Vital Information
By Dr. Beth Gruber, CarbSmart Contributor
Posted 5/11/2002
As we have seen in a previous article, fats and oils are members of a category of substances known as lipids. Other lipids include the compounds known as waxes, phospholipids, and steroids. Last time, we spoke about waxes, and in this article, we'll discuss the other important lipids. Additionally, I'll have some more things to say about cholesterol, since cholesterol is one of these other lipids.
Lecithin
Lecithin is the most important phospholipid in the human body. It is called a phospholipid because it includes the substance known as phosphoric acid. Lecithin is found in all cells, and is essential for life. It is necessary for cell walls, and is involved in the selective permeability of membranes. (Recall that the walls of cells must control what passes in and out of them. The determination of what goes in and what goes out is called selective permeability.)
Lecithin and the steroid cholesterol are components of the body's cellular structure. They assist in the framework which supports the protein constituents of cell protoplasm. The most important steroid in dietary considerations is cholesterol, which takes its name from bile (chole means bile) since it was first discovered in gallstones. Steroids, which are also called sterols, are needed for life, and as I have mentioned before, cholesterol, too, is absolutely necessary.
Cholesterol
Cholesterol is absorbed from the intestinal canal along with dietary fat. Bile is necessary for cholesterol absorption as well as for fat absorption. (In a previous article, I discussed the role bile plays in the digestion of dietary fats. Check it out in the CarbSmart archives, if you missed it.)
Cholesterol is held in solution in the bile by the chemicals known as bile salts. If there aren't enough bile salts, cholesterol drops out of solution, and gallstones may form. But, you should be clear on this point: gallstones are not the result of the presence of cholesterol; they are the result of insufficient bile salts and other factors which allow cholesterol to drop out of solution.
Cholesterol serves as a precursor of various steroid hormones, and it is especially abundant in the nervous system, where it joins with lecithin to make the coverings that surround nerve fibers. It also helps to maintain the skin since it is not soluble in water and does not become rancid.
Since cholesterol is not soluble in blood (because it is not soluble in water), it is transported in the blood in links with certain proteins called lipoproteins. These lipoproteins are known as High Density Lipoproteins (HDLs), Low Density Lipoproteins (LDLs), and Very Low Density Lipoproteins (VLDLs). The HDLs, LDLs, and VLDLs are called the three fractions of cholesterol.
The amount of cholesterol in the blood is referred to as the blood level, which is measured in a series of related blood tests called a 'lipid panel.' The results of the lipid panel usually include blood levels for triglycerides as well as for total cholesterol, and the three fractional parts of cholesterol. The result numbers all relate to one another.
For example, total cholesterol is the sum of the HDLs, the LDLs, and the VLDLs. And, the VLDL value is one-fifth of the triglycerides number. Additionally, the fractional parts of cholesterol are proportional to one another. The higher your HDL level, for instance, the lower your VLDL level will be.
Total cholesterol is usually the number everyone focuses on, but since HDLs, LDLS, and VLDLs all perform different functions, it is not very useful at all to know a number representing their combined total. It's like thinking you can decide what you can afford to buy for cash by knowing the total number of currency bills in your wallet without regard for whether they are fives, tens, or hundreds. Furthermore, each combination of cholesterol fractions will mean something different. In point of fact, you gain almost no insight whatsoever from your total cholesterol level, and you certainly gain no information as to your risk of heart attack or other disease.
Cholesterol Stands Falsely Accused
The public is scared to death of cholesterol. People generally believe that it should be avoided at all costs. But, as we have seen in previous articles cholesterol is not a curse, and if we do not eat enough of it, we will manufacture it in our own bodies.
As early as 1979, one researcher described what he had learned in the previous 30 years of studying fat and cholesterol metabolism. "It is absolutely certain," he said, "that no one can reliably predict whether a change in dietary regimens will have any effect whatsoever on the incidence [the number of cases] of new coronary heart disease."
Preoccupation with cholesterol levels has not reduced any disease, and even the American College of Physicians has suggested that while cholesterol reduction may be worthwhile for those (usually men) at high risk of dying of coronary heart disease in the short term, cholesterol reduction is of much smaller or uncertain benefit for everyone else.
The Data On Cholesterol Is Skewed
Another thing to keep in mind is that much of the dogma concerning dietary fat and cholesterol came from studies done on drugs to lower cholesterol levels, not from studies on dietary changes to accomplish lower cholesterol levels.
Some researchers have started to caution that if studies look only at cholesterol levels, they are likely going to miss something very important. Even those who have been trapped in the idea that cholesterol is close to poison are having to admit that the connection between cholesterol and heart disease is not strong.
It is also becoming increasingly difficult to study the subject because of the effects of the drugs given to change cholesterol metabolism in so many people. Physicians are routinely prescribing drug treatment for patients with even slight risk of heart disease, and they routinely decide who is at risk by looking at total cholesterol levels.
The market for these drugs in the United States alone approaches 5 billion dollars a year as the definition of who "needs" the drugs continues to expand. While it is apparently true that the drugs reduce LDL cholesterol levels by as much as 30%, whereas diet rarely drops LDL by more than 10%, the question still remains as to whether or not it is a good idea to reduce any blood fraction of cholesterol by nearly one-third.
Next time, we'll have a review of what we have learned about fats, lipids, and cholesterol. And, then we'll be ready for a new subject.
See you then.
Further Reading:
Back to CarbSmart Magazine - the online resources for hundreds of articles supporting the low carb dieter, diabetics and people reducing their sugar intake.
Back to Vital Information by Dr. Beth Gruber - Scientific analysis of issues related to the low carb dieter in CarbSmart Magazine.
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