To put this summary post and, more importantly, this 10-part series in perspective, let's examine one of the most pervasive pieces of dietary advice given to people worldwide:
u201CEating foods that contain any cholesterol above 0 mg is unhealthy.u201D
- T. Colin Campbell, PhD, author of The China Study.
No summary of this length can begin to fully address a topic as comprehensive as cholesterol metabolism and the pathogenesis of atherosclerosis. In fact, those of us who challenge conventional wisdom often find ourselves needing to do exactly what Frederic Bastiat suggested:
u201CWe must admit that our opponents in this argument have a marked advantage over us. They need only a few words to set forth a half-truth; whereas, in order to show that it is a half-truth, we have to resort to long and arid dissertations.u201D
So, at the risk of trying to minimize the u201Clong and aridu201D part of this process, below are the 10 things you need to know to be the judge — for yourself — if the conventional advice about cholesterol is correct.
1. The sine qua non of atherosclerosis is the presence of a sterol in an artery wall. How it gets there is the only thing we should be worrying about.
Contrary to popular belief, atherosclerosis is not caused by many of things we think of, such as smoking, high blood pressure, diabetes, high LDL (the so-called u201Cbadu201D cholesterol), or low HDL (the so-called u201Cgoodu201D cholesterol). Some of these are certainly markers of risk — low HDL, for example — while others accelerate the process — smoking, for example — but none of these are the direct cause of atherosclerosis.
The sine qua non of atherosclerosis is the presence of sterols (cholesterol or phytosterol) in arterial wall macrophages. Sterols are delivered to the arterial wall by the penetration of the endothelium by an apoB-containing lipoprotein, which transport the sterols. In other words, unless an apoB-containing lipoprotein particle violates the border created by an endothelium cell and the layer it protects, the media layer, there is no way atherogenesis occurs. If this is a bit confusing, don't worry. It's all made clear below.
2. Cholesterol is vital for life; no cholesterol = no life.
Cholesterol is a 27-carbon molecule shown in the figure below. Each line in this figure represents a bond between two carbon atoms. That's it. Mystery over.
All this talk about u201Ccholesterolu201D and most people don't actually know what it is. So, there you have it. Cholesterol is u201Cjustu201D another organic molecule in our body.
I need to make one distinction that will be very important later. Cholesterol, a steroid alcohol, can be u201Cfreeu201D or u201Cunesterifiedu201D (u201CUCu201D as we say, which stands for unesterified cholesterol) which is its active form, or it can exist in its u201Cesterifiedu201D or storage form which we call a cholesterol ester (u201CCEu201D). The diagram below shows a free (i.e., UC) molecule of cholesterol. An esterified variant (i.e., CE) would have an u201Cattachmentu201D where the arrow is pointing to the hydroxyl group on carbon #3, aptly named the u201Cesterification site.u201D
One of the biggest misconceptions is that cholesterol is u201Cbad.u201D This could not be further from the truth. Cholesterol is very good! In fact, there are (fortunately rare) genetic disorders in which people cannot properly synthesize cholesterol. One such disease is Smith-Lemli-Opitz syndrome (also called u201CSLOS,u201D or 7-dehydrocholesterol reductase deficiency) which is a metabolic and congenital disorder leading to a number of problems including autism, mental retardation, lack of muscle, and many others.
Cholesterol is absolutely vital for our existence. Every cell in our body is surrounded by a membrane. These membranes are largely responsible for fluidity and permeability, which essentially control how a cell moves, how it interacts with other cells, and how it transports u201Cimportantu201D things in and out. Cholesterol is one of the main building blocks used to make cell membranes (in particular, the ever-important u201Clipid bilayeru201D of the cell membrane).
Beyond cholesterol's role in allowing cells to even exist, it also serves an important role in the synthesis of vitamins and steroid hormones, including sex hormones and bile acids. Make sure you take a look at the picture of steroid hormones synthesis and compare it to that of cholesterol (above). If this comparison doesn’t convince you of the vital importance of cholesterol, nothing I say will.
One of the unfortunate results of the eternal need to simplify everything is that we (i.e., the medical establishment) have done the public a disservice by failing to communicate that there is no such thing as u201Cbadu201D cholesterol or u201Cgoodu201D cholesterol. All cholesterol is imperative for life to exist!
The only u201Cbadu201D outcome is when cholesterol ends up inside of the wall of an artery, most famously the inside of a coronary artery or a carotid artery, AND leads to an inflammatory cascade which results in the obstruction of that artery (make sure you check out the pictures in the links above). When one measures cholesterol in the blood we really do not know the final destination of those cholesterol molecules!
3. The cholesterol we eat has little to do with the cholesterol we measure in our bloodstream.
We ingest (i.e., take in) cholesterol in many of the foods we eat and our body produces (u201Csynthesizesu201D) cholesterol de novo from various precursors. About 25% of our daily u201Cintakeu201D of cholesterol — roughly 300 to 500 mg — comes from what we eat (called exogenous cholesterol), and the remaining 75% of our u201Cintakeu201D of cholesterol — roughly 800 to 1,200 mg — is made by our body (called endogenous production). To put these amounts in context, consider that total body stores of cholesterol are about 30 to 40 gm (i.e., 30,000 to 40,000 mg) and most of this resides within our cell membranes. Nearly every cell in the body can produce cholesterol, and thus very few cells actually require a delivery of cholesterol. Cholesterol is required by all cell membranes and to produce steroid hormones and bile acids.
Of this u201Cmadeu201D or u201Csynthesizedu201D cholesterol, our liver synthesizes about 20% of it and the remaining 80% is synthesized by other cells in our bodies. The synthesis of cholesterol is a complex four-step process (with 37 individual steps) that I will not cover here, but I want to point out how tightly regulated this process is, with multiple feedback loops. In other words, the body works very hard (and very u201Csmartu201D) to ensure cellular cholesterol levels are within a pretty narrow band (the overall process is called cholesterol homeostasis). Excess cellular cholesterol will crystalize and cause cellular apoptosis (programmed cell death). Plasma cholesterol levels (which is what clinicians measure with standard cholesterol tests) often have little to do with cellular cholesterol, especially artery cholesterol, which is what we really care about. For example, when cholesterol intake is decreased, the body will synthesize more cholesterol and/or absorb (i.e., recycle) more cholesterol from our gut. The way our body absorbs and regulates cholesterol is really amazing, so I want to spend a bit of time discussing it.