Nov. 12, 2012 -- The requirement to fast before a cholesterol check can be a major inconvenience.
People who forget to fast may be told to reschedule their appointments. For those who remember, sitting in a doctor's waiting room with a growling stomach can make for a rough start to the day.
Now a large new study shows that cholesterol levels aren't radically different in people who ate compared to those who fasted before their blood was drawn.
The study, which is published in the Archives of Internal Medicine, suggests that people may not need to fast before they get a cholesterol test.
Experts who were not involved in the research called the results an eye-opener.
"This information is actually very, very interesting. It might change how we approach a patient," says Suzanne Steinbaum, DO, a preventive cardiologist at Lenox Hill Hospital in New York City.
Fasting and Cholesterol
For the study, researchers looked at the results of all the cholesterol tests processed at the same lab during a six-month stretch in 2011. Because the lab does all the testing for the entire city of Calgary, Canada, that amounted to test results for more than 200,000 people. Doctors also recorded how long it had been since the patient had last eaten.
When researchers broke down the results by fasting time, they found little change. Overall, total cholesterol and HDL "good" cholesterol varied by less than 2%, depending on when a person had last eaten. Total cholesterol and HDL are important because they are the main measures used to calculate a person's risk for heart-related events.
LDL "bad" cholesterol was less than 10% different in people who'd recently eaten compared to those who had been fasting for at least eight hours.
Triglycerides, or blood fats, were the most sensitive to food. They varied by no more than 20% between people who had fasted and those who had not.
Because the study is just a snapshot in time, it has important limitations. It doesn't prove that cholesterol levels don't change significantly before and after a meal for individual patients.
Researchers say the small differences noted in the study may matter for some, including those who are taking specific medications to lower their cholesterol or triglycerides. Those patients may still need fasting tests.
But for many others, eating may not make a difference.
"For routine screening, we're suggesting that a 2% variance probably isn't going to be significant," says Christopher Naugler, MD, MSc, chief of clinical pathology at the University of Calgary, Canada.
Other experts agree.
No Fasting Needed?
"I think we've just taken for granted that we should do fasting for lipid testing," says Samia Mora, MD, a preventive cardiologist at Brigham and Women's Hospital, in Boston.
Mora wrote a commentary on the study, but was not involved in the research.
She says the requirement to fast before a cholesterol test was based on very small studies where researchers fed subjects very high-fat or high-sugar meals.
"Most people aren't having big fat loads before they get their lipids measured," she says.
Currently, guidelines still recommend that people not eat before a cholesterol test. But Mora says a growing body of evidence suggests that fasting isn't necessary.
"We've had several studies now that have all found the same thing," she says.