Introduction

The bacterial environment of the gastrointestinal (GI) tract has long been investigated for its role in health maintenance and relationship to various disease states. In healthy hosts, microorganisms are present throughout the GI tract and are essential for gut barrier function, digestive support, and immune homeostasis.

However, intestinal health is not always in balance and many symptoms can arise. That’s why it is so important to understand more in-depth which factors can impact gut homeostasis.

What is SIBO? (small intestine bacterial overgrowth)

Bacterial overgrowth in the small intestine (SIBO) is a pathological growth of the intestinal microbiota in the small intestine that causes clinical symptoms and can lead to digestive and absorption disorders.

The most common symptoms are excessive accumulation of gas, abdominal distension, chronic diarrhea (watery or fatty), abdominal pain, abdominal fullness, sometimes constipation, malabsorption disorders (vitamin B12, iron, choline, fats, carbohydrates and proteins), progressive malnutrition and weight loss in long-term.

In order to restore intestinal balance, it is necessary to look at the body as a whole and understand what the root causes might be.

Here we will emphasize the link between the liver and gut health.

How the liver impacts SIBO

Significantly the composition, diversity and richness of the gut microbiota determine the efficiency of energy acquisition from food. And an imbalance in this microorganism diversity is associated with an increase in the incidence of chronic metabolic diseases including NAFLD.

The main well-known risk factors for SIBO are hypochlorhydria, disorders of intestinal structure or motor function, pancreatic insufficiency, and chronic liver disease.

Bile acids have antimicrobial activity, which may have a preventive effect on SIBO and gut dysbiosis, controlling bacterial growth.

In liver dysfunction, bile production and flow may be reduced. This can lead to an environment in the small intestine that allows bacteria to overgrow, contributing to SIBO.

Impaired liver function can also lead to altered gut motility, which is a risk factor for SIBO. Reduced motility means that food and bacteria remain in the small intestine for longer, providing an environment where bacteria can multiply excessively.

In conditions like cirrhosis or chronic liver disease, there is a higher prevalence of SIBO. This is due to a combination of factors including altered bile production, impaired immune function, and changes in gut motility.

How SIBO impairs liver function

SIBO also increases the translocation of bacteria and the absorption of bacterial antigens into the bloodstream (due to increased leaky gut), allowing more toxins and bacteria to enter the bloodstream, further burdening the liver. This may promote the development of hepatic inflammation, steatosis and fibrosis.

Untreated SIBO may lead to nutrient and/or energy malnutrition, thus directly impairing liver function (e.g., folic acid and choline deficiency). Thus, SIBO may contribute to liver dysfunction.

The intestinal microorganisms, when in balance,  produce short-chain fatty acids (SCFA), namely acetate, butyrate and propionate. SCFA influences the hepatic metabolism by directly altering the liver metabolism and by influencing epigenetic mechanisms.

Conclusion

There is a bidirectional relationship between SIBO and liver function. Poor liver function can predispose individuals to SIBO, and SIBO can, in turn, exacerbate liver dysfunction. Addressing both liver health and gut health is crucial in managing and preventing these conditions.

Under physiological conditions, the maintenance of homeostasis in the small intestine is possible due to the correct production of gastric acid, proper bowel movement and the production of an appropriate amount of bile by the liver.

References

Figure: Gudan A, Kozłowska-Petriczko K, Wunsch E, Bodnarczuk T, Stachowska E. Small Intestinal Bacterial Overgrowth and Non-Alcoholic Fatty Liver Disease: What Do We Know in 2023?. Nutrients. 2023;15(6):1323. Published 2023 Mar 8. doi:10.3390/nu15061323

Gudan A, Kozłowska-Petriczko K, Wunsch E, Bodnarczuk T, Stachowska E. Small Intestinal Bacterial Overgrowth and Non-Alcoholic Fatty Liver Disease: What Do We Know in 2023?. Nutrients. 2023;15(6):1323. Published 2023 Mar 8. doi:10.3390/nu15061323

Quigley EMM. The Spectrum of Small Intestinal Bacterial Overgrowth (SIBO). Curr Gastroenterol Rep. 2019;21(1):3. Published 2019 Jan 15. doi:10.1007/s11894-019-0671-z

Ghosh G, Jesudian AB. Small Intestinal Bacterial Overgrowth in Patients With Cirrhosis. J Clin Exp Hepatol. 2019;9(2):257-267. doi:10.1016/j.jceh.2018.08.006

Gudan A, Jamioł-Milc D, Hawryłkowicz V, Skonieczna-Żydecka K, Stachowska E. The Prevalence of Small Intestinal Bacterial Overgrowth in Patients with Non-Alcoholic Liver Diseases: NAFLD, NASH, Fibrosis, Cirrhosis-A Systematic Review, Meta-Analysis and Meta-Regression. Nutrients. 2022;14(24):5261. Published 2022 Dec 9. doi:10.3390/nu14245261