Are soil microorganisms missing from the Planetary Health Plate? The Planetary Health plate consists of about half a plate of vegetables and fruits, and another half of whole grains, plant proteins, unsaturated plant oils, and modest amounts fish, meat, or dairy. However, it does not contain soil microorganisms that have been essential for the evolution of the human gut microbiome and immunological resilience.
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By Marja I. Roslund, Olli H. Laitinen, and Aki Sinkkonen.

Read the full paper here.

Children love to bake soil mud cakes that they provide to parents as a fake delicacy. In fact, people have routinely eaten soil in many cultures, either incidentally or intentionally. Evidence suggests that the soil microbiota was essential for the evolution of the human gut microbiome and immunological resilience. The western lifestyle has reduced our contact with soil, which can induce extinctions in the gut microbiota and decrease immunological resilience.

We investigate whether existing scientific evidence supports the hypothesis that eating soil provides immunological resilience. We identify research gaps and challenges that researchers must overcome to understand the effects of soil eating on immunological resilience. We searched for peer-reviewed articles that focused on studies that exposed mammals to soil and measured the gut microbiota and host response.

We found research on the positive and negative aspects of soil contact and the gut microbiome. On the positive side, we found three human intervention trials indicating that soil microbiota provides immunological resilience and one cohort study indicating that soil bacteria are transferred to the gut of gardening families. Based on six mouse studies, the potential benefits of soil microorganisms include gut health, prevention of allergies and autoimmune diseases, as well as better mental well-being. A study with piglets showed that soil exposure modulates the gut bacterial community towards improved fermentation potential, while a study with lemurs showed that soil eating also modulates the gut fungal community. On the negative side, we identified seven studies related to soil eating risks, including heavy metals, polyaromatic hydrocarbons, microplastics and drug residuals, parasites, pathogens, and antibiotic resistant genes. These risks and the lack of suitable technologies have hindered progress toward understanding the soil microbiota in the gastrointestinal tract. Today, there are no clinical trials in which volunteers intentionally ingest microorganisms-containing soil and gut microbiome and human health are monitored.

Since the lack of immunological resilience may be the main reason for the increasing burden of noncommunicable diseases among urban societies, there is an unmet need for preventive approaches utilizing soil microorganisms suitable for oral intake. Large clinical trials and novel technologies are necessary before soil mud cakes can be considered in the Planetary Health Diet.