Fructose, Glucose and Cholesterol

This paper came my way via Eddie Vos, through a discussion in the THINCS group.

OK, what's going on in the paper? It's the metabolic ward study to end all metabolic ward studies. Routine criminals who volunteered to live in a "food proof" prison and to eat a diet based on pure chemicals. This is a prison within a prison:

"The described study was conducted in an especially isolated wing of the California Medical Facility (CMF), a state institution for adult male felons. The isolated area included large indoor recreation, lounge, and shower areas, and 24 individual cells, and was so located as to prevent completely the passage of any food through or near the area."

And what yummy food did the inmates receive?

"These diets were unique in that a) their essential and nonessential nitrogen source was provided exclusively in the form of optically pure L-amino acids and b) they were administered as single, crystal clear aqueous solutions that were nutritionally complete in themselves. In essence, the diets were composed of balanced (but varying) proportions of L-amino acids, the required water-soluble and fat soluble vitamins, the pertinent mineral salts, glucose or other simple sugars as the source of carbohydrate, and ethyl linoleate as the source of essential fat."

Apparently the various versions of the diet all tasted disgusting, for want of a better word.

Apart from the interest of human experiments along these lines, there were a few other tweaks they applied. First we have to note that these diets were essentially ultra low fat diets, the same family as the diets used by McDougal and co. There is not a grain of white rice which does not end up as blood glucose. If you eat brown rice there is a split between the fibre and the minerals it is depriving you of (you know where they get flushed) and the starch, which ends up as blood glucose. So these are seriously low fat, high carbohydrate diets.

What happens when you feed an elemental diet based on glucose alone as its calorie source? Blood cholesterol drops, from a normal value found in a non statinated male of 227mg/dl (while eating 1970s style prison food), to a cardiologic near Nirvana of 160mg/dl. Replacing 25% of the glucose with sucrose produces a rise in cholesterol to 208mg/dl. Removing the sucrose and going back to pure glucose drops the cholesterol level back down to 151mg/dl.

Is that good or bad? You need to remember the old adage that the best cholesterol level is one that has not been measured. But what is happening probably goes back to that short section of the ApoB100 protein which glycates particularly easily, discussed here. I think it is worth pointing out again that fructose should never penetrate in to the systemic circulation, so its whole body damage should be indirect. It probably does this through the induction of hepatic insulin resistance. Fructose has to be metabolised immediately and the end result is raised intracellular hepatic triglycerides. We've seen before that a decent supply of intra cellular lipid makes a cell say no to glucose and that it does this by exhibiting insulin resistance. The liver normally stores glucose in response to insulin. Rendering it insulin resistant would logically stop it storing glucose and pour the stuff out in to the systemic circulation...

That's the basis of this post and it needs bearing in mind when we look at cholesterol variation and heart disease with a given population. But there's an aside first that really creased me up...

A quick pubmed looking for a reference to fructose and insulin resistance (there are hundreds) produced this gem, hot out of cyberpublishing a few days ago.

The group used an antisense oligonucleotide, which is a short section of DNA, RNA or a similar synthetic drug which specifically blocks the activity of a corresponding section of messenger RNA, which means the the relevant gene no longer gets successfully transcribed. By doing this they turned off lipid synthesis in the liver in response to fructose. No hepatic insulin resistance despite fructose intake: Wow!!!!!!!!!! Take this drug and you too can drink Pepsi Max without turning your liver in to foie gras. What else does it do? Oh, it lowers insulin resistance, whole body! Superb, give me some.

Oh oh, it's your butt which soaks up the plasma glucose... As they say of their own technique, it resulted in:

"increased insulin-stimulated whole-body glucose disposal due to a threefold increase in glucose uptake in white adipose tissue"

Translation: "our wonder drug makes you fat".

It is also described as a potential "treatment of NAFLD, hypertriglyceridemia, and insulin resistance associated with increased de novo lipogenesis", I would add "by making you fat". I'd also add that this de novo lipogenesis can easily be avoided by avoiding the fructose in the first place.

What is not remotely obvious from the abstract is: Where does the fructose go to, if it's not used to converted your liver to foie gras?

I guess it's either going to glycosylate your liver (sounds great for longevity) or spill in to your systemic circulation, where it can glycosylate whatever it come in to contact with.... Or it might just overload each liver cell with more pyruvate than it knows what to do with. Now there's grist for the mill of unintended consequences!

Back to the real world:

A fructose intake of 12% of your calories makes your metabolism unhappy enough that it has evolved a technique to increase cholesterol levels under these rather rare (until recent times) conditions. It probably has knock on effects through hepatic insulin resistance resulting in hyperglycaemia and all of the damage that this leads to.

While some fructose is perfectly OK (I too eat home grown fruit in season and a certain amount of sucrose) I suspect a large amount is not OK.

Under highly defined conditions, fructose raises your total cholesterol level.

Peter

EDIT: Sue has pointed out, off blog, that the other reason for a fall in cholesterol is due to minimal production of triglycerides. If glucose is being consumed within the ability of the liver to store it as glycogen there is no reason to convert it to fat and so there is no fat to export as triglycerides. Fructose immediately converts to fat and any fat produced in excess of the needs of the liver will be shipped out as LDL precursor particles, raising both LDL and TC.

Both mechanisms are fructose related but not fructose specific. The average trigs were 93mg/dl but the study did not split anything other than TC by the sucrose/fructose periods early in 19 weeks of the initial part of the diet. The volunteers remained pretty well weight stable throughout, as far as I can see.

So you have a choice of two mechanisms, there may be more, but the association still seems to hold that TC is a marker of fructose intake, with a number of confounders once you get off of chemical diets. BTW the TC went back to a normal >200mg/dl on return to normal food. Or uless you have a TC like mine (and a few other folks), which is a law unto itself.