Sudden decrease in appetite may be related to mental factors, pregnancy, abnormal liver function, etc. 1. Mental factors: low mood, anxiety, tension, depression, etc. due to excessive work pressure or changes in living environment. It may cause abnormal gastrointestinal peristalsis or sensory function and affect appetite. 2. Pregnancy: If a woman who has sex in the reproductive age has delayed menstruation. There will be early pregnancy reaction with nausea, vomiting and decreased appetite. 3. Abnormal liver function: When the liver is infected by pathogens such as bacteria, viruses, parasites, etc., it causes significant impairment of function. Patients will experience gastrointestinal symptoms such as decreased appetite, nausea and vomiting. Sudden loss of appetite can also be seen in other reasons, it is recommended to consult a doctor in time, follow the doctor’s instructions for relevant examinations, with the help of the doctor to clarify the cause, and targeted treatment or therapy.