Spartan Race

Saturday, November 28, 2009

Can what you put on your toast drop your LDL?

It a word, yes. Many of you may have noticed that there are a number of what are described as heart-healthy spreads on the market. Most of these contain monounsaturated fat, which is not particularly heart healthy, or omega-3 fatty acids (most of which are Alpha Linoleic Acid, which may be heart healthy, but the jury is still out on- see the previous discussion on fish oil). If you really look, a few claim to actually lower cholesterol. Most of these contain either plant sterols or stanols, which turn out to be reasonably cool little chemicals.
Plants synthesize a number of very cholesterol like molecules that we usually refer to as plant sterols as a group, though the do have individual names (the poster boy is a compound called sitosterol, more on that later). When we eat these, they actually are absorbed into the cells that line the intestine by the same protein that helps us to absorb animal based cholesterols - a transporter with the fancy name of the Niemann-Pick C1 like 1 receptor (which is actually where the drug Zetia works). When cholesterol is absorbed into these cells, it gets packed into dense balls of fat called chylomicrons, which then ultimately find their way into your blood stream, and the cholesterol subsequently finds its way into the walls of your blood vessels causing atherosclerosis - this is bad.
In most people, however, if one little molecule of a plant sterol finds its way into that ball of fat, your body kicks it and all the animal based cholesterol stuck in the fat globule back out into your intestine where it simply goes the way of all the other waste products that find there way into the intestine. The fancy name for the molecules that do this is are sterolin 1 and sterolin 2, which are almost always mentioned in conjuction with the genes that code for them ABCG5/ABCG8. In other words, for almost everybody, eating plant sterols keeps you from absorbing cholesterol. If it isn't in your blood stream, it isn't in your artery walls, which is what we are aiming for.
At this point you may have noticed that I keep throwing in qualifiers (almost everybody, most people, etc). That's because some very rare individuals have a condition called sitosterolemia (it also goes by a new name phytosterolemia). These individuals lack the mechanism (due to gene mutations in ABCG5and ABCG8) for kicking the the plant sterols out, meaning that they make it in to the body and wreak havoc on blood vessel walls causing heart disease, heart attacks, etc.
So this brings us to the plant stanols I mentioned earlier. There does not seem to be a disease equivalent to sitosterolemia for plant stanols, so the butter substitutes made with stanols rather than sterols should be safe and effective for everybody. Again, the plant sterol based products are really good for the vast, vast majority of people, but not quite everybody, and unfortunately, there's no quick, easy way to tell if someone has phytosterolemia. The stanols keep your body from absorbing cholesterol the same way the sterols do, but at least theoretically work for everybody.
One other thing I get asked a lot is if you have to eat a lot of cholesterol for sterols and stanols to work. The answer to this is unequivocally no. Most of the cholesterol ( a good 80 percent in most people) circulating in our gut is not from what we eat at all, but actually excreted by our liver and then reabsorbed by the body further down in the intestine (a process called entero-hepatic circulation). Whether you are getting rid of the cholesterol that you just ate or cholesterol that was once in your blood makes little difference, it will all make you LDL come down.

No comments:

Post a Comment