Pancreatic Insufficiency: This condition, where the pancreas does not produce enough digestive enzymes, can lead to malabsorption of fats, resulting in oily stools (steatorrhea) and various gastric issues due to inadequate digestion.

Celiac Disease: An autoimmune disorder that causes the immune system to react to gluten, leading to inflammation and damage in the small intestine. This can impair nutrient absorption, including fats, and cause gastric symptoms.
Gallbladder Disease: Issues like gallstones or a dysfunctional gallbladder can affect the release of bile into the intestine, which is necessary for fat absorption, leading to oily stools and gastric discomfort.
Small Intestine Bacterial Overgrowth (SIBO): An excessive growth of bacteria in the small intestine can lead to malabsorption, including fat malabsorption, and cause a variety of gastric symptoms.

Cystic Fibrosis: A genetic disorder that can cause severe damage to the lungs, digestive system, and other organs. It affects the pancreas, leading to pancreatic insufficiency and can cause oily stools and significant gastric issues. Although less common, missing this diagnosis can have severe consequences.
Whipple's Disease: A rare, systemic bacterial infection that can cause malabsorption, including fat malabsorption, and various gastric symptoms. It's crucial to consider due to its potential severity and the need for specific antibiotic treatment.

Short Bowel Syndrome: A condition that results from a significant loss of intestinal tissue, which can severely impair the absorption of nutrients, including fats, leading to oily stools and gastric issues.
Abetalipoproteinemia: A rare inherited disorder that affects the absorption of fat and fat-soluble vitamins, leading to severe gastrointestinal symptoms, including oily stools.
Chronic Pancreatitis: Inflammation of the pancreas that can lead to its damage over time, impairing its ability to produce digestive enzymes and causing symptoms similar to pancreatic insufficiency.