Ever wonder why we talk about feeling butterflies in your stomach? Or have you ever made an important decision based on a gut reaction? While these cliches have merit in mainstream conversation, they likely speak to the relationship shared between the gut and brain.
Emerging research in both biology and medicine studies the interconnected dynamics between gut health and brain health. Also known as the gut-brain axis, studies show that the gut and brain regularly and bidirectionally communicate to maintain functioning throughout the body (1).
Understanding the Enteric Nervous System
Although it’s much less known than the central nervous system (CNS), the enteric nervous system (ENS) controls the body’s digestive tract. The ENS handles numerous functions, including blood flow regulation, gastric acid secretion, immunological support, and the individual breaking down of food nutrients. While the system forms during the last few months of human gestation, it continues developing after birth.
Researchers first began examining its presence in the early 19th century, and subsequent research has focused on its anatomy, development, and function (2).
It’s important to note that the ENS is small but mighty. The average ENS contains 400-600 million neurons that are divided among two significant networks- the myenteric and submucosal plexuses. The ENS is also the biggest and most complicated unit within the peripheral nervous system, and it’s located directly within the walls of the GI tract.
Among the millions of neurons, there are up to 20 synthetic types, all of which contain sympathetic and parasympathetic ganglia. The complex nature of these neuron clusterings and interactions has led scientists to coin the ENS as the “second brain” or “the brain in the gut.”
Myenteric ganglia: These are organized around the gut and mostly consist of motor neurons.
Submucosal ganglia: These are organized in both the small and large intestine and they are largely sensory neurons.
Intrinsic primary afferent neurons: These neurons detect mechanical and chemical stimuli from ingested nutrients.
How the Gut Affects the Brain
It’s known that the gut and brain communicate closely. This may explain why people often feel nauseated before speaking publicly. It can also explain why people may suddenly experience the urge to use the restroom when they feel nervous. The two systems work in tandem and react accordingly to one another.
The ENS focuses on controlling digestion and ensuring the GI tract is operating efficiently. That said, the system may also trigger significant emotional shifts, particularly in people with various conditions, like irritable bowel syndrome (IBS), diabetes, or Crohn’s disease. For instance, people with known gastrointestinal issues have a higher rate of depression and anxiety (3).
Some research suggests that the system occurring within the digestive tract affects cognition and emotion. The brain picks up on these gut signals to control everything from mood and emotion to pain receptivity. In addition, gut bacteria can produce substances that literally impact brain cells (4).
With that, healthy gut function is associated with normal CNS function. Neurotransmitters and hormones excreted from the gut send signals to the brain via autonomic neurons. Recent studies have shown relationships between microbiome and numerous conditions, including anxiety disorders, mood disorders, and schizophrenia (5).
Understanding the Vagus Nerve and Nervous System
The brain and central nervous system are packed with neurons that tell the body how to think and behave. It’s estimated that each human brain contains over 100 billion neurons.
The vagus nerve is one of the largest nerves connecting your brain and gut. This nerve sends signals in both directions, and it’s an imperative part of the gut-brain axis.
In addition to supporting digestion, the vagus nerve is responsible for numerous functions, including cardiovascular activity, breathing, and automatic reflex actions like sneezing and coughing. The vagus nerve is divided into somatic components (sensations felt on the skin or within the muscles) and visceral components (sensations felt inside the body’s organs).
Damage to the vagus nerve can cause problems with swallowing, gag reflex, heart rate, digestion, abdominal pain, depression, and anxiety.
The brain and gut are also connected through neurotransmitters, which refer to chemicals that contribute to feelings and bodily functions. Both the brain and gut have their own set of neurotransmitters. While most people assume the brain is the powerhouse of the feel-good hormone, serotonin, research shows that a significant amount of that neurotransmitter is produced by the gut (6). Similar findings have also been discovered with GABA, the neurotransmitter associated with anxiety.
The gut-brain axis is also connected and influenced by the immune system. If the immune system becomes too inflamed, the body is at risk of developing a brain disorder, including depression or Alzheimer’s disease.
This gut-brain axis has been in the limelight with the recent explosion of vagus nerve stimulation (VNS). This treatment entails placing a small device and generating electrical impulses to stimulate nerves. It’s used to treat some forms of epilepsy and treatment-resistant depression. Some experts believe that VNS may help treat other conditions, including cluster headaches, multiple sclerosis, and Alzheimer’s disease.
Less invasive forms of stimulating the VNS include:
- Deep stretching and yoga
- Cold water immersion
- Diaphragmatic breathing techniques
People with stronger vagal tones may be more apt to relax after stressful events, and their bodies may be more resilient to gut issues and inflammation. Over the long term, this can lead to better overall health.
Signs of Potentially Unhealthy Gut
While poor gut health symptoms can mimic symptoms of other conditions, chronic digestive issues shouldn’t be ignored. It’s estimated that nearly 70 million Americans experience some form of gastrointestinal distress (7). Many variables, including history family and genetic factors, affect gut microbiome, but it’s important to know the potential warning signs of gut issues:
- Chronic digestive symptoms, including constipation, diarrhea, gas, and bloating
- Ongoing sleep disturbances, including fatigue
- Persistent infectious illnesses
- Significant mood shifts
- Dramatic appetite changes
- Chronic and unexplained aches or pains
- New food intolerances
- Unexplained weight gain or weight loss
- Frequent migraines
- Sudden autoimmune problems
Symptoms of digestive disorders include numerous diseases ranging from mild to severe. Some of the most common GI disorders include:
Gastroesophageal Reflux Disease (GERD): GERD is a chronic digestive condition associated with persistent heartburn, nausea, abdomen pain, and difficulties with swallowing.
Celiac disease: Celiac disease refers to having an immune reaction to gluten, the protein found in wheat, rye, and barley. Many people without celiac disease experience gluten tolerance, which can be associated with abdominal pain, bloating, nausea, anemia, and weight loss.
Irritable bowel syndrome: IBS refers to experiencing stomach pain or discomfort chronically and persistently. Along with bloating and gas, some people with IBS have hard, dry stools, whereas others have loose, watery stools.
Hemorrhoids: Hemorrhoids are swollen veins within the anus that can cause discomfort and itchiness. They can be exacerbated by issues with constipation and straining during bowel movements.
Ulcerative colitis: Ulcerative colitis is associated with frequent and urgent bowel movements, pain that coincides with diarrhea, and abdominal cramps. Certain foods may cause discomfort, and it’s a result of the immune system misinterpreting the colon lining for an invader.
Tips for Improving Gut Health
Individual gut microbiomes can affect both physical and mental health. Fortunately, it is possible to strengthen gut health by making simple lifestyle changes (8).
Eat more fiber: Fiber helps improve overall gut function. It’s recommended that women aim for at least 21-25 grams of fiber each day, and men should strive for 30-38 grams. Fiber-rich foods include fruits, vegetables, whole grains, and legumes. Keep in mind that it’s best to add fiber gradually. Adding too much too soon may exacerbate gastrointestinal distress.
Eat more omega-3 fatty acids: These fats are naturally found in oily fish, including salmon, mackerel, and sardines. They can also be found in chia seeds, flaxseed, walnuts, and canola oil.
Prioritize hydration: Water is essential for helping break down food, and it helps the body absorb nutrients. In addition, water helps reduce the risk of constipation and bloating.
Eat fermented foods: Fermented foods are associated with better gut health. Fermented foods include kimchi, kombucha, tempeh, and sauerkraut, and certain types of yogurt.
Eat more polyphenols: Polyphenols refer to plant compounds, and they can be found in a variety of spices and herbs, nuts and seeds, coffee and black and green tea, and cocoa.
Aim to eat more slowly and mindfully: Eating too much or too quickly (or both) can irritate the gut and disregard natural cues for satiety. Instead, aim to eat slowly until you reach about 80% fullness. The slower pace allows your body to break down large food particles into smaller ones, which better aids your digestion.
Aim to manage stress: Chronic stress may adversely impact the gut-brain axis. While some stress is inevitable in daily life, it’s important to implement strategies that can help you feel more relaxed and calm. Seek to prioritize coping skills like mindfulness, meditation, deep breathing, and spending time engaging in restorative hobbies.
Consider allergy testing: You may unknowingly have food sensitivities disrupting your gut health. You may be able to identify some of these trigger foods on your own. But if you continue experiencing flare-ups without a root cause, consider talking to your healthcare professional.
Be mindful of antibiotic use: There is some evidence suggesting that chronic or inappropriate antibiotic use can lead to gut bacteria imbalances. It’s best to only take antibiotics when prescribed by healthcare professionals for treating bacterial infections.
Quit smoking: Smokers may have a less diverse and adaptive gut microbial community than non-smokers. Smoking also reduces blood flow to all areas of the body, including the gut. At the same time, it increases the risk of gut-related cancers, including colon and stomach cancer.
Talk to your doctor about supplementation: Some people may benefit from probiotic supplements, which can help restore gut health. These can be useful if you’re prescribed antibiotics.
Limit alcohol intake: Chronic or heavy alcohol use is associated with poorer gut health. Drinking can exacerbate intestinal inflammation and increase the risk of gastritis and other health conditions. Consider cutting back or eliminating alcohol altogether.
The trope “you are what you eat” may have more truth than people realize. While some health factors are inherently genetic, it is important to consider which improvements you can make on your own. Even small lifestyle changes can dramatically improve how you feel each day.