Merged from 2 sources β review for redundancy.
Cholesterol-derived detergent molecules synthesized in hepatocytes and secreted into the intestine to emulsify dietary fats, functioning simultaneously as endocrine signaling molecules through nuclear receptor FXR and membrane receptor TGR5 that regulate glucose homeostasis, lipid metabolism, inflammation, energy expenditure, and gut-brain axis communication. Primary bile acids (cholic acid, chenodeoxycholic acid) are biotransformed by gut bacterial enzymes into secondary bile acids (deoxycholic acid, lithocholic acid), creating a microbiome-dependent signaling system that links dietary fat intake to metabolic and immune regulation.
Imagine bile acids as recycling trucks that do three jobs at once. First, they're delivery trucks carrying soap (detergent function) to break down fatty meals into absorbable dropletsβwithout them, fat just sits in your gut like oil on water. Second, they're messengers carrying metabolic instructions: when they dock at the TGR5 receptor on gut L-cells, it's like hitting the "increase energy burn" button, triggering GLP-1 release and ramping up your metabolic furnace. When they bind nuclear FXR receptors in the Liver, they tell the factory to stop making more trucks (negative feedback on bile acid synthesis) and start storing glucose differently. Third, they're ecosystem engineers: 95% of these trucks get reabsorbed in the terminal ileum and recycled back to the Liver (the "enterohepatic circle"), but that remaining 5% passes through the gut where bacterial mechanics modify themβsnipping off conjugation tags (taurine, glycine) and removing hydroxyl groupsβcreating entirely new molecular messengers (secondary bile acids) that have different metabolic effects. If your gut microbiome is disrupted (dysbiosis), the mechanics change the truck fleet composition, altering which metabolic buttons get pressed downstream.
ΒΆ Synthesis and Conjugation
Liver hepatocytes synthesize primary bile acids via the classic (neutral) pathway:
- Cholesterol β CYP7A1 (rate-limiting enzyme) β 7Ξ±-hydroxycholesterol β multiple enzymatic steps β cholic acid (CA) and chenodeoxycholic acid (CDCA)
- Alternative (acidic) pathway: CYP27A1 β 27-hydroxycholesterol β CDCA preferentially
- Conjugation: Bile acid-CoA synthetase (BACS) + bile acid-CoA:amino acid N-acyltransferase (BAAT) β conjugation with taurine or glycine β taurocholic acid, glycocholic acid, etc.
- Conjugated bile acids stored in gallbladder, released postprandially via CCK stimulation
In the intestinal lumen, bacterial bile salt hydrolases (BSH) and 7Ξ±-dehydroxylases modify bile acids:
- Deconjugation: BSH enzymes (expressed by Lactobacillus, Bifidobacterium, Bacteroides) β remove taurine/glycine
- 7Ξ±-dehydroxylation: CA β deoxycholic acid (DCA); CDCA β lithocholic acid (LCA)
- Secondary bile acids have different receptor affinities and toxicity profiles (LCA is hepatotoxic, requiring sulfation for excretion)
FXR (Farnesoid X Receptor) β Nuclear Receptor:
- Bile acids bind FXR β heterodimerization with RXR β transcription of:
- SHP (small heterodimer partner) β inhibits CYP7A1 (negative feedback on bile acid synthesis)
- BSEP (bile salt export pump) β enhances bile acid secretion
- FGF19 (intestinal FXR) β endocrine signal to Liver to suppress CYP7A1
- Metabolic targets: improved Insulin sensitivity, enhanced Glucose metabolism, reduced hepatic lipogenesis
TGR5 (Takeda G-Protein Receptor 5) β Membrane Receptor:
- Bile acids (especially LCA, DCA) bind TGR5 β GΞ±s activation β β cAMP β PKA activation β multiple downstream cascades:
- In enteroendocrine L-cells: TGR5 β GLP-1 secretion β improved Insulin secretion, reduced appetite
- In brown adipose tissue: TGR5 β activation of type 2 iodothyronine deiodinase (DIO2) β T3 production β β thermoregulation, β energy expenditure via UCP1
- In leukocytes (macrophages): TGR5 β suppression of NF-kB β reduced TNF-Ξ±, IL-1Ξ², IL-6 (anti-inflammatory effect)
- In enteric neurons: TGR5 β modulation of gut motility and potentially gut-brain axis signaling
- ~95% reabsorption: Terminal ileum enterocytes express apical sodium-dependent bile acid transporter (ASBT/SLC10A2) β active uptake β basolateral export via OST-Ξ±/OST-Ξ² β portal circulation β hepatocyte uptake via NTCP (sodium-taurocholate cotransporting polypeptide)
- ~5% fecal excretion: Primary pathway for cholesterol removal from body
- Cycle frequency: 4-12 times daily; total bile acid pool ~3-5g recycles continuously
graph TB
A[Cholesterol in Liver] -->|CYP7A1| B["Primary Bile Acids<br/>CA, CDCA"]
B -->|BACS/BAAT| C["Conjugated Bile Acids<br/>Taurine/Glycine"]
C -->|"CCK release<br/>Gallbladder"| D[Small Intestine]
D -->|Bacterial BSH| E[Deconjugated BAs]
E -->|"7Ξ±-dehydroxylase"| F["Secondary Bile Acids<br/>DCA, LCA"]
D -->|95% ASBT| G[Terminal Ileum Absorption]
G -->|Portal Vein| H[Liver Uptake via NTCP]
H --> A
F -->|5% Fecal Loss| I[Cholesterol Excretion]
D -->|TGR5 activation| J["GLP-1 Secretion<br/>Energy Expenditure<br/>Anti-inflammation"]
D -->|FXR activation| K["Glucose Metabolism<br/>Insulin Sensitivity<br/>Lipid Regulation"]
L[Microbiome Dysbiosis] -.->|"Altered BSH<br/>dehydroxylase"| M[Abnormal BA Pool]
M -.-> N[Metabolic Dysfunction]
Bile acids represent a critical nexus between dietary fat intake, microbiome composition, and metabolic-immune regulationβembodying both the selfish metabolic system (prioritizing energy extraction and storage) and the selfish immune system (modulating inflammatory responses based on nutrient availability). Their dual role as digestive detergents and endocrine signals exemplifies evolutionary pleiotropy: a single molecular class optimizes both immediate nutrient absorption and long-term metabolic adaptation.
Relevant Clinical Populations:
- Metabolic syndrome, Type 2 Diabetes, obesity**: Altered bile acid composition correlates with Insulin resistance; reduced TGR5 activation decreases GLP-1 secretion and energy expenditure
- Inflammatory bowel disease (IBD): Dysbiotic microbiome reduces secondary bile acid production; lack of TGR5-mediated anti-inflammatory signaling may perpetuate gut inflammation
- Fatty Liver Disease (NAFLD/NASH): Impaired FXR signaling contributes to hepatic lipid accumulation; FXR agonists are therapeutic targets
- SIBO: Bacterial overgrowth in small intestine prematurely deconjugates bile acids, impairing fat digestion and triggering diarrhea via TGR5-mediated fluid secretion
- Post-cholecystectomy patients: Continuous bile drip (no gallbladder storage) alters bile acid kinetics and may contribute to chronic diarrhea
- Bariatric surgery patients: Altered bile acid metabolism post-Roux-en-Y contributes to metabolic improvements independent of weight loss
Evolutionary Mismatch Context:
Modern diets high in saturated fats but low in fiber alter the bile acid pool composition compared to ancestral Hunter-Gatherer Metabolism. Hunter-gatherer microbiomes (high Prevotella, diverse Firmicutes) efficiently convert primary to secondary bile acids, maintaining robust TGR5 signaling. Western dysbiosis (low Akkermansia-muciniphila, Faecalibacterium prausnitzii) impairs this conversion, reducing metabolic flexibility and increasing inflammatory tone.
Intervention Implications:
- Probiotic bacterial strains with BSH activity (Lactobacillus plantarum, Bifidobacterium longum) can modulate bile acid pool
- Dietary fiber (particularly Butyrate-producing substrates) supports bile acid-metabolizing bacteria
- Bile acid sequestrants (cholestyramine) lower circulating bile acids, reducing FXR activation (used therapeutically in cholestatic pruritus but may worsen fat malabsorption)
- FXR agonists (obeticholic acid) and TGR5 agonists (investigational) are pharmaceutical targets for metabolic syndrome
- Deconjugated bile acids as biomarkers: Elevated fecal primary bile acids suggest impaired bacterial deconjugation (SIBO or dysbiosis)
Key Clinical Thresholds:
- Normal fasting serum total bile acids: <10 ΞΌmol/L (elevated in cholestasis, cirrhosis)
- Postprandial peak: 2-4 hours after fatty meal
- GLP-1 response to TGR5 activation: Dose-dependent on bile acid concentration in distal ileum
- Secondary:primary bile acid ratio in stool: Marker of microbiome metabolic capacity (low ratio = dysbiosis)
- Primary bile acids: Cholic acid (CA) and chenodeoxycholic acid (CDCA) synthesized via CYP7A1 in Liver from cholesterol
- Secondary bile acids: Deoxycholic acid (DCA) and lithocholic acid (LCA) formed by bacterial 7Ξ±-dehydroxylation in colon
- ~95% enterohepatic recycling: Bile acids recycle 4-12 times daily via ASBT transporters in terminal ileum
- Total bile acid pool: 3-5 grams in humans; cycles ~20-30 grams/day through intestine
- Conjugation ratio: Glycine:taurine conjugation ~3:1 in humans (species-specific; cats are taurine-obligate)
- TGR5 potency: LCA > DCA > CDCA > CA (secondary bile acids are stronger TGR5 agonists)
- FXR potency: CDCA > DCA > CA > LCA (chenodeoxycholic acid is most potent endogenous FXR agonist)
- GLP-1 secretion: TGR5 activation in L-cells increases GLP-1 2-3 fold postprandially
- Energy expenditure: TGR5-mediated DIO2 activation increases metabolic rate by 10-20% in brown adipose tissue
- Cholesterol clearance: Bile acid excretion (5% daily) is primary route for irreversible cholesterol removal from body
- Bacterial BSH distribution: >90% of gut bacteria encode bile salt hydrolases; enzyme efficiency varies by strain
- Microbiome signature: dysbiosis reduces secondary bile acid percentage from ~70% to <40% of total bile acid pool
- Anti-inflammatory IC50: TGR5 activation suppresses macrophage TNF-Ξ± at bile acid concentrations >10 ΞΌM
- Circadian variation: Bile acid synthesis peaks in evening (21:00-23:00); CYP7A1 expression is clock-controlled
- TGR5 β Membrane receptor activated by bile acids to stimulate GLP-1 secretion, enhance thermoregulation, and suppress macrophage inflammation
- FXR β Nuclear bile acid receptor regulating bile acid synthesis (via SHP/FGF19), glucose metabolism, and lipid homeostasis
- GLP-1 β Incretin hormone released from L-cells upon TGR5 activation by bile acids in distal ileum
- microbiome β Bacterial BSH and 7Ξ±-dehydroxylase enzymes convert primary to secondary bile acids, determining pool composition and receptor signaling
- cholesterol β Precursor for bile acid synthesis; bile acid excretion is primary pathway for irreversible cholesterol elimination
- Liver β Site of bile acid synthesis (CYP7A1), conjugation, and hepatocyte uptake (NTCP transporter)
- CCK β Cholecystokinin released by I-cells in response to dietary fat triggers gallbladder contraction and bile acid secretion
- enterohepatic circulation β Recycling pathway where 95% of bile acids are reabsorbed in ileum and returned to Liver via portal vein
- SIBO β Small intestinal bacterial overgrowth causes premature bile acid deconjugation, impairing fat digestion and causing diarrhea
- dysbiosis β Altered microbiome composition reduces secondary bile acid production, decreasing TGR5 signaling and metabolic flexibility
- metabolic syndrome β Bile acid dysregulation contributes to Insulin resistance, dyslipidemia, and reduced energy expenditure
- Type 2 Diabetes β Impaired FXR and TGR5 signaling reduces GLP-1 secretion and hepatic glucose control
- inflammatory bowel disease β Reduced secondary bile acids and loss of TGR5-mediated anti-inflammatory signaling in IBD
- Fatty Liver Disease β FXR agonism reduces hepatic steatosis; bile acid-FXR axis dysregulation drives NAFLD/NASH
- Short-chain fatty acids β SCFA producers (butyrate-forming bacteria) often co-exist with bile acid-transforming bacteria in healthy microbiome
- Butyrate β SCFA that synergizes with secondary bile acids in maintaining gut barrier and immune homeostasis
- inflammation β Bile acids modulate inflammatory signaling via TGR5 (anti-inflammatory) and potentially via altered NF-kB signaling
- thermoregulation β TGR5 activation in brown adipose tissue increases DIO2 activity, converting T4βT3 and activating UCP1
- migrating motor complex β Bile acid secretion modulates MMC phase III contractions, preventing bacterial overgrowth in small intestine
- gut-brain axis β TGR5 expressed in enteric neurons and potentially in brainstem; bile acid signaling may influence satiety and mood
- Akkermansia-muciniphila β Mucin-degrading bacterium that correlates with healthy bile acid metabolism and metabolic health
- Faecalibacterium prausnitzii β Anti-inflammatory commensal that produces Butyrate and correlates with balanced bile acid pool
- Insulin β FXR activation improves hepatic Insulin sensitivity; TGR5-mediated GLP-1 release enhances pancreatic Insulin secretion
- NF-kB β TGR5 signaling suppresses NF-kB translocation in macrophages, reducing pro-inflammatory cytokine production
- TNF-Ξ± β Pro-inflammatory cytokine downregulated by TGR5 activation in leukocytes
- IL-6 β Bile acid-TGR5 axis modulates IL-6 secretion in immune cells and adipocytes
Bile acids are cholesterol-derived amphipathic steroid molecules synthesized in hepatocytes that function both as digestive emulsifiers for dietary fat absorption and as endocrine signaling molecules regulating metabolism, immunity, and microbiome composition. They undergo continuous enterohepatic circulation (95% reabsorbed, 6-8 cycles daily) and microbial biotransformation in the gut, creating a dynamic pool of primary and secondary bile acids that act as molecular switches controlling systemic energy balance, inflammatory tone, and gut barrier integrity.
Imagine bile acids as dual-function cleaning agents in a restaurant kitchen that also double as communication memos between departments. The head chef (liver) synthesizes these cleaners from old equipment (cholesterol) and stores them in a dispenser (gallbladder). When fatty food arrives (postprandial state), the cleaners spray into the dishwashing area (duodenum) to break up grease on plates (emulsify dietary fats). But here's the twist: 95% of these cleaners flow down a conveyor belt (ileum) and get vacuumed back up to the storage room (portal circulation) β they're reused 6-8 times per shift.
Along the way, the kitchen staff (gut bacteria) modify some cleaners by stripping off labels (deconjugation) or changing their chemical structure (dehydroxylation), creating new variants (secondary bile acids). These modified versions aren't just cleaners anymore β they're also walkie-talkie signals. Some activate the "energy efficiency mode" button (TGR5) telling the body to burn more fuel and release satiety hormones. Others flip the "stop making fat" switch (FXR) in the liver. The aggressive cleaners (deoxycholic acid, lithocholic acid) can damage the kitchen floor (gut barrier) if present in excess, while the milder ones help maintain order. When the recycling system breaks down β whether from bacterial overgrowth, slow gut transit, or liver dysfunction β you get either toxic buildup or insufficient cleaning power, and the whole restaurant (metabolic and immune systems) suffers.
Synthesis pathway:
Cholesterol (hepatocytes) β CYP7A1 (rate-limiting enzyme) β 7Ξ±-hydroxycholesterol β multi-step cascade β Primary bile acids (cholic acid 50%, chenodeoxycholic acid 30-40%) β conjugation with glycine (75%) or taurine (25%) via BAAT enzyme β glyco/tauro-conjugated bile acids β stored in gallbladder β released postprandially via CCK stimulation
Enterohepatic circulation:
Gallbladder β duodenum β fat emulsification (micelle formation with phospholipids) β ileum β ASBT (apical sodium-dependent bile acid transporter) reabsorbs 95% β portal vein β hepatocytes β re-secreted β 6-8 cycles/day. Total pool: 2-4 grams, with 0.2-0.6 g lost daily in feces.
Microbial transformation:
Primary bile acids β gut bacteria (Clostridium, Bacteroides, Lactobacillus) produce BSH (bile salt hydrolase) β deconjugation β bacterial 7Ξ±-dehydroxylase β Secondary bile acids (deoxycholic acid from cholic acid; lithocholic acid from chenodeoxycholic acid). Ratio of primary:secondary reflects microbiome health and transit time.
Receptor activation and signaling:
graph TD
A[Bile Acids] --> B[FXR Nuclear Receptor]
A --> C[TGR5 Membrane Receptor]
A --> D[VDR, PXR Receptors]
A --> E[S1PR2]
B --> F["Hepatocytes: SHP activation"]
F --> G[Inhibits CYP7A1]
G --> H[Reduced bile acid synthesis]
B --> I[Suppresses SREBP-1c]
I --> J[Decreased lipogenesis]
B --> K[Induces FGF19 in ileum]
K --> L[Systemic metabolic effects]
C --> M["L-cells: GLP-1 secretion"]
C --> N["Macrophages: Anti-inflammatory"]
C --> O["Brown adipose: Thermogenesis"]
M --> P[Enhanced insulin secretion]
M --> Q[Satiety signaling]
D --> R[Gut barrier protection]
D --> S[Immune modulation]
E --> T[Gut motility regulation]
FXR (Farnesoid X Receptor) pathway:
Bile acids (especially chenodeoxycholic acid) β FXR activation β induces SHP (small heterodimer partner) β SHP inhibits LRH-1 and LXRΞ± β suppresses CYP7A1 transcription β negative feedback on bile acid synthesis. In ileum: FXR β FGF19 secretion β portal circulation β hepatic FGFR4 β ERK signaling β metabolic reprogramming.
TGR5 (Takeda G-protein-coupled receptor 5) pathway:
Bile acids (especially lithocholic acid, deoxycholic acid) β TGR5 activation β cAMP production via GΞ±s β PKA activation β in enteroendocrine L-cells: GLP-1 secretion; in macrophages: inhibits NF-ΞΊB β reduced cytokine production; in brown adipose tissue: increased UCP1 β thermogenesis.
Hydrophobicity gradient and toxicity:
Lithocholic acid (most hydrophobic) > deoxycholic acid > chenodeoxycholic acid > cholic acid (most hydrophilic). Hydrophobic bile acids β membrane damage β mitochondrial dysfunction β oxidative stress β gut barrier disruption β bacterial translocation. Sulfonation and glucuronidation in liver detoxify hydrophobic bile acids.
Antimicrobial effects:
Bile acids disrupt bacterial membranes (especially Gram-positive bacteria) β selective pressure shapes microbiome composition. Deconjugated bile acids more antimicrobial than conjugated forms β bacterial BSH activity creates self-regulating feedback loop.
Primary conditions involving bile acid dysregulation:
- NAFLD/NASH: Reduced FXR signaling β decreased FGF19 β loss of hepatic lipogenic suppression β triglyceride accumulation. Serum bile acid levels correlate with disease severity. FXR agonists (obeticholic acid) show therapeutic promise.
- Type 2 Diabetes: Altered bile acid profiles (reduced primary:secondary ratio) β impaired GLP-1 secretion β reduced postprandial insulin response. Bile acid sequestrants (colesevelam) improve HbA1c by 0.5-1.0%.
- IBD (Crohn's, Ulcerative Colitis): Ileal inflammation β reduced ASBT function β bile acid malabsorption β colonic bile acid excess β diarrhea and mucosal inflammation. Secondary bile acids activate inflammatory pathways via TLR4 and NF-ΞΊB.
- Colorectal cancer: Chronic exposure to deoxycholic acid β DNA damage β increased COX-2 β prostaglandin-mediated proliferation. High-fat diet β increased secondary bile acid production β cancer risk.
- SIBO: Bacterial overgrowth in small intestine β premature deconjugation β fat malabsorption β deficiency of fat-soluble vitamins (A, D, E, K).
cPNI metamodel connections:
- Metamodel 5 (Gut-Liver-Metabolic Axis): Bile acids are the central communication molecule linking gut microbiome composition, hepatic metabolism, and systemic energy balance. Disrupted enterohepatic circulation β metabolic syndrome phenotype.
- Selfish Brain Theory: Bile acids regulate glucose availability via GLP-1 and insulin sensitivity β when bile acid signaling fails, the brain compensates by increasing systemic insulin resistance to preserve cerebral glucose supply.
- Evolutionary Mismatch: Hunter-gatherer diets (high fiber, intermittent feeding) β frequent bile acid excretion and microbial diversity. Modern diet (low fiber, constant feeding) β bile acid stasis β dysbiosis β metabolic disease.
Intervention strategies:
- Increase fecal bile acid loss: Soluble fiber (psyllium, pectin) binds bile acids β forces de novo synthesis from cholesterol β lowers LDL. Target: 25-35g fiber daily.
- Modulate microbiome: Probiotics (Lactobacillus, Bifidobacterium) alter BSH activity β shift bile acid pool composition. Akkermansia muciniphila inversely correlates with metabolic disease burden.
- Optimize gut motility: Intermittent fasting β enhanced MMC β prevents bile acid stasis. Bile acids themselves activate MMC when deconjugated.
- Support FXR/TGR5 signaling: Polyphenols (berberine, curcumin) act as FXR agonists. Cold exposure β TGR5-mediated thermogenesis.
Clinical thresholds:
- Fasting serum bile acids: <10 ΞΌmol/L (normal), >10 ΞΌmol/L suggests cholestasis or bile acid malabsorption
- Postprandial rise: should be 2-3x fasting values
- Elevated lithocholic acid (>5% of total pool) β microbiome dysbiosis marker
- FGF19 <50 pg/mL β impaired ileal FXR signaling
- Total bile acid pool: 2-4 grams, recirculated 6-8 times daily via enterohepatic circulation
- Reabsorption efficiency: 95% in terminal ileum via ASBT; 0.2-0.6 g lost daily in feces
- Primary bile acids: Cholic acid (50%), chenodeoxycholic acid (30-40%), synthesized from cholesterol via CYP7A1
- Secondary bile acids: Deoxycholic acid, lithocholic acid β produced exclusively by bacterial 7Ξ±-dehydroxylase (no human enzyme equivalent)
- Conjugation ratio: 75% glycine-conjugated, 25% taurine-conjugated in humans (varies by diet and microbiome)
- Hydrophobicity index: LCA > DCA > CDCA > CA (determines toxicity and receptor affinity)
- Postprandial release: Triggered by CCK within 15-30 minutes of fat ingestion; gallbladder contracts 40-70%
- FXR affinity: CDCA > DCA > LCA > CA (chenodeoxycholic acid is most potent endogenous FXR agonist)
- TGR5 affinity: LCA > DCA > CDCA > CA (opposite pattern from FXR)
- Antimicrobial MIC: Deoxycholic acid inhibits bacterial growth at 0.5-2 mM (physiological concentrations 1-10 mM in colon)
- Critical Period: Bile acid pool development in infancy depends on breastfeeding (provides taurine for conjugation) and microbiome colonization
- Cholesterol β primary substrate for bile acid synthesis via CYP7A1 enzyme (7Ξ±-hydroxylation is rate-limiting step)
- Liver β exclusive site of primary bile acid synthesis; hepatocytes express CYP7A1 and conjugating enzymes
- TGR5 β G-protein-coupled receptor activated by bile acids triggering GLP-1 release, thermogenesis, and anti-inflammatory effects
- FXR β nuclear receptor (NR1H4) regulating bile acid synthesis (negative feedback), lipogenesis suppression, and glucose metabolism
- Microbiome β bacterial BSH and 7Ξ±-dehydroxylase convert primary to secondary bile acids; dysbiosis alters bile acid pool composition
- GLP-1 β incretin hormone released from L-cells upon TGR5 activation by bile acids; enhances insulin secretion and satiety
- CCK β triggers postprandial gallbladder contraction releasing bile acids into duodenum for fat digestion
- Insulin sensitivity β FXR activation in liver and adipose tissue improves insulin signaling via suppression of gluconeogenic genes
- NAFLD β reduced FXR/FGF19 signaling and altered bile acid pool (decreased primary:secondary ratio) contribute to hepatic steatosis
- Type 2 diabetes β bile acid sequestrants improve glycemic control by enhancing GLP-1 secretion and modulating incretin axis
- Inflammatory bowel disease β ileal damage reduces ASBT function causing bile acid malabsorption; colonic bile acid excess drives inflammation via TLR4
- Gut barrier β hydrophobic bile acids (DCA, LCA) disrupt tight junctions and increase permeability; FXR activation protects barrier via FGF15/19
- Colon cancer β chronic deoxycholic acid exposure promotes DNA damage, COX-2 induction, and proliferative signaling
- Gut motility β deconjugated bile acids stimulate colonic secretion and motility; activate migrating motor complex (MMC) in fasting state
- Fat absorption β bile acids form mixed micelles with phospholipids enabling lipase digestion and absorption of dietary fats and fat-soluble vitamins
- Inflammation β TGR5 activation suppresses NF-ΞΊB in macrophages (anti-inflammatory); hydrophobic bile acids activate inflammasome (pro-inflammatory)
- Metabolic syndrome β bile acid dysregulation (reduced signaling through FXR/TGR5) central to insulin resistance, dyslipidemia, and visceral adiposity
- Fiber β soluble fiber binds bile acids increasing fecal excretion; forces de novo synthesis reducing serum cholesterol
- SCFA β butyrate-producing bacteria interact with bile acid metabolism; SCFAs enhance gut barrier protecting against bile acid toxicity
- PPARΞ± β bile acids activate PPARΞ± in hepatocytes promoting fatty acid oxidation and ketogenesis
- GPR35 β kynurenic acid receptor also activated by certain bile acids; modulates intestinal inflammation
- Vitamin D β VDR (vitamin D receptor) binds lithocholic acid; bile acids modulate VDR-dependent antimicrobial peptide expression
- Autophagy β bile acids induce hepatic autophagy via FXR-TFEB axis; clears lipid droplets and damaged organelles
- FGF21 β bile acid-FXR signaling induces FGF21 expression coordinating systemic metabolic adaptation to nutrient status
- Akkermansia-muciniphila β inversely correlates with metabolic disease; modulates bile acid pool toward less toxic profile
- SIBO β bacterial overgrowth causes premature bile acid deconjugation in small intestine leading to fat malabsorption and diarrhea
- Module 5 (primary module)
- Module 6 (gut barrier and antimicrobial function)