Answer: D. patient's diet
Explanation: Gigantism is a condition characterized by excessive growth and height due to an overproduction of growth hormone during childhood. To diagnose gigantism, a doctor would typically rely on several sources of information however a patient's diet is not one of them.
While a healthy diet is important for overall growth and development, it would be the least helpful source in diagnosing gigantism. Gigantism is primarily caused by a hormonal imbalance, specifically an overproduction of growth hormone, rather than dietary factors.