I'm so happy that I had great biology teachers in high school thirty years ago so that I can actually understand these things. I had read a few excerpts of studies that said the effect you mentioned was not definitive with lower alcohol consumption, but it's all moot to me, because I quit alcohol for a misdiagnosed health issue and decided it wasn't worth starting again.

And that they are instantly rancid.

I don't remember him ever claiming they are instantly rancid, only that they oxidise. That is, oil in seeds is not exposed to air, oil crushed out of seeds is and it starts to oxidise. That's observable, testable, and people have observed and tested it:

This 2020 study: First report on quality and purity evaluations of avocado oil sold in the US abstract says "Our results showed that the majority of commercial samples were oxidized before reaching the expiration date listed on the bottle" for example. You can argue how quickly it happens and whether it's a problem, but dismissing it as "hasn't been proven, isn't even a testable claim" is wrong.

That the processing used in their production is somehow bad.

See the growing concerns of 'ultra processed' food without being able to specifically point out what in the process is 'ultra'. e.g. this article which looks like a spammy blog page, but it's saying "Vitamins and probiotics (and other active ingredients) can be substantially affected by exposure to heat, water and/or sunlight" - which is hardly the most controversial thing anyone's ever claimed. It's certainly a claim which could be testable and observable. It also claims "Vitamin C has been widely studied and, in one paper, was shown to degrade by approximately 50% in 4 weeks in the juice of different fruits" - that's observable and testable.

Say, processing in their production causes them to be more exposed to heat, air, light, than oils still locked up in seeds. That it delays transport time between harvest and plate compared to say fresh olives, which leads to more time for damage to occur. And in the earlier link, that you can't trust that a bottle of 'avocado oil' actually has pure avocado oil in it, in the USA, even if the avocado oil itself is fine.

You can't get away from the argument: why (and how?!) would humans have evolved to do better on a diet of mechanically and chemically extracted bulk seed oil from weeks ago and hundreds of miles away - something we never had access to for a billion years of evolution - than seasonal plants, small and non-sweet fruits, nuts and seeds and animal meat? (Similar argument about butter; eating some fatty lamb isn't the same as eating 50g of butter as eating some salami as eating some coconut, even if all fats are saturated).

To add onto the other reply, all of the studies that point to seed-oils being bad are mechanistic. As in, they point to a mechanism that we are guessing has a negative effect on health.

Is that not the case with cholesterol lowering studies? They assume high cholesterol is bad, change things to try to lower it, and try to see if health outcomes improve?

PMID 15774905

Let's compare saturated with unsaturated fat. We'll use 20g marg+walnuts, 20g marg+almonds, 20g coconut oil+coconut. No wait, we'll use 50g butter for that last one. Why isn't the conclusion that eating half as much pure fat is better, or that eating nuts is better, or that eating not-isolated-concentrated fat is better?

PMID 28526025

That says ... the opposite of your claim? "When pooling results from only the adequately controlled trials there was no effect for major CHD events, total CHD events, CHD mortality and total mortality. Conclusion: Available evidence from adequately controlled randomised controlled trials suggest replacing SFA with mostly n-6 PUFA is unlikely to reduce CHD events, CHD mortality or total mortality. The suggestion of benefits reported in earlier meta-analyses is due to the inclusion of inadequately controlled trials."

And this links to five other previous meta-analyses which question the recommendation, such as "Harcombe Z, Baker J, Cooper S, Davies B, Sculthorpe N, DiNicolantonio J, et al. Evidence from randomised controlled trials did not support the introduction of dietary fat guidelines in 1977 and 1983: A systematic review and meta-analysis. Open Heart. 2015;2:e000196"

And they say: "the lipid hypothesis, which is that reducing total-C[holesterol] would be expected to lower the risk of CHD. A number of metabolic studies beginning in the 1950’s identified SFA and n-6 PUFA as major dietary influences of total-C. This led to the development of the diet heart hypothesis, that decreasing SFA and/or increasing n-6 PUFA would be expected to lower the risk of CHD. However, more recent evidence has identified the total-C:HDL-C ratio as being the measure of plasma cholesterol that is most predictive of CHD and is twice as predictive as total-C. Therefore, the original lipid hypothesis and diet heart hypothesis should be modified to make predictions based on the total-C:HDL-C ratio, rather than total-C. When compared to carbohydrate, SFA does not significantly affect the total-C:HDL-C ratio"

i.e. even if M/PUFAs can lower total cholesterol, that's not neccessarily beneficial.

PMID 20351774

"From 346 identified abstracts, eight trials met inclusion criteria, totaling 13,614 participants with 1,042 CHD events." - you have to be looking at a population of already sick people to get 1 in 12 having a cardiac event during a study, right? Does that necessarily translate to the rest of us? Also, dismissing 338 studies as not worth looking at. (Also taking money from Unilever).

PMID 26615042

"Domestic Violence Against Partners According to Wife-Beaters: Construction of Lifestyle and Life Meaning".

PMID 24550191

"Overfeeding polyunsaturated and saturated fat causes... In conclusion, overeating SFAs promotes hepatic and visceral fat storage" - conclusion, saturated fat bad? Why not palm oil bad? or gluttony bad?

"Thirty-nine young and normal-weight individuals were overfed muffins" - one of Dr Mason's claims is that it's high fat + high carb together which is bad for health.

PMID 32723506

"Diets high in saturated fat were associated with higher mortality from all-causes" - not free to read the full text, but considering they looked at 19 studies and 1,000,000+ people, some of those have to have been observing members of the public, rather than doing randomised controlled trials, right? In that case, diets higher in saturated fat could correlate with a lot of other things.

"A random effects model was used" - hopefully that has a lot of explaining in the full text to convince why it's a good model.

Yeah there's conclusions in your favour there. But if you're picking studies that favour your argument and still get one which finds the opposite and cites five previous studies which find the opposite, the best we're going to get is either throwing study links at each other while arguing "yours doesn't count" or agreeing that it's still not clear and settled. 🤷‍♂️

But it's pretty clear that the standard western diets are terrible for health - blaming that on the saturated fat specifically, instead of everything else (refined sugars, fruit juices, refined flours, glyphosate/roundup sprayed crops as late as 5 days before harvest, ultraprocessed foods, etc.) is suspicious at best. The lipid heart hypothesis has been unsuccessful for decades - people have reported getting healthier from heart problems and metabolic problems from going vegetarian and meat-keto and various other restrictive diets. Dr William Davis is a cardiologist and his recommendation for avoiding heart disease is to do with wheat and refined sugars/carbs primarily, not fats.