Because the health certificate needs a physical examination, the physical examination mainly includes taking venous blood on an empty stomach to check liver function, blood sugar and biochemistry. So you need an empty stomach and you can't drink water in the morning. If you eat food, it will easily lead to excessive intestinal gas production, interfere with the examination results of abdominal color Doppler ultrasound, and also affect the examination results of liver function and blood lipid. So don't drink for a few days before you get your health certificate. You should get enough sleep and keep a good mental state.