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, 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.
“[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.”
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. 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). 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.”
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.”
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."
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 -
"The 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.
"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.
These various examples of fatty liver reversal diets seem to indicate the synergy of sugars, carbohydrates, and polyunsaturated fat in the NAFLD dietary model.
 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.
 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
 Iritani N, Ikeda Y. J Nutr. Activation of catalase and other enzymes by corn oil intake. 1982 Dec;112(12):2235-9.
 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.
 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.