How Can Nourishing Your Gut Improve Your Mental and Physical Health

The gut microbiome is an essential contributor to overall health. Connections between gut health and neurophysiology have been recognized for some time — now the focus is on how we can use this knowledge to nudge our mental and physical health in the right direction.

What is the gut microbiome?

The human microbiome is the collection of bacteria, fungi, viruses, and their genomes that coexist within us, and on our skin. The gut microbiome interacts with your body and the environment by lining your digestive tract. It supports the process of extracting nutrients from your diet.

Our microbiome is influenced by the first years of life and responds to environmental factors, such as what we put into our bodies each day. These exposures also include medications such as antibiotics which can kill off friendly bacteria.

It is now recognized that the gut microbiome exerts a considerable influence on human neurophysiology and mental health, according to a study published in Molecular Psychiatry in 2022. This recognition has allowed a pivot in research priorities. Scientists are now applying this understanding of the relationship between gut health and mental health to understand how nutrition can influence the human experience. In other words, how can we apply what we know to improve mental health?

Anxiety and depression affect 1 in 4 adults

Approximately 4.4% of the global population is affected by depression, and that number is growing. The National Center for Health Statistics and the U.S. Census Bureau teamed up during the pandemic to administer the Household Pulse Survey, a 20-minute online survey designed to assess mental health indicators in the population.

Among those aged 18–29 years, symptoms of anxiety were reported by 51.7 % of the population in the fall of 2020. Other age groups also reported significant anxiety symptoms. Rates of anxiety were inversely correlated with age — higher among younger people. Among females, anxiety was reported by 41.8% and males by 30.3%.

More recent Household Pulse Surveys suggest a decline in anxiety in early 2023. Depression statistics followed a similar trend. Currently, approximately 1 in 3 young adults ages 18 to 29, and 1 in 4 adults ages 30 to 49, report symptoms of depression.

The visceral connection between gut health and mental health

Our language is replete with expressions that illustrate the inherent connection between the gut microbiome and our mental state, even if we are only now beginning to truly understand the biological mechanisms at play. The following commonly used phrases are examples of how this relationship plays out in our expression of emotional states:

• Having a sinking feeling
• Butterflies in your stomach
• Spilling your guts
• Having your stomach tied in knots

These symptoms of anxiety, when chronic, can trigger an inflammatory state that mimics the symptoms of illness.

The “sickness behaviors” of withdrawal, malaise, heightened sensitivity to pain, difficulty concentrating, depressed appetite and mood all mimic the proinflammatory cytokine signals elicited during the onset of illness. They can also be triggered by stress.

From an evolutionary perspective, developing a stress response that induces a proinflammatory state would ramp up the immune system to combat injury or illness. Jump-starting the healing process might have been good during episodic stressful events, but today pervasive stress is harmful, causing a persistent inflammatory state, chronic anxiety, and often depression.

Despite treatment, more than half of all people living with depression do not experience relief.

Trying to understand the causes of depression

This difficulty in finding relief has prodded experts in mental health to reconsider the causes of depression and in so doing identify various means of preventing its onset.

Early forays in the effort to describe and define depression focused on brain-based theories and medication to address imbalances in brain chemistry. The next pivot in understanding panned out to consider brain regions and neural circuitry.

The last five years have seen an explosion of interest in the microbiome and how it interacts with the nervous, immune, and endocrine systems.

The gut microbiome — is there an ideal “healthy” state?

Yes, but the precise composition of healthy gut microbiota varies from person to person.

The quest to understand whether there is an ideal balance of microbiota in the gut has been challenging given the changes in an individual’s gut microbiota over time, and the variation between individuals. Most of the work to date has been conducted in rodents.

Various stress stimuli, such as maternal separation, social defeat stress, repeated restraint (living in close quarters), and diet-induced obesity are used to create an experimental model to induce depression and its effect on the microbiome.

Balancing healthy and unhealthy microbes in the gut is key to maintaining the right amount of diversity. Eating too many sugary foods can cause an overgrowth of unhealthy bacteria, while focusing on fresh fruits and vegetables promotes the growth of “good” bacteria, which help us extract essential vitamins and minerals from our food.

In humans, our daily bowel movements can provide some insight into whether our gut microbiome is in a “healthy” state of diversity. Having bloating, diarrhea, constipation, fatigue and acid reflux or heartburn may be symptoms of gut dysbiosis — having an unhealthy gut microbiome.

We have known for more than a century that antibiotics can affect gut health. New research suggests that early and frequent exposures may induce autoimmunity and psychiatric illness. Introducing an antibiotic into the gut microbiome has the following effects:

• Kills off the natural gut bacteria
• Enriches antibiotic-resistant bacteria
• Affects the central nervous system

An underappreciated and perhaps rare side effect of some neurotoxic antibiotics is mood dysregulation. Stopping the antibiotic may not have an immediate effect, as the half-life of the drug could be 24 to 48 hours or more.

What dietary changes can boost gut health?

Antibiotics, probiotics, and prebiotics each have an effect on gut health. Antibiotics must therefore be used with care due to their deleterious potential.

Probiotics are fermented foods which contain beneficial microbes. These foods reduce inflammation and improve gastrointestinal health.

Prebiotics are the complex carbohydrates and plant polysaccharides that we cannot digest without the help of gut microbiota.

The gut-brain-axis is an instant messaging platform

The importance of a healthy gut microbiome has far-reaching implications for your overall health, so much so that experts often refer to the gut microbiome as your “second brain.”

The modern framework for describing the interaction between gut health and mental health is a bidirectional highway. The gut microbiota may interface with the peripheral nervous system, releasing neuroactive metabolites into the blood stream.

Conversely, the central nervous system may send signals to the gut affecting microbiota composition via the vagus nerve or the enteric nervous system, which manages gut function.

This bidirectional messaging metaphor vastly oversimplifies the diverse and integral connections the gut has with the rest of the body. For instance, the mucosal membranes lining the entire intestinal tract — from the nose and mouth to the anus — come in contact with everything we eat and breathe and immediately decide if an arriving microbe is a friend or foe.

Given this massive daily sorting job, it is perhaps intuitive that the largest immune organ in the body is the gut-associated lymphoid tissue (GALT). The GALT produces 70 to 80% of the body’s immune cells. These cells remain suspended in a cautious stand-off — avoiding overreaction to friendly bacteria while defending against those which could be deadly.

Circling back to anxiety and the pro-inflammatory state, it is easily appreciated how an anxious state might induce nervous, endocrine, and immune signaling pathways which in turn modify the gut microbiota.

Wellbeing — from the inside out:

In the last five years, research has expanded our understanding of the intersection between depression and the microbiome. However, this bidirectional relationship itself must be situated within the intricate signaling networks connecting the endocrine, immune, and nervous systems.

At the moment, it is reasonable to conclude that our diet, medications, and environmental stressors — including work and relational stressors — can have a profound effect on our overall health and wellbeing.

However, we are not yet at the point where, for instance, an individualized probiotic diet could be prescribed to rebalance gut health. Our intestines do more than just extract calories from food. While we may have built up the habit of eating rather mindlessly while working, shifting our perspective to thinking about food and movement as medicine might help. Some examples of small daily changes include:

• Moderation. Limiting sugar and alcohol intake.
• Probiotics. Incorporating probiotic yogurt and fermented foods into your diet.
• Movement. Taking time to be in nature, walking or exercising in the open air.
• Friends. Developing supportive social networks.
• Sleep. Getting enough quality sleep.
• Mindfulness. Practicing brief periods of meditation and intentionality in our daily routines.

With a renewed appreciation for the work being done 24/7 by our intestinal mucosa, perhaps it will be easier to feed our bodies with intent and nourish our mindset from the inside out.