The Gut-Brain Connection and How Digestive Health Shapes Mental Well-Being
- Brainz Magazine
- Jul 18
- 7 min read
Katarina Lijovic is a Functional Nutrition and Holistic Wellness expert who successfully applies her knowledge and skills to help individuals and communities to optimize their health and quality of life.
For decades, mental health was largely viewed through a neurochemical lens. Depression, anxiety, and even neurodevelopmental disorders were considered issues that began and ended in the brain. But today, we know more, and we know better. Science now reveals that our mental well-being is deeply rooted in and influenced by our digestive system, our gut, often referred to as the second brain.
As a Functional Nutritionist, I’ve witnessed firsthand how healing the gut can transform not only physical health but also mood, focus, and emotional resilience. The link between gut health, brain health, and its function is one of the most exciting and empowering frontiers in modern healthcare and Medicine 3.0.
Gut dysbiosis, leaky gut, and mental health disorders
The gut-brain connection, often referred to as the gut-brain axis (GBA), is a complex bidirectional signaling pathway or communication between the nervous system (brain) and the intestine or gut. The axis consists of several connections or pathways, including the vagus nerve, the autonomic and enteric nervous systems, the immune system, the endocrine system, the hypothalamus-pituitary-adrenal axis (HPA), and microbiota and bacterial metabolites. In other words, the mechanisms behind GBA communication involve neuro-immuno-endocrine mediators. This interaction allows the brain to influence intestinal activities, and vice versa, the gut can influence mood, cognition, and mental health. Studies have demonstrated that crosstalk between the brain and gut via the GBA influences behavior, mental health, and cognitive function. The gut and brain are inseparable. At the heart of the gut-brain connection lies the gut microbiome, the complex ecosystem of bacteria, fungi, viruses, and other microorganisms that live in the digestive tract. When this system becomes imbalanced, known as dysbiosis (or when it’s not diverse or rich in various species), it can set the stage for numerous health issues, inflammation, and neurochemical disruption.
In many cases, gut dysbiosis is accompanied by increased intestinal permeability, or “leaky gut.” This allows toxins, pathogens, harmful bacteria, and undigested food particles to escape into the bloodstream, contributing to systemic inflammation and triggering the immune system, all of which can impact the brain as well.
Research now links dysbiosis and leaky gut with several mental health issues, such as:
Depression
Anxiety
Obsessive-compulsive disorder
Bipolar disorder
Schizophrenia
Cognitive decline
Dementia
Inflammation and disrupted neurotransmitter production, particularly serotonin, can deeply influence our mental state. The gut is involved in the production of 95% of the total body serotonin. Serotonin is a neurotransmitter that has roles in the intestines and peripheral metabolism; it sends messages between the body and the brain and plays a key role in mood regulation. Serotonin deficiencies are associated with depression-like behavior. Moreover, gut dysbiosis and intestinal permeability (leaky gut) cause inflammation, which triggers the inflammasome pathway in the brain. This pathway is associated with depressive and anxiety behaviors. The inflammasome is part of an innate immune system signaling pathway that is activated when pathogens or certain bacteria (dysbiosis) are present. Its activation in the nervous system leads to the production of pro-inflammatory cytokines, which results in neuroinflammatory conditions such as depression.
Additionally, the importance of the gut and gut microbiota on brain health is linked to SCFAs (short-chain fatty acids), which are produced by our gut bacteria. These SCFAs can cross the blood-brain barrier, regulate microglia, and maintain brain tissue homeostasis, which is crucial for adequate brain development and involved in behavior modulation. Altered SCFA metabolism is involved in the pathogenesis of autism through disrupted microglial communication and homeostasis.
Nutritional psychiatry: Food as mental health medicine
These insights into the tight connection between the gut and mental health have given rise to a field of nutritional psychiatry, which explores how dietary patterns influence mood, behavior, and cognition through the gut-brain axis.
In my practice, I can see the incredible power of targeted nutrients and diet on mental state and mental health. Diets rich in anti-inflammatory foods, fiber, fermented products, healthy fats, and phytonutrients/polyphenols can help restore gut health and consequently support brain health, emotional stability, and cognitive function. Remember, the food that is beneficial for gut health is great for brain health, too.
Some standout strategies include:
Probiotic and fermented foods (kefir, sauerkraut, yogurt, kombucha) to restore microbial diversity.
Prebiotics (garlic, onions, asparagus, bananas) to feed beneficial bacteria.
Polyphenols (colorful fruits and vegetables) to fight inflammation and oxidative stress.
Omega-3 fatty acids (fatty fish, flaxseeds, walnuts) to reduce inflammation and support brain health.
Elimination of ultra-processed, high-sugar foods, which disrupt microbiome balance, break the intestinal barrier, and simultaneously increase oxidative stress.
Research continues to support this: individuals consuming traditional Mediterranean diets have a significantly lower risk of depression compared to those on a Western diet. The Mediterranean diet is characterized by the consumption of whole foods, a higher intake of fiber through fruits, vegetables, whole grains, legumes, nuts, and seeds, and healthy fats (fish, avocado, nuts, olives, and olive oil). Fruits and vegetables are sources of polyphenols and antioxidants that are beneficial for gut and brain health. Polyphenols have neuroprotective and anti-inflammatory effects. Moreover, increased intake of fruits and vegetables leads to increased microbial diversity and function. This diet is also linked to increased levels of SCFAs.
Supplements that support mental health
Numerous studies have confirmed that supplementation with probiotics can reduce depression and anxiety symptoms. For instance, Rutsch et al. (2020) pointed out that when probiotics with Lactobacillus acidophilus, Lactobacillus casei, and Bifidobacterium bifidum strains were administered to patients with major depressive disorder, their symptoms reduced in comparison to individuals who received the placebo. Similarly, Carabotti et al. (2015) stated that probiotics reduced anxiety and depressive behaviors and that these beneficial effects appear to be strain-specific. For example, the probiotic formulation of Lactobacillus helveticus R0052 and Bifidobacterium longum R0175 restored the tight junction barrier, reduced HPA axis activity, and prevented changes in hippocampal neurogenesis.
B vitamins are crucial for nervous function, and deficiencies in B vitamins (especially folic acid) have been linked to depression-like behaviors. Other vitamins and minerals that are important for brain functions include vitamin D, magnesium, and zinc. For instance, zinc deficiency can trigger depressive symptoms, and zinc supplementation can improve depressive mood, especially when combined with antidepressants. SAMe regulates the methylation of neurotransmitters, and studies have demonstrated its effectiveness in depression-like behaviors. NAC has antioxidant and neuroprotective effects, and omega-3 fatty acids are vital for brain function, gut microbiome composition, and the proper functioning of the gut-brain axis.
Autism, ADHD, and gut connection
The gut-brain axis is also gaining attention in neurodevelopmental conditions such as autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD).
Many children on the autism spectrum experience chronic gastrointestinal issues, and studies show their gut microbiota differs significantly from neurotypical peers. Interventions targeting gut health, through diet, probiotics, and even fecal microbiota transplantation (FMT), have shown improved behavioral symptoms and quality of life. Furthermore, in ADHD, poor gut health, gut dysbiosis, and nutritional deficiencies are common. Addressing these imbalances, especially through micronutrients like zinc, magnesium, iron, and omega-3s, can support better focus, mood regulation, and overall function.
The vagus nerve: Your inner superhighway
One of the most fascinating aspects of the gut-brain axis is the vagus nerve, a bidirectional communication pathway (superhighway) between the gut and the brain. This nerve innervates and influences everything, from digestion and heart rate to mood and inflammatory responses. When gut health is compromised, vagal signaling can become dysregulated, potentially contributing to anxiety, low mood, and brain fog. However, vagus nerve stimulation, whether through diet, breathwork, meditation, cold exposure, or even gargling and laughter, can help restore balance and resilience. Certain probiotic strains have also been shown to influence vagus nerve activity, offering even more reason to nourish your microbiome.
Toward a gut-centered mental health paradigm
Neurotransmitter production is a process that happens in the gut as well, not just in the brain. Thus, mental health is no longer just the domain of brain chemistry. It’s also about inflammation, immune balance, and gut integrity. The gut and brain are interconnected in numerous ways, through the vagus nerve, neurotransmitters, hormones, and the immune system. As the research evolves, so too does our approach, blending nutrition, lifestyle medicine, and nervous system regulation into a more integrative and empowering model of care.
As a Functional Nutritionist, my goal is to help clients understand that mental health doesn’t live solely in the brain and mind, it lives in the gut, too. By nourishing one, we support the other. With targeted nutrients and diet, my clients have resolved issues such as brain fog, anxiety, lack of focus, and gained mental clarity. Your next step toward emotional balance might not be a psychiatric prescription or session, but a plate filled with whole, nutrient-rich, colorful foods, targeted supplements, and a few deep breaths per day to activate your inner superhighway. When we shift the focus from symptom management to root cause healing, especially through the lens of the gut-brain axis, we begin to unlock true transformation.
Read more from Katarina Lijovic
Katarina Lijovic, Functional Nutrition Counselor/Nutritionist
Katarina Lijovic is a Nutritionist and Functional Nutrition Counselor who focuses on addressing the root causes of nutritional imbalances and health concerns, rather than merely managing symptoms. By using a holistic, personalized approach, Katarina works to optimize an individual’s health through tailored nutrition plans, lifestyle modifications, and evidence-based practices. Her mission is to guide individuals toward long-term, sustainable solutions. With her focus on prevention and balance, Katarina empowers individuals to make informed choices that support their overall health and well-being.
Reference:
Carabotti, M., Scirocco, A., Maselli, M. A., & Severi, C. (2015). The gut-brain axis: Interactions between enteric microbiota, central and enteric nervous systems. Annals of Gastroenterology, 28(2), 203–209.
Rutsch, A., Kantsjö, J. B., & Ronchi, F. (2020). The gut-brain axis: How microbiota and host inflammasome influence brain physiology and pathology. Frontiers in Immunology, 11.
