The past few years have been characterized by incredible social and economic turmoil, and many of us are feeling the impact: 21% of American adults, or 52.9 million people, experienced some form of mental illness in 2020. But you might be surprised to know that our brains aren’t the only things impacted by recent events — and these events aren’t the only thing impacting our brains. Your gut is home to a diverse community of microbes, called the gut microbiome, and an increasing number of studies suggest that these microbes could impact your mental and emotional state. In fact, the gut-brain axis (GBA), the two-way signaling system between your gastrointestinal (GI) tract and your central nervous system (CNS), may play a significant role in your responses to stressful events. Here, we’ll discuss what the science has to say about anxiety and anxiety, separating the hope from the hype and identifying possible ways you might be able to improve your brain health, your gut health — or both.

What are the components of the nervous system?

The nervous system helps us sense the world around us and coordinates our responses to our environment. There are two components of the nervous system: the CNS and the peripheral nervous system (PNS). The CNS features the brain and spinal cord and processes sensory information to send a response. The PNS comprises a network of nerves and neuronal bodies that act as a relay between the CNS and the rest of the body. The PNS is also divided into three components:

• The somatic nervous system (SNS), which comprises nerves that help us move with our skeletal muscles;
  
  
• The autonomic nervous system (ANS), which comprises nerves that help our organs and glands function; and
  
  
• The enteric nervous system (ENS), a special set of nerves that help our intestines and stomach digest our food. Think of the ENS as the GI tract’s own brain, controlling every aspect of the gut’s movements, blood flow, and activity.

How the nervous system operates impacts our feelings as well. This includes those associated with anxiety.  

Gut health and anxiety: What is anxiety, exactly?

People diagnosed with an anxiety disorder tend to feel excessively fearful, anxious or avoidant of perceived threats from the environment. These feelings lead to responses disproportionate to the actual risk or danger posed. The feelings associated with anxiety can persist for a long time, impairing daily, social and occupational functions. Anxiety disorders come in many shapes, including generalized anxiety disorder, phobias and selective mutism. However, the following symptoms are most common among people with an anxiety disorder:

• Trouble sleeping
• Pounding or racing heart
• Chest pains
• Increased fatigue
• Difficulties concentrating
• Unexplained bodily pains
• Out-of-control feelings, including impending doom

Given the close relationship between the gut and the brain, a lot of research has focused on whether what happens in the gut can impact what happens in our brains, too. We do know that gut microbiome changes occur in some patients with anxiety. And, while the research is still young, several studies have connected imbalances in the gut microbiome with other neurodegenerative diseases and mental conditions, such as autism, Alzheimer’s disease and depression. As we’ll see in the next few sections, what happens in our guts can play a critical role in our mental health — and vice versa.

What is the gut-brain axis, and how does it work?

The GBA consists of all the two-way connections between the gastrointestinal (GI) tract, the CNS and the ENS. The interactions between our nervous system and the GI tract can occur in two ways. First, the Hypothalamus-Pituitary-Adrenocortical (HPA) axis produces small molecules called hormones that travel through the bloodstream and alter the function of organs such as the intestines. Under stressful conditions, the brain triggers this axis to alter GI behavior. In the GI tract, gut cells also produce neurotransmitters, molecules that carry messages through the nerves in your body. Changing the concentrations of these compounds can impact the sets of nerves that turn on or off in the GI tract, altering their function. Interestingly, the cells making up your gut produce 95% of your body’s serotonin, a key neurotransmitter.

Gut health and anxiety: There are a few ways that gut microbes can affect the nervous system:

• Neurotransmitters: Pathogenic bacteria (i.e, bacteria that can make us ill), like E. coli O157:H7 and Klebsiella pneumoniae, can respond to or produce the neurotransmitters dopamine and noradrenaline. Bacteria normally found in healthy guts, such as lactobacilli and bifidobacteria, can produce gamma-aminobutyric acid (GABA), another neurotransmitter which when deficient has been linked with anxiety and mood disorders.
  
  
• Short-chain fatty acids (SCFAs): Gut microbes also produce SCFAs after digesting foods they like, namely dietary fibers and resistant starch. While these compounds play direct roles in keeping your gut healthy, they can also travel through the bloodstream to the brain. In the brain, SCFAs can affect the nutrients that pass the blood-brain barrier by altering what gets through from the bloodstream.
  
  
• The vagus nerve: The vagus nerve connects your brain with the heart, lungs and GI tract. It acts alongside the ENS to send signals to the brain that affect your responses to stress.

While we are beginning to understand the role that the gut microbiota plays in the GBA, there are other questions that require answering to better explain the links between the gut microbiome, anxiety and other mental health conditions.

• Mechanisms underneath the links: While we know that changes to the gut microbiota are linked with neurological diseases, it remains unclear how these links come about. For instance, a recent study determined that differences in the gut microbiota among children with autism were explained by picky diets as opposed to a causal relationship.
  
  
• Neurotransmitters: Microbes come in many types, even within a single species. How do we know which ones might provide the strongest benefits for a given anxiety patient? We also do not know how these neurotransmitters alter brain function from the gut.
  
  
• The vagus nerve: While we know that it plays an important role for maintaining gut health and sending signals to the brain, we still need more research connecting the nerve’s activity with mental illness. We also need more work on ways to use the gut microbiome to affect vagus nerve activity. 

How to manage anxiety

Although we still have a lot to learn about the role gut microbes play in anxiety, we know that the ENS and ANS connect the gut with the brain. Due to this connection, many non-pharmacological approaches to managing anxiety focus on what we put in our mouths.

Diet and Supplements

Our diets provide a means to affect the energy sources that microbes use to grow, and some research suggests that changing our diets could alleviate anxiety by altering our gut microbiota. In fact, there is a solid body of research connecting several types of foods and supplements with improved mental health.

• Dietary fibers are indigestible components of plant foods found in vegetables, fruits, whole grains and legumes. A cross-sectional study showed that dietary fiber intake was associated with alleviating depression and anxiety among patients with hypertension. However, no such study has been conducted on anxiety patients without a preexisting medical condition.
  
  
• Fructooligosaccharides and galactooligosaccharides are two distinct kinds of carbohydrates. Fructooligosaccharides are found in fruits and vegetables, such as onion, chicory, garlic, asparagus and bananas. Galactooligosaccharides are found in dairy products, beans and some root vegetables. Three unique clinical trials determined that eating 5.0 g/day of both kinds of sugars improved anxiety and depression symptoms. However, two of these studies were conducted on patients with inflammatory bowel syndrome (IBS).
  
  
• Omega-3 fatty acids, commonly provided as a supplement, are essential unsaturated fatty acids, which means that we cannot produce this fatty acid ourselves. Instead, we obtain Omega-3 fatty acids from our diets. The data for Omega-3 fatty acids is conflicted. On one hand, a 2018 study concluded that taking at least 2,000 mg/day of Omega-3 fatty acids can ease anxiety symptoms. On the other hand, a study released the following year concluded that taking Omega-3 fatty acids probably does little to prevent depression or anxiety symptoms. 

Although we have studies that look into specific nutrients, we must remember that this data remains cursory at best. The preliminary nature of the data stems in part from small patient sample sizes in each of the studies. Few studies have been prepared for anxiety patients without a preexisting disease. Furthermore, some studies include patients not clinically diagnosed with anxiety. Lastly, none of these studies provide a causal link between our gut microbes and anxiety. Thus, more work needs to be done in recruiting otherwise healthy patients and pinpointing the role of the human gut microbiota in driving anxiety. 

Probiotics

The previous discussion on diet focused on specific molecules that could provide clinical benefits. These compounds are called prebiotics because our gut microbes can digest them and help our GI tract behave normally. Prebiotics represent one of the two arms of microbial-based medications. Probiotics represent the other arm. Probiotics are live bacteria clinically proven to exert benefits to their host. A 2019 systematic review determined that probiotics provide positive benefits for treating anxiety. While the review demonstrates the benefits of taking probiotics, the studies included in the review used many kinds of microbes as probiotics. As such, more work needs to be done to identify the specific types of microbes that consistently improve anxiety symptoms.

Stress management activities

Aside from improving our diets, there are other things we can do to benefit our mental health. Yoga and other meditative practices are well touted as ways to improve emotional well-being. But did you know that they may also improve gut health? For instance, a 2015 study showed reduced catastrophizing among IBS and IBD patients when they participated in meditative exercises.

As we discussed earlier, gut microbes can produce chemicals that affect the nervous system, including the vagus nerve. Supporting this, multiple lines of evidence gathered in a 2018 review showed that breathing, yoga and meditation increase the activity of the vagus nerve. This in turn can help improve mood and alleviate mental illnesses — including anxiety, depression and PTSD. Activities that activate the vagus nerve could also prevent excessive inflammation and minimize the risk of gut damage. The research is still young, but nonetheless, these results provide a positive step forward for using yoga and other meditative activities to improve mental and gut health.

Key takeaways

Anxiety remains the most common mental illness faced by people worldwide. Feelings of doom and other symptoms can inhibit your ability to function, making it vital to treat anxiety to ensure your well-being. The gut-brain-axis, the two-way highway between the gut and the brain, appears to play a key role in the relationship between gut health and anxiety — and each can impact the other. However, precisely how this bi-directional communication works, and your gut microbiome’s exact role, has yet to be fully understood. Diet and supplement changes could help alleviate symptoms of anxiety by impacting your microbes, but there are several other lifestyle factors (such as exercise and mindfulness) that can also positively impact your guts and brains. And while fully embracing such healthy lifestyle strategies may position most of us to better manage stress and anxiety, you should talk to your doctor if such changes prove inadequate and you still can’t seem to get a handle on your anxiety.