Doctors have regularly followed national guidelines that recommend an overnight fast before getting blood drawn for a lipid profile that measures levels of total cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides.
Although these various cholesterol levels are not altered by a recent meal, overnight fasting has been recommended because triglyceride levels may be significantly higher if blood is drawn shortly after a high-fat meal.
A recent issue of the Journal of the American Medical Association (JAMA) has published two long-term, prospective studies which show that nonfasting triglyceride levels can be used to predict the future risk of coronary heart disease and strokes.
Both studies were carried out in large populations of healthy people: the one in Denmark included both men and women; the U.S. study was limited to women.
A number of studies have shown that elevated fasting triglyceride levels are associated with an increased risk of cardiovascular events (heart attacks and strokes) that may be comparable to the risk conferred by elevated levels of LDL cholesterol.
These new studies found that both men and women had a greater risk of coronary artery disease, heart attacks, and death with each increase in nonfasting triglycerides after adjusting for multiple risk factors.
Just as shown previously with fasting triglycerides, high nonfasting triglyceride levels pose a greater danger for women than for men. In the U.S. study, nonfasting triglyceride levels were far superior to fasting triglyceride levels for predicting cardiovascular risk among women.
It makes sense to make use of the impact of nonfasting triglycerides on cardiovascular risk. After all, except while sleeping, we spend most of the day within a few hours after a meal or snack (the "postprandial state").
After a fat-containing meal, the dietary fat is absorbed from the intestine and carried in the blood in particles called chylomicrons. The chylomicrons are so large that they cannot enter the arterial wall.
In most people, however, these chylomicrons are broken down over the next 8 to 10 hours into smaller, triglyceride- and cholesterol-rich lipoproteins termed remnant particles. The authors of these two publications attributed the superiority of the nonfasting triglyceride measurements to the presence of these remnant particles.
These particles are small enough to penetrate the endothelial cell lining of the arterial wall and contribute to the formation of the atherosclerotic plaques that narrow the arteries and lead to their obstruction by blood clots.
Remnant particles persist longer in the blood of people with insulin resistance due to obesity or type 2 diabetes, and they may play an especially prominent role in the increased cardiovascular risk associated with diabetes and the metabolic syndrome.
In addition to their greater utility in predicting risk, nonfasting triglyceride tests would make life a little easier for patients who could have blood tests at any time of day, rather than just first thing in the morning.
While I believe these new study results show great promise for improving our ability to determine cardiovascular risk, more research is needed to clarify the use of nonfasting triglyceride levels in clinical practice.
For example, present cut-offs for abnormal triglyceride levels are based on values determined while the patient is fasting, and so we will need to set new standards for determining what levels of nonfasting triglycerides are associated with increased risk.
Nonfasting triglyceride measurements may not be useful for determining the effectiveness of treatment for elevated triglycerides (hypertriglyceridemia), particularly in people with extremely high levels, because a recent high-fat meal could raise triglyceride levels considerably.
But a nonfasting test might be appropriate for most people who are treated for high cholesterol values.
