I have high cholesterol so I have to be on a diet that limits foods high in lipids like butter and red meat.
Every six months or so I go for a cholesterol test where they check the amount of lipids in my blood. I fast for 12 hours before the test because apparently, eating gives abnormally high rates in the cholesterol test. After fasting, the lipids in the blood are said to reach a stable level. The doctors are then able to check lipids and determine if there is high cholesterol or not.
As much as lipids have an important function in the body, too much is clearly not good. It increases our risk of heart disease and obesity. I wish I had been more careful about how much fatty foods I consumed when I was younger. Maybe I wouldn't have cholesterol now.