Which of the following factors is NOT associated with the formation of gallstones?

The formation of gallstones is influenced by various risk factors, and understanding these helps clarify why the choice of age under 30 is not associated with gallstone formation.

Gallstones commonly form due to alterations in the balance of bile salts and cholesterol, as well as the presence of underlying conditions. Factors such as rapid weight loss can lead to increased cholesterol saturation in bile as the body metabolizes fat quickly, increasing the risk of crystallization. High cholesterol intake can also contribute to an excess of cholesterol in the bile, promoting gallstone formation. Additionally, existing gallbladder disease can compromise the normal functioning of the gallbladder, leading to inadequate bile flow and promoting stone development.

In contrast, age under 30 does not significantly contribute to the risk of gallstone formation. While gallstones can occur in younger individuals, the prevalence increases with age, particularly in populations over 40 years. Younger individuals typically have healthier metabolism and bile composition, which helps to prevent the conditions necessary for gallstone formation. Thus, age under 30 is not a recognized risk factor, making it the correct choice for this question.