According to the World Health Organization (WHO), depression is a common mental illness that affects about 280 million people worldwide. Each year approximately 700,000 deaths occur due to suicide caused by depression. Therefore, it is imperative to formulate effective interventions and prevention measures to control depression.
Study: The association between gut health-promoting diet and depression: a mediation analysis. Image credit: SB Arts Media/Shutterstock
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Severe depression is controlled by antidepressant medications (eg, 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 eating habits and a substantial increase in physical activity also alleviates depression and other health-related problems, such as obesity and diabetes.
In particular, healthy diets help control depression because diet regulates several mechanisms, including inflammation, epigenetics, oxidative stress, tryptophan-kynurene 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 demonstrated 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 symptoms of depression.
An individual’s diet can be altered by manipulating macronutrient content, frequency and timing of food intake, amount of food, and restricting specific foods or food groups. Gut health can also be improved by 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.
Recently, the effect of prebiotics on mental health has been reported. These products enhance the growth of commensal bacteria with psychophysiological effects. Similarly, the right probiotics, such as yogurt, buttermilk, kefir milk, kimchi, and natto, improve mental health and neuropsychiatric functions by regulating the metabolic, endocrine, and immune systems. For example, administration of Lactobacillus plantarum and Bifidobacterium infantis decreases depression-like symptoms.
About the study
A recent study in the Journal of Affective Disorders examined the interrelationship between diet, physical health and depression. This study used data from the US National Health and Nutrition Examination Survey (NHANES) collected between 2011 and 2018. Participants who completed both dietary recall interviews and the depression questionnaire.
A total of 16,572 participants (48.59% men and 51.41% women) were included in the analysis. The main aim of this study was to investigate the relationship 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 across the lifespan, the present study examined improvement in physical health based on BMI. BMI was calculated as weight in kilograms divided by participants’ height in meters squared. Participants’ nutrient intakes were calculated using food composition values from the USDA Food and Nutrient Database for Dietary Studies.
All participants’ depression levels were assessed using the 9-item Patient Health Questionnaire (PHQ-9). The frequency of depressive symptoms for all participants was analyzed based on certain response 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 indicated a severe level of depressive symptoms.
Results of the study
In this study, a strong association was established between a diet that promotes gut health, that is, the intake of high intakes of dietary fiber and fermented foods, and reduced symptoms of depression. It found that a diet that promotes gut health can reduce depressive symptoms among people who experienced varying levels of, that is, 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) in relation to diet and depression. Higher BMI was associated with depression. The finding of this study was in line with previous reports indicating that high-fiber diets promoted greater gut microbial diversity, which was negatively associated with subsequent weight gain.
Conclusions
The present study has some limitations, such as the use of a binary variable on fermented foods that did not take into account the amount of fermented foods consumed. Currently, there is no consensus on the recommended daily intake of fermented foods. Therefore, the optimal amount of probiotics, biogenics and prebiotics was not evaluated. Despite its limitations, the current study indicated that a diet that promotes gut health could improve the chance of maintaining a healthy BMI and reduce depression among people with severe depressive symptoms.
Journal reference:
- Lai, C. and Boag, S. (2023) ‘The association between gut health-promoting diet and depression: a mediation analysis’, Journal of Affective Disorders, 324, pp. 136-142. doi: 10.1016/j.jad.2022.12.095.