Should I Fast Before I Have My Cholesterol Test?

Fasting may not be necessary for all cholesterol tests

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Before you have any type of blood test at your healthcare provider’s office, including a lipid profile,  you may be asked to fast ahead of the test. Current recommendations suggest that you refrain from eating anywhere between 8 and 12 hours before having your blood drawn for a lipid profile, also called a cholesterol test, which for most people means fasting overnight.

But this can prove to be problematic, especially if you have an afternoon appointment or if the hunger pangs are just too unbearable for you to wait to eat until after your test.

It’s also a concern for people with blood sugar issues, such as those with diabetes or people with hypoglycemia.

Some studies suggest that you may not need to fast at all before having your cholesterol checked, particularly if you’re not worried about high triglycerides. 

What a Cholesterol Test Looks For

There are four main things a lipid profile cholesterol test is looking for. It will determine total cholesterol concentration, the amount of low-density lipoprotein, or LDL (also known as bad cholesterol), the amount of high-density lipoprotein (HDL), aka "good" cholesterol, and triglycerides. It's the triglycerides, which are a lipid molecule, that usually determine whether or not you'll need to refrain from eating before having a lipid profile tested. 

To Fast or Not to Fast before Your Cholesterol Test

For HDL and LDL levels, studies found a minimal difference between patients who fasted and those who did not.

 But triglyceride levels can vary by about 20 percent between fasting and non-fasting participants.

In other words, while your HDL and LDL levels may vary slightly depending on whether or not you ate before your test, your triglyceride levels could vary more and eating may affect your results.

So as far as most healthcare providers are concerned, if you have a history of high triglycerides, you’ll still need to fast before having them tested.

But research has found that there’s enough evidence showing that fasting before a cholesterol test to determine HDL and LDL levels is not necessary, and in fact not fasting may produce more accurate results.

It’s not entirely clear whether certain types of food could adversely affect cholesterol test results. It’s possible that some foods, such as those high in sugar and saturated fat, could cause triglyceride levels to increase.

Triglycerides and Fasting 

The variation in HDL, LDL, and triglycerides appears to be small in some cases, but it still may be a good idea to refrain from eating before your cholesterol test if you're trying to get accurate triglyceride level results.

If you're unsure whether you should fast before your cholesterol test, check with your healthcare provider before your appointment. And if your healthcare wants to conduct other blood tests during your visit, such as a blood glucose test, that may determine whether or not you should fast.

Sources:

Mora, S., "Nonfasting for Routine Lipid Testing." Journal of the American Medical Association, July 2016 176(7):1005-1006. 

Fisher, N. "Farewell to the fasting cholesterol test?" Harvard Medical School Health Publications, June 2016.

Sidhu D, Naugler C. "Fasting time and lipid levels in a community-based population." Archives of Internal Medicine 2012; E1-E4.

Gazanio JM. "Should we fast before we measure our lipids? Arch Intern Med 2012; E1-E2.

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