The Gut-Brain Connection

What is the gut-brain connection?

Your brain talks to your gut, and your gut talks back. If you’ve ever had a “gut feeling,” you’ve experienced this communication. It’s how the thought of an exciting event can make you feel “butterflies in your stomach,” while the thought of something dreadful might be “gut-wrenching.” And it’s how the feeling in your gut can influence your decision-making, as in “going with your gut”.

Your brain communicates with all of your body through nerves (your nervous system). But your brain and your gut are like besties. They talk about all kinds of things, from practical, physical matters to emotional ones. More information passes between your brain and your gut than any other body system. In fact, there are more nerve cells in your gut than anywhere else in your body outside of your brain. 

What is the purpose of the gut-brain connection?

Our brains and digestive systems have evolved together to help us survive. What we eat is crucial to our overall health, and it has also varied a lot throughout history, depending on what was available. Our brains and guts needed to stay in close contact to make sure we got the nutrients we needed. And if we ate the wrong thing, or we needed to put the brake on digestion, we had to have a good alarm system in place. 

This alarm system includes the emotional part of your brain. After a physical injury, your emotional brain kicks in to help you remember to avoid that injury in the future. Emotion can make physical sensations in your gut seem more intense. Intense physical sensations can also raise your stress levels and your emotional response. This feedback loop is especially strong between your brain and gut.

What types of body functions does the gut-brain connection affect?

Studies suggest that crosstalk between your gut and brain may influence your:

• Hunger and satiety.
• Food preferences and cravings.
• Food sensitivities and intolerances.
• Gut motility (muscle movements).
• Digestion.
• Metabolism.
• Mood.
• Behavior.
• Stress levels.
• Pain sensitivity.
• Cognitive function.
• Immunity.

What body systems are involved in the gut-brain connection? 

What healthcare providers refer to as the gut-brain axis is the network of nerves that connect your brain and gut and send signals back and forth. But your nervous system also works closely with your endocrine system, which produces hormones that communicate things like hunger, fullness and stress. And it works closely with your immune system to respond appropriately to injury or disease in your gut.

Within this network, some of the key players in the gut-brain connection include:

Enteric Nervous System

Your enteric nervous system is the neural network that operates within your gastrointestinal (GI) tract and controls its digestive functions. With more than 500 million neurons, it’s the most complex neural network outside of your brain. It’s also unique in that it can operate somewhat independently from your brain and central nervous system. This has led some scientists to refer to it as a “second brain”.

Your enteric nervous system is a special division of your autonomic nervous system, which governs the automatic functions of your internal organs. It operates as part of your overall autonomic nervous system, but also on its own. It can gather information about the conditions inside your GI tract, process that information locally and generate a response without sending it back to your brain.

Vagus Nerve

Your vagus nerve is the main link between your enteric nervous system and your brain. It’s one of your 12 cranial nerves, which begin in your cranium and travel down through your body, branching out along the way. Your vagus nerve conveys sensory information about the conditions inside your gut from your enteric nervous system to your brain. In response, it conveys motor signals from your brain to your gut.

The vagus nerve mediates various reflexes that operate within your gut in response to changing conditions, like chemical changes or the presence of food. These are called vagal reflexes. Intrinsic vagal reflexes operate within your enteric nervous system without involving your brain. Extrinsic reflexes operate through communication between your enteric nervous system and central nervous system. 

Gut Microbiome

Believe it or not, the bacteria that live in your gut are also involved in your gut-brain connection. Gut microbes produce or help produce many of the chemical neurotransmitters that convey messages between your gut and brain. They also produce other chemicals that can affect your brain through your bloodstream. Your brain and gut, in turn, can affect your gut microbiome by altering its environment.

Recent studies have shown that the gut microbiome may be involved in various neurological, mental health and functional gastrointestinal disorders. Functional disorders are those that cause persistent symptoms but don’t have any obvious physical cause. There’s a significant overlap among people who have functional gastrointestinal disorders, like IBS (irritable bowel syndrome), and who have mental health disorders, like anxiety.

What types of medical conditions or symptoms might involve the gut-brain axis?

Disorders related to the gut-brain axis may include:

• Irritable bowel syndrome and functional constipation or diarrhea.
• Anxiety and depressive disorders.
• Noncardiac chest pain.
• Infant colic.
• Functional dyspepsia.
• Functional dysphagia.
• Gastroparesis. 
• Anismus.
• Chronic stress.
• Chronic fatigue.
• Chronic pain.
• Visceral hypersensitivity.
• Obesity.
• Neurodevelopmental disorders, like autism.
• Neurodegenerative disorders, like Parkinson’s disease.
• Nerve-related pain disorders, like multiple sclerosis.

How do healthcare providers treat disorders of the gut and brain?

Healthcare providers are experimenting with treating some of these disorders by treating your gut microbiome. Animal experiments have suggested that a healthier diversity of microbiota in your gut may help to relieve gastrointestinal, neurological, inflammatory and emotional stress symptoms. Results in humans are still mixed, but intriguing. They might treat your gut microbiome in several ways, including:

• Probiotics.
• Antibiotics.
• Fecal microbiota transplantation.

People with certain functional gastrointestinal disorders may benefit from mind-body therapy with a behavioral medicine specialist. Several different types of therapies may be beneficial in relieving persistent GI symptoms, or at least learning to cope with them. They can also help improve your overall mood and stress levels, which may help your gut indirectly. Some of these therapies include:

• Relaxation therapy. This approach uses different techniques to help you relax and reduce your automatic reactions to stress. Techniques include progressive muscle relaxation, visualization and restful music. Research suggests these therapies are most effective when combined with cognitive behavioral therapy (CBT).
• Cognitive behavioral therapy (CBT). The goal of this approach is to help people with GI disorders change their thoughts, behavior and emotional responses in relation to physical pain as well as mental/emotional stress and anxiety.
• Gut-directed relaxation training. This is a combination of deep relaxation with positive suggestions focused on GI function. An example would be placing your hands on your abdomen while being asked to feel warmth and imagine having control over your GI function. This approach may be helpful for people whose symptoms occur even without obvious stress.
• Biofeedback. This therapeutic training teaches a person how to control automatic body responses. An example would be learning how to control your heart rate or temperature with the assistance of an electronic device that provides feedback on these functions. Research has shown that biofeedback, in combination with other stress and symptom management techniques, has produced positive health effects in people with functional GI disorders.

What can I do at home to nurture my gut-brain axis?

The best way you can take care of your gut health on a day-to-day basis — and maybe your brain health, as a result — is by maintaining a healthy, balanced diet. You can also take care of your brain health — and maybe, through it, your gut health — by doing what you can to manage your stress. Here are some ways to manage stress during intense times, and ways to relieve stress in your day-to-day life.

What type of diet is good for my gut-brain axis?

A good rule of thumb to improve your gut health naturally is to eat a good variety of whole foods, emphasizing plants. More diversity in your diet leads to a more diverse gut microbiome, which is good for your overall gut health. Whole foods and plants also pack more nutrition per calorie than processed foods, leaving less room for harmful additives, sweeteners and saturated fats. Instead, they offer:

• Soluble and insoluble fiber. Most plants have both kinds of fiber, which help keep your bowels regular and feed the helpful microbiota inside. These microbes, in turn, nourish your gut lining.
• Prebiotics and probiotics. Probiotics are the live bacteria in fermented foods, like yogurt and sauerkraut. Prebiotics are the fibers and complex starches that these bacteria like to eat.
• Antioxidants. Antioxidants, which occur naturally in a variety of fruits and vegetables, help to fight free radicals in your body and prevent inflammation. Different foods have different types.
• Anti-inflammatory foods. A whole-food, plant-rich diet is naturally anti-inflammatory because it reduces sugar, additives and cholesterol. This helps keep your gut microbes happy.