Scoping review on soil microbiome and gut health: Are soil microorganisms missing from the planetary health plate?

Abstract

1. Evidence suggests that soil microorganisms, to which humans have been exposed throughout our evolutionary history, were essential for the evolution of the human gut microbiome and immunological resilience. In recent decades, gut microbial diversity has decreased along with urbanization and global loss of biodiversity. At the same time, the prevalence of chronic, non-communicable inflammatory diseases has been increasing in urbanized societies. 2. Here, we investigate whether the existing literature supports the hypothesis that ingesting soil microbiota provides immunological resilience. We focus on identifying research gaps and challenges that must be overcome to understand the effects of eating soil on immunological resilience. A scoping review of the peer-reviewed empirical literature was carried out. The search focused on studies that exposed mammals to direct soil contact and measured the gut microbiota and host response; 12 articles, including four human, six mouse and two other mammal studies, were identified for inclusion in the review. In addition, seven articles related to human health risks associated with soil consumption were included in the review. 3. Studies indicate that ingesting soil-bound microorganisms supports immunological resilience. There is a lack of intervention studies that include human study subjects that test orally the effect of soil microorganisms on the gut microbiota and immunological resilience. 4. Challenges, particularly soil heterogeneity and risks related to soil biological and chemical properties, have prevented progress to fully understand the effect of oral intake of soil-bound microorganisms on human gut microbiota and health. 5. The results encourage the development of technologies that allow daily exposure to soil microbiota. Future research should be aimed to precisely test the importance of oral intake of soil-bound microorganisms in gut microbial homeostasis and immunological resilience.