The relationship between our gut, gut bacteria, and mental health is often referred to as the gut-brain connection or gut-brain axis. The enteric nervous system (ENS) is a highly complex system of nerves found throughout the lining of the gut. The ENS generally communicates with the brain through the vagus nerve.

An obvious example of this communication is triggered by the sight and/or smell of a meal. The parasympathetic nervous system (part of the central nervous system) sends signals to the ENS. These signals cause a release of digestive secretions in both the mouth and stomach. These signals also prepare muscles of the abdomen for the peristalsis that moves food through the digestive tract.

In the other direction, when you are full from a meal, the gut sends signals to the brain to slow your body for rest, so that energy can be directed towards digestion. Unfortunately, sometimes this signaling system is thrown out of whack.

Scientists are delving deeper into the relationship between the gut, gut bacteria, and mental health. It has become clear that the diversity and abundance of certain microbial populations living within the gastrointestinal (GI) tract have a significant influence on the brain. Because of this, a more accurate title for the phenomenon of gut-brain communication is the “microbiome-gut-brain axis”. 

The influence of gut bacteria on mental health

An imbalanced gut microbiome (a condition also known as “dysbiosis”) can cause physical and chemical changes in the brain. These changes affect behavior, mood, and cognition.

Compelling evidence for such an interaction was published almost 30 years ago. It was observed that a course of oral antibiotics resulted in dramatic mental improvement in patients with hepatic encephalopathy [1]. Hepatic encephalopathy is characterized by neuropsychiatric abnormalities as a result of toxins from the gut entering the circulation. When antibiotics ended dysbiosis of the gut, however, a rapid change in neural effects soon followed. It demonstrated an important relationship between changing microbial populations of the GI and brain function.

Since then, data surrounding gut bacteria and mental health have been collected showing a potential role of microbiota in influencing anxiety and depression behaviors [2]. Dysbiosis may even have an effect on the severity of autism [3]. Normal brain development is partially dependent on microbiotic presence in the gut. Animal studies suggest that social development also requires a certain level of health and balance in the GI microbiome [4,5].

We still need more research to elucidate the mechanisms creating a relationship between gut bacteria and mental health. We do know that the gut produces about 90% of the body’s serotonin. Serotonin is a neurotransmitter that promotes a sense of well-being. Bacteria living in the GI can induce enteric secretion of serotonin, along with other signaling molecules (such as dopamine, glutamine, and GABA) and activation of their receptors [6].

The brains of research animals with altered or absent gut microbiota present various molecular differences including brain-region-specific changes in levels of brain-derived neurotrophic factor (BDNF), which is known to be modulated in anxiety and depression [7]. Due to this evidence, healing dysbiosis and caring for your microbiome through diet and the use of probiotic and prebiotic fiber supplements are likely effective measures to support your mental health in combination with your digestion. 

The brain influences microbiota

Conversely, psychological stress such as worry, fear, frustration, grief, and sadness can cause physiological changes that, in turn, alter the bacterial populations in our gut. Conditions such as irritable bowel syndrome (IBS) or stress-induced diarrhea can flush out beneficial bacterial species. As diet has the greatest effect on microbiotic health in the gut [8], eating more unhealthy comfort foods during times of stress can exacerbate dysbiotic conditions, worsening disrupted motility, reducing nutrient absorption, and even negatively affecting immune response. Over time these changes can lead to neurotransmitter imbalances and increased strain on our natural stress response.

When we experience stress, the sympathetic nervous system responds by engaging the body’s “fight or flight” mode. This deactivates signals for digestion, rest, or relaxation, as these physiological functions are not relevant to self-defense or fleeing from an emergency.

When stress becomes chronic, the digestive system becomes confused, and symptoms such as gas, bloating, nausea, reflux, or motility issues crop up. The cause of these symptoms, at least in part, are changes to the microbiome responding to stress [8]. Even events such as a social defeat or a reduction in social diversity have been documented to precede a change to GI microbial species known to affect neurotransmitter synthesis [8]. 

Healing and Maintaining a Healthy Microbiome

Knowing that the microorganisms living inside your gut can hurt or hinder your mental state along with your physical health is important. Caring for gut bacteria is caring for mental health.

But it can be difficult to determine whether your unhealthy gut is the root of a low mood or anxiety, or your stress level is hurting the health of your gut. Either way, changing your diet and lifestyle to support healthy digestion will benefit your well being. 


Animal studies involving microbiome manipulations have not only confirmed hypotheses about connections between gut populations and behavior, they also show supplementing with probiotics can correct some of these effects [7]. 

Taking a daily probiotic supplement is an efficient way to start improving the diversity and abundance of beneficial microbial species in the GI. While many fermented foods contain probiotic species, it is difficult for those probiotics to reach and populate the gut due to enzymes and stomach acids. A high-quality capsulated supplement, such as BioMaintenance Shelf Stable Probiotic, made by parent company Metabolic Maintenance, by design, withstands early stages of digestion. Thus, it can deliver maximum colony forming units (CFUs) of specifically selected beneficial bacteria and yeast strains directly to the intestine.

As there are only so many adherence sites for bacteria in the walls of the gut, it may take some time for the beneficial strains to take root and begin to multiply. As they do, pathogenic bacteria are slowly sloughed through natural bowel movement. This is why it is important to make a probiotic supplement part of your daily health regimen, rather than expecting one capsule to make a noticeable difference.

You may start to notice a difference in physical symptoms of dysbiosis within as little as two days, but secondary benefits like mood may take a couple of months or more to notice a significant change [9,10]. Don’t give up! But do make sure you’re taking the right strains for your needs, a dose that is appropriate for your body condition, that your probiotic is from a trustworthy source, has not surpassed its expiration date, and that you are following that particular product’s instructions along with advice from your healthcare practitioner. 


Another important piece to the probiotic puzzle is the amount of prebiotic fiber in your diet. As living organisms, probiotics need to eat. In order to survive and multiply, the microbial species that benefit the gut require oligosaccharides and fibers considered indigestible by the human gut. Pathogenic bacteria in the gut often thrive on sugar. Therefore, avoiding a high-sugar diet while taking a prebiotic supplement, such as the BioMaintenece Prebiotic + Fiber, is an effective way to nurture the growth and maintenance of desired bacterial species while ending the dominance of pathogenic species.  

Food Intolerances and Sensitivities

If adding probiotics and prebiotics to your daily health regimen does not change uncomfortable GI symptoms over time, you benefit from a deeper analysis of your diet. While an allergic reaction to a food is likely to cause a histamine response such as a rash or sudden inflammation, a food sensitivity or intolerance is more likely to present as a GI issue (bloating, gas, diarrhea, etc.) and may be a bit more difficult to pinpoint. In some cases, the body isn’t producing enough natural enzymes for the abundance of certain food proteins one consumes.

These proteins bypass digestion and ferment in the gut causing uncomfortable, inconvenient, or even painful symptoms. Common intolerances include casein, lactose, and gluten. You can take a natural digestive aid, such as Metabolic Maintenance’s GluDaZyme , which can help break down these proteins (along with fats and other components), so that you absorb their nutritional value and avoid their fermentation (as well as its side effects). If the sensitivity is more serious, an elimination diet can help to determine the culprit so you know which foods to skip completely in the future.

Leaky Gut

Leaky gut is a different story. In order for absorption to occur, the intestinal wall acts as a sieve, allowing water and nutrients to move through the wall into the bloodstream. Toxins and undigested materials are too big to fit through, so they stay in the intestine, destined for excretion from the body. Sometimes, the holes in the intestinal wall (called “tight junctions”) loosen, allowing toxins into the bloodstream along with nutrients and water. This phenomenon is “leaky gut” or “intestinal hyperpermeability”.

Leaky gut can cause symptoms throughout the body including inflammation and skin issues, confusion, and mood-related issues, and even lead to the development of more serious conditions such as diabetes and inflammatory bowel disease [11-14]. This condition can occur naturally, as some people’s genetics predispose them to make more of the chemical zonulin, which loosens tight junctions. Gluten, however, can stimulate zonulin overproduction in some people who have an otherwise healthy gut, causing leaky gut syndrome [15]. 

Gluten is not the only potential cause of leaky gut. There are certain bacteria that also stimulate the overproduction of zonulin, and alcohol and refined sugar have also been linked with the permeability of tight junctions [15-17]. If you think you may be suffering from a leaky gut, your doctor will likely recommend some combination of a low FODMAP diet, pre- and probiotics, and self-care behaviors to destress your system to heal your gut.

This editorial mentions products manufactured by the parent company of MethylPro, Metabolic Maintenance. Metabolic has been an industry leader of professional supplements used and recommended by practitioners for over 35 years. Metabolic Maintenance manufactures both brands and offers them direct to consumers through their respective websites. For more information on the brand relationship and additional high quality nutritional supplement offerings, please visit:

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