Shreya Wunnava

How is the gut microbiome composition influenced by the Mediterranean diet in comparison to the Western diet/ How does the gut microbiota & diet affect the HPA axis and symptom severity of Major Depressive Disorder (MDD)?

Started Feb. 26, 2025

Abstract or project description

Approximately 8% of Americans are diagnosed with Major Depressive Disorder (MDD) each year (Greenberg et al., 2021), with an estimated 17.5 million Americans experiencing changes in mood, memory, and emotional regulation (Greenberg et al., 2021). The majority of existing literature focuses on neurobiological mechanisms being the sole contributor to MDD. However, emerging science is discovering the strong connection between mental health and the gut-microbiota-brain (GMB) axis, connecting the digestive and nervous systems. Gut microbiota, most commonly referred to as probiotics, the ecosystem of bacteria found in the gastrointestinal tract, communicate bidirectionally by releasing neurotransmitters, cytokines, and microbial metabolites through the GMB axis (Misiak et al., 2020). Imbalances in microbiota phyla and species have been observed to cause higher stress vulnerability, anxiety-like and depressive behaviors, and general emotional dysregulation. An imbalance of microbiota is referred to as dysbiosis, known as an unhealthy gut, directly linked to inflammation and immune dysfunction (Severino et al., 2024). Dysbiosis causes the release of toxic molecules into the bloodstream, causing brain inflammation and disrupting neurotransmitters– ultimately resulting in depressive symptoms (Jeon & Kim, 2016). Conversely, eubiosis, known as the healthy gut, promotes a healthy gut barrier and immune tolerance. The primary way to alter the composition of the gut microbiota results from dietary patterns, as micro- and macronutrients present in foods can promote or suppress growth of specific bacteria phyla. In examining the Mediterranean diet, there is significant growth in bacteria from the phyla Firmicutes and Bacteroidetes, present in foods rich in omega-3 fatty acids, probiotics, fiber and complex carbohydrates. Conversely, Western dietary patterns promote the growth of phyla Proteobacteria, increasing inflammation driven by high omega-6 intake, salt, sugar and low-fiber processed foods (Severino et al., 2024). By examining the effects of both the Mediterranean and Western diets, a clear relationship emerges between dietary choices, changes in gut microbiota, and mental health.