I think I choked the forum with the length of this post! I'm going to split it - half in the post window and half in a comment, and see if that will fix the problem.
I've been working on this for a while, and I think it's finally ready to post here. A lot of people post to MDA's forums freaking out about their cholesterol tests after going Primal - their numbers are higher, their doctor wants them on statins, etc. and so forth. I'm usually called on to answer them, because I've done quite a bit of research on the great cholesterol con, and I know how to interpret the results. But I think this is a tool that everyone should have, so without further ado, here's an article for you about cholesterol, what it does, and what those numbers mean.
DEFINITIONS OF TERMS
Total cholesterol: This is the total of all three kinds of cholesterol: HDL + LDL + Triglycerides. Each of them has a different function inside the body.
The recommended level of total cholesterol these days is 200 or less.
Cholesterol: A waxy substance that is actually an alcohol (hence the -ol suffix). It's carried by lipoproteins (fats and proteins) through the water-based environment of the bloodstream (remember that water and oil don't mix). It's necessary to sustain cell wall integrity and to repair damaged cell walls within (among other places) the arterial system of the body. Many things can damage the cell walls in the arteries and veins, including (but not limited to) stress, high blood sugar, high insulin levels, and lack of physical activity. When damage happens to these cell walls, the body has to do something about it. Normally, it will repair them with saturated fat and protein, which is what cell walls are made of, but if we're not eating those things, the body can't produce them out of thin air, so it sends cholesterol in as a stopgap measure. Your body uses cholesterol to make a "patch" over cell walls that need to be repaired, but if we don't give it the proper amount of raw materials (saturated fat and protein) to repair them with, the patch will stay there, and like any old bandage, eventually start to peel off. In the absence of the proper raw materials, the body slaps another layer of cholesterol over them to make sure that the patch doesn't break. This is where cholesterol buildup, or plaque, in the arteries comes from. The longer the body has to go without the right raw materials, the worse the problem gets, and these plaques can eventually break off, just like a scab on the outside of your body does, and block up the arteries, causing a heart attack or a stroke. The technical term used for "increases risk of heart disease" is "atherosclerotic," which, translated out of its non-English roots, means "athero" (artery) "sclerotic" (hardening).
One of the problems with the way that current medical science treats cholesterol is that it doesn't recognize the function of cholesterol. It just sees higher cholesterol readings and naively assumes that since high cholesterol and heart disease "seem" to go together, that cholesterol must be the cause of heart disease. The real cause of heart disease is what causes both the damage to the cell walls and the (ideally) temporary patches of cholesterol: not enough of the right raw materials being given to the body, and too much of the stuff that damages the cell walls being given to the body - to wit, too many carbs and not enough saturated fat or protein. It's like blaming firemen for a fire, or blaming a bandage for the wound, and saying "if we take away some firemen, the fire will die out," or "if we take the bandage off the wound, the wound will heal without help" (even though it's usually a wound that needs stitches in order to close up and heal). It's overly simplistic, it's a junior-high-school-level mistake, and it makes no sense.
LDL (Low-Density Lipoprotein): This has been blamed as the "bad" cholesterol because its job is to go around inside your body, bringing cholesterol from the liver to spots that need repair, and placing cholesterol "patches" on them. There are two types: Pattern A and Pattern B. Sometimes you'll have a mixed bag: Pattern A/B, some of each. When you have a VAP test, this is part of what gets reported. Pattern A is "large and fluffy" and non-atherosclerotic, like a cotton ball. Pattern B is "small and dense" and atherosclerotic, like a BB pellet. You want to have Pattern A. Pattern B is sometimes called "oxidized" cholesterol, and because it's so small and dense, it can penetrate the endothelium (the thin layer of cells that line the inside of the blood vessels), just like a BB pellet penetrates skin. So Pattern B LDL is worrisome, because it can also cause damage to the cell walls inside the arteries. LDL becomes Pattern B due to a number of reasons, but one of the main ones is insulin resistance. If you lower your insulin resistance (which low-carbers almost always manage to do), then your LDL Pattern B goes down, which is good.
The recommended level of LDL these days is no more than 150, and most doctors now want it below 100.
HDL (High-Density Lipoprotein): This is considered the "good" cholesterol because its job is to go around inside your body and clean up used cholesterol. HDL goes around after the patched area has been repaired, and cleans up the old cholesterol patches, taking them back to the liver for processing and breakdown. You can see why HDL is high-density: it carries old cholesterols with it to the liver, so it's got lots of tightly-packed stuff on it, hence high-density. Low-density LDL is just the opposite - it's dropping cholesterol here and there, so it's no longer as dense.
The recommended level of HDL these days is at least 40 for women and 50 for men. Some recommendations are "get it above 60."
Triglycerides: The "cholesterols" made in the liver from the carbs you eat. They are technically not cholesterol at all, but fat. They're used by cells for energy. A third kind of cholesterol called VLDL (very low-density lipoprotein) carries triglycerides around in the body, delivering them to cells for energy. When VLDLs lose most of their triglycerides, they become smaller and denser, and now they're LDLs instead of VLDLs. Triglycerides can shoot the level of VLDL way, way up - the more triglycerides you have, the more VLDL is needed to move it around the body. So if you're eating lots of carbs, your triglycerides are going to be higher, and since VLDL becomes LDL when it deposits its triglycerides into the cells, your LDL will also be higher.
The recommended level of triglycerides these days is under 150.
EQUATIONS USED FOR CHOLESTEROL MEASUREMENT
There are two equations used today for cholesterol measurement. The first one, and the one most commonly used, is called the Friedewald equation. It works fine as long as your triglycerides are at least 100 and below 400, but outside of that range things get wonky. And the main problem is, when your triglycerides are below 100, it overestimates LDL levels. A quick rundown:
The Friedewald formula used to calculate total cholesterol is:
LDL + HDL + [Trigs/5] = total.
But because LDL are so small in comparison to the other particles, what they usually do is calculate your LDL. They measure your HDL, your Trigs and your Total - so the equation becomes:
Total - (HDL + [Trigs/5]) = LDL.
(I don't know why the triglycerides are divided by 5. I haven't yet found that out.)
Because this equation miscalculates LDL if you drop below 100 trigs, I'd recommend that you always, always demand a VAP test, which is a direct measurement of the LDL. People who restrict carbs usually have very low triglycerides, which means that we're going to have problems if the lab uses the Friedewald equation to calculate our LDL levels. According to Dr. Mary Vernon, "These labs in which the LDL is calculated are not accurate if your triglycerides are below 100... The equation used to calculate these numbers makes assumptions which are not accurate when triglycerides are low." (from http://www.livinlavidalowcarb.blogsp...t-results.html).
To give an example of how it doesn't calculate LDL correctly, let's look at a hypothetical cholesterol result. Let's say that Joe the Primal Dude goes in for a lipid profile after six months on the Primal diet. Here's his results (before they do the LDL calculation):
Total: 250 (ideal <200)
HDL: 70 (ideal >60)
LDL: ? (must be calculated) (ideal <100)
Trig: 40 (ideal <150)
This is a common profile for someone who's been low-carbing/eating Primally for a while. Now, when we put that into the Friedewald equation, here's what we get:
250 - (70 + (40/5)) = LDL
250 - (70 + 8) = LDL
250 - 78 = LDL
250 - 78 = 172
This may give Joe's doctor a heart attack if he doesn't know what he's looking at, as many doctors don't. To him, Joe's LDL and total cholesterol levels are way above the "ideal" numbers, and that must mean that Joe is headed for a heart attack or a stroke if he doesn't take a statin drug immediately and get those numbers down.
For many doctors, this level of analysis is as far as they go. The nuanced information about the two types of LDL is something they either don't have or aren't aware of. And recognizing that if Joe's HDL were lower, his total cholesterol would be lower too - they don't often see that, either.
However, there is a newer equation, called the Iranian Equation, that does a better job of calculating LDL when trigs are below 100. That equation is:
(Total/1.19) + (Trig/1.9) - (HDL/1.1) -38 = LDL
Let's plug Joe's numbers into this equation and see what we get.
(250/1.19) + (40/1.9) - (70/1.1) - 38 = LDL
210 + 21 - 64 - 38 = LDL
231 - 102 = 129
Look at that. It's a difference of almost 50 points in Joe's favor. With the Iranian equation, his numbers come out to:
Part of the reason the Friedewald equation doesn't work so well is that Trig/5 issue. The Friedewald equation assumes that anything that isn't HDL or triglycerides is LDL. LDL is the "leftover" number. Well, when your trigs are 200/5, the number it will subtract from the overall total is 40, but when your trigs are 40/5, the number it will subtract from the overall total is 8. That's a big difference, because the smaller your trigs are, the more of the "leftover" number in the equation gets attributed to LDL, and that's really misleading.
(continued in comments)