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publishDate

September 15, 2021

author

Michael Kuefner, PhD (BMS)
Liver, Bile Acids, And Digestive Health
Author

Fact Checked By Michael Kuefner, PhD (BMS)
 September 15, 2021

Digestive Health

General liver function in digestive processes

One of the many functions of the liver is to assist the digestive system, specifically by processing nutrients absorbed from our small intestines.

When digested nutrients are broken down in the intestines, they are transported through the hepatic portal vein to the liver.

Once these nutrients reach the liver, they are filtered before being transported throughout the body to our other organs.

This ensures that toxic or unnecessary substances are not being transported throughout the body when they shouldn’t be.

Likewise, the liver is the primary organ involved in both the digestion and production of fats and simple sugars.

Specifically, simple sugars are broken down by large sugar molecules known as glycogen – once broken down, the smaller sugar molecules can be transported throughout the body and used for energy when needed.

Essentially, you can think of the liver as the body’s ‘chemical factory’ – it processes nutrients for the rest of the body, and creates albumin, a protein which transports hormones, drugs, or fatty acid particles where they are needed (1).

The liver’s role in the digestion of fats and cholesterol, as well as nutrient absorption is mainly due to its production of bile.

Bile acids

Another specific function of the liver is its production of bile – a yellowish-green to dark brown fluid composed of salts, bilirubin cholesterol, water, and bile salts.

Bile acids play a major role in overall sugar and fat metabolism, and are formed by cholesterol catabolism in the liver.

Once produced in the liver, bile is released to the first part of our small intestine (duodenum), or stored in the gallbladder during fasting, where it can be used later in response to a meal.

Research over the last couple decades has outlined the five major functions of bile acid production, showing just how important it is (2).

1. Elimination of cholesterol

  • Bile acids eliminate cholesterol by actually converting the fat molecules to bile acids, along with micellar solubilization of cholesterol in the bile itself.

    Cholesterol solubilization allows for the fat molecules to move from the liver cells (hepatocytes) into the intestines, where it can eventually be eliminated in the feces.

2. Fat transport

  • The regulation of fat transport is primarily regulated by bile acids produced by the liver.

    Normally, these fats are transported in a form known as ‘mixed micelles,’ which are essentially small conglomerates of mixed lipid and bile acid particles.

  • Once bile acid is transported to the small intestines from the liver, it promotes the absorption of fats from our diet. This process is achieved by ‘solubilizing’ the fat particles by mixing them in the micelle aggregates.

    Formation of these mixed micelles enables digestion and elimination of fats and cholesterol particles.

  • The mixed micelle formation (again, aggregates of fats, bile acids, cholesterol, etc.) also promotes absorption of fat-soluble vitamins as well (A, D, E).

3. Bile flow and fat secretion

  • Bile acids in the liver regulate the overall flow of bile throughout the body. Moreover, bile acids also regulate the transfer of fats from hepatocytes into the bile.

  • This process is important as once the presence of fats in the bile results in the existence of mixed micelles of bile acids and fats, which prevent the bile acids from damaging the bile duct epithelium.

4. Negative feedback loops on cholesterol biosynthesis

  • When concentrations of bile acids in the hepatocytes are high, bile acid synthesis is low. However, when concentrations are low, bile acid synthesis boosts up by as much as 15-fold.

  • Interestingly, since bile acids are made from cholesterol, previous research reports that cholesterol synthesis undergoes a parallel increase in order to boost up bile acid production (3).

Liver diseases do exist that dysregulate the normal flow of bile from the liver – the main one being cholestatic liver disease.

Such dysregulation leads to high levels of bile acids in the liver, which can eventually result in severe liver damage due to inflammation and eventually hepatocyte death (4).

Bile acids as potential therapeutics for liver diseases

While further research needs to be carried out on the efficacy of bile acids to treat metabolic disorders (such as diabetes, metabolic syndrome, obesity, etc.), studies do indicate bile acids may be useful in improving fat/cholesterol metabolism and improving glucose homeostasis in humans (4). One secondary bile acid (UDCA, or UrsodiolTM) has even been approved by the FDA for the treatment of some liver disorders, and has been shown to dramatically improve liver function (5).

One review article suggests bile acids may even make you live longer (the jury is still out on this one, though) (6).

So, what are some ways to manage bile acid function, keep your cholesterol/fat metabolism in check and maintain liver health?

For starter’s many of the liver pathologies associated with bile acid complications are related genetically.

Drug and alcohol usage may be causal of cholestatic liver disease, though, so limiting usage and the burden those substances have on the liver may be helpful (7).

Natural substances may improve bile acid regulation in the liver and rest of the body as well.

One of these substances in particular is beetroot.

One clinical study on beetroot supplementation found that beet leaf/beet powder supplementation reduced gallbladder wall thickness and volume compared to the placebo group, indicating the supplement may improve blood circulation (and thus, better filtration throughout the body) to improve gallbladder and liver health. The study included 42 participants (8).

Another study found that beets have binding properties to bile acids to prevent the build-up of secondary bile acids in the gallbladder.

The researchers proposed that this may prevent recirculation of the bile acids, leading to less fat and cholesterol absorption (9).

Concluding remarks

The liver is a multi-functional organ in our body, and consistent declines in overall health can drastically affect its ability to perform these functions.

One of these, as discussed in this article, is absorption and digestion of nutrients. Digestion is mainly regulated by the production of bile, a liquid that processes fats, cholesterol, and much more.

As a final note, if you have any reason to believe bile production may be low (have a hard time digesting fatty meals?) taking a look at your cholesterol and triglyceride levels with your primary physician might be a good first step to help.