Cholesterol levels are a valuable predictor for your risk of heart disease. A lipid profile includes high-density lipoprotein, often called the "good" cholesterol because it appears to protect the blood vessels from damage by the "bad" cholesterol, called low-density lipoprotein. A lipid profile also includes triglycerides, a form of fat that may also contribute to heart disease. Most medical practitioners recommend not eating for nine to 12 hours before a lipid panel to obtain the most accurate reading.
Definition
Fasting means no food intake for the specified period before your blood is drawn. Fasting also prohibits drinking any liquids that contain calories; some medical practitioners will say to abstain from any liquid except for water. If you normally take cholesterol-lowering medications, ask your doctor if he wants you take your medication before the test. Because alcohol can also raise triglyceride levels, Harvard Medical School also suggests abstaining from alcohol for 24 hours before a lipid test.
Purpose
The purpose of fasting is to obtain the lowest possible cholesterol levels to compare to a standard number. Since everyone eats differently and metabolizes food differently, it wouldn't be possible to establish acceptable cholesterol levels if people ate before the test. Normally, recently consumed fats and cholesterol are no longer detectable in the blood 10 hours after eating, according to Columbia Health Services, so most practitioners suggest a 12-hour fasting period.
Benefits
Fasting before a cholesterol test lowers HDL slightly, by between 1 and 4 percent, Columbia Health Services reports. Since HDL is "good" cholesterol, higher numbers are actually more desirable. Low-density lipoprotein readings will be 2 to 4 percent higher than they would be if you had fasted. Triglycerides may rise as much as 20 to 30 percent after eating, Harvard Health Publications warns. The triglyceride reading is especially important because LDL isn't measured directly in the cholesterol test, because of technical difficulties. Instead, LDL is calculated using triglyceride, total cholesterol and HDL levels.
Exceptions
Researchers at the University of North Carolina at Chapel Hill studied samples from 17,000 children, comparing their eight-hour fasting lipid numbers to non-fasting levels. They found little difference in total cholesterol and HDL, and only slight differences in LDL levels. Triglycerides did vary depending on fasting time. During their presentation of the study at the annual Pediatric Academies Study in Vancouver, Canada in 2010, they concluded that obtaining a non-fasting reading during an office visit might be less problematic for children and would provide adequate results.
