Postprandial Lipoproteins:
Part 2 - The triglyceride tolerance test
You test your blood sugar to assess
the effects of a meal. So why not test triglycerides
as yet another feedback tool? Here's a step-by-step guide to
triglyceride tolerance testing,
a way of gauging your per-meal fat tolerance.
The major determinants of triglycerides
during fasting periods are body weight, omega-3 fatty acid intake, and
carbohydrate intake (higher intake leading to higher triglycerides).
However, triglycerides also peak even higher after meals if there is
substantial fat in the meal. Specific genetic patterns also lead to
higher triglyceride levels after eating (e.g., familial
hypertriglyceridemia, ApoE2, familial combined hyperlipidemia, perhaps
lipoprotein(a), and others). We therefore address both aspects of
triglyceride excursions: fasting and after-eating (“postprandial”).
Indeed, higher postprandial peaks of triglycerides have been associated
with greater risk for plaque growth and cardiovascular events.
Postprandial triglyceride values have proven superior to fasting
triglycerides as a predictor of cardiovascular events.
Dietary fats are made of triglycerides. After you consume fat in a meal,
e.g. egg yolks, olive oil salad dressing, butter, etc., blood
triglycerides increase over the ensuing 6 hours, peaking at 3-4 hours
after eating. Very few “free” triglycerides are present in the blood,
since most occur as lipoproteins like chylomicrons, chylomicron remnants
(the partially-degraded form of chylomicrons that are believed to be
among the most atherogenic, or plaque-causing), and VLDL. Triglycerides
therefore serve as our surrogate measure for all the postprandial
(after-eating) lipoproteins developing after a meal; higher levels of
triglycerides and thereby postprandial lipoproteins are associated with
greater plaque growth and cardiovascular risk.
The easiest way to assess your postprandial fat response is to simply
not fast before a blood draw; this will yield a non-fasting triglyceride
value. The blood sample should be obtained 3-4 hours after the meal is
consumed, the usual point of peak triglycerides. Non-fasting
triglycerides are a useful predictor of coronary events. (See below.)
The downside: Friedewald calculated LDL is artifactually increased,
since triglycerides are used to calculate LDL cholesterol. While even
fasting Friedewald-calculated LDL cholesterol values are prone to
inaccuracy, non-fasting LDL values are even more inaccurate and
therefore should not be used.
Beyond non-fasting triglycerides following an “unstructured” meal, there
may be additional value in probing individual tolerance to fat intake by
challenging your body with a single greater “dose” of fat. This can help
determine how much fat is safe without provoking excessive triglycerides
and postprandial lipoproteins.
While carbohydrate intake and body weight are more powerful influences
on fasting triglyceride levels, fat intake is a greater influence on
postprandial triglyceride levels. This can be assessed by challenging
your body with a test meal of known fat composition, then measuring
triglycerides. (Of course, this should be conducted under the
supervision of your healthcare provider.)
To perform a “triglyceride tolerance test,” we use a standard high-fat meal consisting of:
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