The gut and brain are deeply interconnected through the gut-brain axis, a bidirectional highway influenced by the vagus nerve. Up to 90% of vagus nerve fibers relay information, such as inflammatory status, satiety and hunger cues, and energy metabolism signals, from the gastrointestinal tract (GIT) to the brain. In contrast, approximately 10% of vagus nerve fibers bring information from the brain to the GIT. Information that regulates the normal secretion of digestive enzymes and signals when the stomach is full is communicated along the vagus nerve highway.
The vagus nerve is the 10th cranial nerve and is the only cranial nerve to wander into the abdomen. It regulates homeostasis, heart rate, digestion, and breathing; supports normal inflammatory responses; and enhances mood. The gut communicates to the brain directly through the vagus nerve and other spinal pathways. It also communicates through neurotransmitters, immune signaling molecules, and byproducts of microbial fermentation. Examples of each are provided below.
Neurotransmitters:
Immune signaling molecules:
Byproducts of microbial fermentation:
Emerging research highlights the importance of supporting this pathway for improved cognitive and mental health outcomes. Adopting strategies that strengthen gut health may directly and indirectly improve brain health. As we transition into spring, it’s the perfect time to adopt habits that stimulate the vagus nerve and optimize gut and brain health.
The Vagus Nerve, Gut-Brain Axis, And Vagal Tone
Vagal tone is often measured indirectly by heart rate variability (HRV) or the time intervals between heartbeats. High HRV is generally accepted as being associated with a slower heart rate and, subsequently, a higher vagal tone. In comparison, a lower HRV is associated with a higher rate and lower vagal tone. When vagal tone is strong, the body is able to manage stress, support digestion, and maintain a balanced microbiome. Conversely, poor vagal function is associated with digestive disorders, heightened stress responses, and even mental health concerns like anxiety and depression. Many of the interventions aimed at modulating vagal tone work by affecting HRV and include lifestyle practices like humming, gargling, deep breathing exercises, cold exposure, meditation and mindfulness practices, and dietary modifications, including probiotics.
Lifestyle Practices to Activate the Vagus Nerve
1. Humming and Gargling
Humming and gargling may seem simple, but they are effective ways to stimulate the vagus nerve, which is connected to the vocal cords. Studies suggest that activities engaging the vocal cords enhance vagal tone, which supports relaxation and digestive processes.
2. Deep Breathing and Diaphragmatic Exercises
Controlled breathing techniques, particularly those that emphasize slow, deep breaths, activate the vagus nerve and promote parasympathetic activity. Diaphragmatic breathing (belly breathing) increases HRV, a key marker of vagal tone and resilience to stress.
3. Cold Exposure
Cold water immersion and cold compresses to the face have been shown to stimulate the vagus nerve by increasing parasympathetic activity. Exposure to cold water activates the diving reflex, slowing the heart rate and enhancing vagal tone.
4. Meditation and Mindfulness
Mindfulness and meditation have been widely studied for their impact on stress reduction and nervous system regulation. Research indicates that regular meditation increases vagal tone, improves emotional regulation, and enhances gut function.
Dietary Strategies to Support the Gut-Brain Axis
Diet is a cornerstone of gut-brain health, influencing microbiome composition, inflammatory responses, and vagus nerve activity. As mentioned, byproducts of microbial fermentation, including short-chain fatty acids (SCFAs), may facilitate communication between the gut and the brain. Adopting dietary strategies that promote mucin-degrading and SCFA-producing microorganisms may be crucial in supporting the gut-brain axis.
1. Incorporate Probiotic-Rich Foods
Probiotics play a vital role in gut-brain communication by modulating neurotransmitter production, supporting normal gut inflammatory responses, and enhancing vagal signaling. Certain probiotic strains, such as Lactobacillus and Bifidobacterium, have been studied for their effects on mood and cognitive function. A systematic review of fifteen clinical studies (n = 1,209) reported that subjects taking B. longum, B. breve, B. infantis, L. helveticus, and L. rhamnosus with doses between 108 and 1010 CFUs showed efficacy in improving psychiatric symptoms associated with anxiety, depression, ASD, OCD, and memory abilities.
Certain probiotic strains, alone or in combination with prebiotics, have shown positive implications for mental health:
2. Prioritize Prebiotic-Rich Foods
Prebiotics are non-digestible fibers that serve as fuel for beneficial gut bacteria, enhancing microbial diversity and gut barrier function. Prebiotic intake has been linked to improved gut-brain signaling and emotional well-being.
3. Consume Omega-3 Fatty Acids
Omega-3s, particularly EPA and DHA, exert anti-inflammatory effects on the gut and support neuronal health. Research suggests they enhance vagal activity and modulate gut microbiota composition.
4. Reduce Processed Foods and Excess Sugar
A diet high in processed foods and added sugars can disrupt gut microbiota balance, contribute to systemic inflammation, and impair vagus nerve function. Reducing refined sugars and incorporating whole, nutrient-dense foods promotes gut-brain harmony. As part of a 12-week randomized controlled trial, the primary question being studied was if a change in dietary patterns would result in improved markers of depression. Participants (N = 67) were randomized between the dietary and social support groups. Dietary support included nutritional counseling from a clinical nutritionist focusing on increasing the consumption of whole foods and decreasing the consumption of sweetened foods, refined grains, fried foods, fast foods, and processed meats. Compared to baseline, the groups who received the dietary intervention exhibited a decrease in their depression scores (from ~26 at baseline to < 15 after the intervention). Although a slight decrease in depression scores was reported in the group receiving social support, the effect was more significant in the diet intervention group, suggesting the improved mood scores was, at least in part, associated with a change in diet.
Learn more about the gut-brain relationship:
Probiotic Strains Associated with Positive Mental Health
Short-Chain Fatty Acids: What Are They and How Do They Support the Gut-Brain Axis?
Supporting Mood Through the Gut-Brain Axis
By Bri Mesenbring, MS, CNS, LDN, and Antonia Toupet, PhD
Designs for Health has been dedicated to being the most trusted source for superior quality, science-based nutritional products for nearly three decades. We’re committed to maximizing successful health outcomes by providing healthcare practitioners with comprehensive support through our extensive product line, ongoing clinical education, and practice development programs. The blogs we publish here cover a range of topics, including new and original approaches to diet and healthcare, analyses of the latest cutting-edge research, deep-dives into specific nutrients, botanicals, nutraceuticals and more, all fully referenced for those who want to dig deeper into the primary literature.
