According to the World Health Organization (WHO), depression is a common mental health condition affecting approximately 280 million people worldwide. Approximately 700,000 deaths occur each year from depression-driven suicide. Therefore, it is imperative to formulate effective interventions and preventive measures to manage depression.
Major depression is managed with antidepressant drugs (eg, tricyclic antidepressants). However, this line of treatment is not recommended for the treatment of mild depression. Cognitive behavioral therapy and interpersonal psychotherapy are two of the alternative treatments used to prevent the development of depression. Additionally, practicing a healthy lifestyle that includes healthy eating habits and a substantial increase in physical activity also alleviates depression and other health problems, such as obesity and diabetes.
In particular, healthy diets help in the management of depression because diet regulates various mechanisms, such as inflammation, epigenetics, oxidative stress, tryptophan-kynurenine metabolism and neurogenesis, which influence brain function and mental health. .
Recently, more research has been conducted to understand the impact of gut health on mental conditions. Many preclinical and clinical studies have demonstrated the bidirectional interaction between the brain and the gut microbiota. These studies have highlighted how dysbiosis, germ-free conditions, and leaky gut affect neurodevelopment and neuroinflammation. Based on the results of these studies, the scientists hypothesized that adopting a proper diet could improve gut health and potentially mitigate symptoms of depression.
An individual’s diet can be modified by manipulating macronutrient content, frequency and timing of food intake, food quantity, and by limiting specific foods or food groups. Gut health can also be improved through probiotics and microbial (biogenic) metabolites, such as gamma-aminobutyric acid (GABA) and vitamins. Prebiotics can also enhance the growth and survival of beneficial microbes in the gastrointestinal tract.
The effect of prebiotics on mental health has recently been reported. These products promote the growth of commensal bacteria with psychophysiological effects. Similarly, adequate probiotics, such as yogurt, buttermilk, kefir milk, kimchi, and natto, improve mental health and neuropsychiatric function by regulating the metabolic, endocrine, and immune systems. For example, the administration of Lactobacilli plants and Bifidobacterium infantis reduces depression-like symptoms.
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A recent Journal of Affective Disorders study looked at the interrelationship between diet, physical health, and depression. This study used data from the US-based National Health and Nutrition Examination Survey (NHANES) collected between 2011 and 2018. Participants who completed both the food recall interviews and the depression questionnaire were included in the study. .
A total of 16,572 participants (48.59% male and 51.41% female) were included in the analysis. The main aim of this study was to investigate the link between a diet that promotes gut health and the reduction of depressive symptoms.
Because a higher body mass index (BMI) is an established risk factor for depression over the course of a lifetime, the present study looked at improvement in physical health based on BMI. BMI was calculated as participants’ weight in kilograms divided by their height in meters squared. Participants’ nutrient intakes were calculated using food composition values from the USDA Food and Nutrient for Dietary Studies database.
Depression levels of all participants were assessed using the 9-item Patient Health Questionnaire (PHQ-9). The frequency of depressive symptoms of all participants was analyzed according to certain answer options, namely “not at all”, “several days”, “more than half the days” and “almost every day”. A PHQ score of 5 indicated a mild level of depressive symptoms and a PHQ score of 10 suggested a severe level of depressive symptoms.
In this study, a robust association was established between a diet that promotes gut health, i.e., ingestion of a high intake of dietary fiber and fermented foods, and reduced symptoms of depression. A diet that promotes gut health has been found to potentially reduce depressive symptoms among individuals who experienced varying levels, i.e., very mild to severe depressive symptoms.
We examined the mediating roles of subjective physical health (self-reported BMI) and objective physical health (BMI measured by trained health technicians) with regards to diet and depression. A higher body mass index was associated with depression. This study’s finding was in line with previous reports indicating that high-fiber diets promoted greater gut microbial diversity, which was negatively associated with subsequent weight gain.
The present study has some limitations, including the use of a binary variable on fermented food that did not consider the amount of fermented food consumed. Currently, there is no consensus on the recommended daily intake of fermented foods. Therefore, the optimal intake amount of probiotics, biogenics, and prebiotics has not been evaluated. Despite its limitations, the current study indicated that a diet that promotes gut health could potentially improve the chance of maintaining a healthy BMI and reduce depression among individuals with severe depressive symptoms.
- Lai, C. and Boag, S. (2023) “The association between gut health-promoting diet and depression: A mediation analysis,” Journal of Affective Disorders324, pp. 136-142. doi: 10.1016/j.jad.2022.12.095.