The interrelationship between diet, physical health, and depression

By Dr. Priyom Bose, Ph.D.Reviewed by Danielle Ellis, B.Sc.Jan 4 2023

According to the World Health Organization (WHO), depression is a common mental health condition affecting around 280 million people worldwide. Every year approximately 700,000 deaths occur due to depression-driven suicide. Hence, it is imperative to formulate effective interventions and prevention measures to manage depression.

Background

Severe depression is managed via antidepressant medications (e.g., tricyclic antidepressants). However, this line of treatment is not recommended for treating mild depression. Cognitive behavioral therapy and interpersonal psychotherapy are two of the alternative treatments used to prevent the development of depression. In addition, practicing a healthy lifestyle that includes healthy food habits and a substantial increase in physical activity also alleviates depression and other health-related problems, such as obesity and diabetes.                                    

Notably, healthy diets help in depression management because diet regulates various mechanisms, such as inflammation, epigenetics, oxidative stress, tryptophan–kynurenine metabolism, and neurogenesis, that influence brain functions 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 shown the bidirectional interaction between the brain and gut microbiota. These studies have highlighted how dysbiosis, germ-free conditions, and leaky gut affect neurodevelopment and neuroinflammation. Based on the findings of these studies, scientists hypothesized that adopting a proper diet could improve gut health and potentially mitigate depression symptoms.

An individual’s diet can be altered by manipulating the macronutrient content, frequency and timing of food intake, quantity of food, and restricting specific foods or food groups. Gut health can also be improved via probiotics, and microbial metabolites (biogenics), such as gamma-aminobutyric acid (GABA) and vitamins. Prebiotics can also improve the growth and survival of beneficial microbes in the gastrointestinal tract.

Recently, the effect of prebiotics on mental health has been reported. These products enhance 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 functions by regulating metabolic, endocrine, and immune systems. For instance, the administration of Lactobacillus plantarum and Bifidobacterium infantis decreases depression-like symptoms.

About the study

A recent Journal of Affective Disorders study examined the interrelationship between diet, physical health, and depression. This study utilized the US-based National Health and Nutrition Examination Survey (NHANES) data collected between 2011 and 2018. The participants who completed both dietary 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 gut-health-promoting diet and the reduction in depressive symptoms.

Since a higher Body Mass Index (BMI) is an established risk factor for depression across the lifespan, the present study examined the improvement of physical health based on BMI. BMI was calculated as weight in kilograms divided by the height of participants in meters squared. The nutrient intake of the participants was calculated using the food composition values from the USDA Food and Nutrient Database for Dietary Studies.

Depression levels of all the participants were assessed using the 9-item Patient Health Questionnaire (PHQ-9). The frequency of depressive symptoms of all participants was analyzed based on certain response options, namely, “not at all,” “several days,” “more than half the days,” and “nearly 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.

Study findings

A robust association between a gut-health promoting diet, i.e., ingestion of high intake of dietary fiber and fermented food, and reduction in depression symptoms, was established in this study. A gut-health-promoting diet was found to potentially lower depressive symptoms among individuals who experienced varied levels, i.e., very mild to severe depressive symptoms.

The mediating roles of subjective physical health (self-reported BMI) and objective physical health (BMI measured by trained health technicians) with regard to diet and depression were examined. A higher BMI was associated with depression. The finding of this study was in line with previous reports that indicated fiber-rich diets promoted higher gut microbial diversity, which was negatively associated with subsequent weight gain.

Conclusions

The present study has some limitations, including using a binary variable on fermented food that failed to consider the quantity of fermented food consumed. Currently, there is no consensus on the recommended daily intake of fermented food. Hence, the optimal amount of probiotics, biogenics, and prebiotic intake was not evaluated. Despite its limitations, the current study indicated that a gut-health-promoting diet could potentially enhance the possibility of maintaining a healthy BMI and reducing depression among individuals with severe depressive symptoms.