Exploring the Link Between the Gut Microbiome and Anxiety

Humans have recognized for millennia that there is a mind-body connection, and specifically, that there is a relationship between the gut and the psyche. Hippocrates, the Greek father of medicine, opined that all diseases (which would include mental disorders) begin in the gut. Phrases such as “a gut feeling”, “a gut instinct”, “butterflies in your stomach”, “gut-wrenching”, “gutsy”, “stomach-churning” and so on, show that we intuitively understand that there is a connection between the digestive system and the brain. However, it is only recently that the importance of the gut microbiome for our mental health has begun to be scientifically researched. Two new phrases have been coined, “the gut-brain axis”, and the “microbiota-gut-brain axis” (MGB), the former denoting the connection between the brain and the gut, the latter the association between the brain and the microbes in the gut.

Dr. Diane Brain Health/Dr. Diane Stoler

What is the gut microbiome?

The gut microbiota are the trillions (10 to 100 trillion) of microscopic organisms that inhabit the gut. We have bacteria, viruses, fungi, helminths (worms), protozoa (unicellular organisms like amoeba), and archaea (microbes similar to bacteria) in our gut. Most microbes in the gut are bacteria. The bacteria in our gut are being extensively researched nowadays, as they have turned out to be extremely important for our overall health, including mental health.

The gut microbiome denotes the totality of all the microbes in one’s gut and their genetic material.

Humans and our primitive ancestors (which include fish and four-legged reptiles, if one goes back far enough) have always been living in a microbial soup and we have microbes on our skin, in our gut, and elsewhere. Thus, we and our ancestors co-evolved with our gut bacteria, and these bacteria have evolved with us. This means that they produce metabolites (substances, molecules) that have an effect on our bodies and that they depend on us for food. It makes sense for our gut bacteria to be beneficial to us, the host, and so most gut bacteria are commensal or symbiotic “good bacteria” and produce substances that benefit us.

About 90 percent or more of our gut bacteria are supposed to be good bacteria. If more than about 10 percent of our gut bacteria are bad bacteria, then we have what is called “dysbiosis” or an imbalance of the gut microbiome.

Dysbiosis has an effect on mental health, including a person’s level of anxiety.

How does the gut microbiome affect anxiety levels?

Caltech researchers showed in 2022 that a specific microbial metabolite (4-ethylphenyl sulfate) can increase anxious behavior in mice. What’s more, fecal microbiota transplantation from anxious mice to mice that are not anxious causes the latter to become anxious. Also, antibiotic treatment in mice (which affects the gut microbiome) has been shown to affect anxiety levels.

The gut-brain axis is a bi-directional communication pathway. The brain sends signals to the gut via the vagus nerve, and the gut communicates in turn with the brain. The gut microbiome has an influence on the brain by means of hormones, neurotransmitters, and cytokines. Neurotransmitters are molecules that facilitate signaling between brain cells (neurons). Neurons exist in the gut, too. The gut microbiome affects the level of certain neurotransmitters, including serotonin (which is important for mood). Ninety-five percent of the body’s serotonin is made in the gut by neurons that are found in the GI tract, and by immune cells and so-called enterochromaffin cells in the gut. Gut serotonin can activate nerve endings in the digestive tract that lead to the central nervous system.

The gut also produces hormones, and these can influence the brain as well. The gut microbiome can affect gut hormone levels (such as the level of the hormone ghrelin, which affects mood).

Inflammation is an important causal factor for anxiety. An imbalanced gut microbiome (dysbiosis) can lead to leaky gut syndrome, where the intestinal barrier becomes permeable. Bacteria and bacterial metabolites such as LPS (lipopolysaccharide, a molecule stemming from the outer membrane of gram-negative bacteria) and a molecule stemming from the bacterial cell wall, called peptidoglycan, can enter the bloodstream. This leads to a reaction from the immune system, and chronic inflammation, which also affects the brain. Importantly, this inflammation can cause anxiety.

Chronic stress can also lead to gut dysbiosis and to anxiety. Stress activates the HPA or hypothalamic-pituitary-adrenal axis, which in turn leads to an increase in cortisol. That hormone makes the gut lining more permeable, causing leaky gut syndrome. Cortisol levels return to normal when the stressor is removed. However, in chronic stress, cortisol levels remain high. Chronic activation of the HPA axis leads to its dysregulation. Also, stress leads to inflammation via pro-inflammatory cytokines.

How can you improve your gut microbiome health to reduce anxiety?

There are several strategies you can try to improve your gut microbiome health, which may have potential benefits for reducing anxiety:

• Eating healthy foods such as fruits, vegetables, and whole grains helps the gut flora. Also, it’s important to eat high-fiber foods in general, as these foods improve the health of your gut microbiome. GI tract bacteria feed on fiber that cannot be digested in the stomach, fiber that thus makes its way to the intestines. This so-called prebiotic fiber is converted by good bacteria into molecules known as short-chain fatty acids (such as butyrate and propionate). In the brain’s hypothalamus, the short-chain fatty acids modulate the levels of neurotransmitters such as glutamate and GABA.
  
  

  Source: diane stoler / dr diane brain health
• Limit alcohol consumption, processed foods, and added sugars: Highly processed foods and excessive sugar intake can negatively impact the gut microbiome. Try to prioritize whole, unprocessed foods and reduce your consumption of sugary snacks and beverages.
• Supplementation with prebiotics (fiber that gut bacteria view as food) has been shown to decrease anxiety. Fructo-oligosaccharides (a prebiotic) have alleviated anxiety in mice.
• Managing stress levels can also help to improve your gut microbiome health. Chronic stress can disrupt the balance of the gut microbiome. Engage in stress-reducing practices like exercise, yoga, meditation, and deep breathing. Exercise in general is beneficial for the gut microbiome.
• Get restorative sleep: Poor sleep quality or insufficient sleep can affect the gut-brain axis and contribute to anxiety. Establish a consistent sleep routine and create a sleep-friendly environment.
• Limit antibiotics use: While antibiotics can be necessary in certain situations, they can also disrupt the gut microbiome. If prescribed antibiotics, discuss with your healthcare provider to determine if there are ways to mitigate their impact on the gut microbiome.
• And, of course, you can take probiotics to improve your gut microbiome health. It is important to have a preponderance of good bacteria (at least 90 percent good bacteria), and to have a diverse gut microbiome. Psychobiotics are probiotics that can help with mental health issues. Some probiotics might be anxiolytic or reduce anxiety. Lactobacillus plantarum DR7 and a species of Bifidobacterium might be helpful for anxiety.

Microbiome Essential Reads

4 Ways Food Additives Can Be Hazardous to Your Health

Your Mood Is Influenced by What You Feed Your Microbiome

Source: diane stoler / dr diane brain health

Conclusion

The health of our gut microbiome affects our overall health, as gut microbes affect the entire body. They affect the brain and, in fact, play a key role in anxiety disorders. It is important for mental health to maintain a healthy gut microbiome by eating healthy, fiber-rich foods, exercising regularly, and perhaps supplementing with probiotics. It is always advisable to seek professional medical advice for the treatment of anxiety or any mental health condition.

To find a therapist near you, visit the Psychology Today Therapy Directory.