Bile acids start as cholesterol in the liver, which converts it daily into two primary acids, cholic acid and chenodeoxycholic acid. The liver tags them with amino acids and stores them in the gallbladder until a meal arrives.[1] When fat shows up in a meal, the gallbladder releases these bile salts into the small intestine, where they break fat into smaller droplets small enough for digestive enzymes to act on.
| Type | Role | Evidence |
|---|---|---|
| Primary bile acids | Made directly by the liver; break down dietary fat for absorption | Strong |
| Secondary bile acids | Created by gut bacteria; support anti-inflammatory signaling and block pathogens like C. difficile | Moderate |
| Bile acid malabsorption | More than 5% escaping reabsorption reaches the colon in excess, triggering chronic watery diarrhea | Moderate |
Only a specific set of bacteria, including Lachnospiraceae, Clostridium, and Eggerthella species, carry the enzymes needed to make this conversion. Other bacterial byproducts, like butyrate, follow a similar bacteria-made-it-for-you pattern.[1] When those bacteria are depleted, or when a condition like Crohn's disease, celiac disease, or SIBO pushes more bile acids into the colon than normal, the result is bile acid diarrhea. It's chronic, watery, and often mistaken for IBS.
What to do with this
If you have chronic watery diarrhea that hasn't responded to typical IBS treatment, ask your doctor about testing for bile acid malabsorption specifically, since it's a distinct, treatable condition often confused with IBS-D. No reliable over-the-counter way exists to boost secondary bile acid production directly, but a fiber-rich diet supports the broader bacterial community responsible for making it. Cutting fiber too far can undo that support quickly, as described in What happens to gut bacteria you stop feeding. If you've had your gallbladder removed or have a condition affecting the terminal ileum, mention that to your doctor, since both change how much bile acid reaches the colon.
