Because there are some main items to apply for a health certificate, 1 is an imaging examination of the chest to see if there is active pulmonary tuberculosis. The second is to draw blood to detect alanine aminotransferase, so liver function test doesn't need an empty stomach. The third is stool culture, mainly to check whether there are Vibrio cholerae, typhoid Bacillus or paratyphoid Bacillus. These intestinal diseases easily affect people's health.
You don't need an empty stomach to apply for a health certificate, but you need an empty stomach to go to a physical examination, because only an empty stomach can really screen your health.