Do reduced SCFAs and gut dysbiosis increase gut-derived inflammatory signaling to the liver and lead to MAFLD and higher ALT?

The relationship between gut dysbiosis, short-chain fatty acids (SCFAs), and liver health is well-documented within the "gut-liver axis." Current research confirms that alterations in the microbiome and its metabolic byproducts directly influence the progression of metabolic-associated fatty liver disease (MAFLD) and elevated liver enzymes.

Clinical evidence and biomarkers

Clinical studies consistently demonstrate that individuals with MAFLD exhibit distinct dysbiotic signatures compared to healthy controls. These signatures are typically characterized by a loss of microbial diversity and a significant reduction in SCFA-producing genera, such as Faecalibacterium and Roseburia.

• ALT and Liver Injury: Serum alanine aminotransferase (ALT) serves as a key clinical marker for this process. Mechanistic and animal model studies show that a deficiency in SCFAs—particularly butyrate—is strongly associated with higher ALT levels. For instance, butyrate supplementation has been shown to significantly decrease serum ALT and AST by reducing hepatocellular membrane damage and inflammation.
• Disease Progression: The reduction in SCFAs is not merely a byproduct of liver disease but a contributor to it. Low levels of these fatty acids are linked to the transition from simple steatosis to more severe metabolic-associated steatohepatitis (MASH).

Mechanistic pathways

The link between the gut and liver is mediated by the integrity of the intestinal barrier and the systemic transport of microbial metabolites.

• Intestinal Permeability: SCFAs like butyrate and propionate are essential for maintaining the "tight junctions" (proteins such as ZO-1 and occludin) that keep the gut barrier intact. When dysbiosis reduces SCFA production, the barrier weakens, leading to "leaky gut."
• Inflammatory Signaling: A compromised barrier allows lipopolysaccharides (LPS)—pro-inflammatory components of gram-negative bacteria—to enter the portal circulation. Upon reaching the liver, LPS binds to Toll-like receptor 4 (TLR4) on Kupffer cells (liver macrophages), triggering the NF-κB pathway and the release of inflammatory cytokines like TNF-α and IL-6.
• Hepatoprotective Signaling: SCFAs normally protect the liver by activating GPCR43 (FFAR2) and inhibiting histone deacetylases (HDACs). These actions promote a regulatory T-cell environment and upregulate Nrf2-mediated antioxidant defenses. When SCFAs are depleted, the liver loses these protective signals, increasing its vulnerability to oxidative stress and lipid accumulation.

Bottom line

The evidence strongly supports that reduced SCFAs and gut dysbiosis drive MAFLD and elevated ALT through increased intestinal permeability and pro-inflammatory signaling via the gut-liver axis. Maintaining a microbiome rich in SCFA-producing bacteria is critical for preserving liver function and preventing metabolic inflammation.