If there is a persistent weight loss, there may be a major problem in some area of the body. If the patient excludes the weight loss caused by poor eating, it is important to conduct relevant tests to investigate. The most common diseases that cause weight loss are these major categories, first, the most common is the digestive system diseases, such as inflammation of the gastrointestinal tract, ulcers, tumors and liver and gallbladder diseases can cause weight loss. Second, endocrine diseases, such as diabetes, hyperthyroidism, can also cause a dramatic drop in weight. Third, tuberculosis, which is a common disease of the respiratory system, can also cause weight loss. The etiology of continuous weight loss is complex and requires corresponding systematic examination to clarify the cause of weight loss.