Bile acids are synthesized in the liver and play a vital physiological role. They are not only detergent of dietary lipids and nutrients, but also important hormones or nutrient signaling molecules in metabolic regulation process. Because of their unique amphipathic configuration, conventionally BAs were thought to have only the detergent properties for a long time, which contributes to digestion of dietary lipids, elimination of cholesterol and absorption of fat-soluble vitamins. However, studies have shown that Bile acids can act as as hormones or nutrient signaling molecules. Emerging evidence indicates that Bile acids not only regulate their own synthesis and enterohepatic recirculation, but also the regulation of glucose, lipoprotein and lipid metabolism, thyroid hormone signaling, cellular immunity, energy expenditure and inflammatory responses. The most common, cholic acid and chenodeoxycholic acid, are called primary bile acids. Recent studies have shown that bile acids are involvement in various cancers and diseases such as Parkinson’s and Alzheimer’s and liver diseases.
Bile Acid Associated Diseases and Disorders
🌿 Bile Acids – Physiological Functions
Bile acids are amphipathic molecules derived from cholesterol in the liver. They are stored in the gallbladder and released into the small intestine after meals.
✅ 1. Fat Digestion & Absorption
- Primary function
- Bile acids emulsify dietary fats, breaking large fat globules into micelles.
- This increases the surface area for pancreatic lipase to act.
- Micelles formed help in absorption of:
- Fatty acids
- Monoglycerides
- Cholesterol
- Fat-soluble vitamins (A, D, E, K)
✅ 2. Cholesterol Excretion
- Bile acids are the main route for cholesterol elimination from the body.
- Cholesterol is converted into bile acids and excreted into bile.
- Some bile acids are lost in feces, removing cholesterol.
✅ 3. Regulation of Bile Flow
- Bile acids stimulate bile flow (choleresis).
- This helps maintain the fluidity of bile and prevents gallstone formation.
✅ 4. Antimicrobial Action
Bile acids disrupt bacterial membranes and help control gut microbiota.
- This limits bacterial overgrowth in the small intestine.
✅ 5. Signaling Molecules
- Bile acids act as hormone-like signaling molecules via:
- FXR (Farnesoid X Receptor)
- TGR5 (G-protein-coupled bile acid receptor)
- Regulate:
- Lipid and glucose metabolism
- Insulin sensitivity
- Inflammation
- Bile acid synthesis feedback
🧾 Summary Table
| Function | Details |
| Fat digestion | Emulsify fats, form micelles, aid absorption |
| Cholesterol removal | Convert cholesterol to bile acids for fecal excretion |
| Stimulate bile secretion | Promote bile flow and prevent gallstones |
| Antimicrobial | Protect against intestinal bacterial overgrowth |
| Metabolic regulation | Act as signaling molecules (via FXR, TGR5) to influence metabolism |