Nature Brain: The Soil Gut Brain Connection

Wherever you are, not far beneath you, is earth. Maybe it’s only half an inch on the bottom of a shoe sole, or perhaps it’s a couple of feet below tire and road, a dozen feet of your home’s floor and foundation, or tens of thousands of feet as you soar through the air in a piece of metal machinery designed to elevate you above and beyond.

Either way, you will eventually return to the earth—making contact with that dark, damp silt, cool to the touch and smelling somehow fresh, a product of the unique combination of bacteria there: Actinomycetes, and their wonderful contribution to the world—that sweet post-rain scent, otherwise known as petrichor.

Wherever you are, you likely know that feeling of calmness, happiness, and sentimentality from childhood that the smell of soil and the feeling of it beneath your feet invokes. We too often avoid that simple pleasure. Who wants dirty feet? Who wants to step on a sharp rock? What if there is a nail or a thorn?

We then opt instead for rubber soles, paved pathways, and the business of adulthood, with no time for barefoot walks in the moss. Let us return and remember. More so than ever, we know how much the quality of our soil offers us and what happens when we abuse it. 

Keep reading to discover the deep connection between humans and the soil!

Key Takeaways:

• The Interconnected Web of Life: The soil, gut, and brain are not isolated entities but part of a single, interconnected system called the Soil-Gut-Brain Axis (SGBA). Our external environment, internal microbiome, and cognitive functions shape health and well-being. We are dissolving the illusion of separation between humans and nature!

• Soil as the Foundation of Health: Healthy soil, rich in microorganisms, nurtures nutrient-dense plants that feed our bodies and microbiomes. The microbes in the soil are crucial for healthy plant growth, but they also directly influence human health by affecting nutrient density in food and ideally introducing beneficial bacteria into our digestive systems.

• Reciprocal Healing: Caring for Soil and Self: The health of our environment mirrors our own health and vice versa. Just as nutrient-rich, chemical-free soil fosters a balanced gut microbiome and supports mental health, sustainable farming practices and mindful care of our ecosystems help maintain the vitality of our planet and ourselves.

The Great Connection: The Soil-Gut-Brain Axis

The soil, gut, and brain have been treated like three entirely separate items, but they are deeply interconnected—a single system, if you will—via what is known as the soil-gut-brain axis (SGBA for short). Ultimately, we are just beginning to understand the depths of our interconnectedness, how intricately tied we are to our environment, and how our perceived separation is illusory. 

Our external environment (the planet, other creatures, and materials around us), the microbial world inside our bodies, and the cognitive functions that shape our thoughts, moods, and behaviors are like an orchestra, working in synergy to contribute to the formation of the magnificent person you are.

Soil Health: The Foundation of Life

It all starts in the soil—a dynamic, living matrix teeming with billions of microorganisms. These microbes, including bacteria, fungi, and other tiny organisms, contribute not only to the growth of plants but also to the health of the larger ecosystem, including humans. 

The soil is a reservoir of nutrients, minerals, and elements that plants need to thrive. In turn, plants release essential compounds into the soil that feed these microorganisms. What’s even more fascinating is that the soil’s microbes have a profound influence on human health, particularly through the food we consume, but microbes are being killed off by synthetic, agricultural chemicals and pesticides.

Soil biologist, Dr. Elaine Ingham, developed the Soil Food Web Approach, prioritizing soil regeneration as a way to “help to secure the survival of humans and other species,” specifically using carbon sequestering of the soil to offset climate change and improve plant yields.

Building soil biology in regenerative agriculture allows us to capture and store carbon dioxide (CO2) to reduce the amount of carbon in the atmosphere and limit climate change. Ingham has proven that optimal soil biology can sequester carbon up to a mile beneath the earth’s surface!

The Gut: The Microbial Highway Bridging Outside & Inside

Our gut is home to a vast microbiome—trillions of bacteria, fungi, and viruses that aid digestion, immune function, and more. This microbiome is intricately connected to the soil’s microbial population. The food we eat—ultimately derived from plants grown in soil—influences the health and diversity of our gut microbiota. These microbes play a direct role in our digestion, nutrient absorption, and immune responses, which may dramatically influence overall health.

Interestingly, the same beneficial microbes that exist in the soil can make their way into our digestive systems. When we consume soil-based organisms (often present in raw or minimally processed foods), they introduce new strains of beneficial (or harmful!) bacteria into the gut, potentially contributing to a balanced microbiome. This delicate balance affects everything from our immune responses to our mental health via the microbiome.

It’s wild that our digestive system has a direct link between the outside world and our internal ecosystem. You can think of it as alchemy, taking outside materials and transforming them into usable energy, neurotransmitters, hormones, blood, tissue, and more.

The Human Brain: The Gut-Brain Connection

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The story doesn’t end there. Emerging research shows that our gut is connected to our brain through the gut-brain axis—a bidirectional communication system between our digestive system and the brain (Mayer, 2011). 

Signals from the gut directly influence mood, cognition, and behavior. This connection is mediated through the vagus nerve, hormones like serotonin and dopamine, and metabolites produced by gut microbes. Interestingly, we have an astounding 500 million neurons in the gut (Robertson, 2023), which is where the term “gut feeling” comes from! Much of our consciousness and intelligence resides down in our digestive tract, not entirely in our brain as previously believed!

To give some more perspective on how amazing this truly is, dogs have around 530 million neurons in their brains while cats have around 250 million (2018). This could mean that our guts alone have some form of intelligence equal to or greater than some of our favorite pets.

For comparison, humans generally have around 80 to 90 billion total neurons. The only other creatures with more neurons than humans are elephants and some species of whales which, considering the size difference, is quite amazing.

Have you ever felt butterflies in your stomach or had to immediately get to a restroom before a big event or social gathering? It doesn’t have to be a physical threat that causes a fight or flight response. The mind’s general nervousness around an event can create a physiological response, in the gut.

When the gut microbiome is healthy, it produces beneficial molecules like short-chain fatty acids (SCFAs), which have been shown to have anti-inflammatory properties and promote brain health. However, an imbalanced gut microbiome—caused by poor diet, stress, or other factors—can lead to inflammation and mental health challenges like anxiety, depression, and cognitive dysfunction.

”…gut microbiota, especially Firmicutes, and Bacteroidetes, are demonstrated to affect mental health through microbiota-gut-brain axis, and the gut microbiota dysbiosis can be related to mental disorders, such as anxiety, depression, and other mental disorders” (Xiong et al., 2023).

One thing is certain: The gut has a profound effect on our mental health, mood, and behaviors, and our mind likewise has a reciprocal effect on our digestion processes.

Nature’s Role: Autism, Neurodivergence, & The Neurodivergent Brain

In the context of the soil-gut-brain axis, nature plays a vital role in shaping the unique ways neurodivergent brains perceive and interact with the world. Especially for individuals on the autism spectrum or with other forms of neurodivergence, sensory processing, gut health, and emotional regulation are intricately linked. 

Environmental factors, including the microbiome of soil, may influence these processes, especially given that neurodivergent individuals are often more sensitive to environmental stimuli, both positive and negative. 

Moreover, the gut-brain connection is particularly significant, as many neurodivergent individuals experience co-occurring conditions like gastrointestinal challenges, which can impact mood, cognition, and overall quality of life.

Research is currently mixed (Narzisi et al., 2021) on whether or not diet changes like the reduction in sugar intake, gluten intake, and carbohydrate intake can have impactful effects on the health and regulation of neurodivergent folks. As more research comes out, we may discover that the neurochemistry and microbiome are drastically impacted by sugar.

In that case, for people who are more sensitive to neurocognitive differences, it will be increasingly relevant to have individualized care and neuroeducation specific to your exact neurotype and physiology. 

As Above So Below: Health Goes Two Ways in Nature Science

We’ve now established the earth’s soil as a crucial component of human health. It’s relevant to discuss how deeply humanity’s choices impact our soils, for better or worse.

Only ”one ten-millionth of the earth’s total radius” consists of soil (Kopittke et al., 2023), which not only is one of the most valuable resources in existence but also a miracle of nature … We live on a tiny floating rock in space that somehow supports innumerable life forms—all because of the perfect combination of nutrients and materials present in our earth’s soil!

”For planetary health, soil contributes to multiple critical processes…Soil also underpins human health; humans use soil to provide 98.8% of our food and sustain our nutrition, regulate pathogens, and supply medicines. However, humans have tended to focus on soil almost solely for producing biomass…through intensive agriculture, and this narrow focus now causes rapid soil degradation…This degradation directly harms planetary health and reduces the ability of soil to support health of future human generations” (Kopittke et al., 2023).

When it comes to humankind’s activity, “increased cultivation intensity, several-fold increases in pesticide use, and almost 700% increase in inorganic fertilizers, has been identified as the major cause in the degradation of soils e.g., increasing soil erosion, soil compaction and greenhouse gas emissions (11)…decreased abundance of mycorrhizal fungi in roots, soil, and groundwater pollution (11, 12). As such, human interventions have caused some irrevocable changes in the nature and properties of soil” (Fausak et al., 2024).

As we consider the intimate relationship between human activity, the health of the earth’s land, and our dependency on environmental health for our survival, it is pertinent for us to make drastic changes so that we may honor both Mother Nature and ourselves as beings deeply dependent on her.

Mother Nature & Our Reciprocal Relationship

The relationship between the soil, gut, and brain is reciprocal. Healthy soil leads to the growth of nutrient-rich plants, which nourish our gut microbiota. In turn, a thriving gut microbiome supports brain health, enhancing cognitive function and emotional well-being. This interconnectedness suggests that our mental and emotional health is deeply linked to the health of the environment we live in and the food we consume.

The soil-gut-brain axis also underscores the importance of sustainable farming practices that nurture healthy soils. When we take care of our environment, we take care of ourselves. When we take care of ourselves, we take care of our environment. This may ultimately help in the prevention of mental health disorders and chronic diseases—whether of the brain or otherwise.

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