Which of the following conditions might produce ketones in the urine?

The presence of ketones in urine, a condition known as ketonuria, typically occurs when the body resorts to fat metabolism due to a lack of sufficient carbohydrates for energy. Dehydration can lead to a state of ketosis because it often results in a lower availability of glucose. When the body becomes dehydrated, it may not have enough glucose for energy, particularly during periods of stress or illness, and therefore begins to break down fat for fuel, producing ketones as a byproduct.

In contrast, excessive fluid intake does not lead to ketone production; rather, it can dilute the urine and may mask the presence of ketones. A high carbohydrate diet provides ample glucose for energy, thereby minimizing the need for the body to enter a state of ketosis. Similarly, body mass gain does not inherently produce ketones unless associated with changes in metabolic health, such as insulin resistance or diabetes, which would necessitate context beyond mere weight change.