The Gut & Your Mood

In recent years, scientific research has shed light on the powerful connection between gut health and mental health via the gut-brain axis. This communication network allows the brain to influence intestinal activities and the gut to affect mood, cognition, and mental health. These two organs are physically and biochemically connected in many different ways. 

For example, our gut contains millions of nerve cells, which communicate with our brain through the nerves in our nervous system. The vagus nerve (cranial nerve x) plays a crucial role in the parasympathetic, or “rest and digest,” nervous system, which regulates many unconscious bodily functions, including digestion, heart rate, and breathing. One human study found that people with irritable bowel syndrome (IBS) or Crohn’s disease had reduced vagal tone, indicating a decreased function of the vagus nerve and parasympathetic nervous system activity. Furthermore, stimulating the vagus nerve was shown to be effective in improving patients’ moods with treatment-resistant depression. 

The gut and brain also communicate by producing several functionally essential metabolites, such as mood-regulating neurotransmitters, including serotonin, melatonin, glutamate, GABA, histamine, dopamine, and noradrenaline. For example, the digestive tract produces up to 95% of serotonin, a neurotransmitter associated with feelings of happiness. Low serotonin levels don’t necessarily cause depression; however, increasing serotonin through the use of anti-depressant medications such as selective serotonin reuptake inhibitors (SSRIs) is an established treatment for depression. Another neurotransmitter the gut microbiota produces is gamma-aminobutyric acid (GABA), which modulates emotions such as fear and anxiety. Research has demonstrated that specific probiotics can augment GABA production, thereby potentially alleviating symptoms of anxiety and depression in experimental models. Furthermore, gut microbiota can stimulate the vagus nerve and alter serotonin, GABA, and glutamate concentration within the brain—all known to influence mood.

Gut dysbiosis, characterized by an imbalance in the gut microbiota, can lead to a proliferation of harmful bacteria at the expense of beneficial ones. This imbalance can trigger inflammation in the gut, disrupting the delicate ecosystem within our digestive system. The imbalance of bacteria also directly affects the synthesis of neurotransmitters such as serotonin, dopamine, glutamate, noradrenaline, and GABA. On the other hand, beneficial short-chain fatty acids produced by certain gut bacteria have anti-inflammatory and neuroprotective effects, potentially influencing mood and cognitive function.