The Gut-Brain Connection
Jessica Chang, MHC-LP.
Did you know that humans have two brains? Well, not actually, but the gastrointestinal (GI) tract is lined with 100 million nerve cells, making up the gut’s own independent nervous system called the enteric nervous system (ENS). This is why the human gut is often referred to as the “second brain”. You may have been told at some point to listen to your gut or felt butterflies in your stomach or felt your insides twist into knots. Or perhaps you have felt something in your gut before it came to the forefront of your mind. These are all examples of the gut-brain connection, and there is a reason these idioms are so prevalent.
The ENS relies on the same neurons and neurotransmitters as the central nervous system (CNS, consisting of the brain and spinal cord), which helps with communication and interconnection between these systems. One example of this direct communication between the brain and the gut can be seen when one’s fight-or-flight response is activated due to extreme stress in which digestion slows or comes to a halt temporarily such that all of one’s internal energy is channeled towards facing the perceived threat. In less stressful situations, the digestive process may slow or be disrupted, causing abdominal pain or other symptoms of functional GI disorders.
The relationship between environmental or psychological stress and gastrointestinal distress is complex and bidirectional. Each type of stress can activate and exacerbate GI symptoms and vice versa. Stress is especially impactful on gastrointestinal function. Common stress-related GI symptoms include heartburn, indigestion, nausea and vomiting, diarrhea, constipation, and associated lower abdominal pain. These symptoms are not solely psychological or “made up” in one’s head. Pain and other bowel symptoms result from the combination of psychological and physical factors which lead to actual changes in the physiology of the gut. For example, stress, depression, anxiety, etc. may affect movement and contractions of the GI tract.
It is well-acknowledged that psychological stressors can impact one’s gut, but more recent evidence continues to emerge showing that one’s gut also impacts one’s brain.
The Gut Microbiota
Some sources mention that, within the gut, bacteria outnumber human cells 10:1. Other sources refer to that information as a myth and mention there is too much variability to ascribe this information as universal truth. Either way, it is factual that one’s gut is teeming with these single-celled organisms. The diverse community of microorganisms living within the gut is called the gut microbiota. Research continues to accumulate through a multitude of studies which illuminate how the gut microbiota is connected to the brain.
Gut bacteria produce hundreds of neurochemicals that are involved in the brain’s regulation of basic physiological and mental processes such as learning, memory, and mood. Further, the gut produces and interacts with many of the same neurotransmitters as the brain, such as serotonin and gamma-aminobutyric acid (GABA). In fact, the gut produces over 90% of the body’s serotonin, the “happy hormone” strongly associated with mood stability, sleep, and appetite. The presence of various strains of bacteria have been associated with significant increase in activity of brain regions involved in emotion, attention, sensation, and empathy (in addition to memory and processing complex information).
It is clear that the brain and the gut are intimately connected, communicating via signals back and forth between each other. Evidence has emerged which suggests that imbalances in the gut microbiota can disrupt this communication, leading to mental health disorders such as anxiety, depression, and potentially neurodevelopmental conditions. For example, studies have revealed patients with GI disorders like irritable bowel syndrome and ulcerative colitis to have higher rates of depression and anxiety than healthy control groups.
Intersectionality
Functional GI disorders affect 35% to 70% of people at some point in life, women more often than men (Harvard Health, 2019). Health disparities which disproportionately affect one or more ethnic and racial minority groups also exist when looking at certain digestive issues and diseases, some of which can heighten the risk of cancers (e.g. H. pylori–related gastritis and gastric cancer, inflammatory bowel disease and colon cancer, pancreatitis and pancreatic cancer, and cirrhosis and liver cancer) (Singh et al., 2022). Sexual and gender minorities are also at increased risk for digestive health issues, especially QTBIPOC (Vélez et al., 2022). The gut’s sensitivity to stress and the Minority Stress Theory may help to explain some of these disparities, along with discrimination within currently existing health care systems. Gaining understanding and focusing more attention on the brain-gut connection is thus part of the movement for collective liberation, impacting all minority individuals.
Ways to Promote a Healthier Gut-Brain Connection
Add probiotic foods to your diet: Early studies suggest certain probiotic strains to influence brain function, reduce stress, and improve mood. Although there is much more to discover, a healthy gut microbiome generally contains a diverse mix of bacteria as well as certain key beneficial species such as Bifidobacteria.
Eat more plant foods: Prebiotic fiber acts as fuel for the good bacteria in the gut and can typically be found in plant foods such as asparagus, onions, berries, bananas, and oats. Consuming a diverse array of plant foods rich in prebiotic fiber helps one’s unique gut environment thrive and diversify, supporting research which indicates there is no one-size-fit-all combination of bacteria for a healthy gut microbiome.
Consume less “junk” foods: studies show that highly processed foods that are low in fiber and high in additives (i.e. sugar, salt, artificial ingredients) promote “bad” microbes associated with inflammation, heart disease, and poor metabolic health. Be cognizant of a balanced diet, paying particular attention to frequent consumption of soft drinks, white bread and pasta, processed meats, and packaged snacks (e.g. cookie packs, bags of chips, candy bars, etc.).
Exercise and stay hydrated: Clinical studies have revealed higher levels of physical activity and cardiorespiratory fitness to be positively associated with markers of good gut health such as bacterial diversity and quantity of beneficial species present. Research also supports stress reduction in movement which feels good for one’s body. Staying hydrated promotes optimal gut health, aiding in digestion and the elimination of waste, all of which is directly related to one’s mental health and wellbeing.
Manage stress levels: Although stress may be a non-negotiable part of life that cannot be totally eliminated, there are ways to help manage one’s stress. Exercise, meditation, and mindfulness are all examples of stress-management practices. Consider working with a therapist to help tune in to and identify roots of stressors and explore stress-reduction strategies that feel right for you.
Sources:
Carpenter, S. (2012). That gut feeling. Monitor on Psychology, 43(8). https://www.apa.org/monitor/2012/09/gut-feeling
Freitas, M. (2024). Why A Happier Gut Can Lead To A Happier Mind, Explained By An Expert. Forbes Health.
Singh, M. E. et al. (2022). Achieving Health Equity Through Digestive Diseases Research and Scientific Workforce Diversity. Gastroenterology, 162(6), 1597–1601.e1. https://doi.org/10.1053/j.gastro.2022.01.005
Smith, M. (2023). Turns out your ‘gut feelings’ are real. How gut and mental health are connected. Loma Linda University Health.
Stress and the sensitive gut. Harvard Health. (2019).
Vélez, C. et al. (2022). Digestive Health in Sexual and Gender Minority Populations. The American Journal of Gastroenterology, 117(6):p 865-875, June 2022. DOI: 10.14309/ajg.0000000000001804
Wapner, J. (2023). The link between our food, gut microbiome, and depression. The Washington Post.