Which condition is characterized by excessive gastric acid production?

Zollinger-Ellison Syndrome is characterized by excessive gastric acid production due to gastrin-secreting tumors, known as gastrinomas. These tumors, often found in the pancreas or duodenum, lead to an overproduction of gastrin, a hormone that stimulates the stomach to produce more gastric acid. This increased acid can cause recurrent peptic ulcers, diarrhea, and weight loss, as the acid can also affect the gastrointestinal tract's ability to absorb nutrients properly.

In contrast, the other conditions listed do not primarily involve excessive gastric acid production. Refeeding Syndrome pertains to metabolic complications that arise when feeding is restarted in malnourished patients, Ulcerative Colitis is an inflammatory bowel disease characterized by inflammation and ulcers in the colon, and Fat overload syndrome refers to a condition of lipid accumulation often associated with nutritional imbalances and not related to gastric acid secretion. Thus, the characteristic feature of Zollinger-Ellison Syndrome is its direct link to excess gastric acid production.