"If you've ever visited your doctor and required blood test, he or she may have told you to return on another day to have the blood drawn when you haven't eaten overnight. Although it may seem as if the doctor is doing this to make your life inconvenient, there are some real medical reasons for doing these blood tests after a short fast (not eating).
There are two main groups of test that are significantly affected by fasting state, blood sugar and lipids. More specifically, these tests are for LDL and HDL cholesterol, and triglycerides. On a daily basis, the normal range for blood sugar and lipids undergoes changes hour to hour depending on recent ingestion of food and drink. By fasting, one is getting a baseline sugar and lipid value that is not influenced by a recent meal."
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