seed oils do often require chemical extraction and the method of extraction does matter because it may have effects on the chemical structure of the oil in question. For example, to make canola oil, the seeds are ground at high temperatures to extract a very fragile oil. During this harsh process, the oil is oxidized and then needs to be washed with hexane (a known neurological toxin) and then bleached and deodorized so that the product does not smell rancid (which it is after the processing). Contrast this to cold pressing olives.
As for linoleic acid, it does store in adipose issue and cause oxidative stress and inflammation in humans. Below is one of several papers you can find on this.
A high linoleic acid diet increases oxidative stress in vivo and affects nitric oxide metabolism in humans
That study also shows that a diet high in chemically-extracted high-oleic sunflower oil did not have increased urine metabolites compared to control. So that study actually works against the hypothesis that seed oils or chemically extracted oils are inherently bad.
And here’s another study that directly tests the hypothesis that linoleic acid consumption causes damage via oxidative stress and concludes “our results provide no indication of increased oxidative stress or genetic damage as a result of increased dietary intake of linoleic acid. Therefore, we see no scientific basis to reconsider the public health policy to stimulate the intake of polyunsaturated fatty acids aimed at the reduction of coronary heart diseases.”
I agree that there is not consensus in the scientific/medical community about this. You can find MDs who will advise avoiding linoleic acid as a top health prioty (i.e Paul Saladino) and other scientists who do not agree there is sufficient evidence to indict seed oils (i.e Andrew Huberman). Likewise, you can find all sorts of studies.
To address your point about the study I linked -- I think you're mistaken. The LA group did have a significant increase in 8-iso-PGF2alpha urine metabolites, and decrease in nitric oxide metabolites. From the study:
> Urinary excretion of 8-iso-PGF2alpha was significantly increased after the LA diet (170 vs 241 ng/mmol creatinine, P=0.04), whereas the urinary concentration of nitric oxide metabolites decreased (4.2 vs 2.6 mg/mmol creatinine, P=0.03).
also
> In conclusion, the high-LA diet increased oxidative stress and affected endothelial function in a way which may in the long-term predispose to endothelial dysfunction.
The oleic acid group, the group that didn’t see an increase of metabolites, was given high-oleic sunflower oil. I brought that up because it’s a chemically extracted seed oil, and one of the most common seed oils. “Seed oil” is not a significant distinction of fatty acid composition. Seed oils have varying linoleic acid composition (sesame oil for example is quite balanced, high-oleic sunflower is close to olive oil ratios).
The study you linked showed an increase in oxidation metabolites for the LA group. But as far as I understand, those metabolites don’t demonstrate damage to anything or an impact on mortality. That’s why I linked to a study that measures oxidative DNA damage via 8-oxo-dG in blood, which found no impact from increased linoleic acid consumption. So the theory that linoleic acid is dangerous because of damage via oxidative stress isn’t clearly supported by current literature.
Not really. Here’s a study that measured hexane in various oil brands and didn’t find any problem. “The hexane residue was detected in thirty-six out of forty examined samples, ranged from lower than LOD to 42.6 µg/kg. However, in all of them hexane content were below the MRL of 1 mg/kg which set by the European Union.”
As for linoleic acid, it does store in adipose issue and cause oxidative stress and inflammation in humans. Below is one of several papers you can find on this.
A high linoleic acid diet increases oxidative stress in vivo and affects nitric oxide metabolism in humans
https://pubmed.ncbi.nlm.nih.gov/9844997/