Mind Over Microbiome: Talk About Eating Your Feelings! - A Discussion on the Link Between the Gut and the Mind
Brisnid Pardo
Mind Over Microbiome: Talk About Eating Your Feelings!
A Discussion on the Link Between the Gut and the Mind
“You’re not you when you’re hungry”, “go with your gut”, “butterflies in your stomach”, are all famous phrases that unconsciously associate gut ‘feelings’ with the mind. Surprisingly, there is actually some truth behind why those phrases are ingrained into our daily language.
Picture Manhattan on a busy day; It’s a bustling city with diverse people from countless walks of life, contributing to everyday society, always having somewhere to be and something to do. There are new people constantly moving in, others moving out, and some just passing by. Your gut functions the same way. However, instead of people, it’s microbes.
The ‘gut’, or digestive tract, is composed of the organs of the digestive system, from the esophagus to the stomach to the intestines. One of the most important parts of our digestive system is our gut microbiome, a network of trillions of microorganisms that consist of bacteria, fungi, parasites, and viruses. Microbes in our gut coexist within us in a symbiotic relationship, meaning that both us and the microbes benefit from our relationships. We eat and supply nutrients to the microbes, and in turn, certain microbes help break down complex compounds, stimulate the immune system, and synthesize certain vitamins and amino acids [1]. We also have pathogenic microbes that promote disease, but coexist with symbiotic microbes in a healthy balanced body. It’s when our gut undergoes dysbiosis, or imbalance, through contaminants like external illness-causing pathogens, foods, or antibiotics that we become susceptible to disease.
The microbes in your gut are vital to not only your digestive health, but your overall health and wellness, including mental health. There’s some truth behind having ‘gut feelings’ and this is explained by the Microbiota-Gut-Brain Axis. The gut-brain axis is the series of mechanisms explaining the interactions between the gut and the brain, primarily the mechanism of bidirectional signaling between the gastrointestinal (GI) tract and the central nervous system. Signals from the enteric nervous system (nerves from the GI tract) proceed to communicate with nerves part of the central nervous system that send neurotransmitters which the brain uses for memory and mood regulation. There have been studies that show that irritation to the GI tract sends signals to the CNS that trigger mood changes. While the causal vectors have yet to be studied, there is evidence to show that microbiota imbalances can potentially lead to anxiety, depression, neurodevelopmental conditions, and neuropsychiatric disorders, or exacerbate them.
One of the red flags found in people with psychiatric disorders is the high amounts of inflammation in their body. A significant mechanism that leads to inflammation in the body is through increased intestinal permeability, or “leaky gut”. When the GI tract is compromised, it increases intestinal permeability consequently leading to the penetration of unwanted substances in the gut that activate the body's immune response. A study suggests that “the processes of intestinal dysbiosis and neurological deficits are linked through chronic low inflammation, including direct inflammatory stimulation, the production of pro-inflammatory mediators, and the loss of immune regulatory function” [2]. This indicates that the link between mental health disorders and our gut could be through the strength of the body’s immune response.
Over the decades, many studies have been dedicated to finding out the functions of specific strains of bacteria that reside in our gut. It’s important to note that each individual has their own unique set of microbes, just like the way our DNA is specific to us as individuals. We begin to develop our microbiota as we’re exposed to microorganisms inside the womb, after delivery, and especially through our mother’s milk. As we grow older, there are more influences over our microbial landscape, including the food we consume, the air we breathe, and the medicine we take. This opens up a whole pandora’s box of possibilities for why our microbiota is the way it is, and how it affects us without us realizing it.
This leads us to pointing out what in our daily lives has the potential to affect our gut health and thus, our mental health. Contaminants are found in absolutely everything. Defined as harmful substances that negatively affect our wellness, the list goes on from food additives, heavy metals, organic pollutants, pesticides, etc. However, one of the worst contaminants introduced to our society to be over-prescribed and given out like candy are antibiotics. All of the contaminants mentioned have been reported to cause the occurrence of anxiety, depression, schizophrenia, and attention deficit hyperactivity disorder [3]. These substances have the power to disrupt neurotransmitters and the hippocampus, which leads to inflammation in the brain, better known as neuroinflammation, and gut microbiota dysbiosis.
The average American diet and societal norms also contribute to gut imbalances and bodily inflammation. A diet high in sugar and low in fiber is common for the average American; excessive sugar intake increases intestinal permeability and lack of fiber results in the overgrowth of disease-promoting microbes. Alcohol is another irritant to the gut, as it has been shown to cause dysbiosis and increased inflammation in multiple studies on people with alcohol use disorder. Excessive drinking is an ongoing problem in our society, as the CDC estimates that 1 in 6 US adults binge drink regularly [4].
I asked a question to everyone in a room full of 20-something college students in a science writing class. Everyone, including my professor, raised their hand when I asked if they had ever taken antibiotics before. It’s become very common for doctors to overprescribe antibiotics, even for the smallest earache. In a study published in the National Library of Medicine, it was reported that “antibiotics increase the prevalence of both depression and anxiety. Rarely, they can also cause psychotic disorders with a schizophrenia-like picture” [5] One of the most eye-opening cases of this comes from the story of a 75 year old man who had a clean picture of mental health. Following a colorectal cancer surgery, he was prescribed antibiotics to treat a postoperative wound infection, which was later listed as the principal cause of his suicide.
So if destroying the gut is bad for our mental health, can healing our gut heal our mind too? Lots of corporations push the answer ‘yes’ in order to sell their probiotic-rich products. All the ‘-biotics’ are on the rise as new information about keeping the gut healthy becomes available to the public. Probiotic supplements are in fact not regulated by the Food and Drug Administration, meaning that many businesses have an easy time releasing their products into the market. The terms probiotic, prebiotic, and postbiotic are being slapped on a label and attracting millions of consumers.
Within our gut microbiome, we have them all; Probiotics are live beneficial microbes, prebiotics are the food that probiotics consume and break down into compounds, and postbiotics are the beneficial compounds produced by the probiotics. The concept is that probiotics have the power to manipulate the gut microbiota by increasing microbiota diversity and beneficial microbial composition. However, there is no clear evidence that probiotics are beneficial regardless of the countless studies that have been conducted to prove their efficacy, mainly due to the fact that our individual microbial makeup varies so much that there has been no standardized way to study the effects of probiotics. Professor Benezra also puts it into perspective with the statement: “Probiotics are like 6 strains of laboratory produced bacteria, when you introduce those to literal trillions of thousands of species already living in our gut—they don't have a chance.”
While there are many studies that may suggest causal vectors and report strong links, it is still unclear whether mental disorders form in the presence of certain microbes or vice versa. Many studies that report the link between microbes and behavior are done on animals like mice and fish, who have significant physiological differences from humans. Professor Benezra, a sociocultural anthropologist researching how studies of the human microbiome and biomedical ethics intersect, states, “We have only cataloged an estimated 10% of [microbes]! That means we haven't even identified 90% of [microbial] life. We really don't understand what the communities of them inside us are doing well enough to try to manipulate or change them durably.” There is still a lot to explore about these miraculous microbial beings and their functions in the human body.
One of the most interesting studies suggesting causation from specific microbes comes from a Fecal Microbiota Transplantation (FMT) done on mice. Fecal microbiota from drug-free patients with schizophrenia was transplanted in pathogen-free mice, which resulted in the relatively ‘healthy’ mice to exhibit schizophrenia-like symptoms, such as psychomotor hyperactivity, impaired learning, and impaired memory [6]. Another study reports FMT alleviating Alzheimer’s pathology in the brain of mice. A specific systematic review sheds light on patients receiving microbiota from ‘healthy’ donors, which led to a decrease in depressive and anxiety-like symptoms [6]. FMT is commonly used as a treatment for patients with C. Diff, a bacteria that causes fever, diarrhea, and cramping, typically caused through the use of antibiotics. In this case, a FMT reintroduces healthy bacteria in the gut, controlling the growth of C. diff. [7] However, due to the difficulty in standardizing research, there is no strong evidence to show that FMT can be effective for other conditions, especially mental health disorders.
Another drastic therapeutic option that has been studied is vagal nerve stimulation. The vagal nerves run from the stomach to the lower part of the brain on both sides of the body. When stimulated, electrical impulses are sent to the brain to control mood. [8] It has been shown that stimulation of the nerves produces anti-inflammatory activity, leading to desirable outcomes. [6] Implantable nerve stimulators are FDA approved to treat depression in extreme cases.
While we are still trying to grasp the mechanisms of the link between our brain and our gut, it’s safe to say that they’re definitely connected! More research needs to be done in order to fully understand the microbial-gut-brain axis in order to come up with alternative therapies to treat mental health disorders.
If there’s anything to take away, it’s to take care of and listen to your body. It’s no secret that gut health impacts every area of your overall wellness, so knowing how to take care of it properly can lead to a higher quality of life. Probiotic supplements may or may not be effective in maintaining microbial diversity, but consistently eating probiotic and prebiotic rich foods like whole grains, fermented foods, and yogurt can keep your gut healthy in the long run. Understanding what hurts it like sugars, processed foods and alcohol can be key in maintaining balance. Indulging in a donut or a beer isn’t going to obliterate your insides in one sitting, but being mindful and practicing moderation when it comes to consuming foods that negatively impact your gut health can go a long way. Not to sound like an ad in your doctor’s office, but consistent exercise, maintaining a healthy sleep schedule, and managing stress can all lead to feeling better and decreasing symptoms of depression and anxiety. While it may seem like common sense, people don’t realize how excessive cortisol levels brought on by not maintaining a healthy lifestyle increase intestinal permeability and thus, inflammation of the body, making individuals more susceptible to disease and disorders. So when you’re feeling ‘hangry’ and know that “you’re not you when you’re hungry”, don’t reach for that snickers bar; reach for a colorful fiber and prebiotic rich meal that’s sure to make your gut microbes smile. :)
Works cited:
[1] The Microbiome | The Nutrition Source | Harvard T.H. Chan School of Public Health
[2] The role of the microbiota-gut-brain axis in neuropsychiatric disorders - PMC (nih.gov)
[4] Excessive Alcohol Use | CDC
[5] Antibiotics and mental health: The good, the bad and the ugly - PMC (nih.gov)
[6] Full article: Gut microbes in neurocognitive and mental health disorders (tandfonline.com)
[8] Vagus nerve stimulation - Mayo Clinic
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