If you're scheduled to take a cholesterol test, you may be wondering whether what you eat the day before will affect the results. Most people know that high cholesterol levels signal an increased risk for cardiovascular problems, including heart disease and stroke. It's unlikely that what you eat the day before your test will affect your results significantly. However, if you don't fast before your test as you're supposed to do, that will affect your results.
Basics
Cholesterol tests measure the amount of cholesterol, a fatty substance, circulating in your blood stream. Your body uses cholesterol to make cells and important hormones such as vitamin D and estrogen. However, too much circulating cholesterol can lead to clogged arteries and potentially can cause heart attacks and strokes. You want your total cholesterol to fall below 200 mg/dL. If it's between 200 and 239 mg/dL, it's considered borderline high, and cholesterol readings over 240 mg/dL are considered high.
Recommendation
Your doctor most likely has asked you to fast -- in other words, abstain from eating -- for 12 hours prior to your cholesterol test. This guideline seeks to prevent one single meal from having an undue effect on your test results. Failing to fast before the test can affect your results slightly. Results for both your "bad," or LDL cholesterol, and your "good," or HDL cholesterol, can come in up to 4 percent lower than they actually are. This may represent a problem if your cholesterol already falls in the "borderline high" range, since a low reading may affect your doctor's treatment decisions.
Preparation
A single meal consumed the day before your cholesterol test shouldn't affect your readings, even if it's particularly high in fat or cholesterol, as long as you consume it more than 12 hours prior to the test. The immediate effects of a high-fat meal on your cholesterol levels seem to dissipate after about 10 hours. However, if you routinely consume high-fat meals, especially if those meals are high in saturated fat from meat and dairy products, your cholesterol levels most likely will be negatively impacted.
Considerations
Although a single high-fat meal shouldn't affect your cholesterol test if you consume it well enough in advance, it might alter your blood vessel functioning, according to research from the University of Maryland Medical Center. The study included 36 volunteers who consumed a 900 calorie high-fat fast-food breakfast, and found that their blood vessels failed to dilate normally about two to five hours after they ate the meal. The effect dissipated after about six hours, but it could indicate that people with coronary artery disease face a higher risk of a heart attack following a high-fat meal.
