Lipoproteins & apolipoproteins: E, by 'eck.

In December 2008, I wrote about Cholesterol And Coronary Heart Disease , where I used a limousine metaphor to describe how cholesterol & fat are transported around the body. Here's a diagram of a chylomicron lipoprotein "limousine". Chylomicrons transport dietary fat (triglycerides) & cholesterol from the gut to the liver & other tissues. As there's much more dietary fat than cholesterol, the contents are mostly fat.

A chylomicron. T=Triglyceride C=Cholesterol. From http://en.wikipedia.org/wiki/Lipoprotein

The lipoprotein "limousines" vary a lot in size.

(a) VLDL (b) chylomicrons (c) LDL (d) HDL. 
From http://healthcorrelator.blogspot.co.uk/2011/11/triglycerides-vldl-and-industrial.html

Apolipoproteins are the "chauffeurs" which determine to where lipoproteins transport stuff.
Apo A is found mainly on HDL, which transports fat & cholesterol from tissues to the liver.
Apo B is found mainly on LDL, which transports cholesterol from the liver to tissues.
Apo C is found on HDL when fasted, but moves to chylomicrons & VLDL when fat is eaten.
Apo D is found mainly on HDL and is is associated with an enzyme involved in lipoprotein metabolism.
Apo E is found mainly on chylomicrons & IDL and transports lipoproteins, fat-soluble vitamins, and cholesterol into the lymph system and into the blood. In the CNS, Apo E transports cholesterol to neurons. Defects in Apo E result in hyperlipidaemia , cardiovascular & neurological diseases, and is the E referred to in the title.

There's also Apo H, which is a β-glycoprotein involved in the binding of cardiolipin. It has nothing to do with the above lipoproteins.

False dichotomies: serum cholesterol level vs all-cause mortality. Cause or effect?

Here are some plots from the MRFIT study.

From http://sph.bu.edu/otlt/MPH-Modules/PH/PH709_Heart/PH709_Heart5.html

Although the relative risk (RR) for coronary heart disease (CHD) and cardiovascular disease (CVD) mortalities increase with serum total cholesterol (TC) level, all-cause mortality follows a U-curve.

According to Low Serum Cholesterol and Mortality: Which Is the Cause and Which Is the Effect?, certain illnesses that increase mortality lower TC levels. This is the Iribarren hypothesis.

According to Cholesterol and all-cause mortality in elderly people from the Honolulu Heart Program: a cohort study, TC that's low and is still low 20 years later results in a 64% increase in the RR for mortality relative to TC that's intermediate and is still intermediate 20 years later.

Table 4 Relative risk for mortality based on change in cholesterol between examinations three and four

Is low TC level the cause of, or the effect of fatal illnesses? I think that it's both. Cholesterol is an important substance, as a severe lack of it is bad news, as per Smith–Lemli–Opitz syndrome. If certain illnesses result in a depletion of cholesterol and cholesterol synthesis is too low, there's insufficient cholesterol to allow recovery.

Interestingly, TC that's low but is intermediate 20 years later results in a 30% increase in the RR for mortality, whereas TC that's low but is high 20 years later results in a 5% increase in the RR for mortality.

P.S. There's a false dichotomy for vitamin D level vs illness. Ditto for carbohydrates vs calories.

Obesity is multi-factorial, spectra and other stuff.

This post is a hotch-potch of thoughts that are currently whizzing around in my brain.

1) Obesity: Like just about everything in life, obesity is multi-factorial. Each factor may have only a small impact on obesity. Tackling one factor alone won't solve the problem. Every factor has to be tackled, one at a time.

So, New York City Mayor Michael Bloomberg announcing a ban on sales of sugary drinks larger than 16 ounces in restaurants, delis, sports arenas, and movie theaters won't solve the obesity problem, but it will help.

EDIT: In shops and supermarkets in the UK, tobacco products now have to be kept out of sight. I'd like to see the same thing happen to Crap-In-A-Bag/Box/Bottle (CIAB).

2) Spectra: As also mentioned in my first link, there is a spectrum of fatness in the general population which probably follows a bell distribution curve. From skinniest to fattest, there are people who are:-
Extremely skinny. Very skinny. Skinny. A bit skinny. Average. A bit fat. Fat. Very fat. Extremely fat.

If you take somebody in a category who isn't currently consuming CIAB and introduce CIAB to their diet, what happens? They move to a category to the right. Therefore, it's possible for there to be very skinny people who consume CIAB. Therefore, anybody who (or should that be Wooo?) states that the existence of very skinny people who consume CIAB is proof that Food Reward doesn't exist is wrong.

3) Other stuff: I am concerned with people overlooking postprandial (a.k.a. nonfasting) triglycerides (a.k.a. triacylglycerols a.k.a. TAGs a.k.a. TGs) after eating large amounts of fat. According to Fasting Compared With Nonfasting Triglycerides and Risk of Cardiovascular Events in Women, serum TGs 2-4 hours post-meal are very significantly associated with Cardiovascular Events (fully adjusted hazard ratio [95% confidence interval] for highest vs lowest tertiles of levels, 4.48 [1.98-10.15] [P < 0.001 for trend]).

After 4 hours post-meal, serum TGs are cleared from circulation by being burned by muscles and/or by being stored in fat cells. See Figure 3B in Extended effects of evening meal carbohydrate-to-fat ratio on fasting and postprandial substrate metabolism.