Christopher Naugler, MD
Christopher Naugler, MD, assistant professor of pathology and laboratory medicine at the University of Calgary, Canada, and coauthor of the study, which was published in Archives of Internal Medicine.
If you’ve ever had a cholesterol test scheduled for midday or afternoon, then you know what a pain it can be to have to fast for the usual eight hours beforehand—because in reality, you probably won’t have eaten since the previous night’s dinner—a lot longer than eight hours.
Fasting doesn’t bother some people—lucky them. But lots of us find it very difficult. I, for example, don’t only get hungry. I also tend to get a headache and feel dizzy when I don’t eat for much longer than four hours—which makes the eight-hour cholesterol-test fast a bear!
So I’m happy to tell you today that this ironclad fasting rule—which was thought to ensure more reliability in cholesterol test results because eating could make your results spike higher or lower, depending on what you ate—might not be essential. And in fact, as I learned recently from Christopher Naugler, MD, of the University of Calgary in Canada, what you eat before a cholesterol test may not matter much at all. Here’s why…
In addition to his work as a professor, Dr. Naugler is zone clinical section chief of general pathology for Calgary Laboratory Services, which processes an average of 36,000 cholesterol tests each month. With such a large volume of work, “we were looking for ways to avoid turning away nonfasting patients,” Dr. Naugler explained—nonfasting patients create more work for everyone (including themselves) because their appointments need to be rescheduled.
As there were already several small studies suggesting that fasting had only a modest effect on cholesterol levels, researchers at the lab decided to simply begin processing cholesterol tests for all of its patients, regardless of whether patients had remembered to fast or not. (In case this sounds reckless to you, don’t worry. The cholesterol results, as well as the number of hours the patient fasted, were both reported back to the patient’s physician, who could then decide whether the result was acceptable or whether the patient needed to return for a repeat test.) “After six months, we had more than 200,000 cholesterol panels, which is a large amount of data,” said Dr. Naugler. So Dr. Naugler and his team decided to analyze those tests to see whether fasting did indeed impact the results of cholesterol tests.
This was what’s called an observational study, so the researchers did not directly compare, say, two patients of the same gender and age who had similar risk factors for high cholesterol and then ask one to fast and ask the other not to fast. (Hopefully future studies will.) Instead, these researchers compared groups of thousands of individuals (ones who fasted versus ones who didn’t) and then controlled for age and gender. They were curious to see what the broad, overall trends suggested.
Dr. Naugler’s analysis found that levels of HDL cholesterol and total cholesterol stayed relatively stable, varying only about 2%, depending on whether patients had or had not fasted. Levels of LDL cholesterol varied by less than 10% and triglycerides (blood fats) by less than 20%. “The levels that varied the least—HDL and total cholesterol—are the ones that matter the most in terms of estimating risk for cardiovascular problems,” said Dr. Naugler. “The algorithms commonly used for assessing cardiovascular disease risk (the Framingham Coronary Heart Disease Risk Score and the Reynolds Risk Score) use only HDL and total cholesterol levels (not triglyceride or LDL levels).”
Now, you might be thinking, But isn’t a variation of 10% and 20% kind of a big difference? Dr. Naugler didn’t argue that those variations aren’t significant—his point is simply that those variations, no matter how big or small, are not as meaningful when it comes to assessing a patient’s risk for cardiovascular disease.
“This confirmed similar results that had been reported previously, but ours was the first large-scale North American study to report this finding,” Dr. Naugler said. “We suggest that there is now sufficient evidence that most routine cholesterol screening tests can be performed without fasting. This is more convenient for patients and would also benefit labs by transferring some of the morning demand for tests to later in the day.”
Ask your doctor whether fasting is necessary before your next cholesterol test. If your doctor allows you to skip the fast, use common sense and avoid eating high-fat foods in the day or two before the screening, advised Dr. Naugler, since those types of foods are likely to cause cholesterol to spike the most.
But don’t be surprised if your doctor still asks you to fast before your next cholesterol test (especially if he’s ordering other blood work that does require fasting, such as a blood sugar test). “Time will tell,” said Dr. Naugler when asked whether his research is likely to shift any of the official recommendations about cholesterol-screening protocols.