Does Gut Health Begin with "Soil"? The Invisible Microorganisms Connecting Fields, Our Tables, and Our Bodies

Does Gut Health Begin with "Soil"? The Invisible Microorganisms Connecting Fields, Our Tables, and Our Bodies

When you pick up vegetables at the supermarket, not many people imagine the soil in which those vegetables grew. While we pay attention to color, shape, price, origin, pesticide use, and nutritional labels, it's hard to consider what was happening in the dark world beneath our feet.

However, soil is not just a "platform for plants to stand on." It is a vast ecosystem where bacteria, fungi, protozoa, nematodes, mites, and earthworms decompose organic matter, circulate nutrients, and exchange substances with plant roots. Similarly, the human gut is an ecosystem where microorganisms, primarily bacteria, interact with each other, involving food decomposition, metabolite production, gut barrier function, and dialogue with the immune system.

"Soil and the gut are similar." This striking perspective is gaining attention as a theme that crosses agriculture, nutrition, microbiology, and environmental science. However, the important thing is not to end with a romantic metaphor. Are healthy soil and a healthy gut truly connected? What has been confirmed by research, and what remains hypothetical? By following reactions on public social media, I want to organize the current state.


Neither soil nor the gut is a "collection of individuals" but a network

The functions of soil microorganisms cannot be divided into just beneficial and harmful bacteria. One microorganism breaks down plant residues into small molecules, and another microorganism uses those products. Mycorrhizal fungi form symbiotic relationships with plant roots, receiving carbon compounds from the plants while helping them acquire nutrients like phosphorus and water. Some microorganisms are involved in nitrogen cycling, while others suppress plant pathogens. The important thing is not a single "excellent bacterium" but a network of organisms with different functions.

The situation is similar in the gut. Microorganisms ferment dietary fibers that humans cannot fully digest, producing short-chain fatty acids like acetate, propionate, and butyrate. These serve as energy sources for colon cells and act as signals involved in immunity and metabolism. There is also "cross-feeding," where one bacterium uses the metabolic products of another, making it impossible to explain gut conditions by the presence or absence of a single bacterial species.

This commonality supports the idea that "diversity is needed in both soil and the gut." However, the two ecosystems are not identical. Oxygen, temperature, acidity, available nutrients, and the relationship with the host differ significantly, so soil microorganisms do not necessarily establish themselves in the gut and improve health. It's necessary to separate the idea that "soil and the gut operate on similar principles" from "soil bacteria directly heal the gut."


The most certain path from soil to the gut is "food"

Among the pathways connecting soil and the gut, the most understandable and actionable at present is diet.

In healthy soil, organic matter decomposition and nutrient cycling function, making it easier for plants to extend their roots. Good soil structure retains water while allowing excess water to drain, increasing resistance to droughts and heavy rains. The interaction between microorganisms and roots also affects plant growth and disease resistance. Vegetables, fruits, beans, and grains produced in this way provide us not only with vitamins and minerals but also with dietary fibers, polyphenols, and various compounds that serve as substrates for fermentation.

For gut bacteria, it's more important to receive a continuous supply of various plant-based foods than to focus on a single "health-promoting food." Whole grains, beans, vegetables, fruits, nuts, and seeds each contain different structures of dietary fibers and plant components. The diversity of ingredients provides multiple habitats and food sources for microorganisms with different metabolic capabilities.

A randomized controlled trial published in Nature Medicine in 2025 is interesting in considering this point. It involved 77 healthy young men in Tanzania, switching between a traditional Kilimanjaro region diet and a Western-style diet, examining immune, inflammatory, and metabolic markers. The group that switched to the traditional diet, which included vegetables, beans, whole grains, fruits, and fermented foods, showed favorable changes in markers related to inflammation and metabolism. Conversely, the group that switched to a Western-style diet showed inflammatory changes, some of which persisted even after the intervention ended.

This study did not prove that "specific soil microorganisms transferred to the human gut." However, it showed that a plant-rich dietary pattern, born from local land and food culture, can affect human immune and metabolic systems even in a short period. The health effects from soil to humans first appear through crops and dietary composition—this is faithful to the current evidence.


What can be learned by burying underwear in soil

The workings of soil are not easily visible. Therefore, Swiss researchers chose a very noticeable method. About 1,000 citizens buried over 2,000 pairs of cotton underwear and approximately 12,000 tea bags in various soils.

The main component of cotton is cellulose. If microorganisms and small animals in the soil are active, the fabric will decompose over time. By digging it up after a certain period and examining how much fabric has been lost, one can intuitively compare the activity of soil organisms. Tea bags were also used as standardized materials to measure the rate of organic matter decomposition.

The results showed that the degree of decomposition is strongly related to land use and management practices. Decomposition was reported to be faster in private gardens and lower in lawns. However, a simple judgment that "the faster the decomposition, the better the soil" cannot be made. Decomposition speed is also influenced by temperature, moisture, soil type, nutrient status, and vegetation, and in natural ecosystems, excessive nutrients may indicate other problems.

The value of this experiment lies not only in inventing a universal health check but also in making the activity of usually invisible soil organisms visible to citizens. Rather than the abstract term "soil biological activity," the hole-ridden underwear dug up from the soil instantly conveys meaning. It was also excellent as a design connecting science and society.


On social media, "surprise and laughter" became an entry point to soil

Examining related posts on public social media, the Swiss underwear experiment was repeatedly introduced in multiple videos, mainly on Instagram. The unexpectedness of "why scientists buried underwear" became a strong hook, leading viewers to explanations of soil decomposers and biological activity. Unusually for science news, laughter and surprise precede difficult technical terms. As a result, it easily reached audiences who do not usually follow soil research.

 

On the other hand, on X and YouTube, messages like "gut health starts from the ground" and "soil and gut environments are connected" stand out. Many posts also link the discussion to practices in life and agriculture, such as regenerative agriculture, composting, plant food diversity, and fermented foods. There is a movement to reconsider soil conservation not only as an issue of climate change or yield but also as a matter of personal and family health.

 

However, this reaction cannot be seen as the "consensus of social media users." Public posts found through searches are biased toward groups or individuals active in dissemination and videos spread by algorithms. Moreover, while short phrases like "if the soil is healthy, people are healthy" are easy to share, they skip over complex causal relationships. Touching natural soil does not necessarily improve gut bacteria, unwashed vegetables are not better, and taking specific bacterial products does not lead to conclusions. Due to risks like pathogens, parasites, heavy metals, and pesticides, vegetables should be properly washed and hygiene maintained.

The role of social media is not to provide final conclusions but to create an entry point for interest in the ecosystems beneath our feet. The spread of the underwear experiment can be said to have exerted great power as such an entry point.


How much is known about the relationship between "touching soil" and immunity

Aside from diet, contact with microorganisms in the natural environment is gaining attention. The "biodiversity hypothesis" suggests that reduced contact with environmental microorganisms due to urbanization and loss of natural environments may affect human resident microbiota and immune regulation. Studies have shown associations between environments with abundant greenery, rural living, animal contact, and allergy or immune status.

However, caution is needed here as well. People who are in contact with nature differ in many ways, such as diet, exercise, income, living environment, use of antibiotics, and pet ownership. Even if a correlation is found in observational studies, soil microorganisms are not necessarily the cause. It is not uniform which microorganisms, when, and to what extent contact is beneficial.

Spending time in gardens or forests has other benefits like physical activity, stress reduction, sunlight, and social participation. Therefore, rather than "eating soil to strengthen immunity," a realistic approach is to increase safe opportunities to engage with nature and reap its comprehensive benefits.


Soil degradation is both a food and health issue

A large portion of the world's food depends on soil. Nevertheless, UN agencies have warned that up to 40% of the world's land is degraded. Erosion, salinization, compaction, organic matter loss, pollution, overgrazing, monoculture, deforestation, urbanization, and climate change are intricately intertwined.

If soil degradation progresses, it's not just that yields will decline. The ability to store water weakens, making it more susceptible to droughts and floods. The reduction of soil organic carbon is also related to climate change, and biodiversity above and below ground is compromised. Farmers may be forced to rely more on external inputs like fertilizers and pesticides, potentially increasing production costs and environmental burden.

Furthermore, changes in food prices and availability may lead people to lean towards inexpensive, long-shelf-life ultra-processed foods. If access to fresh and diverse plant-based foods becomes unequal, it can indirectly affect gut health and chronic disease risk. Thus, the relationship between soil and the gut is not just a matter of microorganisms. It is also an issue of the "food system," including agricultural policy, distribution, income, and regional food culture.


What can agriculture that protects soil change?

Practices to protect soil include crop rotation, cover crops, organic matter return through compost, reduced tillage, proper grassland management, agroforestry, and securing habitats within farmland. The goal is not to adopt trendy farming names but to reduce the time soil is bare, keep roots alive as long as possible, combine diverse plants, and suppress erosion and excessive inputs.

However, the effects vary depending on climate, soil, crops, and management scale. For example, even if tillage is reduced, increased reliance on herbicides for weed management can pose another challenge. Excessive organic fertilizers can also lead to water pollution. It is necessary to evaluate based on multiple indicators such as soil organic matter, permeability, biological activity, yield, input amounts, greenhouse gases, and biodiversity, rather than judging good or bad by a single label.

The Swiss underwear experiment also taught that differences in land use and management are reflected in underground activities. Measuring invisible changes, trying methods that suit regional conditions, and making long-term adjustments. Soil regeneration is not a one-time measure but continuous management.


What we can do starting today

Consumers cannot directly manage the composition of soil microorganisms. However, there are things we can do through our dining tables and purchases.

First, for gut bacteria, increase the variety of plant-based foods rather than concentrating on specific "superfoods." Combine vegetables, fruits, beans, whole grains, mushrooms, seaweed, nuts, and seeds without strain, according to your health and chronic conditions. Fermented foods are also an option, but they alone do not determine gut health.

Second, be mindful of seasonality and origin, and if possible, choose producers or products that explain their soil conservation efforts. Rather than judging by words like "organic" or "regenerative," look at specific explanations such as crop rotation, cover crops, pesticide and fertilizer management, biodiversity, and verification methods.

Third, participate in home gardening, local greening, or composting. This provides an opportunity to understand soil mechanisms physically. However, consider hygiene, odor, pests, and local rules for kitchen waste composting, and use safe materials for edible crops.

Fourth, verify causal relationships, especially with information claiming "gut health." Is it a mouse experiment or a human study? Is it an observational study or an intervention trial? Are the number of subjects and duration sufficient? Did only inflammation markers change, or did disease incidence decrease? Such differences greatly affect the strength of what can be said.


Don't think of health as only inside the body

Interest in gut bacteria tends to be confined to supplements or individual dietary methods. However, our food is born from fields, and those fields are supported by water, climate, microorganisms, farmers' skills, and the local economy. Health does not end within the body.

The research connecting soil and the gut poses not the narrow question of "which bacteria to increase for health," but the larger question of "how to protect an environment where diverse life can work." Soil diversity supports plants, plant diversity enriches the diet, and dietary diversity supports the metabolic network in the gut. In the middle of this chain are human societal choices such as agriculture, distribution, cooking, income, and culture.

A single piece of hole-ridden cotton underwear visualized the obvious fact that there are living things in the soil. And it reminds us that the activities beneath our feet can connect to our own health through the dining table. Caring for the gut and caring for the soil are not the same. However, both resonate deeply in terms of protecting diversity, not seeking only short-term results, and viewing the entire ecosystem.


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