They act on different tissue. If your problem is mechanical, the most heavily marketed liver supplement in the world is aimed at the wrong place.
Ask for liver support in any health shop and you will be handed milk thistle. It has been the default for decades. If what you actually have is trouble with fatty meals, it is worth understanding what it does and does not do.
Two compounds, two targets
Milk thistle's active fraction is silymarin, a complex of flavonolignans standardised against silybin. It acts on hepatocytes. It is an antioxidant that stabilises liver cell membranes and has been studied for decades as a hepatoprotective agent.
TUDCA acts on the bile pool. It changes the composition of the fluid rather than protecting the cells that make it.
Silymarin has no surfactant activity. It does not alter bile viscosity, it does not change the hydrophobic balance of the pool, and it does not emulsify fat. Those are not criticisms of the compound. They are simply not what it does.
The evidence on milk thistle is large and largely negative
This is the part that usually gets left out, and leaving it out is a mistake, because it is checkable.
A Cochrane systematic review assessed 13 randomised trials covering 915 patients with alcoholic and hepatitis B or C liver disease. Methodological quality was low: 23% reported adequate allocation concealment and 46% were adequately double-blinded.
Against placebo or no intervention, milk thistle had no significant effect on mortality (RR 0.78, 95% CI 0.53 to 1.15), on complications of liver disease (RR 0.95, 95% CI 0.83 to 1.09), or on liver histology. Liver-related mortality was reduced across all trials (RR 0.50) but not in the high-quality subset (RR 0.57, 95% CI 0.28 to 1.19). Adverse events were not increased.
The authors concluded that the results question the beneficial effects of milk thistle in these populations and highlight the lack of high-quality evidence supporting it.
Rambaldi A, Jacobs BP, Gluud C. Milk thistle for alcoholic and/or hepatitis B or C virus liver diseases. Cochrane Database of Systematic Reviews 2007, Issue 4, CD003620. PMID: 17943794.
Note what that review examined: mortality, complications and histology in liver disease. It did not assess digestive symptoms, so it cannot be cited either way on bloating or fat tolerance. Separate meta-analyses in non-alcoholic fatty liver disease do show silymarin lowering ALT and AST by modest amounts. Enzymes move. Disease progression has not been shown to.
What TUDCA has, and how weak it is
An early study assessed TUDCA in 133 patients with dyspepsia of varied origin. Sixty-nine took 500 mg daily, or 250 mg twice daily, for 90 days. Sixty-four controls received no treatment. Symptoms were scored on a severity scale from 0 to 3.
At the end of treatment, 71.1% of the TUDCA group reported complete resolution of symptoms against 19.4% of controls, with a further 18.4% improved against 30.6%.
This study was neither blinded nor placebo-controlled, and the comparison group received nothing at all. That design reliably inflates apparent effect. The result is interesting. It is not proof.
Di Mario F, Del Favero G, Scalon P, et al. Tauroursodeoxycholic acid in the treatment of biliary dyspepsia. Advances in Therapy 1994;11(1):34–41.
The comparison, stated fairly
Milk thistle has far more trials and a weak signal on hard endpoints. TUDCA has far fewer trials, small and mostly old, aimed at symptoms rather than surrogates. Neither of those is a strong evidence base. They are weak in different directions, which is a more useful thing to know than a winner.
What is not in doubt is the targeting. If the complaint is fat-triggered discomfort rather than hepatocellular stress, a hepatocyte antioxidant is aimed at the wrong tissue, however well it is formulated.
References
- Rambaldi A, Jacobs BP, Gluud C. Milk thistle for alcoholic and/or hepatitis B or C virus liver diseases. Cochrane Database of Systematic Reviews 2007, Issue 4, CD003620. PMID: 17943794.
- Di Mario F, Del Favero G, Scalon P, et al. Tauroursodeoxycholic acid in the treatment of biliary dyspepsia. Advances in Therapy 1994;11(1):34–41.
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.