The Connection Between Gut Health And Your Liver

Why Do Probiotics & Prebiotics Improve Liver Health?

You’ve definitely heard of the gut-brain axis.

You may have even heard of the gut-skin axis...

But I’m willing to bet that you’ve probably never heard of the gut-liver axis before.

I certainly hadn’t until I started the research required to write my latest book on fatty liver disease and it was with great surprise that supplements typically associated with gut health, such as pre & probiotics, were among the most frequently studied for helping with NAFLD (non-alcoholic fatty liver disease).

Now, this may not seem like a remarkable statement, but given that 1 in 4 North Americans is living with fatty liver disease and that there is no currently approved pharmaceutical treatment for the increasingly common condition – the role of pre/probiotic supplementation in improving liver health is a pretty big deal.

The 2020 ESPEN Clinical Practice Guidelines For Liver Disease formally endorse probiotics as a means to reduce liver enzymes in people living with NAFLD. 

Another pretty big deal, as they are generally guarded about making affirmative statements about supplements without an abundance of high-quality evidence.

I should also add here that liver health is a topic of generally massive interest among the general public, and I know this because my social media content related to the liver outperforms just about every other topic category.

I mean, heck, that’s why you’re reading this article right?

Time for me to justify your decision, let’s get to the good stuff.

An Introduction To The Gut-Liver Axis

The human liver and stomach are connected through what is known as the portal vein – a vessel that is responsible for carrying blood from the human digestive tract to the liver and sets the stage for what is a significant bidirectional relationship between these two vital organs.

The portal vein carries various metabolites from the digestive tract to the liver and the liver contributes via bile (digestive) acid secretion and the facilitation of certain aspects of the human immune response. 

But what happens when someone’s gut health is less than optimal? 

The state of the gut microbiome is fundamental to a healthy relationship between the gut and liver, and it is perhaps unsurprising to hear that dysbiosis is a common feature of fatty liver disease which also explains the positive evidence around pre/probiotic use.

Dysbiosis And Liver Health 

The current scientific consensus as to why dysbiosis of the digestive tract is so problematic for the liver focuses on a few related concepts:

1. Helpful bacteria make helpful metabolites (like SCFAs) whereas less healthful bacteria produce problematic pro-inflammatory metabolites. In either case, these metabolites travel through the portal vein to the liver where they have differential effects on liver health. Inflammation of the liver, for example, is one of the common characteristics of NAFLD. 
2. Dysbiosis weakens the intestinal barrier which makes the effect of the above more pronounced because this barrier otherwise plays an important role in preventing problematic bacteria (and their metabolites) from entering the portal vein and making their way to the liver which in turn can elicit a damaging immune response.

Inflammation is known to worsen NAFLD and increase one’s risk of advancing to more severe stages of the disease as it contributes to worsening liver damage and scarring.

The evidence for the relationship between liver inflammation and the gut microbiome is enhanced through a 2020 systematic review and meta-analysis published in Scientific Reports which demonstrated that probiotic supplementation reduced numerous well-studied inflammatory markers in NAFLD patients including tumor necrosis factor-α (TNF-α) and C-reactive protein (CRP).

For reference, in the majority of studies in this realm, the probiotic used was generally a multi-strain containing  108  CFUs of various Lactobacillus and Bifidobacterium, where the prebiotic used was generally FOS or inulin.

Final Thoughts & Future Directions

The current state of the evidence is clear in delineating a real and relevant relationship between optimal gut and liver health.

A relationship that is mediated, in part, by dysbiosis of the digestive tract which has the potential to worsen liver inflammation and contribute to the worsening functioning of this vital organ.

While the concept of gut health is ever emerging and ever relevant given its daily quality of life implications, the direct relevance of gut health to a very common and troubling chronic condition (in the form of fatty liver disease) only increases the stakes.

It's important to note as well that pre & probiotic supplementation is only one of so many avenues to be explored for enhanced gut health and surely the content available here on Foodguides.com will provide you no shortage of inspiration in this regard.