Which of the following symptoms suggests a more serious underlying cause of weight loss?

Fatigue is an important symptom that can indicate a more serious underlying condition related to unexplained weight loss. When patients experience fatigue alongside weight loss, it may suggest systemic issues such as malignancies, chronic infections, or endocrine disorders, all of which could lead to both weight loss and a general feeling of tiredness or exhaustion.

In contrast, normal appetite typically suggests that the body is still receiving nutrition, which may indicate that the weight loss could be due to other factors, such as lifestyle changes or stress. Maintaining weight while losing fat or muscle mass may not necessarily indicate a serious issue, as various factors can contribute to body composition changes without a significant loss in overall weight. Increased social activities usually correlate with better overall health and emotional well-being, which makes serious underlying causes less likely in that context.

Overall, fatigue, particularly when seen with unexplained weight loss, warrants further investigation to rule out serious causes and to ensure appropriate management of the underlying issues.