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Thursday, 24 March 2016

The Smoking Gun - the Role of PUFA in Non-Alcoholic Liver Disease

The smoking gun

Public health experts are gradually accepting the idea that sucrose and fructose are, like alcohol, causes of fatty liver disease (non-alcoholic liver disease - NAFLD - and its inflammatory development, non-alcoholic steatohepatitis - NASH).
After all, sugar is unnecessary and, like alcohol, the rogue macronutrient, associated with pleasure rather than nutrition. There’s little or no evidence that there is ever likely to be a health benefit from replacing starch or fat with sugar.
Sugar was first equated with alcohol in a liver disease model by CH Best, co-discoverer of insulin, in 1949,[1] a fact which has a nice aptness to it, because NAFLD is often the first stage that leads to type 2 diabetes and, if you’re not very careful about the quality of food and the calories and carbs, insulin-dependence.

On the other hand, there is little mainstream acceptance of the idea that polyunsaturated fat plays a role in these diseases, with the honorable exception of Canada’s recent obesity report; yet the scientific evidence that dietary fats of 5% or more PUFA are essential for the development of alcoholic liver disease (ALD) is very strong. (See here and here)

Polyunsaturated fat is the Golden Boy of public health – seed oils have saved the world from heart disease, supposedly, so the public presentation of evidence that they promote other diseases has always faced an uphill battle.

For a start, PUFA is a small part of the diet and isn’t measured with great accuracy in epidemiological studies. Its harms are interactive with two other nutrients – sugars and alcohol – the excess consumption of which may not be reported as accurately or honestly as intake of other foods.

Anyway, this new study tells us that the genes that encode proteins (enzymes) needed for the metabolism and detoxification of alcohol are upregulated in NAFLD. I can’t get full-text for this, but the abstract is informative.
“Alcohol-metabolizing enzymes including ADH, ALDH, CYP2E1, and CAT were up-regulated in NAFLD livers. The expression level of alcohol-metabolizing genes in severe NAFLD was similar to that in AH.”

“[I]ncreased expression of alcohol-metabolizing genes in NAFLD livers supports a role for endogenous alcohol metabolism in NAFLD pathology and provides further support for gut microbiome therapy in NAFLD management.”[2]

Well yes, there is definitely a role for probiotics and prebiotics (which now include long-chain saturated fats) in NAFLD and ALD management. But the idea that NAFLD is caused by endogenous alcohol production in all but a few cases seems preposterous to me. Alcoholic liver disease is associated with drunkenness, alcoholism, and thiamine depletion. Are these seen in patients with NAFLD?
However, was alcohol involved, there would be the same disease-promoting role for PUFA seen in ALD.

Why else would alcohol-metabolising enzymes be upregulated? We didn’t evolve drinking alcohol, so why did this enzyme system come to exist?
It exists originally for the metabolism of polyunsaturated fats into eicosanoids, that is to say, into inflammatory molecular messengers, and for the removal of oxidised PUFAs.

For example, if you feed oxidized linoleic acid to rats, their expression of aldehyde dehydrogenase (ALDH) increases.[3] The alcohol dehydrogenase (ADH) enzyme in leeks breaks down essential fatty acids into aromatic metabolites (sure, a leek isn’t a human, but it shows that ADH enzymes act on PUFAs in the absence of alcohol, which is what we want to know). [4]And if you feed PUFAs to cultured hepatoma (HepG2) cells, which is the cell culture model for liver diseases, you get this:

“After 2 hours of cultivation, the lipid peroxide (LPO) in the DHA group increased 600% compared with control, and was much higher than in the groups treated with the other FAs, with LNA > LA > OA > PA. CYP2E1 induction increased with greater effect as the degree of unsaturation of OA, LA, and DHA increased.”[5]

PA was palmitic acid, and had no effect on PKC activity, the marker of cellular stress in the experiment.

CAT is catalase, a heme enzyme which degrades H202 to water and oxygen, the end of this detox disassembly line.

“The effects of linoleic and intake on catalase and other enzymes were investigated by feeding 0, 1, 5 or 10% corn oil diet to rats previously fed a fat-free diet. Rats fed more than 1% corn oil for 2 weeks showed significant increases of glutathione peroxidase and superoxide dismutase in liver cytosol when compared to the controls fed no corn oil. Peroxisomal catalase activity especially was increased.”[6]
So, with a very cursory search, I found that the 4 enzymes found upregulated in ref. [2] metabolise PUFAs, and are upregulated when they are present in quantity.
No endogenous alcoholism is needed to explain this result.

The next question – how does the presence of excess fructose drive this enzyme system? Alcohol upregulates the enzyme system because it degrades alcohol, and PUFA is then caught up in the activated enzymes; but what role does sugar play?

Edit: this is a good place to include recent human evidence for this theory.

5-Hydroxyicosatetraenoic acid (5-HETE) and 9-Hydroxyoctadecadienoic acid (9-HODE) are eicosanoid metabolites of linoleic acid (omega 6 PUFAs). In this Polish study,

Patients (n=12) with stage I NAFLD had a significantly higher level of HDL cholesterol and a lower level of 5-HETE. Patients (n=12) with grade II steatosis had higher concentrations of 9-HODE. Following the six-month dietary intervention, hepatic steatosis resolved completely in all patients. This resulted in a significant decrease in the concentrations of all eicosanoids (LX4, 16-HETE, 13-HODE, 9-HODE, 15-HETE, 12-HETE, 5-oxoETE, 5-HETE) and key biochemical parameters (BMI, insulin, HOMA-IR, liver enzymes).
Conclusion: A significant reduction in the analyzed eicosanoids and a parallel reduction in fatty liver confirmed the usefulness of HETE and HODE in the assessment of NAFLD."[7]

Steatosis resolved completely after 6 months on a diet in which LA was restricted to 4% of energy and sugar to 10%. Though the diet was low in fat (20-35% of energy) dairy was favoured as a source of fat -
type of fat included in the diet was easy to digest, such as cream, butter, oil or milk...The total omega-3 and omega-6 fatty acids consumption was approximately 0.5% E for omega-3 and 4% E for omega-6."

In 2004 the average omega 6 content of the Polish diet was 5.21% "
much higher than the recommended upper limit (3% of energy)." (link) As the NAFLD diet was individually calorie-restricted, the total amount of omega-6 would have been close to the total giving the recommended 3% in the normal diet.

We also find reversal of fatty liver disease, associated with obesity and type 2 diabetes, in the recent pilot trial of Unwin et al, where subjects were told to avoid sugar, grains, and other carbohydrate-dense foods.[8]
"In place of carbohydrate-rich foods, an increased intake of green vegetables, whole-fruits, such as blueberries, strawberries, raspberries and the “healthy fats” found in olive oil, butter, eggs, nuts and full-fat plain yoghurt were advocated."
A 50/50 mix of butter and olive oil (for example) gives a fat of around 6% omega 6; nuts and poultry, which are not necessarily foods eaten every day, supply somewhat higher amounts; in the context of a diet around 60-70% fat, these instructions should amount to a high-fat diet that is not excessively high in omega 6; however the effects of carbohydrate restriction on NAFLD are significant even when fat composition is 15% PUFA in a 60% fat, 8% carbohydrate diet, as in the experiment of Browning et al.[9]

These various examples of fatty liver reversal diets seem to indicate the synergy of sugars, carbohydrates, and polyunsaturated fat in the NAFLD dietary model.

[1] C. H. Best, W. Stanley Hartroft, C. C. Lucas, and Jessie H. Ridout. Liver Damage Produced by Feeding Alcohol or Sugar and its Prevention by Choline. Br Med J. 1949 Nov 5; 2(4635): [1001]-1004-1, 1005-1006.

[2] Zhu R, Baker SS, Moylan CA, et al. Systematic transcriptome analysis reveals elevated expression of alcohol-metabolizing genes in NAFLD livers. The Journal of Pathology Volume 238, Issue 4, pages 531–542, March 2016

[3] Hochgraf E, Mokady S, Cogan U. Dietary Oxidized Linoleic Acid Modifies Lipid Composition of Rat Liver Microsomes and Increases Their Fluidity. J. Nutr. 127: 681–686, 1997.

[4] Nielsen GS, Larsen LM, Poll L. Formation of Volatile Compounds in Model Experiments with Crude Leek (Allium ampeloprasum Var. Lancelot) Enzyme Extract and Linoleic Acid or Linolenic Acid. J. Agric. Food Chem. 2004, 52, 2315-2321

[5] Sung M, Kim I. Differential Effects of Dietary Fatty Acids on the Regulation of CYP2E1 and Protein Kinase C in Human Hepatoma HepG2 Cells. J Med Food 7 (2) 2004, 197–203

[6] Iritani N, Ikeda Y. J Nutr. Activation of catalase and other enzymes by corn oil intake. 1982 Dec;112(12):2235-9.

[7] Maciejewska D, Ossowski P, Drozd A, et al. Metabolites of arachidonic acid and linoleic acid in early stages of non-alcoholic fatty liver disease - A pilot study. Prostaglandins Other Lipid Mediat. 2015 Sep;121(Pt B):184-9. 

[8] Unwin DJ, Cuthbertson DJ, Feinman R, Sprung VS (2015) A pilot study to explore the role of a low-carbohydrate intervention to improve GGT levels and HbA1c. Diabesity in Practice 4: 102–8.

Browning JD, Baker JA, Rogers T et al. Short-term weight loss and hepatic triglyceride reduction: evidence of a metabolic advantage with dietary carbohydrate restriction. Am J Clin Nutr. 2011 May; 93(5): 1048–1052.


Michael Frederik said...

Puddleg said...

Thank you!

raphi said...

Nice exposé George.

Generally speaking, olive oil can do no harm in the nutrition world. Given that it's about 10% PUFAs (if i recall correctly), does it stand to reason that people with NAFLD might do best to avoid it in favor of lower PUFA food sources? Or if, for whatever reason, feel like they MUST have PUFAs, that animal omega3s (like cod liver oil) is preferable?

However, olive oil contains oleocanthal, a TRPA1 receptor agonist (like ibuprofen), causing inhibition of the inflammatory cyclooxygenase. So I wonder if that changes the question of PUFA avoidance for NAFLD sufferers...

Puddleg said...

Thanks Raphi,

I think one should always consider that a washout of stored n-6 might be a good way to start an ALD or NAFLD diet, if one's previous diet was particularly high in seed oils, by a short focus on 3% fats (dairy, coconut, cocoa, ruminant). But otherwise olive oil should be fine, especially considering the oleocanthal in the EVOO and probably a lot else besides.

I wouldn't use cod liver oil. All the evidence seems to suggest that DHA and EPA are as bad or worse than n-6 once you get into similar % territory. Doses of 10-15g fish oil are associated with worsening control of blood sugar in diabetes trials, smaller doses (3-5g) aren't. So, I'd just eat some fish occasionally (sardines or a small piece of salmon), and get some ALA from green veges and dairy fat. If someone does want a n-3 supplement, I'd use krill oil, as you'll get much better n-3 uptake into cells for a much lower exposure to PUFA, and it has a better effect on glycemic control and inflammation than FO.

Passthecream said...

Good stuff George. What do you think of the idea that the harm of partially hydrogenated w6 oils ie trans fats is due to their w6 ancestry?

In response to your last comment there the geekier side of me wants to suggest krillitane oil:

Tucker Goodrich said...

You may find these posts helpful. I got into a lot more detail on the mechanism, and found that it's a lot more fundamental than just fatty liver (hence the title!):

"The Cause of Metabolic Syndrome: Excess Omega-6 Fats (Linoleic Acid) in Your Mitochondria"

"How To Prevent Oxidative Damage In Your Mitochondria"

A study which looks at ALDH2 in the brain:

"A Direct Line From Dietary Linoleic Acid To Alzheimer's Disease?"

Unknown said...

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Enrolled participants will be compensated for time and participation.
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