What does having high triglycerides mean? Is that bad? And can you do anything about it?
High triglycerides, which usually means a value greater than 150 mg/dl after an overnight fast, is among the most misunderstood of common tests. Yet it is among the most important and insightful numbers of the four values on any standard cholesterol panel. (The other values are total cholesterol, LDL cholesterol, and HDL cholesterol.)
One of the most common triglyceride myths is that eating fats increases triglyceride. But that's only a half-truth, since fats do indeed increase triglycerides-but only if triglycerides are measured after eating (i.e., in the postprandial period). The real story is that fats in the diet decrease triglycerides-at all other times except after a meal. The higher the fat content of your diet, the lower your triglycerides will be in a fasting blood draw. This has been well-established in numerous diet trials comparing low-fat with low-carbohydrate diets.
Why do fats increase triglycerides after eating? The reason is simple: Dietary fats are triglycerides. Absorbing the fats thereby increases blood levels of triglycerides up to several-fold.
Here's where it gets confusing: While dietary fats cause triglycerides to increase after eating, carbohydrates cause triglycerides to increase at all other times. This means that carbohydrates (starches), like breads, pasta, breakfast cereals, pretzels, crackers, potatoes, soft drinks, and candies increase fasting triglycerides if consumed habitually.
A carbohydrate food like bread actually contains very little triglyceride . . .
So why would bread cause triglycerides to increase? Because carbohydrates are converted to triglycerides in the liver.
The human body has little capacity to store carbohydrates. So it needs a method to store the energy of excessive carbohydrates. It does so by converting carbohydrates to triglycerides, which are then converted to fat, especially the fat in your abdominal region (visceral fat).
If carbohydrates are consumed chronically at higher levels, weight gain develops and then a condition called insulin resistance sets in: The body no longer responds to insulin very well. This leads to impaired function of the most important enzyme to metabolize triglycerides, lipoprotein lipase. When that happens, triglycerides accumulate, and fasting levels of triglycerides increase. In addition, the liver starts to manufacture triglycerides from carbohydrates, a recently- discovered process called de novo lipogenesis, and triglycerides increase further. Excess carbohydrate intake can cause fasting levels of triglycerides to reach many times higher than normal. Triglycerides of 300, 400, even 500 mg/dl are common when excessive carbohydrates are consumed (as in low-fat diets).
So what? You can't feel high triglycerides. They just show up unexpectedly on a cholesterol panel. Can they do you any harm?
Yes, they can. In fact, the two largest studies to date, the Women's Health Study and the Copenhagen City Heart Study, both showed that increased triglycerides, both fasting and after-eating, were associated with increased risk for heart attack. Triglycerides are lowest after fasting, highest after eating. In these studies, fasting triglycerides as low as 74 mg/dl were associated with increased heart attack risk.
Does that mean a low-fat diet will increase triglycerides? Yes, it does.
That, in fact, has been among the many criticisms waged against low-fat diets.
If carbohydrates increase fasting triglycerides, and fat increases after-eating triglycerides, is there a safe way to eat? Yes, there is, but that's a topic for a future discussion.