Bile acids, particularly ursodeoxycholic acid (UDCA), have been investigated for their potential to treat fatty liver disease, specifically nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH). Bile acids play a physiological role in fat digestion and also act as signaling molecules that regulate lipid, glucose, and energy metabolism in the liver. This scientific rationale has driven research into their therapeutic use.

Several clinical trials have evaluated UDCA in NAFLD and NASH. While some early studies reported improvements in liver enzymes and histology, larger, more recent randomized controlled trials and systematic reviews have generally found that UDCA does not significantly improve key liver histological features compared to placebo. Thus, current major guidelines (such as those from the American Association for the Study of Liver Diseases) do not recommend UDCA as a standard therapy for NAFLD/NASH.

Other bile acid derivatives, such as obeticholic acid (a semi-synthetic bile acid analog), have shown some promise in improving certain histological endpoints in NASH, but their use is still under investigation and not yet standard. In summary, there is a scientific rationale and some evidence supporting the investigation of bile acids for fatty liver disease, but clinical benefit remains unproven, and their use is not routinely recommended.