Gene-diet interactions and the risk of colorectal cancer

There's nothing like a bit of cognitive dissonance to get the brain working if you steel yourself against the instinct to invoke protective stupidity. It's much like Marx's internal stresses of capitalism (or communism for that matter), awareness of contradictions may be the birth-pangs of the next state of existence/awareness, or it may just be the subconscious motivation for repression and consequent dysfunction (it's uncanny how Marxist and Freudian terminologies overlap here, but I digress).

When you join the keto cult, first you have to overcome cognitive dissonance just to entertain the idea that eating high fat can do you some good, and try it. God knows that's hard enough, well done everyone. But that's the beta effect (short term results); what about the alpha effects, i.e. longevity and disease resistance? We know risk markers improve, and why do we have risk markers? Because doctors prefer to diagnose diseases from blood tests, and not your stories about what you had for dinner. Your lipids, BP. HbA1c are measured with considerably more accuracy that saturated fat ever was in any FFQ, so if you have to trust epidemiology trust biomarker epidemiology, and get with the lipid triad and LMHR news over at cholesterolcode.com.

And as for saturated fat and cardiovascular disease in epidemiology, read em and weep saturophobes - latest, biggest meta-analysis the other month, very good methodology, and SFA is beginning to look just a little bit protective.[1]

Cancer though - doesn't that have a biodiversity that's harder to predict than a metabolic disease? Well, most of the common cancers, including colorectal cancer, have a very strong, Bradford Hill strong, association with hyperinsulinaemia (and/or the IGF1/IGFBP3 axis), and we've taken care of that. But still - you read papers where processed meat (way too heterogenous a set of stuff to combine as if it were homogenous, but nutrition epidemiology is what it is, a very blurry snapshot that you need to squint at hard to see anything at all really) is mildly associated with CRC but unprocessed meat isn't, or vice versa, or only in one sex, or in the other, etc etc etc and wonder if there still could be anything in it.
If nothing else, it's good for refuting accusations of orthorexia,

One tool I've found recently that seems to let you look a bit more closely at the murk is the epidemiology of gene-diet interactions. It still doesn't tell you if residual confounding is at play, but it does let you see the spread of association in a population and can help to validate plausible mechanisms, another Bradford Hill criteria. One thing that impresses me is that it's rather full of null results. Dietary patterns are baloney, so they have no interaction with any genes associated with BMI in this Chinese-Singaporean population, (study pulled at random, fairly typical so far of this sort of question). Interestingly there's an interaction with cholesterol, which seems like the opposite of what's happened in the West, maybe just the diets of the wealthy in Singapore, but there it is.[2]

So anyway, to the subject in hand - I looked up gene-diet interactions for CRC and it turns out processed meat (I know, I know) is the only one in this large pooled case-control study.
Genome-Wide Diet-Gene Interaction Analyses for Risk of Colorectal Cancer.[3]

 Our results provide strong evidence for a gene-diet interaction and colorectal cancer risk between a genetic variant (rs4143094) on chromosome 10p14 near the gene GATA3 and processed meat consumption (p = 8.7E-09).

Now, this gene has nothing to do with nitrate metabolism as far as I can see - it seems to be a cell proliferation gene. So we could still be seeing residual confounding, because there's no absolute way to adjust for the huge effect of hyperinsulinaemia on this cancer and processed meat is what you have on a pizza or in a sandwich. And the people who clean up chemical spills for you are unlikely to be vegan and/or rich, so processed meat is kind of their thing. But still.

The study wasn't designed to implicate carbs, by the way (but the fibre results will be interesting)

In this large combined analysis using GECCO from 10 case-control and nested cohort studies comprising 9,287 colorectal cancer cases and 9,120 controls, we build upon these previous reports [13], [14] to examine over 2.7 million common polymorphisms for multiplicative interactions with selected dietary factors (red meat, processed meat, fiber, fruit and vegetables) and risk of colorectal cancer.

Of the 7 studies listed here, the association goes the other way in 2 - NHS and HPFS. This helps to validate it according to my bias, which is that NHS and HPFS are the last place to look if you want results that correspond to reality.
If, on the other hand, you love Harvard epidemiology, then eat more bacon (I know, I know).

There are 3 significant loci and they all have positive interactions. Nothing good.

And here's the spread. This stuff interests me:

Stratified by genotype, the risk for colorectal cancer associated with each increasing quartile of processed meat was increased in individuals with the rs4143094-TG and -TT genotypes (OR = 1.20, 95% CI = 1.13–1.26 and OR = 1.39, 95% CI = 1.22–1.59, respectively) and null in individuals with the rs4143096-GG genotype (OR = 1.03, 95% CI = 0.98–1.07, Table 2). Results are very similar for minimal and multivariable adjusted ORs.

Only 6% of these populations had TT, most people had GG. So all the risk is in one corner. (you could get tested for this these days, but who knows what other genetic factors also influence it at the personal level).

What about red meat etc?

With the other dietary factors evaluated, no interactions using the conventional case-control logistic regression analysis reached the genome-wide significance threshold.

So I dug down into the supplementary data and found this amazing table.



 If you have the most significant interactive allele for red meat, you get a 10% higher cancer risk if you don't eat enough. If you have one of the other 2, you get an 11% increased risk from too much.
And look at fibre - it's pretty much the same.
This helps to explain the Polyp Prevention Trial, doesn't it?[4]
I've long suspected that something like this goes on - that null or near-null results can disguise a mild 2-tailed effect - a little extra harm in one corner of the population and a similar-sized protective effect in another.
If any of this is real - insulin is, as always, the elephant in the room, as are the true carcinogens, which you'll find in the storeroom. But surely it has a bit more validity than the naked FFQ epidemiology it's based on?

Anyway, this seems like a useful reality check, and there are others - does the epidemiology of bowel movements support the motility part of the fibre hypothesis? Not really.[5] Does the epidemiology of aspirin (a drug that notoriously leaches blood into the gut, even when vegans take it) support the heme iron hypothesis? Not really.[6] Maybe this seems like nonsense to some, but if people want to draw drastic conclusions from FFQ epidemiology, they need to get outside the box more.

Oh, and why do people want to draw drastic conclusions from FFQ epidemiology anyway?
Adam Curtis has the best take on how this happened here.


[1] Zhu Y, Bo Y, Liu Y. Dietary total fat, fatty acids intake, and risk of cardiovascular disease: a dose-response meta-analysis of cohort studies. Lipids Health Dis. 2019;18(1):91. Published 2019 Apr 6. doi:10.1186/s12944-019-1035-2

[2] Chang X, Dorajoo R, Sun Y, et al. Gene-diet interaction effects on BMI levels in the Singapore Chinese population. Nutr J. 2018;17(1):31. Published 2018 Feb 24. doi:10.1186/s12937-018-0340-3

[3] Figueiredo JC, Hsu L, Hutter CM, et al. Genome-wide diet-gene interaction analyses for risk of colorectal cancer. PLoS Genet. 2014;10(4):e1004228. Published 2014 Apr 17. doi:10.1371/journal.pgen.1004228

[4] Schatzkin A, Lanza E, Corle D, Lance P, Iber F, Caan B, Shike M, Weissfeld J, Burt R, Cooper MR, Kikendall JW, Cahill J. Polyp Prevention Trial Study Group.

Lack of effect of a low-fat, high-fiber diet on the recurrence of colorectal adenomas. N Engl J Med. 2000 Apr 20;342(16):1149-55.


[5] Kojima M, Wakai K, Tokudome S, et al. Bowel movement frequency and risk of colorectal cancer in a large cohort study of Japanese men and women. Br J Cancer. 2004;90(7):1397–1401. doi:10.1038/sj.bjc.6601735

[6] Qiao Y, Yang T, Gan Y, et al. Associations between aspirin use and the risk of cancers: a meta-analysis of observational studies. BMC Cancer. 2018;18(1):288. Published 2018 Mar 13. doi:10.1186/s12885-018-4156-5

Why the High-Fat Hep C Diet? Rationale and n=1 results.

[pinned post hence the unusual date]

I originally started this blog to publicise the hypothesis that a diet low in carbohydrate and linoleic acid, but high in saturated fat and long-chain PUFA, will inhibit HCV replication.

The blog header with the pig above is the abstract for this hypothesis.

I first worked this out in 2010 after reading Dr Atkins New Diet Revolution while studying HCV replication. The lipid patterns in low-carb dieters - low TG and VLDL, high HDL, normal or high LDL - are those associated with lower viral load and improved response to treatment in HCV cases.
The mechanics of HCV replication and infection support this link.

HCV inhibits PPAR-a, a ketogenic diet reverses this inhibition

I wrote a fairly comprehensive version of the hypothesis in 2012:
http://hopefulgeranium.blogspot.co.nz/2012/02/do-high-carbohydrate-diets-and-pufa.html

Recently I was sent a link to an article that cited this paper:
http://www.journal-of-hepatology.eu/article/S0168-8278(11)00492-2/pdfHCV and the hepatic lipid pathway as a potential treatment target. Bassendine MF, Sheridan DA , Felmlee DJ, et al. Journal of Hepatology 2011 vol. 55 j 1428–1440

This review compiles a great deal of supporting evidence regarding the interaction between HCV and lipids, and between lipids and HCV. The only thing missing is the role of carbohydrate. It mentions multiple lipid synthetic pathways as targets for indirect-acting antiviral drugs (IDAA), pathways which are also well documented as targets of low carbohydrate ketogenic diets, or of saturated fat in the diet (in the case of the LDL-receptor complex).

From 2012:
A little n=1 experimental data; 4 years ago (2008) my viral load was 400,000 units, now after 2 years of low carb dieting and intermittent mild ketosis (2012) it is 26,000.

Later in 2012:Total Cholesterol:  6.7  H     
Triglyceride:          0.8         
HDL:                     1.63              (63.57)
LDL (calc.)            4.7   H    
Chol/HDL ratio:     4.1          

HCV viral load on this day (21st May 2012): 60,690 IU/mL (4.78 log)



Lipid panel from 07 Feb 2012, during ketogenic diet phase (non-fasting)

Total Cholesterol: 8.9   HH  (347.1)
Triglyceride:         1.3          (115.7)
HDL:                    1.65         (64.35)
LDL (calc):           6.7    H    (261.3)
Chol/HDL ratio:     5.4   H

HCV viral load on this day: 25,704 IU/mL (4.41 log)

From 2014:
On a personal note, I have started an 8-week trial of Sofosbuvir and GS-5816 (Vulcan). It is day 11 and it seems tolerable so far.
A pre-trial blood test on 22nd October was normal except for these counts:
AST 74
ALT 174
and viral load was 600,419 (log 5.78), counts consistent with the tests I've had done this last year.

But the day the trial started, 18th November, before my first dose, things were different:
AST 21
ALT 32
Viral load 27,167 (log 4.43)

The low viral load is easy to explain; I get a consistent 1 log drop (to 14,000-60,000*) when I try to eat very low carb (50g/day or lower) and an elevation to 400-600,000 when my carbohydrate intake is over 50g/day. When I ate very high carb (but took antioxidant supps) it was as high as it was on 22nd October. So for me the tipping point seems to be where ketosis begins, and other variations don't have much effect; it's an on/off switch, not a dial (and the name of that switch is PPAR-alpha).
[edit: though the very low scores are at ketogenic, or nearly so, carb intakes, the exact increase in carbohydrate needed to cause a significant increase in viral load seemed to vary]
(I do however, according to CAPSCAN elastography, have zero excess fat in my liver, which is an effect of low carb in general, as well as avoiding vegetable seed oils).
My belief is that my viral load was much higher than any of these counts previous to 2003. This was the year I started taking antioxidant supplements, eating a bit better (in a normal, confused "healthy eating" pattern), and using herbal antivirals like silybin. Prior to that I was seriously ill, and I believe that my viral load would have reflected my extra autoimmune symptoms, signs of liver failure, and elevated enzymes. Unfortunately in those days one didn't get a PCR unless one was considering donating one's body to interferon, which I was not.

* I don't seem to have a record of the date of the 14,000 VL reading, but will include it when I find it.

Summary:
A very low carbohydrate ketogenic diet, without enough PUFA to lower LDL artificially, had a significant inhibitory effect on HCV viraemia in my case.
Effective DAA drugs for HCV infection are now available. There is a ~98% SVR rate at present. These drugs are expensive, they sometimes have side effects (though much less so than interferon + ribavirin), and interferon + ribavirin is still being used.
If my results are more generally applicable, VLCKD diet offers an adjunct therapy for patients with a high viral load, steatosis that relates to diet and lifestyle as well as HCV infection, or a need to postpone treatment. In people who oppose or cannot complete or afford treatment, it offers a way to manage the disease, and in particular to reverse the autoimmune syndromes caused by immune complexes when viraemia is excessive.

Two important new papers on climate change.

Whad'ya mean, this has to last me a year?

People in the LCHF community can be resistant to considering climate change and greenhouse gas levels because this argument can be used to shift the goalposts in a clumsy, overt fashion in order to sidestep the evidence on health and keep everyone eating nutrient-poor diets.
Our critics even use these manufactured opportunities to resuscitate their zombie saturated fat and TMAO hypotheses, knowing that most of the audience for ecological debates has no clue how intellectually bankrupt and scientifically desperate these arguments are and have been for some time.
So people can be forgiven for both hiding their heads in the sand and distrusting all "consensus" authority - in our specific area of health, consensus authority has been damagingly wrong for many people's entire lifetimes. And ironically some of this wrongness, the saturated fat question, has contributed to global warming - we'll discuss how later.

However, I for one believe in keeping a close eye on existential threats, and whether you see climate change as a threat to your access to a diet that will keep you healthy, or merely as a threat to the future of human existence on this planet, I think you should too.
Don't listen to headlines, certainly don't listen to the dodgy and ideologically skewed EAT-Lancet commision, but do listen out for the people doing the hard work; the people working out how we should most accurately measure the things that the usual suspects want us to think were measured most accurately back when the results were more favourable to them.
And try to understand the systems involved.

There are essentially two - the usual cycling of carbon through plants and animals back into the atmosphere, which has shaped our climate through most of our history, with fluctuations due to  deforestation and reforestation that mattered (as we shall see) yet did not wipe out life on Earth.
And then there is the geological cycle - carbon from Earth's hothouse youth slowly trapped under the crust as fossil hydrocarbons, which make excellent fuel.
The system of free trade and free travel that fossil fuels allow has replaced warfare since WW2 for most of the world's countries; but it is a potlatch peace, dependent on wasteful gestures, firstly the making and transportation of shit that will either be thrown away, or that in most cases could be made closer to home with lower energy costs, in order to keep wages at a level consistent with a desire for peace, and secondly the transportation of people who will stay in herds or on their phones at the world's beauty spots, only visited for the bragging rights, and for something to do instead of making war against the people who live there.

In the ecological cycle, plants sequester CO2 as they grow, though the soil around them, if very fertile, will release methane (CH4) - recently noted with alarm in the Amazon rainforest, as well as in rice paddies.
CO2 in plants is released by forest or grass fires, and by the metabolism of animals that eat them, which also sequester some of the carbon in their bodies during their lives, mainly in stored fat and protein. When plants and animals rot to return nutrients to the soil this can also release methane, as can the fermentation of plants in the gut by bacteria - the bacteria in the foregut of ruminants are great at processing inedible (to us) fibre to energy substrates, so are high producers of methane (which escapes in burps, not farts).

Our first paper looks at the contribution of methane to the warming effect. CH4 is much more warming than CO2. This is why we hear that 51% of NZ's GHG come from agriculture, when the proportionate amount of CH4 released by ruminants compared to fossil fuel CO2 in NZ each year is much smaller than this - because GHG emissions have, till now, been calculated on the warming effect of each gas. However CO2 lasts for hundreds of years; CH4 has a half-life of only 10 years before turning to CO2. Thus, if we are looking at a 10-year GHG emissions target, half the CH4 should be counted as CO2, and the further out we get, the smaller the difference between CH4 and CO2 gets.
The full model is more complex than this, but the gist of it is the mathematical demonstration that GHG as methane is being badly overestimated whenever the calculation is for a long term impact.

Climate mitigation: An improved emission metric 

A new approach allows the temperature forcing of CO2 and short-lived climate pollutants (SLCPs) to be examined under a common cumulative framework. While anthropogenic warming is largely determined by cumulative emissions of CO2, SLCPs—including soot, other aerosols and methane—also play a role. Quantifying their impact on global temperature is, however, distorted by existing methodologies using conventional Global Warming Potentials (GWP) to convert SLCPs to "CO2-equivalent" emissions. A team of international scientists led by Myles Allen at the University of Oxford provide a solution. A modified form of GWP—GWP*, which relates cumulative CO2 emissions with contemporary SLCP emissions—is shown to better represent the future climate forcing of both long- and short-term pollutants. Use of GWP* could improve climate policy design, benefiting mitigation strategies to achieve the Paris Agreement targets.

Dr Michelle Cain explains the meaning of this paper in this twitter thread and this short YouTube video.

You can't get fossil fuels off the hook. The billionaire owners of EAT-Lancet make their money from a hotel chain. No doubt the hotels are eco-friendly and serve vegan meals. But you can't fill hotels without jet aircraft and cars and cruise ships. Without unnecessary travel, that is - because people with sounder reasons to travel tend to stay with family or friends. A successful hotel chain today is a prime symptom of the fossil fuel binge-for-gold mentality that is breaking the planet.



Our second paper looks at the effects of reforestation on the climate after 56 million mesolithic farming peoples died following the colonisation of the New World.[2] It supplies the evidence for an earlier claim that when their disused cropland was overtaken by forest regrowth, the additional retention of CO2 carbon involved in the creation of standing forests caused the Little Ice Age. Animal numbers are not mentioned in the paper but it is extremely unlikely that ruminant numbers in the Americas declined as a result of the tragic deaths, mainly through introduced diseases, of much of the human population that hunted them. Any additional methane release during forest regrowth also did not stop the Ice Age.



Again, this paper revises the estimates used in GHG calculations - the retention of carbon in forests was missed before - again a case of early GHG formulas missing the all-important effect of time scaling.

Now, let's do some modelling of our own. It's silly, I admit, but no sillier than anything EAT-Lancet have proposed. We have an obesity epidemic; a 2012 estimate of the extra food needed to maintain that extra weight was, that biomass due to obesity was 3.5 million tonnes, the equivalent of 56 million people of average body mass (1.2% of human biomass globally).[3] In other words, if the obesity epidemic could be entirely reversed, the food savings would be roughly equivalent to the annual food consumption of Australia and Canada combined (minus that of little New Zealand).
The reduction in biomass would also be exactly the same as the population drop that caused the Little Ice Age.

In our model all the weight lost is lost because of a reduction in wheat, corn, rice and sugar consumption, and their cropland is replaced by permanent forest (not forestry). Of course farming today is more intensive, and thus causes more harm to biodiversity, soil health, and marine health, so the total hectarage saved will be less - but we can compensate for that if we also tell people they can eat the fat from the animals they eat instead of soy oil or palm oil. This will reduce demand for the two human foods that most drive deforestation. If palm and soy plantations collapse as a result and the Indonesian and Brazilian rainforest takes back the land, so much the better.
Of course, the Adam Curtis voiceover should be telling you about now, "but it was a fantasy". But it was a fantasy that demonstrates how misguided public health experts and their inability to correct error on the saturated fat question have helped to change the climate. We can afford to eat meat, we just can't afford to keep eating lean meat and avoiding the fat-and-cholesterol rich parts of the animal. We can't afford to keep cooking exclusively with vegetable oil (and then often throwing it away). Keep on crowbarring that rubbish advice into climate change statements and no-one but vegans will ever believe you.

References

[1] Myles R. Allen, Keith P. Shine, Jan S. Fuglestvedt, Richard J. Millar, Michelle Cain, David J. Frame & Adrian H. Macey. A solution to the misrepresentations of CO2-equivalent emissions of short-lived climate pollutants under ambitious mitigation. NPJ Climate and Atmospheric Science volume 1, Article number: 16 (2018).

[2] Alexander Kocha, Chris Brierley, Mark M.Maslina, Simon L.Lewis. Earth system impacts of the European arrival and Great Dying in the Americas after 1492. Quaternary Science Reviews
Volume 207, 1 March 2019, Pages 13-36. https://doi.org/10.1016/j.quascirev.2018.12.004

[3] Walpole SC, Prieto-Merino D, Edwards P, Cleland J, Stevens G, Roberts I. The weight of nations: an estimation of adult human biomass. BMC Public Health. 2012;12:439. Published 2012 Jun 18. doi:10.1186/1471-2458-12-439 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3408371/

Don't Drink (oil) and Fry (in the sun) - the link between polyunsaturated vegetable oil and skin cancer

It was good to see this well-researched burst of sunscreen scepticism doing the rounds this (southern) summer - Is Sunscreen the New Margarine? *
I was particularly struck by the unintentionally ironic title, because margarine's role in this story goes well beyond that of a handy analogy for a misguided public health initiative.

When I first read the Nanji and French research - countless rat experiments, consistent with what human epidemiology there was - showing that high PUFA oils potentiated the progression of alcoholic liver disease, were indeed essential fats if one wanted to develop this condition, I replaced the rice bran oil I had been conned into using with beef fat. One of the first things I noticed, being a clumsy cook, was that my skin stopped blistering when I burned myself. At the worst I might get a short-lived patch of dead skin, but I've had about 2 blisters in the 7 years since then and neither became painful. Then gradually I noticed I wasn't getting burnt in the sun as easily. I wasn't big on the sun in those days, but as I got more exposure to sun and less exposure to linoleic acid my resistance grew. I try to limit exposure, using clothes and shelter, to what seems reasonable, having no desire to turn nut-brown and wrinkled in my dotage, but occasionally I've been caught out for far longer than I intended, and no harm has ensued. In part this has been due to a policy of tanning early and often so that the protective pigment is in full effect once the summer reaches its peak, but dietary choice is a critical factor, as we shall see.

The first experiment I came across showing the photosentising effect of linoleic acid was this one (in hairless mice - obviously you can't use a hairy animal) [1];

However, dietary ALA inhibited the increase in erythema score after UVB irradiation compared with LA. The peroxidizability index of the skin total lipids was significantly higher, but UVB-induced prostaglandin E2 (PGE2) production was significantly lower in the group fed an ALA-rich diet compared with the group fed an LA-rich diet. 

There's a lot of this stuff recently, showing that omega-3 fats, and especially the long-chain fish oil ones, are protective - but also that their irradiation puts more strain on the antioxidant defense system, depleting vitamin C and glutathione. The Linus Pauling Institute website has an excellent summary of this research, including human trials, but if you think like me you want to know, is saturated fat protective too? I mean there are people out there exposed to very high UV levels eating not-especially-oily fish and coconut or ghee for generations - are they OK?

The Linus Pauling Institute doesn't tell us, nor does it really warn us about omega-6. The modern idea is just to increase our intake of flaxseed oil and salmon and antioxidant vitamins and minerals. Sounds expensive, for one thing, and I'm not sure our obsession with fish will prove to be sustainable if we're not allowed to eat anything else.

To answer this question we need to go back to the 1990's, when researchers were mostly looking at omega 6 fats and using saturated fats as controls.

We find:

When polyunsaturated fat intake had been increased, tumorigenesis had been exacerbated and a remarkable persistence of immunosuppression remained measurable. There was no difference apparent in the CHS responsiveness in mice fed 20% sunflower oil or saturated fat in the absence of UV irradiation, indicating that the persistent immunosuppression was likely to have been induced by the carcinogenic irradiation regime.[2]

Diet 1 is 20% hydrogenated cottonseed oil, diet 5 is 20% sunflower oil

Now 20% sunflower oil is exactly the kind of exposure you'd get if you replaced other fats with oil in a low fat diet, as the experts want you to. It's an amount of LA that the epidemiologists at Harvard Chan have no problem with, using as they do data collection methods unreliable enough to produce false negatives as well as false positives, and not controlling for UV exposure anyway. Note that the control here - hydrogenated cottonseed oil - is 69.25% trans fat, the rest all SFA.

Here's another, where there are two controls - 12% menhaden oil (basically fish oil) and 0.75% corn oil.[3]
The most interesting finding is that while menhaden oil is protective, crossing over to 12% menhaden oil from 12% corn oil is not; it's about the worst thing you can do; crossing over from 12% corn oil to 0.75% corn oil seems safer.

In summary, we have shown that (1) high dietary level of an omega-6 FA source (corn oil) enhances photocarcinogenic expression, both with respect to tumor latent period and multiplicity; (2) that this lipid-induced exacerbation of cancer expression occurs at the post-UV initiation, or promotion, stage of carcinogenesis; (3) modification of diet to low lipid level (corn oil), after UV-initiation, negates the enhancement of cancer expression exhibited by high level of corn oil; (4) high level of dietary menhaden oil containing omega-3 FA, when compared to an equivalent level of corn oil, inhibits photocarcinogenic expression; and (5) menhaden oil mediated inhibition of UV-carcinogenesis appears to occur during the initiation stage and by a mechanism dissimilar to that exerted by low levels of corn oil.

These data suggest a complexity of dietary lipid effects upon cancer expression that perhaps has not been widely appreciated.

But here's my favourite - finally someone uses butter and ghee as controls.[4]


They're measuring ear swelling in response to a hapten test, which I assume is some sort of irritant. Low swelling means the immune system is suppressed, and this predicts that the risk of cancers is increased, just as it did in the other experiments. Note this took 4 weeks of a 20% fat diet - the protective effect of butter wasn't obvious after only 2 weeks, but the harmful effect of sunflower oil was.

Now, how do we know that this applies to human populations or has anything to do with the high rates of melanoma (the most fatal skin cancer) in New Zealand or Australia?
There is a natural experiment we can look at. NZ, unlike Australia, is not a land of extreme natural sunlight - it's the "land of the long white cloud", so that travel to the tropics greatly increases UV exposure. (However, we do have greater UV variability at our lower latitude, described by NIWA's Richard Mackenzie here.) Kiwis didn't travel much in the past, especially to the tropics, with one important exception; around 140,000 men (mostly) served overseas in WW2, around 10% of the population, and most of them served in places like Greece, Crete, Egypt, Libya, Italy and the Solomon Islands. Wearing shorts and short-sleeved shirts - US naval officials in the Solomons were appalled by the lack of protection the NZ sailor's uniform gave against flash burns - with only a Tommy helmet for shade (too hot and heavy to wear all the time). Sunburn on arrival in the combat zone is mentioned in memoirs - in the Armed Forces you stay where you're told and work where you're told, shelter or not.

Soldiers of the 2nd NZEF, 20th Battalion, C Company marching in Baggush, Egypt, September 1941.

The NZ diet, and British Army rations, at this time were very low in omega 6. In NZ, margarine wasn't even legalised until 1972. We cooked with butter, hydrogenated coconut oil, and beef and lamb dripping - even chicken and pork were unusual foods until the 70's. Some time during that decade the use of oil (mostly soy and corn oil at first) took off and was entrenched by the 1980's.
Now if exposure to the excess UV rays of the tropics, rather than the combination of UV and oil, caused skin cancer we'd expect to see an age-specific curve in skin cancer mortality in NZ that rose after the war (starting in the mid-1950's would match the usual cancer latency) then dropped as that generation began to die off from all causes, and a generation raised on "slip slop slap" UV protection took over.
Instead we see this:



And if you check different age groups in this part of the Mortality Trends website, you find the same pattern (most obvious where there is highest mortality), despite the different rates of overseas service in each age group, and the dying off of each generation - mortality from skin cancer climbs rapidly from the 1970's, when the NZ nutritional transition to high-PUFA oils began, and has not declined at all as the Greatest Generation dies off and the lesser slip, slop, slap-happy generations take its place (melanoma mortality in NZ has remained stable from 2001 to the present, I can't find earlier stats specific for melanoma but of course it is the most lethal skin cancer). This data is a better fit for diet than it is for UV exposure. (Of course there's the ozone hole, dating from the 70's, but "The ozone hole does not have a large effect on the concentration of ozone over New Zealand. However, when the ozone hole breaks up in spring, it can send ‘plumes’ of ozone-depleted air over New Zealand." The relative unimportance of this is mentioned on page 6 of Mackenzie's paper.)
Which is not to say that UV exposure has unlimited safety, of course this is not the case, but that heart-healthy vegetable oil and margarine advice has made even limited exposure more dangerous than it needs to be. Much the same phenomenon we see with alcohol and liver disease (and, who knows, alcohol and the risk of other cancers).
Anyway, if you plan to go out in the sun for long enough to raise some vitamin D and nitric oxide, or drink enough alcohol to get drunk, or especially both, skip anything cooked in or made with a vegetable oil other than coconut or, within reason, olive oil (this includes mayonnaise), [Edit: olive oil is rich in the terpenoid antioxidant squalene, perfectly configured to quench singlet oxygen radicals released by UV exposure, likely to offset risk from its moderate 10-12% linoleic acid content], eat some butter or cheese or full-fat yoghurt, some fatty fish, chocolate, tomatoes and all the other antioxidant-rich foods with some evidence as UV-protective (caffeine seems to help too). Also keep insulin low - that means no refined carbs, intermittent fasting, low carb diet if necessary. Insulin and IGF-1 are important in skin repair and insulin resistance due to excessive insulin response to diet creates all sorts of skin problems, as well as underwriting most of those non-communicable diseases we hear so much about. (it's not easy to get insulin tested here but the TG/HDL ratio after a 12-14 hr fast is a decent proxy for the 2-hour insulin response).

[EDIT 11/02/19 - analysis of NHS/HPFS data has confirmed an association between omega 6 PUFA and skin cancers, up to 1.23 (1.08, 1.41) for squamous cell carcinoma. Of course this is an unreliable FFQ data set, but the finding runs contrary to the direction we'd expect conscientiousness bias to take in this population. It's not obvious what the range of omega 6 was, this information may be in supplementary tables I can't access.
Park MK, Li WQ, Qureshi AA, Cho, E. Fat intake and risk of skin cancer in u.s. adults. Cancer Epidemiol Biomarkers Prev. 2018 Jul;27(7):776-782. doi: 10.1158/1055-9965.EPI-17-0762. Epub 2018 Apr 10. http://cebp.aacrjournals.org/content/27/7/776]


* IMO the vitamin D supplement scepticism in this article is premature - vit D3 works if you use it for the right reason and take enough of it. It's just as good as sunlight for fixing my minor but annoying psoriasis, but I need 10,000 iu a day till it goes away. This only takes 6 days every month or two now - I used to need to take that amount all winter.

References:
1] Takemura N, Takahashi K, Tanaka H, Ihara Y, Ikemoto A, Fujii Y, Okuyama H. Dietary, but not topical, alpha-linolenic acid suppresses UVB-induced skin injury in hairless mice when compared with linoleic acids. Photochem Photobiol. 2002 Dec;76(6):657-63. link

2] Reeve VE, Bosnic M, Boehm-Wilcox C. Dependence of photocarcinogenesis and photoimmunosuppression in the hairless mouse on dietary polyunsaturated fat. Cancer Lett. 1996 Nov 29;108(2):271-9. Full-text link

3] Homer S. Black  John I. Thornby  Janette Gerguis  Wanda Lenger. INFLUENCE OF DIETARY OMEGA‐6, ‐3 FATTY ACID SOURCES ON THE INITIATION AND PROMOTION STAGES OF PHOTOCARCINOGENESIS. Photochemistry and Photobiology Vol. 56, No. 2, pp. 195-199, 1992.
https://doi.org/10.1111/j.1751-1097.1992.tb02147.x

4] Cope RB, Bosnic M, Boehm-Wilcox C, Mohr D, Reeve VE. Dietary butter protects against ultraviolet radiation-induced suppression of contact hypersensitivity in Skh:HR-1 hairless mice. J Nutr. 1996 Mar;126(3):681-92. free full-text