During an assessment, a patient is convinced that his gastrointestinal discomfort is due to food poisoning by nursing staff. Which nursing diagnosis is appropriate?

The appropriate nursing diagnosis for a patient who believes that his gastrointestinal discomfort is the result of food poisoning caused by the nursing staff is related to disturbed thought processes. This diagnosis aligns with the patient’s false belief or perception, indicating that his thoughts about the cause of his illness are not grounded in reality.

Disturbed thought processes can encompass a range of cognitive challenges, including irrational beliefs or misconceptions. In this case, the patient's conviction that the nursing staff caused his food poisoning reflects a significant deviation from reality.

The other options do not adequately address the core issue present in this situation. While delusional could be considered, it tends to imply a more severe and persistent disorder than what might be assessed in the context of acute distress or misunderstanding. Impaired mentation refers more to a general cognitive impairment rather than a specific delusion. Altered nutrition, although important, does not pertain specifically to the patient's perception of the cause of his gastrointestinal symptoms. Thus, disturbed thought processes is the most appropriate diagnosis as it captures the nature of the patient's belief regarding his condition.