Because it seemed to beg the important question of linoleate intake, while addressing both fructose intake and insulin resistance, I took the (for me) relatively unusual step of contacting the corresponding author. I never received a response, but because my email summarised my view of the role of linoleate in chronic Hepatitis C infection (CHC) I have decided to reproduce it here.
Dear Dr Petta,
I am an independent Hepatitis C researcher looking at the relationship between HCV and diet, and I was interested by this paper which you authored.
Low cholesterol (OR 0.988, 95%CI 0.975–0.999,P = 0.04) was independently linked to severe fibrosis, and high LDL was the only independent positive predictors of both RVR and SVR (OR 1.036; 95%CI 1.017–1.055; P < 0.001; and OR 1.016; 95%CI 1.001–1.031; P = 0.04 respectively).
Although these do not seem very large OR differentials (as presented in this example), the finding is often replicated (the ORs will vary depending how "high" and "low" LDL are defined).
Your paper cites one possible mechanism "These aspects have been related, on one hand, to a competition for LDL receptor sites which prevents viral entry into hepatocytes and thus to an increased exposure of HCV to the host serum immune response".
It seems to me that LDL-R numbers, given their role in HCV life cycle, are something that it would be worthwhile for people with CHC to mimimize, and that this is easily possible through diet.
I notice the correlation between fibrosis and fructose consumption, but I feel that if one looked for a correlation between linoleic acid intake and HCV pathology, this would be stronger. I am aware of one study where high polyunsaturated fat intake correlated with steatosis (OR 2.7), while saturated fat was neutral and MUFA was protective. This study did not distinguish between linoleate and other PUFA (ALA, EPA, DHA and arachidonic acid). I believe that if this distinction had been made, linoleate would have shown an even stronger correlation with pathology.
There are a number of reasons why this should be the case.
Secondly, steatosis-promoting effect of linoleate. The animal model of NAFLD uses high-linoleate diets and fails to produce steatosis when fats such as butter or coconut oil are fed. NAFLD has become a much more common disease since high-linoleate oils have replaced tallow in deep frying, and linoleate-based spreads have replaced butter.http://www.ncbi.nlm.nih.gov/
Thirdly, the heating of polyunsaturated oils produces peroxides which directly promote liver inflammation.http://journal-of-hepatology.
Fourthly, in animal models alcoholic liver disease can only be produced when high-PUFA oils or fats are added to the diet, and it is prevented when beef fat, coconut oil etc are fed concurrently with alcohol.http://download.journals.
Fifthly, linoleate increases both hepatic uptake of cholesterol and its synthesis, and high intakes result in elevations of hepatic free cholesterol and non-esterified fatty acids.
Because EPA, DHA and arachidonic acid all suppress HCV replication and can substitute for dietary linoleic acid in much smaller amounts, it is relatively easy to compose a nutritious diet which is low in linoleate. Many diets today are deliberately designed to minimize this problematic, and currently over-supplied, nutrient, especially diets of the "Paleo" type, such as the "Perfect Health Diet". These diets, which also minimize fructose and high-GI carbohydrates, are often higher in dietary cholesterol than might be considered optimal for someone with CHC, but this could easily be adjusted (or one could supplement with taurine).
My own health has improved since I stopped using rice bran oil and other cooking and salad oils and started cooking with dripping (tallow) and adding butter and olive oil as a seasoning.(*)
Huia New Zealand
(* one way in which my health improved after this switch was instructive; being on drugs at the time, I often used to burn myself on the stove, with blisters an inevitable consequence. After increasing saturation of dietary fats, any encounters with hot elements now result instead in patches of dead skin, which quickly clear, and not the classic deep blister.)
Since then, another link between linoleic acid and CHC has turned up; the role of cannabinoid receptors, the natural ligand for which is anandamide (an endogenous cannabinoid derived from omega 6 fatty acids).
The endocannabinoid system (ECS) includes cannabinoid (CB1 and CB2) receptors and their endogenous ligands (i.e., the endocannabinoids anandamide and 2-arachydonylglycerol) as well as proteins involved in endocannabinoids biosynthesis and degradation (1). The ECS is present in the liver and undergoes adaptive changes in response to noxious stimuli. Endocannabinoids as well as CB1 and CB2 receptors (which are, respectively, either faintly or not expressed in normal livers) are up-regulated in experimental liver injury and liver cirrhosis of various etiologies. In vivo, CB1 receptor activation promotes fat accumulation, triggers inflammation in nonalcoholic and alcoholic fatty liver diseases, contributes to the progression of chronic hepatitis to cirrhosis by stimulating fibrogenesis, and is also implicated in hemodynamic and neurological consequences associated with liver cirrhosis, including portal hypertension, encephalopathy, and cardiomyopathy (2–4). Conversely, activation of CB2receptors exerts antifibrogenic and antiinflammatory effects in experimental models of liver disease (5). These pharmacological effects make CB2 agonists and CB1 antagonists promising candidates for the treatment of fibrosis in chronic liver pathologies. By disclosing a prominent CB1-mediated role of anandamide in the early phase of liver regeneration, Mukhopadhyay et al. (6) provide additional and significant support to the prominent role of the ECS in liver biology in an article in PNAS.
Cannabinoids present in Cannabis sativa (marijuana) exert biological effects via cannabinoid receptors CB1 and CB2. We recently demonstrated that CB1 and CB2 receptors regulate progression of experimental liver fibrosis. We therefore investigated the impact of cannabis smoking on fibrosis progression rate in patients with chronic hepatitis C (CHC). Two hundred seventy consecutive untreated patients with CHC of known duration undergoing liver biopsy were studied. Demographic, epidemiological, metabolic, and virological data were recorded, and detailed histories of cannabis, alcohol, and tobacco use over the span of hepatitis C virus infection were obtained. Fibrosis stage, steatosis, and activity grades were scored according to Metavir system. Patients were categorized as noncannabis users (52.2%), occasional users (14.8%), or daily users (33.0%), and the relationship between cannabis use and fibrosis progression rate (FPR) or fibrosis stage was assessed. On multivariate analysis, six factors were independently related to a FPR greater than 0.074 (median value of the cohort): daily cannabis use (OR = 3.4 [1.5-7.4]), Metavir activity grade A2 or higher (OR = 5.4 [2.9-10.3]), age at contamination of more than 40 years (OR = 10.5 [3.0-37.1]), genotype 3 (OR = 3.4 [1.5-7.7]), excessive alcohol intake (OR = 2.2 [1.1-4.5]), and steatosis (OR = 2.0 [1.0-4.1]). Daily cannabis use was also an independent predictor of a rapid FPR (>0.15) (OR = 3.6 [1.5-7.5]). Finally, severe fibrosis (≥F3) was also predicted by daily cannabis use (OR = 2.5 [1.1-5.6]; P = .034), independently of Metavir activity grade, excessive alcohol intake, age at liver biopsy, steatosis, and tobacco smoking. , daily cannabis smoking is significantly associated with fibrosis progression during CHC. Patients with ongoing CHC should be advised to refrain from regular cannabis use. (H 2005;.)
Though some studies disagree:Conclusions In this prospective analysis we found no evidence for an association between marijuana smoking and significant liver fibrosis progression in HIV/HCV coinfection. A slight increase in the hazard of cirrhosis and ESLD with higher intensity of marijuana smoking was attenuated after lagging marijuana exposure, suggesting that reverse causation due to self-medication could explain previous results.
Naturally occuring delta-9 THC is a weak agonist ligand of the cannabinoid receptors, thus can exert both agonist and antagonist effects depending on what other ligands are present. This is why it is non-toxic compared to most synthetic cannabinoids, which are designed as strong agonist ligands.
To cut a long story short, Dietary Linoleic Acid Elevates Endogenous 2-AG and Anandamide and Induces Obesity. Or, if one has chronic Hep C, steatosis. As in this paper (the one I mentioned above in the email, with the 2.7 OR between high polyunsaturated fat intake and steatosis - the methodology leaves a lot to be desired, but the the differential between the correlations of the 3 different fat types impresses me).
BTW, CB1 receptor is only strongly expressed, or expressed at all, in injured liver. So it's very unlikely that cannabis causes problems in people without a pre-existing liver condition like Hep C. Synthetic cannabinoids can however cause kidney failure. Which is probably a worse outcome than a little scarring of the liver.
Nothing demonstrates the lack of legitimacy behind cannabis prohibition as much as the trade in synthetic cannabinoids. But then, consider where sugar sweetened beverages (sodas) came from originally; as "soft drinks", SSBs were developed by temperance advocates as an alternative to hard liquor. The law of unintended consequences is a bitch.
For additional information about linoleic acid's cancer and obesity-promoting effects, this post is a good place to start, and this one has some interesting further data. In fact, there are papers relating to linoleic acid and liver health scattered throughout this blog and I find the search engine pretty useful for recovering them.