Fecal Transplants May Cause Unintended Metabolic and Immune Effects

Fecal microbiota transplant (FMT) has emerged as a promising treatment for various gut disorders, but new research reveals it may cause unintended consequences when used to restore small bowel microbiota. The fundamental issue is that fecal microbes are predominantly anaerobic, while the small intestine has different environmental conditions that favor different microbial communities.

Researchers used antibiotic-treated mice to compare three types of microbial transplants: jejunal microbiota transplant (JMT), cecal microbiota transplant (CMT), and traditional fecal microbiota transplant (FMT). They tracked changes in regional microbiota, metabolism, and gene expression over 1-3 months. Human studies confirmed these findings by examining duodenal biopsies from patients receiving FMT.

The results showed that regional microbial mismatches led to persistent alterations in intestinal identity genes and metabolic pathways. JMT favored metabolic pathways while FMT activated immune responses. These transplants altered energy balance, liver function, and intestinal cell differentiation markers. Importantly, the effects persisted for months, suggesting long-term consequences from microbiome mismatches.

The findings have significant implications for microbiome-based therapies. Current FMT protocols may inadvertently disrupt small bowel homeostasis by introducing microbes poorly suited to that environment. This could explain some variable outcomes in FMT treatments and suggests the need for region-specific microbiome interventions.

The research points toward personalized microbiome therapies that consider the distinct microbial ecosystems of different gut regions, potentially improving treatment efficacy while avoiding unintended metabolic and immune consequences.