically significant (28.5 % vs. 25.9 %).
Depression and Refined Sugar
Although nutritional deficiencies have been associated with an increased risk of depression, an excess of macronutrients, particularly refined sugar, has also been linked to depression . A cross-national study  including 6 countries (Canada, France, Germany, Korea, United States, and New Zealand) established a strong, positive correlation between national sugar consumption and rates of depression.
Multiple epidemiological studies have demonstrated that a connection exists between the risk of depression and dietary habits. Studies have linked deficiencies in micronutrients (folic acid, thiamine, magnesium) and omega 3 fatty acids to an increased risk of depression.
Other studies have found associations attributing low intake of fish, fruits, and vegetables and high intake of refined sugar, desserts and processed meats to an elevated risk of depression. More clinical trials are needed to ascertain whether correcting nutrient deficiencies or minimizing the excessive intake of certain micronutrients or foods would reduce the risk and/or the symptoms of depression.
Proper nutrition may prove to be an affordable investment for people diagnosed with depression to mitigate their symptoms and improve overall health.
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