**Question:** Incidence of gall stone is high in:

A. Obese individuals
B. Smokers
C. Pregnant women
D. People with diabetes mellitus

**Core Concept:**
Gallstones are formed when there is a disturbance in the biliary system, which consists of the liver, gallbladder, and the bile ducts. The primary components of bile are cholesterol, bilirubin, and bile salts. In the presence of supersaturated bile, due to factors like obesity, pregnancy, or diabetes, these components can precipitate out and form gallstones.

**Why the Correct Answer is Right:**
Option A, obesity, is the most common risk factor for gallstone formation. Obesity increases the production of bile, leading to increased cholesterol levels in the bile. This, combined with the disturbance in bile composition (increased cholesterol saturation) due to the higher energy intake in obese individuals, increases the likelihood of cholesterol stones formation.

Option D, diabetes mellitus, is also associated with an increased risk of gallstone formation. Diabetic patients often have impaired gallbladder motility and altered bile composition, which may lead to stone formation.

**Why Each Wrong Option is Incorrect:**
Option B, smoking, is not directly linked to gallstone formation. However, smoking can worsen the symptoms of gallstones by causing spasm of the sphincter of Oddi, leading to increased bile reflux into the pancreas, which may cause pancreatitis.

Option C, pregnant women, also does not directly increase the risk of gallstones. However, pregnancy-related changes in bile composition (increase in bilirubin and bilirubin saturation) can lead to the formation of pigment stones, which can be associated with pregnancy.

**Clinical Pearl:**
The incidence of gallstones is higher in patients with obesity, diabetes mellitus, and pregnant women, due to altered bile composition, motility, and other factors. Smoking can worsen the symptoms of gallstones by causing pancreatitis.

**Correct Answer:** A. Obesity