Gastroenteritis: This is the most likely diagnosis, as vomiting without food intake for 2 days can be a symptom of a viral or bacterial infection of the stomach and intestines, leading to inflammation and irritation.

Food poisoning: Although the question specifies vomiting without food, it's possible that the patient consumed something contaminated before the onset of symptoms.
Dehydration: Prolonged vomiting can lead to dehydration, which in turn can cause further vomiting, creating a vicious cycle.
Gastritis: Inflammation of the stomach lining can cause vomiting, and it may not be directly related to food intake.
Morning sickness (in pregnant women): If the patient is pregnant, morning sickness could be a cause of vomiting without food intake.

Appendicitis: Although less common, appendicitis can present with vomiting, and it's crucial to rule out this condition due to its potential for severe complications if left untreated.
Intestinal obstruction: This is a life-threatening condition that requires immediate medical attention, and vomiting can be an early symptom.
Pancreatitis: Inflammation of the pancreas can cause severe vomiting, and it's essential to consider this diagnosis due to its potential for serious complications.
Diabetic ketoacidosis: In patients with diabetes, vomiting can be a symptom of diabetic ketoacidosis, a life-threatening condition that requires prompt treatment.

Brain tumor: Although extremely rare, a brain tumor can cause vomiting due to increased intracranial pressure.
Meningitis: Inflammation of the meninges can cause vomiting, among other symptoms like headache and fever.
Addison's disease: This rare endocrine disorder can cause vomiting, among other symptoms like fatigue and weight loss.
Porphyria: A group of rare genetic disorders that can cause vomiting, among other symptoms like abdominal pain and neurological issues.