Two new studies, published in the Journal of the American Medical Association, provide evidence that postprandial (after eating) triglycerides may deserve more attention in the assessment of risk of heart disease. These studies suggest that a blood sample taken a few hours after your last meal may identify a risk for heart attack and other serious cardiovascular problems that are not identified from the traditional fasting triglyceride test after a 12-hour fast (today’s preferred test).

Nonfasting Test Reveals Heart Risks
In a study by Nordestgaard and colleagues, nearly 14,000 Copenhagen residents, aged 20 to 93, were followed over a 28-year period. During that time, 1793 of the subjects had a heart attack, 3479 suffered ischemic heart disease, and 7818 died.

The researchers concluded that higher nonfasting triglyceride levels were associated with increased deaths, heart attacks, and ischemic heart disease, particularly in women. They found that:

• Men with the highest levels were twice as likely to die from a cardiovascular event versus men with the lowest levels.
• Women with the highest levels were five times as likely to die from a cardiovascular event versus women with the lowest levels.

As a possible explanation, the researchers noted that a high level of nonfasting triglycerides coincides with increased levels of remnant lipoproteins in the blood after a meal. These fat remnants may promote arterial wall damage and cholesterol deposits (atherosclerosis), they explained, but fasting tests miss this information. This may explain why the nonfasting test could independently predict the risk of heart attack, ischemic heart disease, and death due to a cardiovascular event. Further research is needed to confirm this role.

The report acknowledges that the study was small and included only white Danes. The difference between male and female risk was probably due to greater alcohol consumption by Danish men. Nevertheless, the findings open the possibility “that nonfasting rather than fasting triglyceride levels should be used for risk prediction,” wrote the researchers.

Nonfasting Test Tops Fasting Test
A larger US study compared fasting triglyceride tests to nonfasting tests to see which was better at predicting cardiovascular risk. The study, by Bansal and colleagues, followed 26,509 women (part of the Women’s Health Initiative) for 11 years. Of the 1001 who experienced a new cardiovascular event, 276 had a nonfatal heart attack, 265 had an ischemic stroke, 628 underwent coronary revascularization, and 163 died.

The researchers found that the fasting triglycerides values followed the same patterns as fasting cholesterol and added no new information to that already identified by the HDL and LDL cholesterol values. The nonfasting test, however, identified risk that was not predicted by the fasting test. Therefore a nonfasting test might identify a person who is at risk when a standard fasting lipid profile would not show that risk. The nonfasting test was found to be most valuable when the sample was taken two to four hours after a meal.

The researchers also suggested that using data from nonfasting tests may improve the assessment of triglyceride-lowering therapeutics. Almost all drug trials to date have used fasting results, rather than nonfasting ones, to evaluate drug effectiveness. The ability of the drug to lower levels of postprandial lipoprotein remnants may be a valuable property that should be included in the drug assessment.

More to learn
Don’t expect a quick shift in the tests your healthcare provider recommends. Better tests—without fasting—are an appealing concept, but reliability is harder to ensure with nonfasting tests. For example, in the study if the sample was taken more than four hours after eating, the data were no longer predictive. Therefore, for interpretation to be most reliable, the timing of the blood draw for the test will need to occur in a limited time window that may be difficult to meet. An editorial in the journal noted this challenge.

One point these studies do make clear: the medical community now has good reason to look more carefully at the use of postprandial tests since they have the potential to identify people whose risk of heart disease is not reflected by traditional fasting tests. In the meantime, follow your doctor’s instructions regarding fasting before your triglyceride test.

Sources
S1
Bansal, S. et al. Fasting Compared With Nonfasting Triglycerides and Risk of Cardiovascular Events in Women. JAMA. 2007;298:309-316.

S2
High nonfasting triglyceride levels associated with increased risk for cardiovascular events (news release). 17 Jul 2007. JAMA. On the Internet: http://pubs.ama-assn.org/media/2007j/0717.dtl#2. Accessed 25 Jul 2007.

S3
McBride, P. E. Triglycerides and Risk for Coronary Heart Disease. JAMA. 2007;298:336-338.

S4
Nordestgaard, B. et al. Nonfasting Triglycerides and Risk of Myocardial Infarction, Ischemic Heart Disease, and Death in Men and Women. JAMA. 2007;298:299-308.