The human body basically has two brains - one in the head (aka the one we all think of when we talk about the brain) and one in the gut. Although it is the lesser known of the two, the gut brain has a very important role within the body. This complex network of nerves functions as the control center for digestion, creating and breaking down different components necessary for the body’s functioning. Through the digestive system, the body can utilize the nutrients it takes in and protect itself against infections (1). The gut brain reads all of this information and lets us know what has been going on down there.
Specifically, this “second brain” is made up of two thin layers containing more than 100 million nerve cells, and it runs from the esophagus all the way to the tail end of the body (2). This network is more technically referred to as the enteric nervous system (ENS), connecting to the central nervous system via the vagus nerve (3). However, the ENS actually works independently of the brain. It controls its own reflexes and senses (4). Even if the connection between the brain and the gut were cut, the ENS would still be able to function (3).
Recent discoveries have revealed how information and signals are passed throughout the system. Researchers found that the enteric neurons use a distinct pattern of rhythmic firing to communicate with other neurons in the network. As a result, the body is able to move food through the digestive system in a coordinated effort (3).
As more research becomes available, it is important to try and understand what all this information means to us. Parts of the medical and nutritional communities have funneled energy into exploring the connection between the digestive system and the mind – and what they’ve found is thought-provoking. For example, think about all the phrases we have in English that allude to this gut-brain connection: “gut-wrenching”, “makes me nauseous”, “butterflies in my stomach”, and more. What about the times when you felt yourself getting hangry? The idea is definitely out there, but the specifics behind the association are not so obvious.
Numerous studies have looked into the ways in which mood affects the GI tract and the reverse. Psychological factors such as stress and depression have been shown to have an effect on the environment of the GI tract (1). Interestingly, 95% of the serotonin found in the human body is located in the bowels. That might be why antidepressant medications called selective serotonin reuptake inhibitors (SSRIs) may cause patients to have GI issues as a side effect. The SSRIs help increase serotonin levels in the body, so these could affect your mood and your stomach (4). In addition, about half of dopamine that our bodies make is found in the digestive system (3). Both of these substances are neurotransmitters that play central roles in the regulation of mood and appetite, among others. So, some of the mood changes people experience may be due to irritation in their gastrointestinal systems (2). In people with gastrointestinal disorders, there is a higher-than-average incidence rate of neuropsychiatric problems such as bipolar disorder and depression (1). Further research into this association could potentially help improve symptom relief and medications for these conditions.
In a study examining the relationship between diet and mood, researchers found that children who consumed lower than recommended amounts of healthy food or ate unhealthier and processed foods were more likely to report that they had depression (5). Although you cannot completely rule out confounding variables, studies like this offer a promising look into the interconnectivity of the body. If we continue to explore these connections, we may be able to learn how to mitigate the impact of mental and physical illnesses. Just some food for thought.
1. Weir, K. (2018). The future of psychobiotics. Monitor on Psychology 49(11), 43. https://www.apa.org/monitor/2018/12/cover-psychobiotics
2. “The Brain-Gut Connection.”https://www.hopkinsmedicine.org/health/wellness-and-prevention/the-brain-gut-connection
3. Vartan, Starre. “Scientists find a second ‘brain’ in the gut.” com, 7 June 2018. Narrative Content Group. https://www.mnn.com/health/fitness-well-being/blogs/scientists-find-second-brain-gut
4. Hadhazy, Adam. “’Second Brain’ Influences Mood and Well-Being.” Scientific American, 12 February 2010. Springer Natural America, Inc. https://www.scientificamerican.com/article/gut-second-brain/
5. Jacka, F.N., Kremer, P., Leslie, E., Berk, M. (2010). Associations between diet quality and depressed mood in adolescents: Results from the Australian Healthy Neighborhoods Study. Australian and New Zealand Journal of Psychiatry 44(5), 435-442. https://www.researchgate.net/publication/43180450_Associations_Between_Diet_Quality_and_Depressed_Mood_in_Adolescents_Results_from_the_Australian_Healthy_Neighbourhoods_Study
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