system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do you have to fast before getting certain blood tests?
gpt
it depends on the blood tests, however, its typically to get rid of all the fats and sugars that are suspended in your blood following a meal.

If you fast, then your body will process those fats and sugars from your blood. Whats left over are the risiduals which are produced by your body (ie, chloresteral, insulin etc...). By fasting they can get a somewhat accurate snapshot of the levels in your blood to know if you have high chloresteral due to your liver producing too much or insulin levels due to diabetes etc...