**Core Concept**
The formation of gallstones is a complex process involving multiple factors, including bile composition, gallbladder motility, and lipid metabolism. **Bile supersaturation** with cholesterol or bilirubin is a key factor in the development of gallstones.

**Why the Correct Answer is Right**
Cholesterol gallstones form when there is an imbalance between cholesterol secretion and bile salt secretion, leading to **bile supersaturation** with cholesterol. Bilirubin gallstones, on the other hand, are formed when there is an excess of bilirubin in the bile, often due to hemolysis or liver disease. Gallbladder stasis, which can be caused by various factors including obesity, pregnancy, and certain medications, also contributes to gallstone formation.

**Why Each Wrong Option is Incorrect**
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**Clinical Pearl / High-Yield Fact**
The **Nash formula** is a useful tool for estimating the risk of gallstone formation in patients undergoing rapid weight loss. However, a more accurate predictor is the **percentage of body weight lost** in a short period of time.

**Correct Answer:**
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