Gastroenteritis: This is often the most common cause of nausea, vomiting, and an inability to tolerate solid food, typically resulting from a viral or bacterial infection.

Food Poisoning: Similar to gastroenteritis, food poisoning can cause severe nausea, vomiting, and an inability to eat due to consuming contaminated food.
Viral Gastrointestinal Infections: Infections like norovirus can lead to these symptoms.
Peptic Ulcer Disease: Ulcers in the stomach or duodenum can cause nausea, vomiting, and difficulty eating, especially if the ulcers are bleeding or perforated.
Gastroparesis: A condition where the stomach takes too long to empty its contents, often causing nausea, vomiting, and an inability to tolerate food.

Appendicitis: Although it primarily presents with abdominal pain, nausea, and vomiting can be significant components, and missing this diagnosis can lead to severe consequences.
Intestinal Obstruction: A blockage in the intestine can cause severe vomiting and an inability to pass gas or stool, which is a medical emergency.
Pancreatitis: Inflammation of the pancreas can cause severe abdominal pain, nausea, vomiting, and an inability to eat.
Cholecystitis: Inflammation of the gallbladder can cause right upper quadrant pain, nausea, vomiting, and difficulty eating, especially fatty foods.

Cyclic Vomiting Syndrome: A rare condition characterized by recurrent episodes of severe vomiting with no apparent cause.
Rumination Syndrome: A condition where food is regurgitated and then chewed and swallowed again, which can lead to nausea and vomiting.
Eosinophilic Gastroenteritis: A rare condition where eosinophils infiltrate the gastrointestinal tract, causing inflammation and symptoms like nausea, vomiting, and difficulty eating.
Neurological Causes: Such as increased intracranial pressure or brain tumors, which can cause nausea and vomiting, though these are less common causes of the inability to tolerate solid food.