What condition is characterized by both fasting and post-prandial hypoglycemia?

Insulinoma is a condition characterized by the presence of a tumor in the pancreas that secretes insulin, leading to episodes of hypoglycemia. This condition can result in both fasting and post-prandial (after eating) hypoglycemia due to the tumor's continuous secretion of insulin. When a person with insulinoma is fasting, the elevated insulin levels can cause their blood glucose to drop dangerously low. After eating, the tumor may still produce excess insulin inappropriately, causing blood sugar levels to drop following the intake of food, resulting in post-prandial hypoglycemia.

In contrast, gastric cancer primarily presents symptoms related to obstruction or local invasion and is not characterized by hypoglycemia associated with fasting and meals. Type 1 diabetes, while it can lead to hypoglycemia, typically does not reflect the pattern of constant post-prandial hypoglycemia post meals unless insulin is mismanaged. Adrenal insufficiency can lead to other metabolic dysfunctions and hypoglycemia, but it does not specifically cause reactive hypoglycemia as seen with insulinoma.

The definitive characteristic of insulinoma is the dysregulated insulin secretion resulting in hypoglycemia in both states, making it the correct answer to the question posed.