Normal Bile Composition & Gallbladder Function
A healthy gallbladder keeps cholesterol dissolved and empties on cue.
- ~0.8: Cholesterol Saturation Index (below 1.0, undersaturated)
- ~30 mL: Fasting GB volume (typical adult)
- 70–80%: Post-meal emptying (CCK-stimulated contraction)
- ~3 g: Bile salt pool (recirculates ~6×/day)
Bile as a mixed micelle solution
Cholesterol is water-insoluble; bile salts and lecithin package it into micelles.
Normal ratio keeps cholesterol solubilized.
Gallbladder motility at baseline
Meals trigger CCK release, contracting the gallbladder to empty stored bile.
Fat Mobilization Under GLP-1 Therapy
Rapid fat loss floods the liver with cholesterol destined for bile.
- 5–15%: Typical GLP-1 weight loss (body weight over months)
- >1.5%/mo: Rapid-loss threshold (linked to higher stone risk)
- ↑↑: Hepatic cholesterol flux (from mobilized fat stores)
- unchanged: Bile salt synthesis (cannot scale up quickly)
Where the cholesterol comes from
Adipose tissue breakdown releases cholesterol that the liver secretes into bile.
Rate matters more than total loss
Faster weight loss concentrates cholesterol output into a shorter window.
Cholesterol Outpaces Bile Salts & Lecithin
Solubilizing capacity is exceeded — excess cholesterol nucleates crystals.
- >1.0: Cholesterol Saturation Index (supersaturated bile)
- shortened: Nucleation time (crystals form faster)
- exceeded: Micelle capacity (bile salts overwhelmed)
- cholesterol monohydrate: Crystal type (stone precursor)
The saturation index (CSI)
CSI above 1.0 means bile can no longer hold cholesterol in solution.
From crystal to aggregate
Microscopic crystals clump together, seeding future gallstones.
GLP-1 Slows Gallbladder Motility
Delayed gastric and gallbladder emptying lets supersaturated bile stagnate.
- ↓ 20–40%: GB emptying fraction (vs baseline on GLP-1)
- ↑: Residence time (bile sits longer in GB)
- blunted: Fat-stimulated contraction (especially low-fat diets)
- crystal growth: Stasis effect (more time to aggregate)
Motility slowdown mechanism
GLP-1 receptor activation delays gastric emptying and dampens GB contraction.
Stasis compounds supersaturation
Stagnant, cholesterol-rich bile gives crystals time to grow undisturbed.
Gallstone Risk & Mitigation Strategies
Combined supersaturation and stasis raise gallstone and cholecystitis risk.
- 2–3×: Gallstone risk on GLP-1 (vs non-users, rapid loss)
- much lower: Risk with slow, steady loss (<1.5%/month)
- adequate fat intake: Protective factor (stimulates GB emptying)
- may need cholecystectomy: Symptomatic stones (if biliary colic occurs)
Why rate of loss drives risk
Slower weight loss reduces peak cholesterol flux into bile.
Practical mitigation
Adequate dietary fat keeps the gallbladder emptying regularly.