Gut Microbiome and Gallstones: Emerging Research

The gut microbiome – a brief overview

The human gut microbiome consists of trillions of bacteria, archaea, fungi, and viruses residing primarily in the colon. It plays a crucial role in digestion, immune modulation, and metabolism. Key functions relevant to gallstones include:

• Fermentation of dietary fibre to short‑chain fatty acids (SCFAs).
• Deconjugation and dehydroxylation of bile acids (bile salt hydrolase activity).
• Regulation of cholesterol metabolism and enterohepatic circulation.

Bile acid metabolism and the microbiome

Bile acids are synthesised from cholesterol in the liver (primary bile acids: cholic acid and chenodeoxycholic acid). They are conjugated to glycine or taurine, stored in the gallbladder, and released into the duodenum after a meal.

Microbial modification of bile acids:

• Deconjugation: Bacterial bile salt hydrolase (BSH) removes glycine/taurine, producing free bile acids.
• Dehydroxylation: 7α‑dehydroxylation converts primary bile acids to secondary bile acids (deoxycholic acid, lithocholic acid).
• Effects: Secondary bile acids are less soluble and can promote cholesterol crystallisation in bile. High levels of deoxycholic acid are associated with cholesterol gallstones.

Dysbiosis (imbalanced gut microbiota) alters the bile acid pool, increasing cholesterol saturation in bile – a key step in gallstone formation.

Dysbiosis and gallstone formation – what the evidence shows

Multiple human studies have compared the gut microbiome of gallstone patients vs. healthy controls:

• Increased Firmicutes/Bacteroidetes ratio – similar to obesity‑associated dysbiosis.
• Reduced microbial diversity – lower abundance of beneficial genera like Lactobacillus, Bifidobacterium, and Faecalibacterium.
• Overgrowth of pro‑inflammatory bacteria – Escherichia coli, Klebsiella, Clostridium species.
• Increased bile salt hydrolase (BSH) activity – leading to higher deconjugated bile acids and secondary bile acid production.

Animal studies (mice, hamsters) confirm that transferring the gut microbiota from gallstone‑prone animals to germ‑free recipients induces gallstone formation, supporting a causal role.

Key bacterial species involved in gallstone disease

Research has identified specific microbial signatures:

• Clostridium clusters XIVa and XI: High 7α‑dehydroxylation activity, produce deoxycholic acid – promotes cholesterol crystallisation.
• Escherichia coli and Klebsiella pneumoniae: Enriched in gallstone patients; associated with pigment stones and biliary infections.
• Lactobacillus and Bifidobacterium: Reduced abundance. These genera have BSH activity but produce less deoxycholic acid; their depletion may indirectly favour pathogenic species.
• Bacteroides: Variable findings – some studies show increased, others decreased.
• Faecalibacterium prausnitzii: Anti‑inflammatory butyrate producer – consistently reduced in gallstone patients.

Table: Summary of microbiome changes in gallstone disease

Can probiotics prevent or treat gallstones?

Given the association between dysbiosis and gallstones, probiotics have been explored as a preventive strategy. Current evidence:

• Animal studies: Probiotic supplementation (Lactobacillus, Bifidobacterium, Propionibacterium) reduces cholesterol gallstone formation in mice and hamsters by lowering cholesterol saturation and modulating bile acids.
• Human studies: Limited. A few small trials suggest that probiotics may improve bile acid profiles and reduce lithogenic risk factors, but no large RCT has shown prevention of gallstones.
• Post‑cholecystectomy: Probiotics may help with post‑cholecystectomy diarrhoea (small evidence base).
• Safety: Generally safe for immunocompetent individuals, but not a substitute for proven treatments.

Clinical bottom line: Probiotics are not currently recommended for gallstone prevention or treatment outside of research settings. However, maintaining a healthy, fibre‑rich diet that supports a diverse microbiome is advisable.

Gut microbiome changes after cholecystectomy

Removal of the gallbladder alters bile flow from continuous (instead of pulsatile) release into the duodenum. This affects the gut microbiome:

• Increased secondary bile acids: Without gallbladder storage, bile acids enter the colon more frequently, increasing deoxycholic acid levels.
• Microbial shifts: Some studies show increased Bacteroides and decreased Lactobacillus post‑cholecystectomy.
• Clinical correlates: May explain post‑cholecystectomy syndrome (diarrhoea, bloating) and increased risk of colorectal cancer (still debated, but a concern).
• Potential interventions: Bile acid sequestrants (cholestyramine) for diarrhoea; dietary fibre to bind bile acids.

Therapeutic potential: prebiotics, FMT, and personalised medicine

Beyond probiotics, other microbiome‑targeted strategies are under investigation:

• Prebiotics (inulin, fructo‑oligosaccharides): Promote growth of beneficial bacteria (bifidobacteria) and increase SCFA production. Animal studies show reduced gallstone formation.
• Dietary interventions: High‑fibre, Mediterranean diet – known to improve microbiome diversity and reduce lithogenic risk.
• Faecal microbiota transplantation (FMT): Experimental. One small animal study reversed gallstone‑prone phenotype, but human studies are lacking.
• Personalised microbiome profiling: Future algorithms may identify individuals at high risk for gallstones based on gut microbiota and tailor preventive strategies (probiotics, diet, or even UDCA).

These approaches are not yet ready for clinical use. The most evidence‑based “microbiome‑friendly” advice remains: eat a high‑fibre, plant‑rich diet, avoid unnecessary antibiotics, and maintain regular meal patterns.

Interactive FAQ – Gut microbiome and gallstones

Disclaimer: This information is for educational and research purposes. Microbiome science is rapidly evolving. Current clinical management of gallstones remains diet, UDCA, or cholecystectomy. Consult a gastroenterologist at Vivekananda Hospital for evidence‑based care.