Understanding the Gut-Brain Connection

You’ve likely heard or read something about the gut-brain connection. That’s because there has been a surge in animal and human studies to better understand how the gut microbiome affects mental health and vice versa. While there is much more to be learned, it’s clear that there is a bi-directional effect between intestinal microbiota and mood disorders.

To cite one statistic, about 60 percent of anxiety and depression patients have gastrointestinal issues such as irritable bowel syndrome (IBS).

Let’s consider the mechanisms through which this bi-directional effect occurs and the treatment options that this new understanding makes available for patients suffering from mood disorders or functional bowel issues.

Neurobiochemical, Neuroendocrine, and Neuroimmune Systems

On one level, the gut-brain connection is quite simple. Your digestive system communicates with your brain to let you know when you’re hungry, when you’re full, and when something is “a little off” with your digestion.

If you’ve ever felt “butterflies in your stomach” before getting up to give a presentation, you’ve noticed your second brain at work. Scientists call this little brain the enteric nervous system (ENS), which is two thin layers of over 100 million nerve cells lining your entire gastrointestinal tract. And researchers have discovered evidence that irritation in the gastrointestinal system sends signals to the central nervous system (CNS) that trigger mood changes.

On another level, this gut-brain axis includes mechanisms of the neurobiochemical, neuroendocrine, and neuroimmune systems. So it might be more accurate to say that we have “little brains” throughout our bodies.

Neurobiochemical

The intestinal tract is controlled by both intrinsic and extrinsic biochemical factors. Intrinsically, the intestinal neural system is composed of 200-600 million neurons. Extrinsically, this system is controlled by nerve fibers including the vagal, sacral, and parasympathetic. Truly, though, the pathways of control run in both directions.

The bacteria and chemicals making up the intestinal microbiota have the ability to regulate nerve signals (the vagus nerve is the primary connection between the brain and intestinal tract) and alter neurotransmitter levels in the brain. This means that molecules secreted by our digestive system can affect brain function including sleep, appetite, mood, and cognition.

For individuals suddenly experiencing high levels of stress, for instance, the neurobiochemical connection suggests that their stress may not be an indication of changes in their (first) brain so much as an indication of changes in their gut microbiome. This also explains why people dealing with irritable bowel syndrome (IBS) and other functional bowel issues such as diarrhea, constipation, bloating, acid reflux, and upset stomach, often experience big emotional shifts.

Neuroendocrine

The endocrine system is the set of glands that produce hormones that regulate metabolism, growth and development, tissue function, sexual function, reproduction, sleep, and mood. It turns out that the brain and gut are also connected through the endocrine system.

We’ve known for years that stress activates the hypothalamic, pituitary, and adrenal (HPA) axis, which increases cortisol, your body’s main stress hormone. Long term, this leads to increases in anxiety, intestinal movement, and intestinal microbiota changes. However, more recently, scientists have been studying how intestinal microbiota can also prevent an increase of cortisol levels through the HPA axis to relieve anxiety and depression.

Neuroimmune

In addition, chronic or acute stress can break down the lining of the gut allowing certain toxins to enter the bloodstream and activate the immune system. And these toxins can cause everything from inflammation to fatigue to autonomic nerve and gastrointestinal symptoms. Studies have also shown that when these toxins are present, symptoms of serious anxiety and depression, cognitive deficit, and an increase in pain sensitivity are also present. These negative symptoms can also feedback on the brain activating a vicious cycle.

Treatment Strategies

Now that we understand the deeper connection between ENS and CNS, let’s consider how these discoveries affect treatment options. Clearly, if there is a bi-directional connection, then we can expect that treating gastrointestinal issues may also improve mood disorder symptoms.

On the flip side, mindfulness tools such as meditation, breath work, and gut-directed hypnotherapy, can help to improve gastrointestinal symptoms, in addition to improving mood, and decreasing stress. These tools work because they soften the body's stress response, inhibiting the secretion of cortisol, decreasing inflammation, and supporting the immune system.

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For clinicians working with patients experiencing mood disorders along with gastrointestinal issues, it’s important to be aware of how treatment of one area may affect symptoms in the other. For example, certain antidepressants work by calming nerve cells in the gut. It stands to reason that in addition to prescribing antidepressants, treatment of any gastrointestinal issues could enhance treatment for depression and anxiety.

For patients, in addition to doing what you can to decrease stress, dietary changes can greatly improve your gut microbiota and help with any mood disorders. We know that certain foods can trigger reactions, such as inflammation, in individuals with sensitive guts. Eating a plant-based diet with fewer refined carbohydrates and less or no red meat can lead to an overall healthier microbiome.

A food journal can be an especially helpful tool here. Not only will keeping a food journal likely help those experiencing gastrointestinal distress notice patterns, but it can also be surprisingly helpful for patients suffering from mood disorders, such as stress and anxiety. You may notice that certain foods not only trigger gastrointestinal issues, but also mood issues.

The number of studies examining the bi-directional connection between the brain in our skull and the second brain in our guts (or various tiny brains throughout our bodies), offers hope for the millions suffering from mood disorders and gastrointestinal issues. Although everybody is different, in many cases some combination of integrative approaches can reestablish a healthy gut and a healthy brain.