Gut Health & Mental Health: Is There a Link?

Many of us have learned to “trust our gut.” But if we ask most people what our digestive tract is for, they’ll probably explain it as a way of absorbing nutrients and disposing of waste. So where do phrases such as “trusting our gut” or “unable to stomach the results” come from? It turns out there is a two-way street between our digestive organs and our brains. What we eat and the state of our digestive tract can have a profound impact on our moods and behaviors. And probably unsurprisingly at this point, our gut microbiome is also involved.
Our vagus nerves, which control much of our “rest and digest” response, make a direct connection from our brains to our digestive tracts. Incidentally, these nerves also innervate our heart and communicate with our immune systems.1 These nerves help our brains communicate to our stomachs to start releasing stomach acid and digestive enzymes, and they carry signals from our digestive organs that tell our brains whether we’re hungry or full.1 But there’s a whole lot more to the story than these basic logistical messages.
Our thoughts and moods are sending signals to our digestive tract (and immune system) and vice versa.1 Have you ever felt nausea from a stressful situation or lost your appetite from bad news? That message was carried from your brain to digestive tract via your vagus nerve.2 What might be news is that the situation in your digestion can also send signals to your brain.2 Is your digestive system reacting with something you ate? That signal is conveyed to your brain and can color the rest of your day or night.2
And to add another layer of complexity, the bacteria and other organisms in our gut can make or simulate neuroactive molecules like gamma-aminobutyric acid (GABA), melatonin, and serotonin.2 As you may know, these substances can make a big impact on our mood and how alert we feel. And stress can change the number of healthy bacteria (such as lactobacilli) in our guts and weaken the digestive tract and blood-brain barriers—letting molecules and even bacteria in that would be excluded under normal conditions.2,3 Conversely, consuming some probiotic species can improve our mood.2
This is all to say, everything is connected. I’ve seen many patients with digestive troubles (myself included) who’ve been told by someone, “It’s all in your head.” This is an oversimplified message, because stress and emotions absolutely play a role in digestive health, and the opposite is also true. Likewise, many patients who come in for issues with their mood have related concerns in their digestion that must be addressed before they see significant progress. Often when it comes to health, the symptoms can lead to the root of the problem, but only when you understand the connections.
​References:

1. Breit S et al. Vagus nerve as modulator of the brain-gut axis in psychiatric and inflammatory disorders. Front Psychiatry. 2018;9:44.
2. Petra AI et al. Gut-microbiota-brain axis and its effect on neuropsychiatric disorders with suspected immune dysregulation. Clin Ther. 2015;37(5):984-995.
3. Obrenovich MEM. Leaky gut, leaky brain? Microorganisms. 2018;6(4):107.