The liver is the body’s powerhouse of detoxification. The main function of the liver is to filter blood that comes directly from the intestines to the liver via the portal vein. The health of the liver, therefore, is very much dependent on the health of the gut. The intestinal lining is the main interface between the immune system and the external environment, and the health of the intestinal lining is determined by its balance of bacteria. When gut bacteria are out of balance, the intestinal lining can become damaged. As a result, a higher amount of toxins are able to pass through the lining and into the bloodstream, accessing the immune system as they travel directly to the liver for processing.
Because of the close proximity and intimate relationship between the gut and the liver, conditions that affect the liver are being increasingly linked to gut bacterial disturbances. There are two main ways in which researchers believe that gut bacteria contribute to non-alcoholic fatty liver disease (NAFLD), as discussed in a recent review paper published in the Journal of Functional Foods:
- Increased production of ethanol (alcohol) by gut bacteria2
- Increased absorption of bacterial toxins (such as lipopolysaccharide, or LPS)3
These toxins trigger inflammation in the liver via upregulation (increase) of immune function, which initiates the development of NAFLD. These toxins more readily flow to the liver under three main conditions, all known to be contributing risk factors of NAFLD:
- Leaky gut (increased intestinal permeability)
- Small-intestinal bacterial overgrowth (SIBO), a form of dysbiosis in which bacteria from the colon back up into the small intestine and overgrow.
- Bacterial translocation, or the migration of bacteria from the gut through the intestinal lining and into the mesenteric lymph nodes, where they trigger inflammation that reaches the liver.
To reverse or prevent the harmful effects of gut bacterial disturbances on the liver, probiotic administration has been suggested. The researchers note the following possible mechanisms by which probiotics can improve NAFLD:
- Decreased inflammation
- Decreased SIBO
- Immune system regulation
- Decreased LPS production
- Decreased bacterial translocation
An important function of probiotics is the protection of the intestinal lining. This function explains the protective functions of these beneficial bacteria. In a human clinical trial, patients with non-alcoholic steatohepatitis (NASH)—a condition that often follows NAFLD—received a multi-strain, high-dose probiotic and were found to have significant decreases in inflammation and improvements in levels of the liver enzyme aminotransferase.4 In another uncontrolled trial on the same probiotic formula, NAFLD and alcoholic cirrhosis patients experienced decreased inflammation and lipid peroxidation.5 In another clinical trial, the probiotics Lactobacillus bulgaricus and Streptococcus thermophilus supplementation resulted in improved liver aminotransferase levels in people with NAFLD.6
“Probiotics, as safe and effective compounds, have the potential to influence gut barrier functions and immune cell regulations resulting in liver health improvements,” noted the researchers.
Due to the scarcity of treatments available for NAFLD, probiotics are a promising option. More studies are needed to further pinpoint just how the probiotics exert their benefits in people with fatty liver disease.
- Mohammedmoradi S, Javidan A, and Kordi J, “Boom of probiotics: This time non-alcoholic fatty liver disease—A mini review.” J Functional Foods. 2014 Nov;11:30–35.
- Compare D, Coccoli P, Rocco A, et al., “Gut—liver axis: the impact of gut microbiota on non alcoholic fatty liver disease.” Nutr Metab Cardiovasc Dis. 2012 Jun;22(6):471–6.
- Vanni E and Bugianesi E, “The gut-liver axis in nonalcoholic fatty liver disease: Another pathway to insulin resistance?” Hepatology. 2009 Jun;49(6):1790–2.
- Loquicercio C, De Simone T, Fe3derico A, et al., “Gut-liver axis: a new point of attack to treat chronic liver damage?” Am J Gastroenterol. 2002 Aug;97(8):2144–6.
- Loquicercio C, Federico A, Tuccillo C, et al., “Beneficial effects of a probiotic VSL#3 on parameters of liver dysfunction in chronic liver diseases.” J Clin Gastroenterol. 2005 Jul;39(6):540–3.
- Aller R, DeLuis DA, Izaola O, et al., “Effect of a probiotic on liver aminotransferases in nonalcoholic fatty liver disease patients: a double blind randomized clinical trial.” Eur Rev Med Pharmacol Sci. 2011 Sep;15(9):1090–5.