There are several reasons why you need a health certificate on an empty stomach:

1, eating will affect the test results, such as blood lipid test, hemorheology test, six sex hormone tests and so on.

2, food or drugs will affect the biochemical indicators in the blood, so you need an empty stomach before the examination.

It should be noted that you can't eat at least 8 hours before you apply for a health certificate, and you need to draw blood on an empty stomach. If you eat it, it may affect such test indicators in the blood, leading to the failure of health certificate processing.