Okay, I know that genetics can be a factor, but I’m talking strictly dietary influences (as well as exercise). I’ve always thought it was odd to assume that eating cholesterol would cause cholesterol. After all, if I eat chocolate, it doesn’t cause chocolate to appear in my bloodstream, yet alcohol is detectable in blood. I’ve already dug into this quite a bit and I know that saturated fats and partially hydrogenated vegetable oils cause the body to produce cholesterol in the bloodstream. So is there any evidence that eating food that has cholesterol in it will give you high cholesterol, or does it all come out the other end? I wonder if people are just playing it safe because no one has given a solid answer.
As you noted, eating fat causes synthesis of cholesterol, not eating cholesterol. So products that advertise “cholesterol free” are meaningless if they contain fats, esp. saturated fats. However, we need some cholesterol for many body needs and your liver synthesizes cholesterol. Moreover, HDL cholesterol is good and the higher this number the healthier your arteries are. Alcohol increases HDL. Saturated fat increases LDL. Unsaturated fat increases HDL. Omega-3 fatty acids is a type of unsaturated fat. They are found primarily in fatty fish and underwater plants.
Dietary cholesterol per se has only a minor effect on blood levels of cholesterol. Conversely, high dietary intake of saturated (and to some extent, trans) fatty acids has a much more significant effect to raise blood cholesterol (LDL).
Why does dietary cholesterol play only a small role in affecting blood levels of cholesterol (LDL)? At least two reasons:
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Most (LDL) cholesterol in the blood arises from your body’s production of it, not absorption of it. The usual figure is that around 75% comes from your body’s production (and even more in genetically predisposed people).
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Much dietary cholesterol is not even absorbed from your digestive tract in the first place.
One real world consideration, though. Often, foods high in cholesterol are high in saturated fats too. So, even though the cholesterol they contain is relatively harmless, their saturated fat is not.
Another interesting point has nothing to do with the amount of cholesterol or saturated fats in the diet. Rather, it may be the case that how the food is prepared is also important. For example, if the food is fried, there may be a chemical change in the dietary fats (oxidation) that promotes atherosclerosis. Eating the same foods, but after boling not frying, may be more benign.
For a bit more information on fatty acids check out this thread.
Well, my biochemistry text devotes 12 pages to the subject.
Here’s the lowdown:
Cholesterol is made from acetyl-CoA in four stages. Acetyl-CoA is actually an intermediate in the conversion of glucose–>energy + water + carbon dioxide. It is the input into the Kreb’s cycle, which is the sourse of most of the ATP [energy] produced during aerobic metabolism.
In stage 1, the 3 acetate unites condence to form a 6-carbon intermediate, mebalonate. Stage 2 involves the conversion of mevalonate into activated isoprene units. Stage 3 is the polymerization of 5 5-carbon isoprene units to form the 30-carbon linear structure of squalene. In stage four, the cyclization of the squalene forms the four rings of the steroid nucleus. A further series of changes (oxidations, removal or migration of methyl groups) leads to the final product, cholesterol.
You can look up the chemical structures of some of the compounds mentioned at www.chemfinder.com.
Cholesterol, like anything, is good in small doses. It’s the precursor to all of the steroids, including testosterone and estrogen. It is found in bile salts, where it is used to aid fat digestion. All growing animal tissues (it is not found in plants–they synthesize a different sterol) need cholesterol for membrane synthesis. It helps mainain the fluidity of the membrane, especially at low temperatures (if I remember freshman bio correctly).
Obviously, if you consume a lot of cholesterol, your body would rather use that than synthesize it’s own.
Also, when digesting food, fats move from the intestines into the liver via the lymphatic system. When the diet contains more fatty acids than are needed immediately (as fuel) they are converted into triacylglycerols and packaged as very-low-density lipoproteins (VLDL’s). Excess carbs can also be converted to VLDL’s.
Loss of triacylglycerols converts some VLDL’s to VLDL remnants (also called intermediate density lipoproteins, IDL’s). Further removal of triacylglycerols results in low-density lipoproteins (LDL’s). These are very rich in cholesterol and cholesterol esters.
High-density lipoproteins (HDL’s) begin in the liver and small intestine and contain relatively little cholesterol and no cholesterol esters. Eventually, HDL can form a core of cholesterol andmove through the bloodstream, dropping it off where needed. Depleted HDL can also pick up cholesterol in tissues and take it to the liver.
Whew, I hope that helps.
**easy e ** When you say “triacyglycerols” do you mean “triglycerides,” and if not what is the relation between them? Apparently they are not the same, but from the name there must be a close relation.
just sayin’ that a figure I got from my doc was that of the serum cholesterol (i.e. the stuff floating around in our blood) only about 5% is from dietary intake.
You will also manufacture cholesterol when from carbs as carbs are stored as fat with some exception. A low carb diet (high fat/protien) will in general lower cholesterol once your body gets accustomed to it (Initally it might raise, sometimes a lot) and raise the good to bad ratio.
This is from my experence with a low carb diet and many low carb listserves.
The terms can be used interchangeably, but triacylglycerols is the more proper form, nowadays at least.