Nutritional approaches for treatment of Major Depressive Disorder

By Doris Amaro, Medical Student, UTMB

“Let food be thy medicine, and medicine be thy food” so brilliantly stated by Hippocrates, may have been a declaration that we can use the nutrients from the earth to heal our bodies. However, it is difficult to imagine how the food we put into our bodies influences our thoughts, emotions, and particularly our development of mental illness. There are a number of different integrative and complementary approaches for major depressive disorder that include lifestyle modifications, dietary supplementation, psychotherapeutics, and pharmaceuticals that are prescribed for patients. However, currently there is no clinical research supporting the use of diet for treating depression. As we elucidate the mechanisms of inflammation, the gut microbiome, and their contribution to mental health, dietary manipulation is surely on its way.

 

The anti-inflammatory diet, which recommends high fish intake, is commonly recommended to patients for a variety of health conditions due to its favorable omega-3 to omega-6 ratio. A healthy omega-3 to omega-6 ratio has been shown to be important for neurocognitive function. Omega-3 is known to be anti-inflammatory, while omega-6 is proinflammatory. Omega-6 fatty acids are found in animal foods such as meat and poultry and Omega-3 fatty acids are found in high amounts in certain types of fish. Thus, increasing fish intake and decreasing meat and poultry intake is hypothesized to have a positive effect on mood. In a 2-week pilot randomized controlled trial , participants were separated into 3 different groups according to diet. These groups consisted of the omnivore group (OMN), the fish group (FISH), and the vegetarian group (VEG).¹ Results showed that mood scores were unchanged in the OMN and FISH group, but had increased significantly for the VEG participants. One possible explanation for this, as stated in the article, is that the VEG diet was high in antioxidants which possibly conveys overall mood protection. Similar results were found in a cross-sectional study done on Seventh Day Adventist in which the population was separated into omnivores and vegetarians. Vegetarians reported significantly less negative emotion and higher linoleic acid (LA) and alpha-linoleic acid (ALA) intake than omnivores.² These substrates have been shown to inhibit desaturases, preventing the formation of arachidonic acid (AA), a substrate that is pro-inflammatory. Many studies have revealed that the AA content of serum lipids was either similar or significantly lower in vegetarians than in omnivores despite higher LA concentrations and lower docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) concentrations, which are anti-inflammatory. Therefore, low intakes of EPA and DHA may not be linked to adverse mood states in vegetarian populations because of high ALA intake, low AA intake, and regulation of the LA to AA conversion.

Another possible mechanism in which diet can affect mental health is through the gut microbiome. In a double-blind, randomized, placebo-controlled study, psychobiotic supplementation alleviated depression symptoms, achieving similar effects to common antidepressants.³ These psychobiotics contain the same type of bacteria that are shown to increase in the gut on a plant-based diet, namely Lactobacillus and Bifidobacterium. Therefore, a plant-based diet may have similar effects on mood states in depression as do the psychobiotics, given their comparable modification of gut microbe diversity.
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One concern about the Mediterranean diet is how safe it is to consume enough fish to get the recommended amount of DHA in your diet to have any anti-inflammatory effect. Some fish were shown to have high levels of these toxins that are possibly carcinogenic such as polychlorinated biphenyls (PCBs), mercury, polybrominated diphenyl ethers (PBDEs), furans, and other dioxins. Thus, if patients are advised to eat more fish, they should be educated about risks of toxins, particularly in pregnant and breastfeeding women. A high carbohydrate plant-based diet may be helpful for improving the gut-microbiota axis and thus overall mood.
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Plant-based diets have been shown to reverse diabetes, improve many different inflammatory markers in the body, and overall well-being in the diabetes population. They are   also low in cholesterol, important for the prevention of atherosclerosis and our leading cause of death, heart disease. The Dietary Approaches to Stop Hypertension (DASH) diet, which promotes a plant-based diet low in animal product intake, has been shown to be superior to the Mediterranean diet for hypertension and prevention of colorectal cancer. Given all of the evidence in favor of a plant-based diet, properly guided dietary interventions for treatment of major depressive disorder is a promising field for patients who would like a more holistic treatment approach.
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References:

1. Beezhold, B. L., & Johnston, C. S. (2012). Restriction of meat, fish, and poultry in omnivores improves mood: a pilot randomized controlled trial. Nutrition journal, 11, 9. doi:10.1186/1475-2891-11-9
2. Beezhold, B. L., Johnston, C. S., & Daigle, D. R. (2010). Vegetarian diets are associated with healthy mood states: a cross-sectional study in seventh day adventist adults. Nutrition journal, 9, 26. doi:10.1186/1475-2891-9-26
3. Liang, S., Wu, X., Hu, X., Wang, T., & Jin, F. (2018). Recognizing Depression from the Microbiota⁻Gut⁻Brain Axis. International journal of molecular sciences, 19(6), 1592. doi:10.3390/ijms19061592