Liver and metabolism
The gut-liver axis and its role in metabolism
The gut-liver axis is the two-way connection between the intestine and the liver. Blood from the gut flows directly to the liver through the portal vein, carrying nutrients and bacterial products. The liver sends bile back into the gut. When the gut lining is weakened or the balance of gut bacteria is disturbed, the liver receives more inflammatory material, which contributes to fatty liver and its progression. A fibre-rich diet with little sugar and alcohol protects both organs.
In short
- The liver is the first organ to receive everything absorbed from the gut.
- Bile acids made by the liver are modified by gut bacteria and act as signals that regulate fat and sugar metabolism.
- A weakened gut barrier lets more bacterial products reach the liver, where they trigger inflammation.
- This connection is already used in treatment: in advanced liver disease, medicines that act on gut bacteria prevent confusion caused by toxins from the gut.
How are the gut and the liver connected?
The portal vein
About three-quarters of the liver’s blood supply comes from the intestine. It carries sugars, amino acids and fats, along with substances produced by gut bacteria.
Bile
The liver releases bile into the small intestine. Bile digests fat and restrains bacterial growth. Most of it is reabsorbed and recycled.
Bile acids as messengers
Gut bacteria convert bile acids into other forms. These act on receptors in the gut and liver that control the production of fat, the handling of sugar and the release of gut hormones.
The immune system
The liver contains a large population of immune cells that filter the incoming blood and react to bacterial material.
What happens when the connection is disturbed?
The diet shifts
More sugar, refined carbohydrate and alcohol, and less fibre.
Gut bacteria change
Fibre-fermenting bacteria decline, and the community becomes less diverse.
The barrier weakens
The mucus layer thins, and the seals between cells loosen. See the gut lining.
More bacterial material reaches the liver
Liver immune cells respond with inflammation.
Fat and inflammation build
Over years, in some people, this progresses to scarring.
Most of the evidence for this sequence comes from animal studies. In people with fatty liver, the same changes in gut bacteria and gut permeability are found, more so as the disease advances.
Which conditions involve the gut-liver axis?
| Condition | The gut’s part |
|---|---|
| Fatty liver (MASLD) | Excess fructose is converted to fat; altered gut bacteria and a weaker barrier add inflammation |
| Alcohol-related liver disease | Alcohol itself makes the gut lining more permeable |
| Cirrhosis | Bacteria and their products cross the gut wall more easily, causing infections and confusion |
| Gallstones | Changes in bile composition and gut movement |
| Bacterial overgrowth | More common in people with liver disease |
Where is this already used in treatment?
In advanced cirrhosis, ammonia and other substances made by gut bacteria reach the brain and cause confusion and drowsiness. The standard treatment acts on the gut: a laxative sugar that changes the conditions in the colon, and a gut-specific antibiotic. This is clear evidence that changing what happens in the gut changes the course of liver disease.
For fatty liver, small trials of probiotics have shown improvements in liver enzymes. They are not yet part of standard treatment.
What protects both the gut and the liver?
- Fibre from varied plants, which feeds the bacteria that strengthen the barrier
- Much less sugar, especially sugary drinks. See sugar and gut health
- Little or no alcohol
- Weight loss around the waist, where needed
- Regular exercise, which lowers liver fat directly
- Enough sleep
- Care with antibiotics, painkillers and herbal products
When should I see a doctor?
Ask for a liver check if you have diabetes, weight around the waist, raised triglycerides or raised liver enzymes. A risk score and, where needed, a FibroScan show whether there is scarring. Yellow eyes, abdominal swelling, black stools or confusion need urgent attention.
Questions patients ask me
Can improving my gut health improve fatty liver?
The measures that support the gut, such as more fibre, less sugar, less alcohol and weight loss, are the same ones proven to reduce liver fat. They work through several routes at once.
Should I take a probiotic for fatty liver?
It is not part of standard treatment. Early studies are encouraging, but diet, exercise and weight loss have far stronger evidence.
Does constipation harm the liver?
In healthy people, no. In people with cirrhosis, regular bowel movements are important, because they reduce the absorption of substances that affect the brain.
Is bloating a sign of liver disease?
Usually not. Bloating that comes and goes is nearly always a gut matter. Persistent, increasing swelling of the abdomen is different and should be examined.
Sources
This page is written for patients and is based on the guidelines and studies below. It is for education and does not replace a consultation.
- Review of the gut-liver axis and the microbiome. Tripathi A et al. Nat Rev Gastroenterol Hepatol. 2018. PubMed 29748586
- American Association for the Study of Liver Diseases practice guidance on fatty liver disease. Rinella ME et al. Hepatology. 2023. PubMed 36727674
- European guideline on metabolic dysfunction-associated steatotic liver disease (MASLD). EASL, EASD, EASO. J Hepatol. 2024. PubMed 38851997
- Review of fructose, sugar and fatty liver disease. Jensen T et al. J Hepatol. 2018. PubMed 29408694
- Review of intestinal permeability: mechanisms, measurement and clinical implications. Camilleri M. Gut. 2019. PubMed 31076401