The Gut-Brain Connection and Mental Health

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Have you heard the term “gut-brain connection”? This is a relatively new concept in modern research and it’s a fascinating one. Mental health has become a topic on everyone’s minds, and it’s a subject that researchers are finding out more about all the time. One of the most interesting discoveries about mental health is the influence of our gut bacteria on our brain. Who would’ve thought that the tiny microbes in our intestines would affect our mood and brain function! Our body contains more gut microbes than human cells and the weight of all our gut bacteria is about the same as the weight of our brain. Needless to say, what’s in our gut has a big influence on the body as a whole. Let’s dive into what the research says about the gut-brain connection and its implications for mental health.

What is the gut-brain axis?

The gut-brain axis is a bidirectional pathway that includes various interactions between the gut microbiome, endocrine system, immune system, nervous system, and the brain. It is bidirectional in the sense that there are signals from the brain that are received by the gut, and also changes in the gut that influence changes in the brain. Both the brain and the gut are affected by each other and influenced by each other. The main connection pathways between them are the spinal and vagal nerves1.

Perhaps the most interesting part of the gut-brain axis is the influence of the gut microbiome on the rest of the body, particularly the brain. Gut microbes can affect peristalsis, the body’s ability to detect pain and injury, brain chemistry, and mood. The gut microbiome is critical for nervous system development. In mice without microbiomes, the nervous system did not develop properly, affecting the signals that allow for moving the muscles of the digestive system. The gut microbiome also affects mental wellbeing via the vagus nerve, changing the signal that the brain receives1.

What causes imbalanced gut bacteria?

Lack of pre- and probiotic foods can cause an imbalance or an inadequate amount of gut microbes. Probiotic foods contain beneficial bacteria that colonize the gut. When a diet is lacking in probiotic foods, the gut does not receive any “newcomers” and it will not flourish like it does with a consistent influx of beneficial bacteria. Additionally, a diet lacking in prebiotic foods can cause a lack of diversity and quantity of beneficial gut bacteria because prebiotic foods contain the short-chain oligosaccharides that serve as the food required to allow for proliferation of a community of bacteria.

Lack of food diversity or quantity in chronic dieters is another issue when it comes to the gut microbiome. Many chronic dieters eat the same foods over and over again. This means that they are likely not ingesting a variety of probiotic-containing foods, and also that they are not ingesting enough of the prebiotic foods required for the beneficial bacteria to proliferate. The varying strains of bacteria require varying food types so a variety of foods is key for nurturing a healthy gut microbiome.

Stress can also lead to an impaired gut microbiome. Animal studies show that when animals are subjected to stress, they have less total gut bacteria than their non-stressed counterparts, and their guts also contain less gut microbe diversity. In humans, there is a high level (over 50%) of comorbidity when it comes to IBS (a disorder of the gut) and chronic stress and mental illness. Chronic life stress and gut imbalance are linked, with stress leading to reduced gut diversity but also in the other direction, with gut imbalances leading to lowered resilience to stress. It is theorized that stress makes the gut “leaky”, by loosening up the connection between cells, thus allowing what should not be going in or out of the gut to come through the gaps3.

Antibiotic usage is a major factor in imbalance microbiomes. Antibiotics wipe out both the harmful and the beneficial bacteria in the body. This can cause population reduction of beneficial bacteria which in turn sets the stage for harmful bacteria to over-colonize the gut, resulting in dysbiosis (microbial imbalance and impairment).

What happens to the brain when the gut is imbalanced?

Mood disturbance occurs when the gut microbiome is lacking or imbalanced. An unhealthy balance or nonexistent presence of gut bacteria is linked to anxiety in animal studies2. As mentioned above, gut-related health conditions such as IBS are highly comorbid with mood disorders and lowered stress resilience. Studies indicate that not only does stress reduce the health of the gut, but the gut bacteria are critical for optimal mental wellness. This creates a feedback loop in which stress and mood disorders impair the gut microbiome which in turn further impairs mental health4.

What improves gut balance, and therefore mental health?

Probiotic supplementation is a great way to improve the health of your gut microbiome. Look for a supplement that contains several strains. This helps to repopulate your gut with a variety of beneficial bacteria which improves the overall health of your microbiome. This is a helpful solution in most cases of gut health imbalance, however there are some more severe versions of gut imbalance that are worsened by probiotic intake so it is important to work with a holistic nutritionist to determine what the best course of action is for each individual.

Eat probiotic and prebiotic foods. Probiotic foods contain the bacteria themselves, while prebiotic foods contain what the bacteria need to thrive. Prebiotics are a food source for the bacteria that live in your gut. Foods that contain probiotics are typically fermented foods such as kimchi, sauerkraut, yogurt, kefir, and fermented pickles. Prebiotic containing foods include asparagus, onions, garlic, bananas, artichokes, apples, and leeks. A variety of fruits and vegetables will provide a variety of prebiotics for your gut flora.

Exercise plays a role in the health of our gut bacteria populations. It’s unknown how exactly it plays a role, but studies have shown that aerobic activity increases the diversity of particular bacteria, including Lactobacillus and Bifidobacterium. Researchers also note that forced exercise in animal studies, which is perceived as a psychological stressor, actually decreases the diversity and amount of beneficial bacteria5. If we over-exercise or we do activities that stress us out, we may be depleting our gut bacteria instead of helping it flourish. Do exercise that feels challenging but still enjoyable, and if you are exhausted and chronically stressed, it’s probably best to rest.

References & further reading

    1. Moody microbes or fecal phrenology: what do we know about the microbiota-gut-brain axis?
    2. Stress & the gut-brain axis: Regulation by the microbiome
    3. Melancholic microbes: a link between gut microbiota and depression?
    4. From gut dysbiosis to altered brain function and mental illness: mechanisms and pathways
    5. Exercise influence on the microbiome–gut–brain axis

Contributed by Melanie Maxwell, R.H.N.