This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
All cause weight gain, except : 
Select and explain. 
A. Diabetes mellitus, B. Cushing's syndrome, C. Hypothyroidism, D. Insulin secreting tumour
A: Diabetes mellitus
Answer: A: Diabetes mellitus 
Explanation: Answer is A (Diabetes mellitus) : Endocrine and metabolic causes of weight loss include Hypehyroidism Diabetes mellitus Pheochromocytoma Adrenal insufficiency