An animal study on bile acids and the microbiome produced striking numbers. Those numbers are from mice, and that qualification is the point.
Blood leaving the intestine goes straight to the liver through the portal vein, carrying whatever has crossed the gut wall. That anatomical fact is why intestinal barrier function and liver inflammation are linked, and why the gut-liver axis has become such an active research area.
The proposed sequence
Conjugated bile acids have antimicrobial activity. Circulating through the small intestine, they exert selective pressure on bacterial populations and help keep the upper gut relatively sparse.
When bile flow falls, that pressure weakens. Bacterial populations expand, the tight junctions of the intestinal lining are compromised, and lipopolysaccharide from bacterial cell walls crosses into the portal circulation. Arriving at the liver, it activates resident immune cells and triggers inflammatory signalling, which shows up as fat accumulation in hepatocytes and raised transaminases.
That is a coherent model. Here is what has been tested.
Specific-pathogen-free male C57BL/6 mice were fed a lithogenic, high-cholesterol diet for eight weeks to induce gallstones and liver injury. One group received TUDCA at 5 g per kg of feed.
Diet-only animals developed heavy hepatic fat infiltration, barrier disruption and sharply raised transaminases: ALT 546.4 IU/L and AST 618.5 IU/L. In the TUDCA group these were far lower, at ALT 28.4 IU/L and AST 160.2 IU/L.
Hepatic TNF-α expression was suppressed in the treated animals. Sequencing showed a shift in the microbiota, with Firmicutes rising and Bacteroidetes falling, moving the Firmicutes to Bacteroidetes ratio by roughly threefold.
Lu Q, Jiang Z, Wang Q, Hu H, Zhao G. The effect of tauroursodeoxycholic acid (TUDCA) and gut microbiota on murine gallbladder stone formation. Annals of Hepatology 2021;22:100289.
Reading this honestly
These are mice, on a diet engineered to produce gallstones quickly, at a dose expressed as a percentage of their feed rather than anything comparable to a human capsule. The effect sizes are large partly because the injury model is severe.
No human trial has shown TUDCA normalising transaminases, restoring tight junction integrity or shifting the microbiome in the way described above. The transaminase numbers in that box are not numbers you should expect to see in yourself, and anyone presenting them as though they are is misusing the study.
What the work does support is narrower and still worth knowing: bile acids exert real selective pressure on gut bacteria, that pressure is plausibly part of how bile flow and liver inflammation are connected, and hydrophilic bile acids modify it in an animal model. Whether that translates to people is an open question, and it should be described as one.
References
- Lu Q, Jiang Z, Wang Q, Hu H, Zhao G. The effect of tauroursodeoxycholic acid (TUDCA) and gut microbiota on murine gallbladder stone formation. Annals of Hepatology 2021;22:100289. DOI: 10.1016/j.aohep.2020.100289.
- Wang W, Zhao J, Gui W, et al. Tauroursodeoxycholic acid inhibits intestinal inflammation and barrier disruption in mice with non-alcoholic fatty liver disease. British Journal of Pharmacology 2018;175(3):469–484. DOI: 10.1111/bph.14084.
Educational and scientific information only. Tauroursodeoxycholic acid (TUDCA) is sold as a food supplement and has not been assessed by the Food Standards Agency, the MHRA, the European Food Safety Authority or the US Food and Drug Administration for preventing, treating or curing any disease. Ursodeoxycholic acid (UDCA) is a prescription-only medicine in the UK. Nothing here is a substitute for prescribed treatment. If you are under medical care or taking prescribed medication, speak to your doctor or pharmacist before starting any supplement.