Probiotics may modestly lower ALT, AST and GGT in adults with fatty liver disease, but they are not proven to treat liver disease or reverse fibrosis.
A 2025 meta-analysis of 12 randomized trials in 657 people with metabolic dysfunction-associated steatotic liver disease (MASLD) found probiotic supplements cut ALT by about 8.12 IU/L, AST by 7.98 IU/L and GGT by 6.43 IU/L compared with placebo. That is a real signal, and it is also the entire ceiling of what the evidence currently supports.
The sections below lay out what the trials actually measured, who should not take probiotics, and how to read a blood test result without mistaking a small drop for a cure.
What Do The Trials Actually Show?
Probiotics lower liver enzymes slightly in some people, mostly in early-stage fatty liver disease, and the effect is short-term and strain-specific.
A 2025 network meta-analysis of 37 randomized trials covering 1,921 people with NAFLD reported reductions in ALT, AST, liver-stiffness readings and steatosis after probiotic use. The authors of both reviews were blunt that more randomized trials are needed before anyone treats this as settled.
An earlier review found the picture messier. Some trials showed lower ALT, AST, GGT or alkaline phosphatase after roughly 12 weeks of supplementation. Other trials found no meaningful change in ALT, AST, triglycerides or insulin resistance at all. That review concluded any benefit may be limited to earlier-stage NAFLD, with long-term effects on fibrosis still unknown.
Other liver conditions tell a different story:
- Alcohol-associated liver disease: a meta-analysis of 12 trials published between 2008 and 2025 found ALT and AST reductions, but no significant effect on GGT or alkaline phosphatase. The authors called for larger, higher-quality trials.
- Hepatitis C: the National Center for Complementary and Integrative Health states the evidence does not clearly show probiotics improve liver function. A 2014 randomized trial of 53 people with chronic liver disease found short-term improvement in bacterial overgrowth and symptoms, but not in liver function.
- Hepatic encephalopathy: NCCIH reports that a 2017 review of 21 studies with 1,420 participants found probiotics probably helped compared with placebo or no treatment, but the studies were generally low quality and it stayed uncertain whether probiotics beat lactulose.
| Liver Condition | Enzyme Change Seen | Evidence Strength |
|---|---|---|
| MASLD / NAFLD | ALT −8.12, AST −7.98, GGT −6.43 IU/L vs placebo | Moderate; 12 trials, 657 people |
| Early-stage NAFLD | ALT, AST, liver stiffness, steatosis all reduced | Moderate; 37 trials, 1,921 people |
| Alcohol-associated disease | ALT and AST down; GGT and ALP unchanged | Limited; 12 trials |
| Hepatitis C | No clear improvement in liver function | Weak; small trials |
| Hepatic encephalopathy | Probable benefit vs placebo; not clearly better than lactulose | Low quality; 21 studies |
| Fibrosis / cirrhosis | Not shown to reverse or prevent | Insufficient |
| Healthy adults | No established benefit | Not studied for this purpose |
Which Strains And Doses Work?
None. No single product, strain, dose or treatment length is established by the research as the standard for improving liver enzymes.
Trials used different single-strain and multi-strain preparations, which is a major reason the results are hard to generalize. Reported research includes organisms from the genera Lactobacillus, Bifidobacterium, Pediococcus, Bacillus and Saccharomyces, but evidence for one commercial product cannot be applied to another. A strain that lowered ALT in one trial tells you nothing reliable about the bottle next to it on the shelf.
The research applies mainly to adults enrolled in clinical trials, especially people with MASLD or NAFLD. It does not establish equivalent benefits for healthy adults, children, pregnancy, advanced cirrhosis, viral hepatitis, autoimmune liver disease or drug-induced liver injury. If you want to see which specific products have actually been tested and how they compare on strain content and labeling, our roundup of the best probiotic supplements for liver support breaks down what each one contains.
Who Should Be Careful With Probiotics?
Probiotics are usually well tolerated by healthy people, with possible mild gastrointestinal effects, but safety data are limited and risk rises sharply in people who are severely ill or immunocompromised.
The NIH Office of Dietary Supplements notes that reported potential harms include infections and transfer of antibiotic-resistance genes. Anyone with serious underlying illness should talk to a clinician first and be monitored, not self-treat.
Four mistakes show up constantly. Do not assume “natural” means liver-safe. Do not use probiotics to offset alcohol consumption. Do not read a lower ALT or AST as proof that liver disease has resolved. And do not swap probiotics for weight management, diabetes and lipid control, alcohol reduction or abstinence when indicated, vaccination, prescribed medicines, or evaluation of abnormal liver tests.
Persistent or substantially abnormal ALT, AST, GGT, alkaline phosphatase or bilirubin — or symptoms like jaundice — need medical evaluation, not a supplement. The American Association for the Study of Liver Diseases publishes current clinical practice guidelines that your doctor will use to assess and manage liver disease.
Common Questions
Can Probiotics Reverse Liver Damage?
No. No probiotic has been shown to reverse fibrosis or cirrhosis, prevent liver failure, or extend survival. The trials measured enzyme levels and steatosis over weeks to months, not scarring or long-term outcomes. If you have diagnosed liver damage, probiotics are at most a small addition to the treatment your doctor prescribes — not a substitute for it.
How Long Do You Take Probiotics Before Enzymes Change?
Most trials that reported improvements ran for about 12 weeks or longer, though durations varied widely across studies and no optimal length is established. A single blood test before and after is not enough to judge anything. Ask your doctor to track results over time with consistent testing, since enzyme levels move for many reasons besides supplements.
Are Probiotics Safe If You Have Cirrhosis?
Caution is warranted. NCCIH and the NIH Office of Dietary Supplements both flag higher risk in people who are severely ill or immunocompromised, with reported harms including infections. People with advanced cirrhosis or any serious underlying illness should consult a clinician before starting probiotics and be monitored, rather than self-treating with an over-the-counter product.
Sources
- National Center for Complementary and Integrative Health. “Probiotics: Usefulness and Safety.” Supports safety data, tolerability, and the hepatic encephalopathy review findings.
- NIH Office of Dietary Supplements. “Probiotics—Health Professional Fact Sheet.” Supports risk in severely ill and immunocompromised people, including infection and resistance-gene transfer.
- American Association for the Study of Liver Diseases. “AASLD Practice Guidelines.” Points readers to the clinical guidelines doctors use to assess and manage liver disease.